UNITED STATES DEPARTMENT OF THE INTERIOR, Douglas McKay, Secretary //9 FISH AND WILDLIFE SERVICE, John L. Farley, Director GULF OF MEXICO ITS ORIGIN, WATERS, AND MARINE LIFE Prepared by American scientists under the sponsorship of the Fish and Wildlife Service, United States Department of the Interior Coordinated by Paul S. Galtsofl FISHERY BULLETIN 89 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE VOLUME 55 UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1954 For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C. Price $3.25 LIST OF CONTRIBUTORS Anderson, William W., Chief, Gulf Fishery Investigations, Fish and Wildlife Service. Banner, Albert H., Associate Professor of Zoology, University of Hawaii. Bayer, Frederick M., Associate Curator, Division of Marine Invertebrates, U. S. National Museum. Behre, Ellinor H., Professor of Embryology, Louisiana State University. Butler, Philip A., Fishery Research Biologist, Fish and Wildlife Service. Chace, Fenner A., Jr., Curator, Division of Marine Invertebrates, U. S. National Museum. Chandler, Asa C, Professor of Biology, Rice Institute. Chitwood, B. G., formerly Professor of Biology, Catholic University of America. Clark, Austin H., Associate, Department of Zoology, U. S. National Museum. Coe, Wesley R., Professor Emeritus, Yale University. Conger, Paul S., Associate Curator in Charge Diatom Collection, U. S. National Museum. Cooper, G. Arthur, Associate Curator, Division of Invertebrate Paleontology and Paleobotany, U. S. National Museum. Davis, Charles C, Assistant Professor of Biology, Cleveland College, Western Reserve University. Deevey, Edward S., Jr., Osborn Zoological Laboratory, Yale University. Deichmann, Elisabeth, Curator, Museum of Comparative Zoology, Harvard College. GaltsofT, Paul S., Fishery Research Biologist, Fish and Wildlife Service. Graham, Herbert W., Chief, North Atlantic Fishery Investigations, Fish and Wildlife Service. Gunter, Gordon, Acting Director, Institute of Marine Science, University of Texas. Hartman, Olga, Allan Hancock Foundation, University of Southern California. Hedgpeth, Joel W., Marine Biologist, Scripps Institution of Oceanography, Universit3^ of California. Henry, Dora Priaulx, Oceanographic Laboratories, University of Washington. Hyman, Libbie H., American Museum of Natural History. Lasker, Reuben, Research Assistant, Marine Laboratory, University of Miami. Leipper, Dale F., Head, Department of Oceanography, Agricultural and Mechanical College of Texas. Lindner, Milton J., Chief, Fishery Mission to Mexico, Foreign Service of the U. S. A. Lowery, George H., Jr., Museum of Zoology, Louisiana State University. Lj-nch, S. A., Head, Department of Geology, Agricultural and Mechanical College of Texas. Manter, Harold W., Professor of Zoology, University of Nebraska. Marmer, H. A., Late Assistant Chief, Division of Tides and Currents, U. S. Coast and Geodetic Survey. m IV LIST OF CONTRIBUTORS Moore, Hilary B., Assistant Director, Marine Laboratory, University of Miami. Newman, Robert J., Museum of Zoology, Louisiana State University. Osburn, Raymond C, Allan Hancock Foundation, University of Southern Cali- fornia. Parker, Frances L., Scripps Institution of Oceanography, LTniversity of California. Phleger, Fred B., Scripps Institution of Oceanography, University of California. Pierce, E. Lowe, Associate Professor, Department of Biology, University of Florida. Price, W. Armstrong, Department of Oceanography, Agricultural and Mechanical College of Texas. Rehder, Harald A., Curator, Division of Mollusks, U. S. National Museum. Rivas, Luis Rene, Associate Professor of Zoology, University of Miami. Rounsefell, George A., Fishery Research Biologist, Fish and Wildlife Service. Schmitt, Waldo L., Head Curator, Department of Zoology, U. S. National Museum. Sears, Mary, Planktonologist, Woods Hole Oceanographic Institution. Shigley, C. M., Dow Chemical Company. Shoemaker, W. S., Department of Photographic Technology, Rochester Institute of Technology. Smith, F. G. Walton, Director, Marine Laboratory, University of Miami. Sprague, Victor, Director, Lake Chatuge Biological Laboratory. Taylor, Wm. Randolph, Professor of Botany, University of Michigan. Thorne, Robert F., Professor of Botany, State University of Iowa. Tierney, J. Q., Research Assistant, Marine Laboratory, University of Miami. Timm, R. W., Catholic University of America. Tressler, Willis L., U. S. Navy Hydrographic Office. U. S. Public Health Service, Division of Water Pollution Control, Shellfish Branch, Division of Sanitation. Van Name, Willard G., Curator, American Museum of Natural History. Voss, Gilbert L., Research Assistant, Marine Laboratory, University of Miami. Williams, Robert H., Chairman, Department of Marine Sciences, Marine Labora- tory, University of Miami. ZoBell, Claude E., Professor of Microbiology, Scripps Institution of Oceanography, University of California. PREFACE The purpose of this book is to summarize in a convenient form the present knowledge about the Gulf of Mexico. Such a summary is needed in con- nection with a large number of new investigations which are now being conducted in the Gulf of Mexico by Federal and State organizations and private institutions. It is hoped that the background information presented here will be useful to the investigators engaged in the new research projects and will save their time and effort. Scientific data concerning the Gulf of Mexico have been accumulating since the first explorations in the sixteenth century. They are scattered in thousands of technical publications, some of them rare and not readily avail- able to persons in the Gulf States. The preparation of a digest of the existing knowledge about the Gulf was suggested by a group of scientists attending, in November 1949, the meeting of the Gulf and Caribbean Fisheries Institute at Miami. The idea, proposed independently by Dr. Lionel A. Walford of the Fish and Wildlife Service and Dr. Waldo L. Schmitt, head curator, Department of Zoology, U. S. National Museum, was unanimously approved, and Paul S. Galtsoff was selected to carry out the project. The magnitude of the task has proved much greater than had been expected. Only through the hearty cooperation of the 55 contributors to this volume has it been possible to complete the work in about 3 years. For the purpose of this book the Gulf of Mexico is defined as a partially landlocked body of water indenting the southeastern periphery of the North American Continent. Its eastern boundary was drawn from Cabo Catoche at the tip of the Yucatan Peninsula to Key West at the southernmost tip of Florida. This boundary does not constitute a natural barrier; it was arbi- trarily determined because of the necessity of restricting the scope of the project. Inland the area under consideration extends to the limits of tidal waters. The book comprises a number of articles each written by a recognized authority in his field; these are arranged, with minor exceptions, in a taxo- nomic order following a list of phyla, classes, and orders prepared in 1936 for the American Association for the Advancement of Science and published by Duke University Press. This plan was carried out with the following exceptions: the sections on Rotatoria and Branchiopoda were omitted be- cause of the inability to find anyone willing to review these two groups; and, for the sake of convenience, the articles on parasitic worms were assembled in a single chapter. A pertinent bibliography is given at the end of each section. A greater number of bibliographical references, comprising more than 4,000 author and subject cards, was prepared in cooperation with Mrs. Margaret M. Quat- tromini of the Fish and Wildlife Service. The 12 sets of these files have been assembled for distribution among the institutions engaged in research in the Gulf of Mexico. No claim is made that these files are complete, and additional items can be added as new references become available. VI PREFACE In organizing and carrying out the project, splendid cooperation and valuable suggestions were received from the contributors to the book. The writer wishes to express his profound thanks to them for their continuous interest, the great amount of work required to prepare the articles, and their constructive criticism. Waldo L. Schmitt, head curator, U. S. National Museum, and William Randolph Taylor showed unremitting interest in the progress of the work, gave valuable advice in the formulation of the plan, and were most helpful in suggesting some of the authors and persuading them to undertake the review of various groups. My thanks are also due Richard S. Green, Chief, Shellfish Branch, Division of Sanitation, Public Health Service and A. F. Bartsch, biologist. Division of Water Pollution Control, Public Health Service, for organizing the material in the chapter on water pollution; to William S. von Arx of the Woods Hole Oceanographic Institution, Francis P. Shepard of Scripps Institution of Oceanography, Remington Kellogg, Director, U. S. National Museum, Frederick C. Lincoln, assistant to the Director, Fish and Wildlife Service, and Isaac Ginsburg, Ichthyologist, Fish and Wildlife Service, for valuable comments and constructive criticism of certain parts of the book. The work of Mrs. Margaret M. Quattromini in retyping the text and ar- ranging the bibliographies is gratefully acknowledged. Paul S. Galtsoff, Fishery Research Biologist. CONTENTS Chapter Pago I. Historical sketch of the explorations in the Gulf of Mexico. By Paul S. Galtsoff 3 Sources 3 Pre-Columbian era 3 Discovery of the Gulf of Mexico 4 Sixteenth and seventeenth centuries 8 Eighteenth century 18 From the beginning of the nineteenth century to the present time 22 Bibliography 32 II. Geology. Shorelines and coasts of the Gulf of Mexico. By W. Armstrong Price 39 Status of studies of coasts and shorelines 39 Shoreline classification 39 Sources of information 42 Acknowledgments 43 Structural and regional geo-oceanographic approach to shoreline descrip- tion and classification 43 Coasts and hinterland 43 Regional coastal types 44 Young erogenic coasts 44 Alluvial coasts 46 Drowned limestone-plateau coastal plains 48 Biogenous environment 50 Emergent and submergent shorelines of the Gulf 53 Use of terms 53 Submergent shoreline features 54 Emergent shoreline features 55 Shoreline changes and processes 58 Shoreline simplification 58 Equilibrium profiles of continental shelf bottom 59 Directions of longshore drift 62 References 62 Geology of the Gulf of Mexico. By S. A. Lynch 67 Early concepts 67 Gulf coast geosyncline 68 Geomorphology of Gulf of Mexico 71 General characteristics 71 Origin of major features 71 Geomorphology by areas 72 Eastern Gulf area 73 Mississippi Delta area 73 Northern Gulf of Mexico - 74 Mexico 75 Mexican Basin 75 Sediments of Gulf of Mexico 75 Source of sediments 75 Place of deposition 76 Early studies of submarine deposits 77 Recent studies of submarine deposits 77 Sedimentary provinces 78 Eastern Gulf 78 Mississippi Delta 80 7495? VIII CONTENTS Chapter — Continued II. Geology of the Gulf of Mexico — Continued Sediments of Gulf of Mexico — Continued Page Louisiana shelf 81 Western Gulf 81 Yucatdn Peninsula 82 Cuba 82 Mexican Basin 82 Conclusions 82 Bibliography 83 III. Marine meteorology of the Gulf of Mexico, a brief review. By Dale F. Leipper 89 Extra tropical cyclones 89 The general air circulation and some of its consequences 89 Average conditions 90 Weather observing stations 93 Typical upper air soundings 93 Northers 95 Meteorological tides 95 Hurricanes 96 Applications of marine meteorology in the Gulf 96 Further sources of information 96 Conclusion 97 Literature cited 97 IV. Physics and chemistry of Gulf waters. Tides and sea level in the Gulf of Mexico. By H. A. Marmer 101 Harmonic constants 104 Types of tide 108 Semidaily type 110 Daily type 110 Mixed types 112 Characteristics from harmonic constants 113 Disturbing effects of wind and weather 113 The tide in the Gulf of Mexico 114 Sea level 115 Availability of tidal data 117 Literature cited 118 Physical oceanography of the Gulf of Mexico. By Dale F. Leipper 119 Ocean currents 119 Sea surface temperatures 125 Sea temperature variations with depth 131 Salinity 135 Temperature-salinity relationships 135 Ocean wind waves and swell 136 Shallow water oceanography 136 Bibliography 136 Light penetration in the Gulf of Mexico. By William S. Shoemaker 139 Distribution of chemical constituents of sea water in the Gulf of Mexico. By Robert H. Williams 143 Salinity H3 Dissolved oxygen 145 Phosphorus 145 Nitrate-nitrogen 147 Nitrite-nitrogen 148 Hydrogen ion concentration (pH) 148 Alkalinitv and carbon dioxide components 148 Copper.] 148 Miscellaneous chemical constituents 148 CONTENTS IX Chapter — Continued IV. Distribution of chemical constituents of sea water — Continued Paee Summary 149 Literature cited 150 The recovery of minerals from sea water. By C. M. Shigley 153 V. Plant and animal communities. Phytoplankton of the Gulf of Mexico. By Charles C. Davis 163 The zooplankton of the Gulf of Mexico. By Hilary B. Moore 171 Material 171 Bibliography 172 Red tide. By Reuben Lasker and F. G. Walton Smith 173 Sketch of the character of the marine algal vegetation of the shores of the Gulf of Mexico. By Wm. Randolph Taylor 177 General nature of the flora ^ 177 Marine botanical studies of the Gulf of Mexico 177 Collateral works of reference for the Gulf algal flora 178 Chief types of algal vegetation 179 Shifting sandy beaches and estuarine mud flats 179 Stable sand and mud; pools, small lagoons and coves 179 Protected coves and pools with a marine channel 180 Protected bays and lagoons 180 Mangrove thickets 180 Tidal streams 1 80 Sandy shallows and "reefs" of shell and coral rubble 183 Rocky shores and inshore reefs 183 Pelagic seaweeds 185 Local features of the Gulf coast marine algal flora 186 Cited literature of Gulf of Mexico algae and bibliography of principal works dealing with comparable West Indian marine algae 189 Flowering plants of the waters and shores of the Gulf of Mexico. By Robert F. Thorne 193 Submarine meadow 193 Mangrove swamp 194 Salt marsh 196 Sand-strand vegetation 198 Conclusion 199 Bibliography 199 Bottom communities of the Gulf of Mexico. By Joel W. Hedgpeth 203 Investigations of recent facies 205 The oyster community 206 Serpuloid reefs 210 The jetty community 210 Sand beach communities 211 The shrimp ground community 211 The coral and sponge communities 213 Literature cited 213 VI. Bacteria, fungi, and unicellular algae. Marine bacteria and fungi in the Gulf of Mexico. By Claude E. ZoBelL., 217 Dinoflagellates of the Gulf of Mexico. By Herbert W. Graham 223 Present status of diatom studies in the Gulf of Mexico. By Paul Conger. 227 Literature 227 Campeche Bay 227 Mobile Bay 228 Tortugas and west coast of Florida 228 Other records 228 Diatom floras of Gulf and adjacent waters 229 Ecology 229 Productivity 229 Silica relationships 230 Bibliography 23 1 CONTENTS Chapter — Continued VII. Protozoa. Page Gulf of Me.xico Foraminifera. By Fred B. Phleger and Frances L. Parker. 235 Benthonic Foraminifera 235 Planktonic Foraminifera 241 Literature cited 241 Protozoa. By Victor Sprague 243 Survey of the literature 243 Distribution of Protozoa 244 Mastigophora 245 Sarcodina 246 Sporozoa 247 Unidentified species of Nematopsis 249 Ciliata 251 Suctoria 255 Literature cited 255 VIII. Sponges, coelenterates, and ctenophores. The Porifera of the Gulf of Mexico. By J. Q. Tierney 259 Biology of commercial sponges. By F. G. Walton Smith 263 Hydroids of the Gulf of Mexico. By Edward S. Deevey, Jr 267 Collecting 267 Zoogeography 268 Check list of Gulf of Mexico hydroids 269 Summary 27 1 Literature cited 27 1 Hydromedusae of the Gulf of Mexico. By Mary Sears 273 Siphonophores in the Gulf of Mexico. By Mary Sears 275 Scyphozoa. By Joel W. Hedgpeth 277 Anthozoa: Alcyonaria. By Frederick M. Bayer 279 Anthozoa: The anemones. By Joel W. Hedgpeth 285 Notes on common species 287 Bibliography 290 Gulf of Mexico Madreporaria. By F. G. Walton Smith 291 Ctenophores in the Gulf of Mexico. By Mary Sears 297 IX. Free-living flatworms, nemerteans, nematodes, tardigrades, and chae- tognaths. Free-living flatworms [Turbellaria] of the Gulf of Mexico. By L. H. Hy man 30 1 The nemertean fauna of the Gulf of Mexico. By Wesley R. Coe 303 Geographical distribution 303 Reproduction and regeneration 304 Ecology 304 Food 304 Key for identification 305 Systematic description of species 305 Paleonemertea 305 Heteronemertea 306 Hoplonemertea 307 Bdellonemertea 309 Bibliography 309 Eehnioderida of the Gulf of Mexico. By B. G. Chitwood 311 Free-living nematodes of the Gulf of Mexico. By B. G. Chitwood and R. W. Timm 313 Nematode anatomy 313 Historical r&um6 314 Classified list of species 314 Phasmidea 314 Aphasmidea 314 CONTENTS XI Chapter — Continued IX. Free-living nematodes of tlie Gulf of Mexico — Continued Page Geographic distribution 318 Ecology and life habits 319 Li terat ure cited 320 Tardigrades of the Gulf of Mexico. By B. G. Chitwood 325 Notes on the Chaetognatha of the Gulf of Mexico. By E. Lowe Pierce 327 Notes on the range of species collected in the Gulf of Mexico 328 Summary 328 Literature cited 329 X. Parasitic worms. Parasitic helminths. By Asa C. Chandler and Harold W. Manter 333 Trematoda of the Gulf of Mexico. By Harold W. Manter 335 Monogenea 335 Aspidogastrea 336 Digenea 336 Gasterostomata 336 Prosostomata 336 Host specificity of trematodes of marine fishes of the Gulf of Mexico. . 342 The geographical distribution of trematodes of fishes at Tortugas, Florida 343 Trematodes of turtles 345 Trematodes of birds 346 Trematodes of mammals 346 Studies on larval stages and life cycles of trematodes of the Gulf of Mexico 347 Summary 348 Literature cited 348 Cestoda. By Asa C. Chandler 351 Tetraphyllidea 351 Trypanorhyncha 352 Incertae sedis 353 Pseudophyllidea 353 Cyclophyllidea 353 Acanthocephala. By Asa C. Chandler 355 Eoacanthocephala 355 Palaeacanthocephala 355 Nematoda. By Asa C. Chandler 357 Ascaridata 357 Incertae sedis 358 Bibliography (Cestoda, Acanthocephala, Nematoda) 358 XI. Bryozoa, Brachiopoda, Phoronida, and Enteropneusta. The Bryozoa of the Gulf of Mexico. By Raymond C. Osburn 361 Brachiopoda occurring in the Gulf of Mexico. By G. Arthur Cooper 363 Phoronida. By Joel W. Hedgpeth 367 Enteropneusta. By Joel W. Hedgpeth 369 XII. Echinoderm. Echinoderms (other than holothurians) of the Gulf of Mexico. By Austin H. Clark 373 Crinoidea 373 Echinoidea 374 Asteroidea 375 Ophiuroidea 376 Bibliography 378 The holothurians of the Gulf of Mexico. By Elisabeth Deichmann 381 Technique 382 Key to the orders 383 Elasipoda 383 Aspidochirota 384 XII CONTENTS Chapter — Continued XII. The holothurians of the Gulf of Mexico — Continued Page Dendrochirota 394 Molpadonia 405 Apoda 406 Bibliography 408 XIII. Annelids and miscellaneous worms. Polyehaotous annelids of the Gulf of Mexico. By Olga Hartman 413 Review of the families 413 Appendix on some ecological associations 416 Literature cited 416 Miscellaneous vermes. By Joel W. Hedgpeth 419 Echiurida 419 Sipuneulida 419 Literature cited 420 XIV. Arthropods: Xiphosura, Pycnogonida, and Crustacea. Xiphosura. By Joel W. Hedgpeth 423 Pycnogonida. By Joel W. Hedgpeth 425 Marine Ostracoda. By Willis L. Tressler 429 Ecology 430 Ostracoda reported from adjacent regions 436 Caribbean Sea (off Colon) 436 West Indies . 436 Cuba 1. 436 Bahama Islands 436 Conclusions 436 Bibliography 436 Copepoda. By Waldo L. Schniitt 439 Cirripedia. The barnacles of the Gulf of Mexico. By Dora Priaulx Henry,. 443 Mysidacea and Euphausiacea. By Albert H. Banner 447 Stomatopoda. By Fenner A. Chace, Jr 449 Decapoda of the Gulf of Mexico. By Ellinor H. Behre 451 General physiographic regions 451 Comparison of faunas 453 Reference collections 453 Papers of particular reference to Gulf decapods 454 Biology of commercial shrimps. By Milton J. Lindner and William W. Anderson 457 XV. xMollusks. Biology of the spiny lobster. By F. G. Walton Smith 463 Mollusks. By Harald A. Rehder 469 Past work done in this area 469 General 469 Florida 469 Alabama-Louisiana 470 Texas 470 Mexico 470 Cuba 470 Deeper waters 47 1 Ecology 47 1 Caribbean Province 471 Carolinian Province 472 Deeper waters of the Gulf of Mexico 472 Bibliography 473 Cephalopoda of the Gulf of Mexico. By Gilbert L. Voss 475 Systematic list 477 Literature cited 477 Summary of our knowledge of the oyster in the Gulf of Mexico. By Philip A. Butler 479 Oyster reefs of the Gulf of Mexico. By W. Armstrong Price 491 CONTENTS XIII Chapter — Continued XVI. Tunicates and lancelets. P«Be TheTtinicataof the Gulf of Mexico. By Willard G. Van Name 495 Ascidian fauna of the Gulf of Mexico 495 The pelagic Tunicata 496 Bibliography 497 The lancelets. Branchiostomidae. By Joel W. Hedgpeth 499 XVII. Fishes and sea turtles. The origin, relationships, and geographical distribution of the marine fishes of the Gulf of Mexico. By Luis Rene Rivas 503 Shore fishes 504 Pelagic fishes 505 Deep sea fishes 505 Literature cited 505 Biology of the commercial fishes of the Gulf of Mexico. By George A. Rounsefell 507 Taxonomy and distribution of sea turtles. By F. G. Walton Smith 513 Family Cheloniidae 513 Family Dermochelidae 513 Key to the Gulf of Mexico sea turtles 514 Distribution in the Gulf of Mexico 515 Bibliography 515 XVIII. The birds of the Gulf of Mexico. By George H. Lowery, Jr., and Robert J. Newman 519 Offshore birds 520 Birds of the coast 526 Coastal breeding birds 529 Regular visitants on the coast 530 Visitants to coast not of regular annual occurrence 532 Land birds over the open Gulf 535 Literature cited 538 XIX. Mammals of the Gulf of Mexico. By Gordon Gunter 543 Pinnipedia 543 Sirenia 543 Cetacea 545 General information 545 Cetaceans of the Gulf of Mexico 546 Odontoceti. Toothed whales 546 Mysticeti. Baleen whales 550 Literature cited 550 XX. Pollution of water. Aspects of water pollution in the coastal area of the Gulf of Mexico. Pre- pared in the Division of Water Pollution Control, and Shellfish Branch, Division of Sanitation, Public Health Service, U. S. Department of Health, Education and Welfare 555 Nature of pollution affecting the Gulf waters 555 Water pollution control agencies, programs, and laws 556 Florida 557 Alabama 557 Mississippi 557 Louisiana 557 Texas 557 Federal-State shellfish control program 557 Summary of water pollution data 558 Damages to resources caused by pollution 561 Lower Florida area 564 Peace River area 564 Tampa Bay area 564 Withlacoochee River area 565 XIV CONTENTS Chapter — Continued XX. Aspects of water pollution — Continued Damages to resources caused by pollution — Continued Page Suwannee River area 565 Ochlockonee River area 566 Apalachicola River area 566 Choctawatchee River area 566 Perdido-Escambia area 567 Mobile Bay area 567 Pascagoula River area 568 Pearl River area 569 Lower Mississippi River area 569 Atchafalaya River area 569 Calcasieu River area 570 Sabine River area 570 Neches River area 570 Trinity River area 571 Brazos River area 571 Colorado River area 572 Guadalupe River area 572 Nueces River area 572 Lower Rio Grande area 573 The Gulf coast of the Republic of Mexico 573 Literature cited 574 Index 577 CHAPTER I HISTORICAL SKETCH OF THE EXPLORATIONS IN THE GULF OF MEXICO HISTORICAL SKETCH OF THE EXPLORATIONS IN THE GULF OF MEXICO By Paul S. Galtsoff, Fish and Wildlife Service, United States Department of the Interior The brief historical sketch of discoveries and explorations in the Gulf of Mexico presented m this paper is based on published materials avail- able in this country. Fortunately, the large collection of books and maps in the Library of Congress, Harvard University, American Geo- graphical Society, and the Public Library of New York York City provided abundant material from which the progress of scientific knowledge of the Gulf of Mexico could be traced with reasonable completeness. A wealth of data about the earlier discoveries in the Gulf can be found in the classical works of Winsor (1884-89), Thacher (1896), Lelewel (1852), in 20 volumes of history of voy- ages by Prevost (1746-89), Harrisse (1900), and Fiske (1892). A student of history of explorations in the New World finds in the writing of Alexander von Humboldt, especially his Examen Critique . . . (1836-39) a rich source of critical information. A catalog of maps of the Spanish possessions published by the Library of Congress under the title, The Lowery Collection (Lowery 1912) not only gives detailed descriptions of maps printed from 1502 to 1820 but also contains a great amount of information about the explorations and cartography of the Gulf. A brief but com- prehensive review of the explorations between 1492 and 1543 is given by Kohl (1863). Many other publications and maps in various institutions in the United States were consulted. The more important of them are the catalog of maps, British Museum (1884, 1885), the catalog of geographical documents in the national library in Paris (Paris, Bibliothqeue nationale, 1892), Phillips' list of maps of America, list of geo- graphical atlases (U. S. Library of Congress, 1901, 1909-20), and the description of Mexican maps by Torres Lanzas (1900). The publications of Phillips are listed in some libraries under his name, while in others they appear only under his titles (see Bibliography) ; the work of Torres Lanzas may be found under "Spain," "Torres," 259534 O— 54 2 and "Lanzas." Other references not discussed in the text are listed in the bibliography. Reports, letters, and other documents written by the earlier explorers show clearly that ad- venture, military conquest, and search for fabulous riches were the principal impelling forces that lured thousands of men of the sixteenth and seventeenth centuries to embark on the daring voyages beyond the unknown western ocean. Science played only a minor part in these risky undertakings, and scientific observations made in the course of these explorations, which so greatly enhanced the knowledge of the inhabitable world, were merely incidental byproducts of mercenary or military ventures. History of the discovery and colonization of the New World is beyond the scope of this chapter. The following pages contain, therefore, only a brief summary of scientific achievements of the many explorations in the Gulf of Mexico from the time of its discovery to the present days. The author hopes that the picture of the scientific progress in the studies of the Gulf which he pre- sents here has not been distorted by errors or omissions. PRE-COLUMBIAN ERA Written history of the explorations in the Gulf of Mexico naturally begins with the discovery of the New World by Columbus in 1492, but long before the white man set foot on the shores of the islands of America the existence of a large, landlocked body of water now called the Gulf of Mexico was known to the tribes that inhabited its coastal plains and sailed and fished in its waters. Indians living along the west coast of Florida did not venture beyond a narrow coastal zone in which they fished from small dugout canoes. This conclusion is well substantiated by archaeological research in Florida and especially by the study of the contents of numerous shell heaps (Walker 1880, 1885; Wiley 1949), which contain the rem- 3 4 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE nants of birds, fishes, and mollusks found only in coastal waters. The Aztecs, who developed their own system of navigation, were fairly well acquainted with certain parts of the Gulf. This is probably true also of the Mexican and Yucatec Indians, who sailed over considerable distances off shore. Evidence for this is given in the report of the fourth voyage of Columbus, who on July 2,1502, sighted a large Indian ship of the size of a Spanish galley about 80 miles east of the Yucatdn coast (Kohl 1863). The art of map making practiced by Aztecs had reached a high degree of perfection as can be judged from the incident described by Bernal Diaz de Castillo (Hakluyt Society Works, 2d ser.. No. 24, p. 129, quoted from W. Lowery, 1912, p. 27). During the Cortes invasion of Mexico, he writes, "The great Montezuma gave our Captain a henequen cloth on which were painted and marked very true to nature, all the rivers and bays on the northern coast from Pdnuco to Tabasco, that is, for a matter of one hundred and forty leagues, and the river of Coatzacoalcos was marked on it." For more than 1,400 years of the Chi'istian era the geography of the western world was under the influence of the writings of Claudius Ptolemy, an Egyptian who lived in Alexandria about the middle of the second century (the dates of his life are usually given as between 90 and 168 A. D.), and spent 40 years in making astronomical observations. For many centuries Ptolemy's data on the locations of many places on earth with reference to the parallel of Alexandria were the principal source of information for map makers. No existing Ptolemy maps are known earlier thaa that of the thirteenth century, the first printed edition of which was executed in 1475 in Vicenza (Thacher 1896). Some idea of the type of maps available to navigators at the end of the fifteenth and the beginning of the sixteenth century can be gained from examining figure 1 representing the map of the world by Johannes Ruysch, copied from Ptolemy's geography of 1507-08. The discovery of the New World has been already incorporated in it, and the name "Mundus novus" appears for the first time on the engraved map. During the last 40 years of the fifteenth century the Portuguese seamen made persistent and almost continuous efforts to search for new Atlantic islands beyond the Azores. So far, no docu- mentary proof has been found of the pre- Columbian discovery of western lands by Portu- guese, but, as stated by the Portuguese historian, Antonio Baiao, "... there are numerous in- dications that the existence of other islands be- yond the Azores was known or suspected in Portugal. It was in the wake of these indications that Columbus sailed. His voyage is integrated with cycle of Portuguese explorations of the Western Ocean." (Quoted from Morison, 1940, p. 75.) Because of the secrecy attached by the Portu- guese Government to the discoveries of new lands and their location, the findings of Portu- guese seamen were lost, and only inconclusive traces of their efforts remain on certain documents originated in Lisbon. One of these is the famous map by Alberto Cantino which is discussed in the next section of this article (p. 8). DISCOVERY OF THE GULF OF MEXICO The discoverer of the New World came almost to the very entrance of the Gulf of Mexico but failed to enter it. On his second voyage, June 1494, Columbus followed the southern shores of Cuba as far as Isia de Pinos, where he stopped. Disregarding the infoi'mation received from the Indians that the end of the land was not far, he changed his course and sailed eastward. The decision was influenced by his strong belief that Cuba represented the end of the new continent. As it is generally known, he asked his companions to sign a statement to this effect. The declaration, however, was not universally accepted since the earliest maps of the New World by Cosa, 1500 (fig. 3, p. 9), and Waldseemiiller, 1507 (fig. 2), show Cuba (Isabella) as an island. The question who was the first European ex- plorer to sail along the coast of the American continent is by no means settled. The credit is usually given to the man whose name is forever associated with the New World. Amerigo Ves- pucci, the third son of a Florentine notary, was born on March 9, 1451. He studied diligently and became proficient in astronomy and in the use of the astrolabe, but his principal interest was in a commercial career. After establishing himself as an agent for the House of Cadiz, Vespucci undertook to settle the claims left after the death GULF OF MEXICO o a oi o a c o ■-s a o Oh a o FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE GULF OF MEXICO of his friend, Juanito Beranii, who contracted to supply and equip 12 vessels of 900 tons each for the Spanish Crown. In 1497, at the request of the king, Vespucci joined the expedition to the New World. In his own words, "the King, Don Fernando of Castile, being about to dispatch four ships to discover new lands toward the west, I was chosen to aid in making discovery" (Thacher 1896, p. 69). He never explained his exact duties aboard the ship, but judging from his previous experience in commercial methods he probably went as a sort of supercargo to supervise the distribution of food, to weigh the gold, and to keep accurate tally of the Crown's share which, according to the royal decree of 1495, was one- third of the total gold obtained by the expeditions. Vespucci started from Cadiz on May 10, 1497. After reaching the Canary Islands in about 10 days, the fleet sailed west and quarter-southwest for 37 days (27 days according to the Latin text of Vespucci's letter) until land was sighted a thousand leagues from the Canaries. Making allowance for an error of 1° latitude and about 8° longitude, Thacher (1896) estimated that the landfall would be off the coast of Honduras in the vicinity of Cabo Gracias a Dios. It is interesting to note that the ships passed between the islands of the Caribbean without noticing them. A safe harbor was found after 2 more days of sailing northward. Vespucci describes how, skirting the coast, he saw villages one of which, consisting of 40 houses, was built, like Venice — upon the water. It was near this village that a fierce encounter with Indians took place in which 15 or 20 natives were killed. The place is probably on the shores of Campeche Bay, north of Tabasco. Continuing for 80 leagues farther along the coast, the expedition came to a place inhabited by different people. It was called the Province of Lariab, a name which later on caused a great deal of confusion and argument since in the Latin edition of Vespucci's letter the name was trans- lated "Parias," a mistake that led many to believe that the explorer referred to the Gulf of Paria off the Venezuelan coast discovered by Columbus in 1498 during his third voyage. According to Thacher, the word "Lariab" is a compound word of Quiche dialect which means "there are many." It is assumed that the expres- sion was used by the natives, who misunderstood the question addressed to them by Spaniards about the name of their province and answered that there were many people in the land. Vespucci states that this land, which is probably near Tampico in Mexico, is "within the torrid zone, close or just under the parallel described by the Tropic of Cancer where the pole of the horizon has an elevation of 23° at the extremity of the second climata." (Quoted from Thacher, 1896.) The term "clima" (plural "climata") of ancient Greek cartographers denotes parallel zone or belt, the width of which, according to Hipparchus, is determined by astronomical observations on the basis of the longest day of the year. The rest of the letter (Vespucci, 1926 edition) caused endless arguments among geographers. Vespucci states that from Lariab they navigated in sight of land and covered 870 leagues, still going in the direction of the "maestrale." This course, corresponding to northwest, would have brought the expedition over the continent nearly to the coast of California. Harrisse (1900) ignores the western component of the direction of "maestrale" and considers only its northerly meaning. He states that plotting 870 leagues along the American coast would bring Vespucci's ships as far north as Cape Hatteras. According to Vespucci's narrative, the expedition turned east toward Bermuda from this place and returned to Cadiz on October 15, 1498. Humboldt (1836-39) expresses doubt whether Vespucci ever made this voyage and denies him the credit of discovery of the new continent. According to Humboldt, at the time of his sup- posed voyage Vespucci was engaged in equipping the third expedition of Columbus and could not possibly have taken part in the explorations he describes. Obvious inconsistencies in the text of Vespucci's informal letters are unfortunately augmented by errors in translation. The accusa- tions that Vespucci was a fake (see Winsor 1886, v. 2, pp. 129-136; Harrisse 1895) are answered, however, by pro-Vespuccian writers (Varnhagen, 1865, 1869a, 1869b, 1870), and final settlement of the question awaits further historical research. Bremer (1940) advances an entirely new theory that the honor of the discovery of the Gulf of Mexico belongs to a Portuguese by the name of Caspar Corte Viall who, shortly before 1500, sailed to the west and upon returning to Portugal spread the news of the existence of a new continent and islands in the western ocean. In support of his 8 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE hypothesis, Bremer mentions a place on the northern coast of the Gulf of Mexico known by tradition as Portuguese Field, which he considers may be a landing place of Portuguese sailors. The evidence, however, is not convincing. SIXTEENTH AND SEVENTEENTH CENTURIES The progress of early discoveries in the Gulf may best be followed by studying the maps of this period. Since the data concerning the location of new lands were considered by the Spanish Govern- ment a state secret, maps and reports which the captains of the ships were requested to submit to tte government immediately upon their return to Spain were carefully guarded, and all means were taken to prevent them from falling into the hands of other European powers. As a consequence of this policy of secrecy the first maps of the New World were engraved and published outside Spain (in Italy, France, and Germany), using data which were often surreptitiously obtained or smuggled out of the countr3\ Many of the original docu- ments, usually drawn on parchment or oxhide, were lost or destroyed in war and by accidents; only a few of these valuable documents were recovered in more recent years after many vicissitudes. The first map of the world summarizing the discoveries in the western ocean and showing the Gulf of Mexico was drawn by Juan de la Cosa, the companion and pilot of Columbus and owner of the caravel, Santa Maria, which bore the admiral's flag and was the first ship to reach the New World. The map embodies the results of seven important voyages: the three voyages of Columbus in 1492, 1493, and 1498; the first and second voyages of Vespucci in 1497 and 1498; and the first and second voyages of Cabot in 1497 and 1498. The date of the execution of the map is established by the inscription which reads, "Juan de la Cosa el fiso en el porto de Santa Maria en ano de: 1500." The history of this unique historical document is interesting. After being lost for tlu-ee centuries, the map was found in 1832 in a Paris bric-a-brac shop where it was purchased for a small sum by Baron de Walckenaer. Its great significance was pointed out by Humboldt (1836) when in 1832 he drew public attention to its importance. After the death of Walckenaer . the map was offered for sale at public auction and was purchased for 420 francs by the Hydrographic Department of the Spanish Government. Today it hangs in the Naval Museum of Madrid, listed in the museum guide book as number 553, with a detailed descrip- tion and a brief history of this remarkable docu- ment (Madrid, Museo Naval, 1945). The original map is drawn on oxhide, 5 feet 9 inches long, cut square at the tail of the hide where its width is 3 feet 2 inches. The Tropic of Cancer runs vertically through the middle; the top corresponds to the extreme west and includes the Caribbean Sea and the Gulf of Mexico. The latter area, instead of geographical details, is occupied by a rectangular drawing representing St. Christopher bearing the Christ child, a rather crude imitation of the famous woodcut engraving of 1423. Originally the map was rich in blue and gold and illuminated after the fashion of medieval manuscripts, but today it is torn and faded. Peter Martyr, who saw it in 1514 in the house of the Bishop of Burgos, head of the Maritime Department of the Casa de Contratacion, re- marked on its highly colored beauty. The photographic reproduction of the Cosa map available in the Library of Congress is too blurred and cannot be clearly copied in the text. The part of the map referring to the Gulf of Mexico can be seen in figure 3, representing a copy found in volume 4 of Humboldt's Examen Critique (1836-39); this part of the map was redrawn and oriented by Humboldt in the con- ventional manner. One of the earliest documents showing certain details of the New World and a part of the Gulf of Mexico is Cantino's map of the world. It represents for the first time what appears to be the west coast of Florida and the adjacent part of the Gulf (fig. 4). It was drawn as a large planisphere on parchment in gold and various colors. The map derives its name from Alberto Cantino, Ambassador of the Duke of Ferrara t«. the King of Portugal. The original, located in Biblioteca Estense in Modena, was obtained by Cantino for 12 ducats and was sent by him with a letter to Senor "Duca Hercole" in Lisbon. In later years the map was used as a screen and finally was recovered in a damaged condition from' the shop of a pork butcher in Modena and deposited in the library. Some cartographers (see Lowery 1912, pp. 5-6) GULF OF MEXICO Figure 3. — Western part of the map of the new discoveries drawn by Juan de la Cosa. Reproduced from a copy Humboldt's Examen Critique (1836). 10 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE Miisartittis: H, #(cm\^ v n ^ iTt P 36 antllbaetitf ^cyttcalld la: *^ t-^ 5 ^ Ml '\ .M '-^A ^nSd r(k f>frti^W.rmUhi n maSWtf Figure 4. — Western portion of the Cantino map of the world, 1502. Original without name, date, or title. Reproduced from a copy in Harrisse's Les Corte-Real 1883. GULF OF MEXICO 11 consider that Cantino was familiar with the Portufjuese voyages to the New Workl and incor- porated their discoveries in his drawing. This subject, as well as the questions whether "Ilha Ysabella" on the map represents the island of Cuba or the Crooked Islands group called "Isa- bella" by Columbus, and whether the peninsula west of it is Florida, are critically discussed by Morison (1940). The Gulf of Mexico is very crudely shown on the map of the world made by the German carto- grapher, Waldseemiiller, and printed in 1507 in St. Die, Lorraine. This map is famous because for the first time the continent of the New World is shown with the name "America" attached to it in honor of the Florentine explorer. The origi- nal is owned by Franz Joseph II of Liechtenstein.' Of the many expeditions that sailed to the New World during the first decade of the sixteenth century, the more important ones were those headed by Hojeda, 1499; Nino and Guerra, 1500; Pinzon, 1499-1500; Lepe, 1500; Bastidas, 1500-02; Hojeda and Vergara, 1502-03; and Cosa, 1504-05. Results of these ventures materially enlarged the knowledge of the geography of the eastern part of the Caribbean area, but its western section, in- cluding the Gulf of Mexico, remained unexplored. In 1513 the expedition headed by Ponce de Le6n made a formal discovery of Florida, the existence of which was probably known to Spanish and Portuguese adventurers who visited the land north of Cuba but left no records of their findings. On Easter Sunday, March 27 of that year. Ponce de Leon with his three ships was in sight of land not far from the present city of Jacksonville. To commemorate the holiday the land was named la Florida. Failing in his attempt to circumnavi- gate the "island" Ponce de Le6n turned south and on May 12 of the same year found a chain of islands which he named las Islas de los Mdrtires (present Florida Keys), and about a month later he discovered the Tortugas. In the following year, 1514, the King of Spain incorporated the newly discovered land in an administrative re- gion known as Adelantado de la Isla Bimini e la Florida. Ponce de Le6n was the first explorer who re- corded the existence of a strong current along the • In May 1950 the map was offered for sale at an auction in New York City with the condition that bids should exceed $50,000, but in the last minute was withdrawn by the owner. east coast of Florida. He reported that his ships' while crossing the stream near Cape Canaveral, frequently were swept by strong current. He obviously was referring to that part of the Gulf Stream which at present is known as the Florida Current (Herrera 1601, 1728; Stommel 1950). In 1516 Diego Miruelo undertook another ex- pedition to Florida, and in the following year, 1517, Fernando de Cordoba and Antonio de Ala- minos explored the northern and western coasts of Yucatin. Driven for several days by a severe storm they finally saw land with a large Indian town, near Cabo Catoche. The expedition re- corded many points, bays, and harbors along the west coast of the Gulf and safely reached the Bay of Campeche, giving it its present name. Trouble started, however, near the place called Champo- ton where C6rdoba and his landing party were attacked by Indians. In this encounter, C6rdoba was badly wounded and many of his soldiers were killed. Alaminos, the principal pilot of the ex- pedition, decided to take advantage of the pre- vailing easterly winds and sailed north to Florida and then turned south toward Cuba. His deci- sion was a right one. In a few days the ships crossed the Gulf and returned to Cuba, where C6rdoba died of his wounds. Scientific results of the expedition were signifi- cant. More than 500 miles of the Gulf coast were mapped; proof was obtained of the existence of an open channel between the Florida and Yucatdn Peninsulas; and valuable information was accumulated regarding the prevailing winds, cur- rents, and depth of water. Alaminos was still under the impression that Yucatan was an island. The name Yucatdn was taken from the expression "Uyucatan" which the Spaniards frequently re- ceived from Indians in reply to their questions, the meaning of which was "we don't understand you." Before his death, C6rdoba appointed his nephew , Juan de Grijalva, commander of a force consisting of 4 ships and 250 men. Experienced Antonio de Alaminos was again the senior pilot of the expedition which on April 20, 1518, sailed from the harbor of Matanzas (Cuba) and followed C6rdoba's former route toward the Cape of Yuca- tdn. Stormy weather drove the expedition far- ther south along the eastern coast of the peninsula toward an island called by the Spaniards la Isla de Santa Cruz but known at present as Isla de 12 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE Cozumel. From this point the ships turned north around the Yucatan Peninsula and on May 26 passed the point reached by the previous expedi- tion and entered a large bay which was called Boca de Terminos (Laguna de Terminos on mod- ern charts) . Grijalva thought that he had reached the end of the YucatAn island which he named La Isla de Santa Maria de Remedios, the name which appeared on maps of that time. The expedition continued along the unknown coast for nearly a thousand statute miles to a point a short distance south of the present location of Tampico. Grijalva's expedition substantially contributed to our knowledge of Gulf geography. The names of many familiar places such as Grijalva River, the bay and river of Tonola, Coatzacoalcos River, Alvarado River, and many others were established and their positions indicated on maps. Alaminos made many astronomical observations between Yucatan and Tampico. Some of his determina- tions of latitude — for instance, that of a small island where the present town of Veracruz is located — were accurate within 1°. He also ob- served and recorded the currents along the coast and made soundings and other hydrographical observations. When the expedition entered the mouth of the Grijalva River the Spaniards were encountered by many Indians having gold in their possession. When asked for the name of the land the metal came from, the Indians replied, "Mexico." In this way the Spaniards heard for the first time the name of the country which played such an important role in the expansion of Spanish power in America. Upon reaching his farthermost point at Pinuco, Grijalva became convinced that he was exploring the coast of a large continent and not of an island as he had first believed. Realizing the importance of this discovery, he dispatched Pedro de Alvarado on a fast ship to inform Governor VeMsquez of Cuba of his important finding and saOed back fol- lowing the same route the expedition took from Cuba. A new expedition organized by Velasquez in 1519 was in command of Hernando Cortes with Antonio de Alaminos again serving as chief pilot. In May of the same year the expedition sailed around Cape Catoche, following in general the route taken previously by Grijalva. This time the Laguna de Terminos was explored more care- fully by Captain Escobar who established its true nature as a shallow, landlocked body of water not suitable for establishing a colony on its banks. Antonio de Alaminos, who was sent northward to Cabo Rojo south of Tampico, discovered a large river emptying into the Gulf and named it Rio Grande de Pdnuco. Besides the surveys of the coast from Cape Catoche to Tampico, Alaminos' principal con- tribution to the exploration of the Gulf was the discovery of a free passage between Florida and Cuba which represented the shortest route for Spanish vessels carrying silver from Mexico to Europe. In 1519 Francisco de Garay, Governor of Ja- maica, sponsored an expedition of Don Alonzo Alvarez de Pineda to explore the northern coast of the Gulf. Four ships provided by Garay sailed from Jamaica toward Florida. Believing that Florida was an island, Pineda followed the west coast looking for a passage and, not finding it, turned west along the northern coast of the Gulf. In the course of his exploration he discovered the mouth of the Mississippi River which he called "Rio del Espiritu Santu" and described the body of water east of the delta as "Mar Pequena" or a small sea, the name of the present Mississippi Sound which persisted on many charts for nearly two centuries. Pineda noted the physiographical character of the shoreline, recorded the positions of dunes, low-lying sandspits, bays, knolls, marshes, and oyster banks {ostiales) which abounded in the Mississippi Sound and in the delta of the Missis- sippi River. He realized that the majestic fresh- water stream which he ascended for several miles must originate on a large land area, and other observations convinced him that he was exploring the coast of a great continent. Although the majority of writers agree with Hari'isse (1900) that the river Pineda named Rio del Espiritu Santu is the present Mississippi River, there are others who think that the de- scription of the country given in his reports does not agree with that of the mouth of the Mis- sissippi and that Pineda's expedition actually was in Mobile Bay (Scaife 1892). This question probably never will be answered with complete certainty. As a result of his explorations Pineda produced several new maps showing, with ap- proximate accuracy, the outlines of the Gulf coast. Only one of them, bearing the title "Traza GULF OF MEXICO 13 de Costas de Ticrra Firme y las Tierras Nuevas," was published. The original, datod 1521, is in the Archive General de Indias, in Seville, and its reproduction is given by Navarrettc (1837) and Winsor (1884, v. 2, p. 218), In 1521 the west coast of Florida was revisited by Ponce de Le6n, who landed probably in Char- lotte Harbor where he was seriously wounded in a battle with Indians. He died within a few days, after being taken back to Cuba. This expedition added nothing to the progress of geo- graphical knowledge of the Gulf, The next attempt to conquer Florida and ex- plore the northern part of the Gulf was made by Panfilo de Narvaez, who had distinguished himself in the conquest of Cuba under Velasquez and was at the head of an expedition sent by the Spanish Goverimient to compel Cortes to relinquish his command in Mexico, His defeat and imprison- ment by Cortes did not reflect on his reputation, and upon returning to Spain he obtained from Charles I a grant to colonize a vast expanse of land from Florida proper as far west as Rio Panuco, On June 17, 1527, five ships under the command of Narvaez sailed from San Lucas, Spain, with 600 men and officers aboard. One of his com- panions was Cabeza de Vaca, the treasurer of the fleet. After leaving the south shore of Cuba in March 1528, the ships, driven north by strong winds, found shelter in a large bay which the Spaniards called Bahia de Santa Cruz. Ac- cording to the description given by Cabeza de Vaca, the bay extended from 7 to 8 leagues inland, had many islands, and presented an excellent anchorage with a depth of water of about 6 fathoms. There is no doubt that it was the present Tampa Bay. Misinformed by Indians that the land north of the bay, known as Apalachee, was rich in gold, Narvaez marched overland with 300 officers and men while his ships under the command of Miruelo followed the northern direction along the coast. The rendezvous was supposed to be in a bay north of the point of their departure. In about 2 months, Narvaez's column reached the village of Apalachee where with great difficulty the men found only a few bushels of corn. Trying to establish contact with the ships, Narvaez turned south and discovered a river, Rio de Magdalena, as the Spaniards called it, which probably cor- responds to the present Apalachicola River, The party suffered many hardships in the swamps of this region, and many men perished of exhaustion and disease. Failing to contact the ships, Narvaez decided to march west rather than to return to Tampa Bay, On the shores of a bay, which probably corresponds to the present St, George Sound and which was named Bahia de los Caballos, the Spaniards were compelled to slaughter their last horses to make crude boats of their skins, and sailed westward. They followed the shoreline, entering different lagoons (Pensacola, Santa Rosa, and others). In November they reached a bay with many islands (probably Chandeleur Sound in the Mississippi Sound), Since the water was fresh they realized that thej' were near the mouth of a great river which they attempted to enter, but strong wind and current drove them into the sea where Narvaez perished in the storm. His companion, Cabeza de Vaca, found refuge on a small island 5 leagues long and 2 leagues wide which he named Isla de Malhado. The place may be Ship Island, Horn Island, or some other island in the Mississippi Sound, Scattered by the storm, most of Narvaez's men perished. With a few men, Cabeza de Vaca succeeded in landing on the mainland, where for 6 years he lived among the Indians. In 1533 he gave up hope that any European ship would visit the coast and with Lope Oviedo decided to march westward. Encountering a few small streams they came to the banks of a very large river which they considered to be Rio del Espiritu Santu (Mississippi River), and after crossing it marched for a long time through Texas until they reached the Bay of California. In 1536 Cabeza de Vaca returned to Europe where the results of the unfortunate expedition became known. Its principal scientific achieve- rnents can be briefly summarized as follows: The Mississippi River was seen for a second time; Tampa Bay was more fully explored, and new names, such as Apalachee Bay, were added to geography. After waiting in vain for Narv&,ez at the place of rendezvous, Miruelo returned with his ships to Tampa Bay. It is interesting to note that, al- though he failed to reach the bay at the north coast of the Gulf where he was supposed to meet Narvaez, the name of Bahia de Miruelo 14 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE appeared for many years on the charts in the place of the present Apalachee Bay. Shortly after the tragic end of the Narvaez expedition, Fernando de Soto, a Spanish captain and explorer, was preparing for a new adventure. De Soto acquired a large fortune from the con- quest of the Inca Empire in Peru in which he played a prominent role. He obtained from Charles V a commission as "Adelantado" of the lands of Florida and Governor of Cuba and invested his large fortune in a new adventure. On May 18, 1539, seven ships comprising De Soto's flotilla carrying 700 soldiers, 200 horses, mules, supplies, and materials, sailed from Havana. On May 25 they reached Tampa Bay, known as Bahia de Espiritu Santu. From Tampa Bay, De Soto with a large detachment of horsemen and foot soldiers went by land to Apalache. One of his companions, Juan de Anasco, a prominent seaman, cosmographer, and astronomer was en- gaged in making scientific observations during this military expedition. After reaching the land north of Apalachee, De Soto despatched Anasco south to find a harbor. During this travel the party discovered the bones and other remains of Narv^ez's men, and coming finally to the shores of the sea discovered a large bay which they called Bahia de Ante (present Apalachee Bay). In January 1540, De Soto ordered Captain Diego Maldenado to sail for 100 leagues along the coast to take records of all the bays, harbors, and rivers and to return in 2 months. In the course of this survey Maldenado found a bay 60 leagues west of the Bay Aute which he described as the most beautiful harbor in the world ("un hermosis- simo puerto"), protected against all winds. He named it Achusi. The entire harbor was sounded with great detail, for De Soto wanted to use it as a rendezvous and a base for his operations. De- tailed descriptions made by Maldenado leave no doubt that Achusi corresponds in every respect to the present Pensacola Bay. After exploring the east coast of the American continent as far north as the Savannah River, De Soto returned to the Gulf and in October 1540 investigated the place called Mavill or Mauvill which is the present Mobile. His further ex- plorations lead him inland and westward to the banks of the Mississippi which he crossed at Chickasaw Bluffs near the present location of Memphis, Tennessee. In 1542 he died and was buried at the bottom of the Mississippi River. Before his death he ap- pointed Luis de Moscozo de Alvarado as his successor. After many vicissitudes the Spaniards, under the leadership of their new chief, constructed several boats in which they sailed down the river, successfully evading the pursuit of Indians. Upon reaching Gulf waters they turned westward with the hope of landing somewhere on the Mexican coast. All navigation instruments were lost when the Indians burned the Spanish camp at Mobile, but one astrolabe was saved by Aiiasco. Being a careful and resourceful man, he managed to make a sea chart from a parchment of deerskin, and with a forestaff, made from a ruler, and an astrolabe salvaged from the fire at Mobile, at- tempted to guide the course of the flotilla. His worthwhile efforts were so much ridiculed by the other seamen because Anasco had never before embarked on any other maritime expeditions, that in disgust he threw his instruments, except the astrolabe, into the sea. One day, because of bad weather, the ships sought refuge in a small cove. While some of the Spaniards were gathering shellfish along the shore they foimd some slabs of black bitumen almost like tar which the ocean had cast upon the beach. Garcilaso, who tells this story (Garcilaso de la Vega, Vamer's translation, 1951, p. 601), says, "This substance must come from some spring which flows into the sea or which is born in the sea itself. The slabs weighed 8, 10, 12, and 14 pounds; and they were found in quantity." The tar-like substance was successfully used by the Spaniards to repair the leaky vessels, and after spending a few days on the shore they continued westward. This is probably the earliest reference to the finding of asphalt along the Gulf coast. After many days of sailing along the coast line Moscozo entered the mouth of the Panuco River and landed in Mexico.^ The discovery of Pensacola Bay, exploration of the delta of the Mississippi River and of the northern coast of the Gulf, and the convincing evidence that the Mississippi was a mighty stream draining from a large continent, were the principal scientific contributions of the De Soto expeditioh. ' Detailed account of De Soto's expedition can be found in the report of the U. S. De Soto Commission (1939). GULF OF MEXICO 15 Its unliappy completion marked the end of the period of the earliest explorations in the Gulf. Sbcteen years after the return of Moscozo a Spanish conquistador, Don Tristan de Luna, organized a new expedition to the Gulf. This expedition contributed little to the science of geography. By this time Spain's interest in the new land across the ocean and the enthusiasm of her rulers for new explorations and colonization of the New World somewhat slackened. Although the great advantages derived from the possession and colonization of the newly dis- covered territories were fully appreciated by the Spanish Government and by the educated class of the Spanish nation, the country lacked ability and resources to develop them. At the same time, the Spanish Government jealously watched the efforts of other nations to establish themselves in the New World. It tried by every means to prevent French colonization of the country sur- rounding the Gulf of Mexico and did not hesitate to send military expeditions to destroy French colonies. The results of many expeditions in the Gulf conducted during the first half of the sixteenth century provided the cartographers with new, reliable material for the construction of new maps, and consequently, the outlines of the Gulf shown by them in their drawings began to assume more or less correct configuration. This can be noticed, for instance, by examining figure 5, representing Mercator's map of 1538, in which for the first time the name America was applied to the entire western continent. It may be of interest at this point to make a brief survey of the geographical names which were given to the Gulf of Mexico. No special name for the Gulf is found on the map of Juan de la Cosa of 1500 or the Waldseemiiller map of 1507, al- though in both of them the location of the Gulf is clearly shown. Cortes, in his despatches, referred to the Gulf as Mar del Norte, while the names Golfo de Florida and Golfo de Cortes are found in the writings of other explorers. The name Sinus Magnus Antilliarum appears on an old Portuguese map made in 1558 by Diego Homen (original in British Museum). Probably the most remarkable name is that of Mare CathajTium (Chinese Sea) which is foimd on one chart of the middle of the sixteenth century (copy reproduced in the Memoirs de la Societe de Nancy, 1832). In 1550 the name Golfo de Mexico appears for the first time on the world map the original of which, according to Kohl, is in the Bodleian Library in Oxford. Earlier Spanish geographers used, also, the name of Golfo de Nueva Espana. Herrera (1728) called it Ensenada Mexicana and Seno Mexicano, the names which persisted in Spanish admiralty charts until the eighteenth century. The present name, the Gulf of Mexico, and the corresponding names, Golphe du Mexique in French and Golfo Mexicano in Spanish, appear to have been in use since the middle of the seventeenth century. During the latter half of the sixteenth century the French Huguenots, trying to escape religious persecution in Europe, made many attempts to establish colonies in Florida. Their efTorts were primarily directed to the east coast of Florida where the French penetration lead to many bloody encounters with the Spaniards. Probably the most significant French contribution to geo- graphical knowledge of this time was Le Moyne's map of Florida. Jacques Le Moyne de Morgues was an artist who accompanied a French expedi- tion to Florida under Laudonniere in 1564. His map shows only a part of the Gulf of Mexico east of the Mississippi River. Since it is known that French observations were limited to the east coast of America between the point south of St. Augustine and Rio Jordedan (Charleston Harbor) in the north, the rest of the map was obviously borrowed from Spanish sources. The names of many places are corrupted as, for in- stance, Apalache Bay is indicated as Sinus Morquel, corrupted from the Bay of Miruelo, and the Bay of Ponce de Leon (Tampa Bay) is called Sinus Joannis Ponce. This map, published by De Bry in 1591 after the death of the artist, was for 50 years copied by Dutch and French cartog- raphers but was completely ignored by the Spaniards. Le Moyne produced, also, a series of extraor- dinarily interesting drawings depicting the home life, habits, methods of hunting, and cere- monies of the Timucua Indians. Excellent repro- ductions of these illustrations together with a translation of the Latin text of De Bry were published in English (Le Moyne, 1564, ed. 1875) and some of the drawings are reproduced by Swanton (1946, tables 51, 53-57, 81, 82, 85, 87, and 106). Examination of these illustrations gives an insight into the tribal life of Florida 16 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE o O >. « 3 o GULF OK MEXICO 17 Indians as it was inter reted by a French artist. Particularly amusing are the scenes of alligator hunting in wliich the beast exceeds many times its normal size and the peaceful scene of the Timucua Indian women sowing their fields, the latter drawing conveying a bucolic atmosphere in conformity with the prevailing artistic taste of that time. No significant advance in geographical knowl- edge of the Gulf was made during the latter part of the sixteenth and the first half of the seven- teenth century. In this period Spanish ships loaded with gold and silver continued to sail from Mexico to Havana following the northern coast of the Gulf ami passing the delta of the Mississippi River which was called Cabo de Lodo, or Mud Cape. The names of the earlier discoverers, such as Pineda, Narvdez, Ponce de Le6n, De Soto, and others whose exploits made possible the relatively safe sailings of these ships, were almost forgotten. During the last quarter of the seventeenth cen- tury -a new era of explorations was initiated by French adventurers who attempted to reach the Gulf coast from the north in order to establish there new colonies. In 1673 two French explorers, Louis Joliet and Father Marquette, descended the Mississippi River from Lake Michigan and voyaged south to the mouth of tiie Arkansas River. In 1682 La Salle entered the Mississippi by way of the Illinois route, explored the river to its mouth, and in the name of France took possession of its entire drainage basin. Seeing great political and economic advantages in establishing a colony at the mouth of the Mississippi River, he obtained support of the French Government and in 1684 sailed from Europe with four ships, one of which was shortly captured by Spaniards. La Salle missed the mouth of the Mississippi River and landed farther west in Matagorda Bay, Texas, where he established his colony. Misfortunes, disease, and death so devastated the ranks of the colonists that in a few years only 45 survivors remained from several hundred who comprised the original party. In desperation. La Salle decided to reach Canada by land and during this journey was assassinated by his men. One of the results of La Salle's exploration, which is of definite interest to the geography of the Gulf, is the sketch map of the location of his camp on the shores of Matagorda Bay with the soundings sliown in feet. The reproduction of this map, in tlie form of a tracing from a photo- graph of the original, is given by Dunn (1917, p. 33). Rumors of the French penetration in the land bordering the Gulf aroused the half-dormant rivalry between Spain and France and induced the Spanish Government to send several military expeditions with orders to destroy French colonies. As one of the official documents of that time stated, it was necessary to "desarraygar esta espina que se a yntroducido en el corazon del cuerpo de la America" which means to uproot the thorn that had been thrust into the heart of America (Dunn, p. 42). In 1686 Martin de Echegaray, a naval captain of the presidio of St. Augustine, Florida, attempted to interest the Spanish Government in strength- ening Spanish influence in the domain of Florida by transporting 50 Spanish families from the Canary Islands and 25 Indian families from Cam- peche. In support of his plan, Echegaray sub- mitted a map, wdiich is a good example of the defects of the geographical knowledge of that time, of the interior of the American continent. The Echegaray map shows the large "river Canada," or St. Lawrence River emptying into a lake from which two rivers lead southward to the Gulf of Mexico, both emptying into Espiritu Santu Bay (Mississippi River). Echegaray's scheme was not accepted, but the Spanish Gov- ernment took other measures to counteract the French penetration into the new continent and to destroy La Salle's colony of which they were afraid. An interesting account of these attempts is given by Dunn (1917). It is sufficient to men- tion here that not less than four maritime ex- peditions were sent by the Spanish Government, and the whole Gulf of Mexico was examined with great diligence. One of the important results of this search for French colonies was the rediscovery of Pensacola Bay which the Spaniards decided to occupy. Admiral Pez was placed in command of an expedition organized for this purpose in 1693. One of his principal companions was Dr. Carlos de Siguenza y Gongora, professor of mathematics in the Royal University of Mexico and chief cos- mographer of the kingdom. Siguenza kept a detailed journal of the journey in which he re- corded his observations. The vessels of the expedition reached Pensacola Bay on St. Mary's 18 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE Day, August 14, 1693, and following their custom, the Spaniards immediately renamed it "Bahia de Santa Maria de Galve," the last name being added to the holy name of the Virgin in honor of the viceroy of the territory. Siguenza made a detailed survey of Pensacola Bay and described its configuration, depth, islands, and rivers. The expedition proceeded farther east and after some difficulty entered Mobile Bay, made soundings in the channel, and found that the depth was only 20 "palmas." As a result of Siguenza's observa- tions strong recommendations were made to oc- cupy Pensacola, but a final order for this action was not issued until 1698. Rivalry among the western European powers in establishing a foothold on the shores of the Gulf of Mexico greatly enhanced the geographical knowledge of the region. As a military necessity the whole northern coast of the Gulf, with har- bors, rivers, and lagoons, was surveyed; fairly accurate navigational charts were prepared; and information was accumulated regarding the pre- vailing winds and currents. In this way marked progress was attained in the cartography of the Gulf and adjacent coastal lands. EIGHTEENTH CENTURY At the beginning of the eighteenth century sailing vessels of European powers engaged in trade or in pursuit of military designs continued to traverse the waters of the Gulf in ever in- creasing numbers, but the era of ambitious ex- peditions and daring adventures, which in the past fired public enthusiasm, was over. As a matter of routine the ships made astronomical observations and determined the longitude and latitude of the places already known, surveyed the harbors and passes, made numerous soxmd- ings, and recorded the direction and velocities of winds and currents. These navigational data were eagerly sought by the cartographers to be incorporated in new maps, numbers of which ap- peared in various European countries and in Mexico. Examples given below, which illustrate this progress, have been selected from a large array of the cartographic material issued during this period. French interest in the Mississippi River and the surrounding country is clearly expressed in the work of the famous French geographer, Guillaume Delisle (in the French publications the name is spelled "de L'Isle" and "Del'Isle") whose chart of Louisiana and of the course of the Mississippi was composed in 1719. The inscription reads that it was drawn after consulting many memoirs of Le Maire and others. The map shows the routes of De Soto and of other explorers and depicts the course of the principal rivers. The name Texas (Los Teijas) for the first time appears in cartography. According to Kohl (1857, No. 238), the Delisle map is "the mother and main source of all the later maps of the Mississippi and of the whole West of the United States." The entrances to the Mississippi River, being of great importance to the French mariners, were surveyed with great persistency. Among the many persons who contributed to our knowledge of the physiography of the river, Lemoyne de Serigny occupies a prominent position. In 1719 he participated in military operations in Florida and Louisiana and led a successful attack from the sea against Pensacola. His observations along the northern part of the Gulf coast are incorporated in a map drawn by an anonymous French cartographer and entitled "Carte de la cote de la Louisiane depuis I'Embouchure du Mississippi jusqu' a la Baie de St. Joseph, etc." The Library of Congress has a photographic reproduction of this document. The original is in Paris in Dep6t de la Marine. Serigny produced, also, a detailed map in colors of the approaches to Pensacola Bay. The notation on the body of the latter map contains reference to a strong surface current and the rise and fall of tides approximating 3 feet during a 24-hour period. In connection with the construction of fortifica- tions around the recently founded city of New Orleans, the French Government detailed many engineers to Louisiana. Among them Bernard de la Harpe distinguished himself by numerous observations which were incorporated in the de Beauvilliers map of 1720. The map shows many streams, mountains, towns, and Indian villages along the Gulf of Mexico and many islands off the coast of Yucatan. The chart of the Louisiana coast drawn about the same time (1719-20) by Devin was also made on the basis of the reports of De la Harpe and other French army officers. It shows many soundings and the positions of shallows and reefs in St. Louis Bay and adjacent waters. The necessity of having accurate maps for safe GULF OF MEXICO 19 navigation along the coasts of America was fully recognized in England. Among tlie many charts published tliere chiring the first half of the eighteenth century that of Henry Popple, issued in 1733 on 20 sheets with an index, is of particular interest. This large chart, measuring 232 by 239 centimeters has the following title: "A Map of the British Empire in America with the French and Spanish Settlements adjacent thereto." A prospectus attached to the first impression con- tains a detailed description of the map. The Librarj' of Congress has three impressions, one of which is imperfect. About the middle of the eighteenth century the Spanish Government, feeling the need for more accurate information regarding the extent of its dominions in the New World, demanded by the royal decree of 1741 the submission by local authorities of detailed suveys of their adminis- trative districts. Data thus obtained were summarized by Don Jose Antonio de Villasenor y Sanchez, Auditor General of the Department of Quicksilver, who enjoyed a reputation as a "distinguished mathematician, accurate historian, and a good citizen" (Bancroft, 1883-86, v. 3, p. 510). The entire undertaking resulted in the map issued in 1746 under the title, "Icomismo hidro- terro 6 Mapa Geographico de la America Sep- tentrional" (original in Arch. Gen. de Indias, Seville ; copy in Library of Congress) . In the same year the Spanish Government detailed Fernando Consag to explore the upper part of the Gulf coast. A reproduction of his map is given by Bancroft (1883-86, v. 1, p. 463). Jacques Nicolas Bellin, an engineer of the French navy, was probably the most outstanding cartographer of the second half of the eighteenth century. In carrying out official orders of the French Govermnent he made a detailed survey of the coast of Louisiana and of the course of the Mississippi River, drew a plan of Pensacola Bay (1742), published marine atlases and many maps (BeUiu 1749, 1755, 1764). His map of the Gulf of Mexico and of the islands of America, issued in 1754 and published in volume 12 of Prevost's Histoire generale des voyages (1746-89, pp. 8-9), illustrates the state of geographical knowledge of that time. One can see from this map (fig. 6) that the configuration of the Gulf, especially along its west coast, is still incorrect, and the shape of the Florida Peninsula is far from being true. 250D34 0—54 3 In this respect, as well as in the manner of drawing and the angularity of the coastal line, BcUin's map resembles the one prepared by liis predecessor, Royal Cartographer D'Anville, in 1731 (fig. 7). Although the outlines of Florida are almost identi- cal in the two maps, it is interesting to note that Bellin does not show such a fantastic array of bays and sounds as are indicated in the southern- most part of Florida by D'Anville. One of the most notable documents of the second half of the eighteenth century is a map of the British and French dominions in North America published in London by John Mitchell in 1775 in accordance with the Act of Parliament (Mitchell 1755, 1757). The original of one of the earlier issues, identified by only one insert (Hudson Bay) instead of four in the later editions, can be found in the library of Harvard University. A copy of a French edition of 1756 is in the Library of Congress. Mitchell's map was first used by American and British diplomats at the Paris peace conference of 1782-83 after the surrender of Cornwallis at Yorktown. Since that time it had been referred to and quoted as an authentic document in many boundary disputes between the United States and European countries. The Harvard University copy has an interesting quotation from John Adams attached to the map which reads as follows: "We had before us ... a variety of maps but it was the Mitchell's map upon whicli was marked out the whole boundary lines of the United States." The map shows only a small section of the northern part of the Gulf of Mexico between longitudes 83°4' and 97° W. and latitudes 28°20' and 30°20' N. Tampa Bay is still called Baia del Espiritu Santo, and there are interesting notations regarding the depth of the water "20 feet water over the Bar of Pensacola the Chief Harbour hereabout" and the depth of "Y* Missisipi" stated to be "18 feet water into Balise, 12 feet over the Bar, 45 feet within, 50, 60, and 100 afterwards." In 1764-71 George Gauld ordered by the British Admiralty to make a survey of the coast of the provinces of West Florida and Louisiana, produced a map known as "Admiralty Chart." He also gave accounts of his surveys of Florida and sailing directions in the West Indies and Florida Keys (Gauld 1790, 1796). Several edi- tions of Gauld 's maps were issued in the United 20 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE GULF OF MEXICO 21 :;^} .^ -.-1 'K' <■■ K2t^ ^J^C^ \" ^s ^\^i-: 4* ■•■'/ ^■■] ' /:^.:\, i (1*1' ;;^. ^ H • >-■*■ r^:: .1 • lAj, V \ ^^'•.jt .:i ■' li'- ?■ i ? • ). ) : y. - H I ;• „■>.- illy 4- 03 •a is 03 3 C 03 x: o 03 ^iffi^ir,^^ GULF OF MEXICO 25 line explorations by authorizing the President to "cause a survey of the coast of the United States and to employ proper persons in accomplishing the purpose prescribed in the act," for which a sum not exceeding $50,000 was appropriated. From 1816 to 1843 the reports of the Superin- tendent of the United States Coast Survey, made in compliance with this act, contained no references to the work in the Gulf of Mexico. Some explorations in the Gulf were conducted, however, by the United States Navy. In 1839 the U. S. S. Vandaiia, under the command of Uriah B. Levy, was engaged, from February 4 to August 3, in the hydrographic exploration between Galveston and the southwestern pass of the Mississippi River.^ The reconnaissance survey of the Gulf coast was commenced by the United States Coast Survey in January 1845 (Report of the Super- intendent for the year ending November 1846), and since that time the work of the organization, renamed in 1878 United States Coast and Geodetic Survey, is being continued at the present time. A large number of hydrographic and topographic charts issued during this time show the high degree of perfection achieved by this agency during more than a century of continuous work. The years of different surveys made in various sections of the Gulf can be found in the Hydrographic Index Charts, Nos. 80-91, and Topographic Index Charts, Nos. 20-32, issued by the United States Coast and Geodetic Survey. The main features of the Gulf — the configura- tion of its bottom and the circulation of water and its emergence as the Gulf Stream — were the ob- jects of many investigations. The exploration of the Gulf Stream was commenced in 1844 by Davis (Report of the Superintendent, U. S. Coast Sur- vey, year ending November 1846) and was continued by Bache in 1846, who inaugurated a series of deep-sea investigations of the physical problems connected with the Gulf Stream (Bache 1852, 1859). This work was expanded by his successors in the United States Coast Survey, Benjamin Price, Carlile P. Patterson, and Julius E. Hilgard. The results of the Gulf Stream ex- plorations, including observations of distribution of water temperatures in the Florida Channel ' Copy of the chart of the cruise of the Vandaiia is in the Library of the American Geographical Society of New York. and Straits, were discussed by Bache in several articles (Bache 1854, 1860). In 1850, at the recjuest of the United States Coast Survey, Professor Louis Agassiz undertook an extended biological survey of Florida reefs and obtained valuable information concerning the topography of Florida, the mode of formation of reefs by cementation, and the origin of the Florida Keys (L. Agassiz 1880). Occasional references to bottom animals of the Gulf are found in French publications of Folin and Perier (1867-72), in which are described several new species of mollusks and ostracods from the bottom deposits collected near Veracruz and in Laguna de Terminos. Maury's (1858) classical book on the physical geography of the sea contains no specific reference to the Gulf of Mexico except a brief note con- cerning the corrosive action of Gulf waters, which were observed to be more destructive to copper sheeting of ships than the water from any other part of the world. Systematic deep-sea explorations carried out in 1867 and 1868 by Pourtales and Mitchel on the United States Coast Survey ships Corwin and Bihh consisted in dredging between Florida and Cuba, at some places at a depth of 850 fathoms. Many new types discovered in these collections and the finding of species of corals and echinoderms which were considered related to an antique fauna of the Cretaceous period, proved that a study of bottom organisms thriving along the course of the Gulf Stream is of great scientific interest (Pour- tales 1867; L. Agassiz 1852; A. Agassiz 1888, V. 1, p. 49; Peirce and Patterson 1881). Explorations along the west coast of Florida undertaken in 1872 by Commander Howell were continued in 1875-78 in other parts of the Gulf under the direction of Lieutenant Commander Sigsbee aboard the United States Coast Survey steamer Blake. In the following years the opera- tions were extended, under the command of Commander Bartlett, through the Caribbean Sea and the Straits of Florida. Alexander Agassiz, in charge of dredging operations of the Blake expedition, made a geological study of Florida reefs which had already attracted the attention of his father, Louis Agassiz, Le Conte, and Hunt (A. Agassiz 1888, v. 1, pp. 52-92).* < The geology of the Gulf of Mexico is discussed in an article by S. A. Lynch in this book, pp. 67-86. 26 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE Three cruises of the Blake, from 1877 to 1880, represent an outstanding event in the history of scientific explorations of the Gulf of Mexico. The expeditions obtained a wealth of information re- garding the oceanography and biology of the Gulf, and the two volumes describing the work of the Blake written by A. Agassiz (1888) until the present day remain an important source of refer- ence concerning the bottom fauna, the structure and origin of coral reefs, and the distribution of invertebrates and fishes at depths extending to 2,000 fathoms. Collections obtained by the Blake served as material for many important publications on corals, antipatharians, crinoids, and Crustacea (Pourtales 1870, 1880) ; echinoderms (A. Agassiz 1863, 1869, 1878, 1883); hydroids (Clarke 1879); annelids (Ehlers 1879) ; mollusks (Dall 1880, 1886, 1889) , and many others. Numerous papers dealing with various taxonomic groups gathered by the expeditions can be found in the first 19 volumes of the Bulletin of the Museum of Comparative Zoology at Harvard College. A discussion of the deep-water fauna of the Gulf Stream was given by Pourtales (1863-69). The establishment, in 1871, of the United States Commission of Fish and Fisheries marked the beginning of the study of the important coastal and marine fisheries of the Gulf. With the building of the 1,000-ton steamer Albatross in 1883, the first Commissioner of Fisheries, Spencer F. Baird, initiated worldwide explorations of the sea fisheries. At the time of her completion, the Albatross was the best equipped dredger for deep- sea work in existence. One of her first details was to explore the bottoms of the Gulf of Mexico. The instructions given in 1883 by Spencer F. Baird to the commanding officer. Lieutenant Commander Z. L. Tanner, read in part as follows: "In returning (from the Caribbean) by way of Cape San Antonio it will be well to make a run into the Gulf of Mexico and spend a short time in making soundings and dredging therein, for the purpose of obtaining a general idea of the natural history and the fisheries of the Gulf, preliminary to a more lengthened visit to be made hereafter" (Tanner 1886). The instructions specified that in addition to the purely physical work, soundings, temperature, and observation of currents, the Albatross should secure "a fair representation of the shore fauna of the Caribbean Sea and its surroundings including shallow water, to collect parasites of the larger fish, birds, reptiles, fresh- water fish, and the various species of mammals as well as to obtain aboriginal relics in the way of articles of stone, pottery, etc." Large collections made by the Albatross and deposited in the Smithsonian Institution testify that the instruc- tions were faithfully carried out. During the first visit to the Gulf in 1884 the Albatross explored the bottoms around the west- ern tip of Cuba (fig. 10, open squares) but return- ing in the following j'ear made more detailed explorations around Cozumel Island, along the eastern edge of Campeche Bank, on red-snapper banks off Cape San Bias in the northeastern part of the Gulf, and occupied a few stations along the west coast of Florida and at Key West (fig. 10, black double circles). A brief but interesting account of the history of the Albatross is given by Hedgpeth (1945, 1947). Simultaneously with the oceanographical stud- ies the United States Fish Commission conducted an exploration of the fishery resources of the Gulf of Mexico. Accounts of this work with reference to red snappers, shore seine fishery, oysters, and sponges are given by Stearns (1884, 1887), Collins (1887), and Stearns and Jordan (1887). In 1880 the United States Commission of Fish and Fisheries built a steamer. Fish Hawk, for the purpose of assisting in fish-hatching operations and conducting surveys of fishing grounds. From November 1895 to 1896, under the command of Lieutenant Franklin Swift, the Fish Hawk sur- veyed oyster regions of St. Vincent Sound, Apala- chicola Bay, and St. George Sound, Fla. (Swift, 1897), the work which 20 years later was repeated with the same ship by Danglade (1917). In 1898 the Fish Hawk was used by the United States Coast and Geodetic Survey in hydrographic in- vestigations of the inshore waters of Alabama. In 1901 and 1902 the ship was engaged in sponge investigations along the west coast of Florida. The exploration in 1901 covered the grounds be- tween Anclote Anchorage, St. Marks, and Tampa Bay. In the following year the operations ex- tended along the western coast of Florida, to the depth of 10 fathoms, from Cedar Keys to Key West. In 1905 the Fish Hawk was detailed to survey the oyster bottoms and make hydro- graphic investigations in Matagorda Bay, Tex. (Moore 1907), in 1911 made a similar investiga- GULF OF MEXICO 27 28 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE tion in Mississippi Sound (Moore 1913a, 1913b), and in 1913 was used as the base for a survey of oyster bottoms in Lavaca Bay, Texas (Moore and Danglado 1915). The completion of the latter investigation by Moore marked the ending of the Fish Hawk activities in the Gulf. In 1917 the research ship Grampus of the United States Bureau of Fisheries cruised over the con- tinental shelf from Key West to Aransas Pass in a study of shrimp and fishery grounds (U. S. Bureau of Fisheries, 1919). The results of systematic hydrographic work conducted by the United States Coast and Geo- detic Survey and the Hydrographic Office of the United States Navy with the additional data accumulated by other explorations served as a source of material for a general discussion of the physiography of the Gulf. Forshey (1878) at- tempted to describe the configuration of the bot- tom of the Gulf, stressing particularly the deposi- tion of sediments brought in by the Mississippi River which he believed eventually will fill up the Gulf. Lindenkohl (1896) summarized tem- perature and salinity data taken primarily from the reports of the United States Coast and Geo- detic Survey. In order to obtain basic data on physical ocea- nography of the Gulf a plan was adopted in July 1905 by the Hydrographic Office of the United States Navy to supply all vessels crossing the Gulf with a form for daily use in giving ship's position, direction and force of the wind, direction and force of the current, and temperature and color of the water. The reports of hundreds of observers extending over a period of years, when plotted on the montlily charts, agreed remarkably. The data were summarized by Soley (1914) on a chart entitled, The Gulf Stream in the Gulf of Mexico (see Pilot Chart of the North Atlantic Ocean for June 1914), reproduced in figure 11. Soley's chart shows the basin of tidal equilibrium (Sigsbee Deep) more than 2,000 fathoms deep in the western part of the Gulf, the direction of the main current, and the Gul Stream which comes from the North and South Equatorial Current in the Yucatdn Channel. The Northwestern Branch of the Current leaves the main stream at the northeastern corner of Campeche Bank, while the Eastern Branch turns eastward from the Yucatdn Channel. The chart shows, also, the two counter- currents, the Cuban and the Western, and the position of the Central Sea, a circular body of dead water about 80 miles in diameter. From the time of the first publication of Soley's chart basic information given in it is being incorporated in monthly pilot charts regularly issued by the Hydrographic Office of the United States Navy with the additional data supplied by ships and provided by the United States Weather Bureau of the Department of Commerce (formerly a part of the U. S. Dept. of Agriculture). In January-March 1914 Bigelow (1915), work- ing on board the United States Coast and Geo- detic Survey steamer Bache, made observations in the Straits of Florida studying vertical distri- bution of temperature and salinity from the sur- face to the depth of 1,800 meters along the profiles drawn across the Straits from Key West to Havana, from Cape Florida to Gun Bay, and from Jupiter Inlet to the northern end of Little Bahamas Bank. He noticed the banking up of cold water against Florida as a result of upwelling from deep layers on the left side of the channel and concluded that the cold, comparatively fresh water next to Florida is largely true abyssal water from the Gulf of Mexico. In 1926 the oyster bottoms in the bays along the coast of Texas were surveyed by Galtsoff (1931) with special emphasis on salinity distribu- tion in these bodies of water. From 1936 to 1939 a detailed work on the hydrography of Texas tidal waters was carried out by Collier (Collier and Hedgpeth 1950). The natural history of redfish and other sciae- nids on the Texas coast was studied by Pearson (1929) who pointed out the scientific importance in a study of the biological relationship between the Gulf and its inland waters. Marked advance in the knowledge of the hydrog- raphy of the Gulf was made in 1932 by the Yale Oceanogi-aphic Expedition of the Mabel Taylor sponsored by the Bingham Oceanographie Founda- tion. One of the chief problems of the investi- gation, formulated by the leader of the expedition. Parr (1935), was to study "the relationship between the waters in the region of the Straits (i. e., the area southward between the Yucatdn Channel and the Straits of Florida) and in the Gulf of Mexico proper." Such a study became highly desirable in view of Nielsen's (1925) objections against the purely two-dimensional picture of surface movements of water in the Gulf GULF OF MEXICO 29 83 3 T3 J2 O 03 V 3 O 3 o 30 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE of Mexico given in Soley's chart. The expedition occupied 87 stations (fig. 10, triangles) at which temperature and sahnity of water were recorded at different levels from surface to a depth of 3,000 meters (1,640 fathoms).^ In 1934 the Atlantis of the Woods Hole Oceano- graphic Institution occupied, from January to March, a series of hydrographic stations in Yucatdn Channel and the Straits of Florida, and in January to May 1937, jointly with the Bingham Oceanographic Foundation, made observations in the Caribbean Sea and Gulf of Mexico (Parr 1937a, 1937b). During the cruise of 1947, sponsored jointly by the Woods Hole Oceano- graphic Institution and the Geological Society of America, the Atlantis occupied 551 stations in the western part of the Gulf between Sigsbee Deep and the coasts of Louisiana and Texas. In 1951 observations were made by this ship at 240 stations. As a result of this work, combined with the data obtained by the United States Coast and Geodetic Survey, a very detailed map of submarine topography on the northwest quarter of the Gulf was issued by the Institution in 1951. In 1951 the Fish and Wildlife Service of the United States Department of the Interior initiated a comprehensive research in oceanography and fishery resources of the Gulf of Mexico. This work is carried on bj^ the U. S. S. Alaska and the U. S. S. Oregon, the latter ship being primarily concerned with the explorations of new fishing grounds. Material dredged by the Oregon and deposited in the U. S. National Museum in Washington proved to be of exceeding interest to zoologists, for it comprised many rare species which heretofore were represented only by iso- lated specimens. A steady growth of interest in marine biology in the United States during the last half century is reflected in an increase in the number of labora- tories or stations devoted to marine biological research in general, or to a study of specific problems of utilization and management of fishery resources. One of the earliest institutions of that type in the Gulf was the Gulf Biologic Station established in 1902 by the State of Louisiana at the mouth of Calcasieu Pass in Cameron, La. In 1910, by an act of the General Assembly, the Gulf station was merged with the State Conser- • For the discussion of Parr's work see article by D. F. Leipper. Physical Oceanography of the Gulf of Mexico in this book, pp. 119-137. vation Commission, and about 2 years later the property consisting of 10 acres of land and the building in which the laboratories were located reverted to the original donor, Judge Henry, and the operation of the laboratory ceased. During its brief existence the Gulf Biologic Station was concerned primarily with the biology and cultivation of oysters, scallops, and clams in Louisiana waters and in studj-ing the distribution and biology of local marine and brackish-water plants and animals. The contributions of the laboratory were published in 15 issues of the Bulletin of the Gulf Biologic Station issued from 1902 to 1910 and in 3 small biennial reports of the director dated 1906, 1908, and 1910. « Brief data regarding the founding of this station and its policy are given by Foote (1942). In June 1904, the Carnegie Institution of Washington, D. C, established a marine labora- tory at Loggerhead Key, Dry Tortugas, 68 miles west of Key West, Fla. The site was chosen because of the purity of the ocean water surround- ing the group of seven, small, sandy islands, the proximity of the Gulf Stream with its abundant life, the presence of rich coral reefs in Florida, and the absence of local fisheries which could have affected the undisturbed life of the sea. Despite adverse conditions due to the difficulties of regular communication with the mainland, hurricanes which frequently swept the Keys, and the short season of its operation (restricted to 3 summer months), the station was very productive in scientific research. Its work inaugurated and conducted under the inspiring directorship of the late Dr. Alfred G. Mayer, covered a very broad field of research in marine biology and general physiology. The 33 volumes of the Papers from Tortugas Laboratorj' contain many fundamental works dealing with a great variety of problems such as biology of coral reefs by Mayer, the physiology of Valonia cells by Osterhout, the metamorphosis of ascidian larvae by Caswell Grave, observations on color, habits, and local distribution of the fishes of Tortugas by W. H. Longley, ecology and geologic role of mangroves by H. J. Davis. Many other papers of permanent scientific value came from the institution, which more than any other laboratory contributed to our knowledge of the marine life of the Gulf. • I am grateful to Joel W, Hedgpeth for supplying the data regarding the Oulf Biologic Station. GULF OF MEXICO 31 American scientists interested in marine research were grieved to learn from the report of the direc- tor of the Carnegie Institution for 1939 of the discontinuance of the laboratory due to the •'relatively high cost of its maintenance." At the time of this action the Laboratory was receiving a modest annual grant of $12,000 which constituted about 0.8 percent of the total budget of the Carnegie Institution of Washington for that year. Brief mention should be made of the attempt of the United States Bureau of Fisheries to establish a fishery laboratory at Key West in 1917. Owing to the lack of funds for salaries and equipment the station never became functional and was abandoned in 1928. A small laboratory is maintained by Louisiana State University on Grand Isle. The laboratory is used every summer from June to July for teach- ing. Despite modest equipment and lack of modern research facilities a number of valuable scientific papers resulted from its operations which have enhanced our knowledge of the Gulf fauna. From 1935 to 1937 the United States Bureau of Fisheries maintained a temporary laboratory at Indian Pass in Apalachicola Bay, Florida, for the purpose of studying the biology of the oyster leech iStylochu~s inimicus) and other enemies of the oyster. Upon completion of this work (Pearse and Wharton 1938) the laboratory was abandoned in 1937 and the equipment transferred to the fisheries laboratory near Pensacola, Fla. The latter laboratory, established in 1937 primarily for shellfish research, is located on a small island in Santa Rosa Sound about 7 miles from Pensacola. The laboratory, with several auxiliary buildings, occupies the site of the abandoned quarantine station. It is equipped with running sea water and outdoor cement tanks for experiments on shellfish. The current work consists in ecological and biological research on oysters in Florida, Alabama, Mississippi, and Louisiana waters. The Marine Laboratory of the LTniversity of Miami was established in 1942 at Coral Gables, Fla., for research and teaching in oceanography, marine biology, conservation, and management of fishery resources. Its operations extend over the waters of the West Indies and the Gulf of Mexico. The laboratory maintains a station at Apalachicola for oyster studies and, as circum- stances require, establishes temporary head- quarters along the west coast of Florida. Principal research projects, some of which are sponsored by the United States Navj', deal with the circulation of water in the Gulf (Smith, et al., 1951), seasonal changes in the composition of plankton of Biscayne Bay and adjacent oceanic waters, red tide, sponge disease and sponge culture, physiology of fouling organisms, and many others. Several of the articles by the members of the laboratory staff appeared in the newly established Bulletin of Ma- rine Science of the Gulf and Caribbean and in the Proceedings of the Gulf and Caribbean Fisheries Institute founded by the laboratory. The Gulf and Caribbean Fisheries Institute represents an effort to integrate the work of oceanographers, biologists, economists, fishermen, and admin- istrators. It seems appropriate to point out here that the idea of preparing a digest of the existing literature on the biology and oceanography of the Gulf of Mexico originated at the Second Annual Session of the Institute and has materialized through the efforts of several members of this organization (Walford 1950). Several other institutions devoted primarily to the study of Gulf problems, were established in recent years. The Institute of Marine Science of the University of Texas in Port Aransas was founded in 1948 with a grant from the General Education Board and with funds provided by the Texas Agricultural and Mechanical Research Foundation. The Texas Game, Fish, and Oyster Commission established, in 1949, a marine labora- tory at Rockport, Tex. The Fish and Wildlife Service of the United States Department of the Interior has maintained, since 1949, a temporary laboratory for red-tide studies at Sarasota, Fla., and in 1950 established headquarters with lab- oratory facilities at Galveston, Tex., for the con- duct of oceanographical and biological studies of the Gulf. The Oceanographic Institute of Florida State University was established in 1949 with two seaside stations, one at Alligator Harbor and another at the mouth of the St. Johns River about 12 miles east of Jacksonville at Mayport, Fla., on the Atlantic coast. Research facilities of these stations, engaged primarily in teaching, are limited. Since 1947 the State of Mississippi has main- tained the Gulf Coast Research Laboratory at Ocean Springs, Miss., for instruction in zoologj' and botan}^ Recent oil-development activities in the coastal 32 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE area of the Gulf provided an opportunity to make continuous observations from fixed platforms erected several miles off shore. Analyzing these records, Geyer (1950) discovered that the salinity of water of the Louisiana coast at a distance from 5 to 6 miles from the shore undergoes seasonal variations ranging from 15 to 35 parts per thousand at 10 feet below the surface. Extensive investiga- tions of the hydrography of the inshore waters and the effect of crude oil and brine on aquatic life have been recently sponsored by the oil com- panies. Unfortunately, the results of these studies are not available to the public. The outlook for scientific investigations of Gulf problems appears to be bright. There are at present many laboratory and field facilities available at various scientific institutions located along the Gulf coast. Furthermore, Federal and State organizations show great interest in the research problems and are in a position to conduct or sponsor various oceanogi'aphic and biological projects. It is therefore reasonable to expect that the progress in our knowledge of the Gulf of Mexico will be rapid and productive. BIBLIOGRAPHY Agassiz, Alexander. 1863-69. Preliminary report on the echini and star- fishes dredged in deep water between Cuba and the Florida Reef by L. F. de Pourtalfes. Bull. Mus. Comp. Zool. Harvard Coll. 1: 253-308. 1878. II. Report on the echini by A. Agassiz, crinoids and corals by L. F. de Pourtalfes, and ophiurans by Theodore Lyman preceded by a bibliographical notice of the publications relating to the deep-sea investigations carried out by the U. S. Coast Survey. In: Reports on the results of dredging . . . Bull. Mus. Comp. Zool. 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The general history of the vast continent and islands of America . . . Translated into English by Capt. John Stevens. 6 vols. Printed for J. Batley, London. 1728. Historia general de las Indias occidentalis . . . Nueva impression enriguecida con lindas figuras y re- tratos. Amberes, J. B. Verdussen. 4 vols., pis., fold, maps. Also 1720 edition in 5 vols. Madrid. HuLBERT, Archer Butler. 1904-8. The Crown collection of photographs of Amer- ican maps, selected and edited by Archer Butler Hul- bert. 5 vols. The A. H. Clark Company, Cleveland, Ohio. Humboldt, Alexander von. 1836-39. Examen critique de I'histoire de la geographie du nouveau continent, et des progr&s de I'astronomie nautique aux 15"* et 16°"" sifecles. 5 vols., 4 fold, maps. Paris. Kerhallet, Charles-Philippe de. 1853. Manuel de la navigation dans la Mer des Antilles et dans le Golfe du Mexique. 2 vols., 3 fold. maps. Paris. Kohl, J. G. 1857. A descriptive catalogue of those maps, charts, and surveys relating to America, which are mentioned in vol. Ill of Hakluyt's great work. Washington. Kohl, J. G. 1862. A popular history of the discovery of America from Columbus to Franklin. Trans, from the German by R. R. Noel, 2 vols. London. 1863. Aelteste Geschichte der Entdeckung und Erfor- schung des Golfs von Mexico und der ihn umgebenden Klisten durch die Spanier von 1492 bis 1543. Zeit- schrift fiir Allgemeine Erdkunde. Vol. 15, pp. 1-40 and 169-194. BerUn. 1868. Geschichte des Golfstroms und seiner Erforschung von den Altesten Zeiten bis auf den gros.sen Ameri- kanischen Btirgerkrieg; eine Monographic zur ge- schichte der Oceane und der geographischen Enteck- ungen. 224 pp. Bremen. 1885. History of discovery and exploration on the coasts of the United States. Report Supt. U. S. Coast and Geodetic Survey, 1884, App. 19, pp. 495-017. Wash- ington. Lelewel, Joachim. 1852. Geographie du Moyen Age. Vol. 2, pp. 135-140. Bruxelles. Le Moyne, Jacques. 1564. Narrative of Le Moyne, an artist who accom- panied French expedition to Florida under Laudon- nifere. Translated from the Latin of de Bry, Boston, 1875, 15 pp. with 42 hehotypes of the engravings taken from the artist's qriginal drawings. Lindenkohl, a. 1896. Resultate der Temperatur-und Dichtigkeitsbeo- bachtungen in den Gewassern des Golfstroms und des Golfs von Mexico. Durch das Bureau des U. S. Coast and Geod. Sur., Petermanns Geogr. Mitteilun- gen 42: 25-29, map. Lowery, Woodbury. 1912. Descriptive list of maps of the Spanish possessions within the present limits of the United States, 1502- 1820. Edited with notes by Philip Lee Phillips, F. R. G. S., Chief, Division of Maps and Charts. Li- brary of Congress. The Lowery Collection. 567 pp. U. S. Govt. Printing Office, Washington. Madrid, Museo Naval. 1945. Catdlogo guia. 9th ed., 248 pp. Madrid. Maury, Matthew Fontaine. 1858. The physical geography of the sea. XXIV, 25, 274 pp. incl. map, 3d ed. Harper & Bros., New York. Mitchell, John. 1755. A map of the British and French dominions in North America. London. 1757. The contest in America between Great Britain and France . . . 260 pp. London. MooRE, H. F. 1907. Survey of oyster bottoms in Matagorda Bay, Texas. U. S. Bur. Fish. Doc. 610, 86 pp., 13 pis., 1 map. Washington. MooRE, H. F. 1913a. Condition and extent of the natural oyster beds and barren bottoms of Mississippi east of Biloxi. U. S. Bur. Fish. Doc. 774, pp. 1-41, 6 pis., 1 map. 1913b. Condition and extent of the natural oyster beds and barren bottoms of Mississippi Sound, Alabama. U. S. Bur. Fish. Doc. 769, pp. 1-61,5 pis., 1 map. Moore, H. F., and Ernest Danglade. 1915. Condition and extent of the natural oyster beds and barren bottoms of Lavaca Bay, Texas. Rept. U. S. Comm. Fish., 1914, App. II, 45 pp., 5 pis., 1 map. Washington. MoRisoN, Samuel Eliot. 1940. Portuguese voyages to America in the fifteenth century. Harvard Hist. Monog. XIV, 151 pp. Harvard University Press, Cambridge. Navarrete, Martin Fernandez de. 1837-80. Colecci6n de los viajes y descumbrimientos que hicieron por mar los Espanoles desde fines del siglo XV, con varios documentos in^ditos con- cernientes a la historia de la marina castellana y de los establecimientos espaiioles en Indias, coordinata e illustrada. Imprenta uacional. 5 vols. Madrid. 1943. Coleccion de diarios y relaciones para la historia de los viajes y descubrimientos . . . Instituto his- torico de marina. 5 vols., ilhis., fold. maps. Madrid. Nielsen, J. N. 1925. Golfstrommen. Geografisk Tiddsskrift. 28 Bind. 1 Hefte. Copenhagen. Paris, Bibliotheque Nationale. 1892. Quatrieme ceutenaire de la d^couverte de I'Am^rique: Catalogue des documents g^ographiques exposes a la Section des cartes et plans de la Biblio- theque nationale. Paris, J. Maisonneuve. 77 pp. GULF OF MEXICO 35 Parr, Albert E. 1935. 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Distribution of vertical water movement calcu- lated from surface drift vectors. Bull. Mar. Sci. Gulf and Caribbean 1(3): 187-195. SoLEY, John C. 1914. The Gulf Stream in the Gulf of Mexico, by Lieut. John C. Soley, U. S. N., in charge of the Branch Hydrographic Office at New Orleans, La. Reprinted from the Pilot Chart of the North Atlantic Ocean for June 1914. Washington. Stearns, S. 1884. On the position and character of the fishing grounds of the Gulf of Mexico. Bull. U. S. Fish Comm. 11: 289-290. 1887. The fishing grounds of the Gulf of Mexico belong- ing to the United States, 1887. In: The Fisheries and Fishery Industry of the United States by George Brown Goode. See. Ill, pp. 55-60. Washington. 1887. The red snapper fishery and the Havana market fishery of Key West, Florida. In: The Fisheries and Fishery Industries of the United States by George Brown Goode. Sec. V, 1, (10): 585-594. Washington. Stearns, S., and David Starr Jordan. 1887. Fisheries of the Gulf of Mexico. In: The Fish- eries and Fishery Industries of the United States by George Brown Goode, Sec. II, (15): 533-587. Washington. Stommel, Henry. 1950. The Gulf Stream. A brief history of the ideas concerning its cause. Scientific Monthly 70: 242-253. SwANTON, John R. 1946. The Indians of the Southeastern United States. Smithsonian Institution, Bur. Amer. Ethnology, Bull. (3) 943 pp., 107 pis. SwEiTZER, N. B., Jr. 1898. Origin of the Gulf Stream and circulation of waters in the Gulf of Mexico, with special reference to effect upon jetty construction. Trans. Am. Soc. Civil Engrs. 40: 86-98. Swift, Franklin. 1897. Report of a survey of the oyster regions of St. Vincent Sound, Apalachicola Bay, and St. George Sound, Florida. U. S. Comm. Fish and Fish., Rep. of the Comm. for 1896, App. 4, pp. 187-221, fold, map. Washington. Tanner, Z. L. 1886. Report on the work of the United States Fish Commission steamer Albatross for the year ending December 31, 1884. U. S. Comm. 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Final report of the United States De Soto Ex- pedition Commission. 76th Cong., 1st Sess., House Doc. No. 71, XVI, 400 pp. incl. maps. GPO, Washington. United States Library of Congress. 1901. A list of maps of America in the Library of Con- gress, preceded by a list of works relating to cartog- raphy. By P. Lee Phillips, F. R. G. S., Chief of the Division of Maps and Charts. 1137 pp. GPO, Washington. 1909-20. A list of geographical atlases in the Library of Congress, with bibliographical notes. Comp. under the direction of Philip Lee Phillips, F. R. G. S., Chief, Division of Maps and Charts. Vols. 1-2 paged continuously. GPO, Washington. Uring, Nathaniel. 1928. The voyages and travels of Captain Nathaniel Uring (first published in 1726). The Seafarers Library, London, 253 pp. Varnhagen, F. A. DE. 1858. Vespuce et son premier voyage. 31 pp. Paris. Imp. de L. Martinet. 1865. Amerigo Vespucci, son caractfere, les Merits et sa vie. Lima, Peru. 1869a. Nouvelles recherches sur les derniers voyages du navigateur florentin. Vienna. 1869b. Le premier voyage de Amerigo Vespucci. Vienna. 1870. Nouvelles recherches sur les derniers voyages du navigateur florentin, et le rest« des documents et eclaireissement sur lui. 57 pp. Vienna. Vespucci, Amerigo. 1926. The letter of Amerigo Vespucci describing his four voyages to the New World, 1497-1504. 5 p. 1., 28 pp. The Book Club of California, San Francisco. 1893. The first four voyages of Amerigo Vespucci reprinted in facsimile and translated from the rare original edition (Florence, 1505-06). X., 32 p. facs. B. Quaritch, London Walford, Lionel A. 1950. A coordinated program of marine studies for the Gulf and Caribbean. Proc. Gulf and Caribbean Fish. Inst., Second Ann. Sess., p. 129. Miami, Florida. Walker, S. T. 1880. Report on the shell heaps of Tampa Bay, Florida. Ann. Rep. Bd. of Regents Smithsonian Inst, for 1879, pp. 413-422. Washington. 1883. The aborigines of Florida. Ann. Rep. Bd. of Regents Smithsonian Inst, for 1881. Pp. 677-680. Washington. 1885. Mounds and shell heaps on the west coast of Florida. Ann. Rep. Bd. of Regents Smithsonian Inst, for 1883, pp. 854-868. Washington. Willey, Gordon R. 1949. Archeology of the Florida Gulf coast. Smithso- nian Misc. Coll. 113: 599 pp., 60 pis. Washington. WiNSOR, Justin. 1884-89. Narrative and critical history of America. 8 vols. Houghton Mifflin and Company, Boston and New York. 1904. The Kohl Collection (now in the Library of Congress) of maps relating to America. A reprint of Bibliographical Contribution number 19 of the library of Harvard University. GPO, Washington. CHAPTER II GEOLOGY SHORELINES AND COASTS OF THE GULF OF MEXICO By W. ARMSTRONG PRICE,= Agricultural and Mechanical College of Texas INTRODUCTION The scientific study of shorelines is inextricably involved with that of the hinterland, the coastal zones, the adjacent inshore waters and the climate. This linkage brings together regional geology, geomorphology, sedimentation, oceanography of the inshore zone, meteorology, climatology, biol- ogy, chemistry, late geologic history and the ecology of some marine and coastal organisms. As the study of shorelines and their classification is in somewhat incomplete and controversial condition today, it is necessary to give a brief review of the subject before discussing the shore- line of a particular region, such as the Gulf of Mexico, where there are new types and where we have previously had few over-all geological oceanographic conceptions to guide us. STATUS OF STUDIES OF COASTS AND SHORELINES The geological study of shorelines and coasts has been intermittently' developed by numerous geologists and geographers. The principal dis- cussions of costal geomorphology that are readily available are Johnson's (1919) detailed treatise on shoreline development and his study of the New England- Acadian shoreline (1925), Shepard's (1937a, 1948) revision of Johnson's shoreline classification. Steers' (1946, 1952) analytical de- scription and history of the shoreline of England, Wales, and Scotland, and Russell's (1940) study of the development of variations in deltaic shore- lines in Louisiana. McCurdy's (1947) discus- sion of criteria for the delineation of shorelines from air photographs yields critical details of some types not found elsewhere. Fleming and Elliott (1950) have made a beginning of an over-all quantitative and qualitative oceanographic ap- proach to the study of shorelines which is here revised, enlarged and treated in greater detail, in ' Contribution from the Department of Oceanography of the Aericultural and Mechanical College of Te.xas, No. 15, April 1953. ' Professor of Geological Oceanography. Formerly, independent petroleum geologist of Corpus Christi, Texas. some of its aspects, for the Gulf of Mexico. Some of the oceanographic data treated by these workers have not been considered here. Among the greatest present needs in geomorphic coastal studies are a critical analysis and descrip- tion of the coastal plain shoreline and regional studies combining the geomorphic and ocean- ographic approaches. The research on which this paper is primarily based was a comprehensive survey of the shorelines of the Gulf from existing data, including results of the writer's 20-year study of the northwestern Gulf Coast. The survey was made by the writer in 1951-1953.' It has revealed a number of new types and re- lationships not yet critically discussed in publica- tion. Because of this situation, the writer is handicapped in attempting a discussion of the coasts of the Gulf of Mexico within as condensed a scope as that of the present paper. The application of quantitative oceanographic science to the analysis of the development of shore- lines is being slowly accomplished through the work of numerous scientists and engineers by isolated studies of beaches, cliffs, deltas and estuaries, but has only lately been attempted for whole regions. In the writer's current research, an attempt is being made to apply a quantitative regional approach to the study of the influence of oceanographic processes on shorelines and the associated coastal and shallow-water bottom con- ditions. Some of the results of this work are reflected in this paper. SHORELINE CLASSIFICATION Eduard Suess (1888) showed that regional or continental shorelines might be classed as con- cordant or discordant with the grain (dominant trend) of the geologic structures of a coastal region, but King (1942, p. 99) cautioned that marine activities subsequent to the drowning of a coast or the formation of its folds and faults mav have 3 Contains no references to the work of others after March 1, 1953. 39 40 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 67- -■,--, ^- Figure 12. — Shorelines of Gulf of Mexico, showing locations of major geographic features. (Contour lines off the Mississippi delta are drawn at 200-fathom intervals.) GULF OF MEXICO 41 altered the shoreline so that it may no longer con- form to a simple structural classification. Johnson (1919) assembled and extended previous ideas of coastal development and classification to pro- duce a detailed genetic-geomorphic system that has since been followed by most writers. How- ever, it seems not to have been applied by its users to the detailed mapping of the coasts of a large, diversified region such as the Gulf of Mexico, although Johnson (1925) applied it to the drowned and largely discordant shoreline of the New England-Acadian region of northeastern North America. Shepard (1937a, 1948) modified and extended Johnson's system, giving a tabulation in which shoreline and coastal types then described were inserted. His major divisions differ from John- son's and seem not to have been accepted by all of Johnson's followers, although the scarcity of papers on the classification of shorelines indicates that this may be due to inertia rather than to a working appraisal of the usefulness of Shepard 's revised system. Johnson's text is out of print and has not been supplemented by a similarly detailed work. Regional variations in the known physical oceanographic conditions in the "inshore" zone* of the coasts of the United States and Mexico were discussed by R. H. Fleming and F. E. Elliott (1950) in lectures. They regarded the scarcity of such information too great for elaboration of their method at that time. It, however, classifies coastal sectors into glacial, alluvial, young orogenic and biogenous types, with erosional and depositional sub-types for the first three. The continental coasts of the Gulf of Mexico were included in the maps and discussion. The Fleming-Elliott system has been modified and extended in some of its aspects for use in the present study as the geo- oceanographic classification system. Changes in their mapping of the Gulf coasts include the intro- duction here of young orogenic sectors and the relegation of biogenous coasts to a secondary condition imposed on a framework of regional geologic and geomorphic types. In the latter instance, the suggestion made by Shepard (1948, pp. 78-79) is followed that a regional classification could be made by using large subdivisions such as coasts with young mountains, old mountain ranges, * Shallow water or nearshore zone. Some writers use "inshore" for la- goonal and estuarine environments. broad coastal plains, glaciated coasts, and such specific but less common items as volcanic coasts and tableland coasts. Space does not permit including here an elabora- tion of the detailed genetic-geomorphic classifica- tion systems. As detailed knowledge of many coasts accumulates, including coastal plains such as those of the Gulf, the list of the distinctive small-unit features becomes encylopedic and the classification headings numerous, beyond the simplicity desired (Lucke 1938) for text-book and lecture purposes. Definitions. — The shoreline is the line where land and water meet. It moves back and forth over the shore or shore zone. The shore on a beach has been defined (Beach Erosion Board, Corps of Engineers, U. S. Army) as the zone between mean low tide (or lower low tide) and the inner edge of the wave-transported sand. The lagoonal shore is that of the tidal bays and lagoons. Estuaries are tidal stream courses. Their shores are not studied here except where they are em- bayed. On some coasts there are extensive, muddy shore-flats. Tidal flats are properly those within the range of normal gravitational tides. In some places winds blow the water across broad, gently sloping wind-tide flats * that extend inland from the ti-ue shore, hence, beyond the high tide limits for gravitational tides, and have been floored by deposits left by the water. The coast is a zone of indefinite width back of the shoreline that is affected by or closely affects offshore or shoreline processes and forms. The waters lying near the coast where the effect of a shallow bottom is felt may be called coastal waters. The continental shelf (fig. 13) is a submerged, gently sloping plain that extends the continent ocean- ward to varying depths ranging, generally, between 40 and 100 fathoms. The shelf is terminated sea- ward by the steeper shelf slope that descends, in places precipitously, to the depths. Additional definitions will be given in later paragraphs when the barrier island, the shelf and its equilibrium profile, and the mangrove coastal ridge are discussed. New and undescribed types. — New types recog- nized on the shorelines of the Gulf of Mexico which will be readily understood from previous geomor- phological knowledge are (1) the drowned karst (sub-aerial limestone solution topography) of parts *New term. 42 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE of Florida and the Yucatin Peninsula (fig. 12; fig. 14, sector 2.1); two minor forms: (2) sand dunes briefly drowned by exceptionally high tides; and (3) wind-tide flats, previously described. Other new types that form striking features on the coast of southern Florida and the Yucatan peninsula, are (1) the great mangrove barrier ridge (fig. 12; fig. 14, Sector 4.1); (2) the irregular mangrove coastal lagoon between the mainland and the ridge, (3) the drowned lacustrine plain of the Bay of Florida (fig. 14, Sector 4.1 north of Florida Keys and east of Cape Sable; fig. 15) as interpreted by the writer, with former lakes of marsh or swamp now invaded and enlarged by salt water, and (4) what the writer believes is the same type of coast slightly elevated (elevated lacustrine plain) to form the pocket harbors (Hayes, Vaughan, and Spencer, 1901) of northwestern Cuba (fig. 12; fig. 14, sector 3.1). The present paper does not offer an oppor- tunity for full critical discussion of these new types. Besides the distinctly new types of shoreline and coast, noted here, a number of fairly well known geomorphic forms were found which have not previously been included in shoreline classification lists. Prominent examples for the northwestern Gulf coast are the broadlj' to roundly embayed drowned-stream valley with shallow, pan-shaped depositional bottom previously described and in- vestigated by the writer (Price 1947) and the drowned deltaic topography (fig. 12, betweenBird- foot delta of Mississippi and Lake Pontchartrain) described by Russell (1936, figs. 6, 7; 1940). SOURCES OF INFORMATION Published articles include (1) the numerous detailed geological reports and maps on coastal land areas in the United States' with a few general- ized and regional reports on those of Mexico and Cuba, (2) shoreline and coastal studies of the United States Army Engineers, (3) a few ecolog- ical studies of coastal areas chiefly in Florida and Louisiana, (4) progress reports of the ocean- ographic survey of the Gulf of Mexico being conducted by the Department of Oceanography of the Agricultural and Mechanical College of Texas (Leipper, p. 125) and progress reports on investigations of sedimentation and other shallow water conditions of the northwestern Most complete for Florida and Louisiana. Gulf of Mexico by the American Petroleum Institute and similar commercial projects. Among scattered reports on previous oceanographic cruises yielding shoreline or shallow water data (5) is a study of foraminifera in bottom sediments by Phleger and Parker (1951). Much geographic and some geomorphic information is found in Tamayo's (1949) extensive text and atlas of the general geography of Mexico. Important raw data, some of which are listed in the following paragraph, include (7) topo- graphic maps and air photographs of the land, (8) original Federal hydrographic surveys, in- cluding some old surveys of the British Ad- miralty, (9) navigation and (10) aeronautical charts made from these sources, with (11) the coast pilot and sailing directions handbooks of these organizations, and (12) bottom-sediment charts of the shelf of the northern Gulf. Topo- graphic data are scarce outside the United States and of unequal detail and coverage for the dif- ferent States. For Mexico, air photography made by the United States and Mexican governments is available under restrictions. The Cuban hydro- graphic organization has issued a coast pilot (Derrotero) containing new coast charts. Charts and other aids in study of coasts. — For any detailed study of these shorelines it is necessary to have first, a set of nautical charts. Figure 12, a finding map for this study, is drawn on the base of the general chart for the Gulf. The less accurate and detailed these aids are for any coastal sector, the more they need to be supplemented by air photography, topographic maps and geologic reports. The following charts are recommended. U. S. Coast and Geodetic Survey Nautical Charts {U. S. Scores) .—General Charts, 1002, 1007, 1290: Sectional Charts 1113-1117; Coast Charts 1249-1280. For special details, some of the large-scale charts of islands, harbors and canals, and Chart A634. See catalog: Serial No. 665. Hydrographic Office, U. S. Navy, Nautical Charts (Mexico and Cuba). — General (coastal) Charts 1125BS, 1126, 1126BS, 2145, 2056, 0966, 5487. See catalog: Pub. I-N. Marina de Guerra, Departmento de Inspeccion, Officina Hidrograjica, Republica de Cuba. — Der- rotero de la Isla de Cuba (sailing directions). Parte Segunda, 1951, 173 pp. 21 figs, has coast GULF OF MEXICO 43 charts from recent surveys done on thin paper, bound in the book. Soundings and underwater contours are given to depths of from 30 to 60 brazos de agua (Cuban fathoms). World Aeronautical Charts, U. S. Air Force {Mexico and Cuba) .—Charts 522, 586-589, and 643-645. See: Aeronautical Chart Catalog, Coast and Geodetic Survey. Topographic Maps, Air Photographs and Geo- logical Reports. — The U. S. Geological Survey publishes a series of key maps for the United States, Alaska, and Insular possessions showing the status of topographic mapping and air (aerial) photography, including mosaic sheets and with some geologic mapping. State maps showing the areas covered by all published geological re- ports and articles are available for some States from this agency. The State geological surveys and bureaus also furnish lists of their publications. The Geologic Map of North America, Geological Society of America, 1946, and the American Geographical Society's Map of North America are useful regional aids, besides State geologic and topographic maps. Areal summaries of oceanographic data. — Since Vaughan's (1937) survey of information available in this field no general key maps have been published. Articles on geological oceanography of coastal areas are now listed in geological bibliographies. ACKNOWLEDGMENTS The writer is indebted to a large number of persons and organizations too numerous to list here. Valuable aid was received from the State geological surveys of Florida and Louisiana, and some former members of the latter; several mem- bers of the United States Geological Survey; officials of the Coast and Geodetic Survey, Hydro- graphic Office, photographic branches of the Arm}^ Navy, and Department of Agriculture, and the corps of Engineers; geologists of the Mexican federal geological survey and petroleum development agency, as well as numerous individ- ual geologists, biologists, ecologists, and other persons familiar with remote and little-known parts of the shorelines of Mexico, Florida, and Louisiana. To his colleagues in the Department of Oceanography of the Agricultural and Me- chanical College of Texas, the writer is deeply indebted for orientation and guidance in oceanog- raphy during the years of 1950-53, as well as for specific information and aid. The develop- ment of the research on which this condensed paper is based was followed closely by Warren C. Thompson and Charles C. Bates, while doing research in the Department, with whom many helpful discussions have been held. The impetus in the development of the geo-oceanographic classification here used, as has been said, came from the manuscript by E. H. Fleming and F. E. Elliott. STRUCTURAL AND REGIONAL GEO-OCEANOGRAPHIC APPROACH TO SHORELINE DESCRIPTION AND CLASSIFICATION FOR GULF OF MEXICO COASTS AND HINTERLAND The Gulf provides a good example of the well- recognized relation (Weaver 1950) of the topography of the hinterland to the width of coastal plains and continental shelves (fig. 13). ^ The geolog ic structure of any hinterland largely ' Taken from Price (1951 b). controls its topography and has a direct or indirect effect (Suess 1888) on the character and positions of shorelines. These factors are dominant in determining the drainage and hence, the transport of sediment from the land to coastal areas. 44 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE Figure 13. — Major geologic structures exposing uplifted rock masses surrounding Gulf of Mexico. Cross-hatched, folded sedimentaries, granitic areas, volcanic belts. Stippled, uplifted arches or horsts. Stipple and dash, emerged parts of arches form limestone plateaus at south and east. Under-water contours, 100 and 1,900 fathoms, the former out-lining the continental shelf, the latter, the Mexican Basin (Sigsbee Deep) . Long broken lines, axes of arcuate Caribbean folding (axis of Gulf coast geosyncline, supposedly along northwest shore, not yet located. Scale: Hun- dreds of miles. REGIONAL COASTAL TYPES YOUNG OROGENIC COAST Where geologically young mountains (Tertiary to Quarternary) closely border the coast (Umb- grove 1947, pi. 5), as in Cuba and the south- western Gulf coast in Mexico (figs. 12, 13; fig. 14, Sector 3), coastal plains and the continental shelf are absent, narrow or of irregular width, and the shelf tends to be rocky with shoals and irregular elevations (Fleming and Elliott 1950) as well as somewhat steep (slope greater than about 5 feet per statute mile). Sand and mud* occur on the shelf and mud along the outer margin and in shelf deeps. The coast may have alternating narrower erosional and wider depositional sectors, the latter with smooth shorelines and bottoms, the former with uneven surfaces. These coasts and shelves are unstable and subject at any time to earthquakes, fracturing and warping of the crust. s Sediment terminology used is that of the coast charts. "Mud" is a field term implying no accurate knowledge of the clay fraction. GULF OF MEXICO 45 Young orogenic coasts have their shorelines dominantly parallel (concordant, Suess 1888) with the structural trends (folds and faults) of the mountains. The Gulf provides no ex- amples of coasts where the shoreline is more than very locally discordant with the structural trends on land.' This accounts to a large extent for the almost complete lack of islands in the Gulf other than sandy barriers close to shore, karst islets of Florida, some lava-rock islets in Sector 3 in Mexico, and coral and detrital reefs on shoals. From the meager data of the charts we conclude that, because the Mexican mountains are mostly not younger than Miocene, coastal sediments have built out around or otherwise protected most of their outpost hard rock folds from the Gulf. However, a large mountain range projects eastward under water some 50 miles off Tampico and two parallel mountain ridges trend northwestwardly from the edge of the continental shelf off the Rio Grande delta. The Tertiary mountains of Cuba (Palmer 1945) rise from a short distance back of the coast. The folded rocks come down to the coast or are overlain there by a thin cover of younger deposits. The island may be divided into several areas of different tectonic structure, but overthrust folds rising up to the south dominate some sectors, as in the extreme west. The Gulf bottom off the north coast descends at angles of 4° to 6° or more, a slope which conforms fairly well to some of the folds. A narrow shelf occurs only where fringing reefs have grown up with a rising sea level to form barrier reefs, so that the lagoon has been filled to a shallow depth with sediment and organic growths (3.2 Sectors, fig. 14). The drainage of northwestern Cuba is largely southward, so that only small streams enter the Gulf and the coralline lagoons. The sedimenta- tion along the northwest shore has, therefore, been negligible except where coral reefs and mangrove growth have trapped marine and land- derived materials. An erosional sector occurs between the barrier reefs east and west of Havana. The Sierra Madre Oriental, the eastern Cordil- lera of Mexico, slants southeastward toward the coast, one of the outpost folds in limestone rock making a minor protuberance at Punta Jerez (fig 13).'° The coastal plain becomes gradually narrower southward from the delta of Rio Grande. It is, however, as much as 60 or more miles wide in places. The Southern Volcanic Range of Mexico (Sierra Neo-Volcanica, Tamayo 1949), a zone of Tertiary-to-Recent volcanic peaks, runs from the Pacific coast due east through Mexico City to form the broadly protuberant Jalapa Salient north of Veracruz at 20° N. Lat. A similar salient south of the city, that of San Martin Tuxtla, separated from the range, may be geo- logically associated with it. The range includes some of the greatest peaks of Mexico, including at the east, in sight of the Gulf, Orizaba and Cofre de Perote, reaching elevations of 18,696 and 14,048 feet, respectively, above sea. Between and on each side of these salients are sedimentary embay- ments (fig. 14, 3.2) with fairly broad coastal plains. Only a narrow belt of low shoreline deposits seems to be present along the fronts of the vol- canic salients. These salients are composed of confluent and overlapping flows of volcanic rocks, some of which make small jutting points at the shoreline. Of these, Roca Partida and Punta Delgada have cliff ed faces reported to be 1,000 feet high, with islets of lava rock. There are several volcanic peaks in the San Martin salient, including San Martin Tuxtla, which has been active in historic time. On air photographs of this sector, the writer counted some 20 small cinder cones aligned in a zone about 10 miles wide and 40 miles long parallel with the coast. One of the cones stands in the intermountain Lake Catemaco with its crater invaded by the water. The continental shelf off the orogenic coast of Mexico is poorly mapped. It is narrow and, where mapped, the gradient is convex, becoming steep, like that near the outer edge of the shelf of Texas and Louisiana. The grain sizes of the sediments, so far as is revealed by the data on the charts, decrease more regularly outward than on some better-known orogenic coasts, as that of California where there are separate offshore sedimentary basins both on and off the shelf, each with its own sedimentary distributional pattern. The small size of the sub-aerial drainage basins where mountains stand near the coast has ' Discordant coasts are found today chiefly where old mountain areas, as from New England to Newfoundland, have been drowned by sinking of coasts under load of Pleistocene ice sheets. '0 The convexity here is exaggerated on O. O. Chart 2056 as compared with the later W. A. C. 689, made from a photographic base. 46 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE Figure 14. — Regional geo-oceanographic classification, shorelines and coasts, Gulf of Mexico: 1, alluvial coasts; 2, drowned limestone plateaus; 3, young orogenic coasts; 4, biogenous (organic) development on various coasts. Sub-sectors: 1.1, deltaic coasts, with 1.11, unentrenched simple deltaic plain, and 1.12, entrenched and embayed compound deltaic plain. 1.2, terraced deltaic coastal plain; 2.1, unsimplified to little simplified drowned karst ; 2.2, limestone karst with beaches; 3.1, erosional, and 3.2, depositional, orogenic coasts; 4.1, broad shelf; 4.2 shelf absent to narrow; 4.3 lesser biogenous development (more extensive than shown). The two southerly Mexican 3.1 Sectors are volcanic salients. been shown to restrict coastal sedimentation. This is true here, in that the shelf is wide off the several sedimentary salients, but narrow in front of the coastal mountain salients. ALLUVIAL COASTS Where the closest mountains, usually old mountains, are located far or moderately far in- land (Umbgrove 1947, pi. 5), the runoff and sedi- ment load from the lands has been large and long continued, interior plains are succeeded by broad coastal plains and continental shelves, and the coast is of the deltaic (Fleming and Elliott 1950) or alluvial coastal plain type. On such a coast, after sufficiently long stillstand, shelf bottoms are smooth except toward their outer margins, organic reefs are inconspicuous, few or absent, and shorelines are smooth or irregularly deltaic (fig. 13, and No. 1 Sectors, fig. 14). .Sediments here ai-e generally of even distribution to somewhat spotty (Lynch, fig. 16). Sands extend from shore out to about 5 or 10 fathoms, followed by silt or sand and mud (charts), with mud further out to the edge of the continental shelf. Mud or silt GULF OF MEXICO 47 may come in very close to the mouth of a deltaic river that drains a large basin. Tiie chief excep- tions to the outward banding of sediments (Emery 1952) are any coai-se sediments of local organic or chemical origin, or, along the northwestern shelf of the Gulf, sediments on mounds believed to lie above buried intrusive salt dunes (Shepard 1937 b). The alluvial sectors of the Gulf of Mexico (Sec- tors Nos. 1.11, 1.12, and 1.2, fig. 14) have smooth shorelines with sandy beaches on the mainland, or on barrier islands (Price 1951 a). The beaches may be more or less interrupted by deltas of vary- ing degrees of protuberance and shoreline irregu- larity (Russell 1940; Bates 1953). Offshore, the alluvial sectors have broad, smooth continental shelves, 130 miles wide at the maximum, with relatively steep inshore shelf-bottom profiles (fig. 15, Sector VII) and a rather uniform gradation of sediment from sand (generally inside the 5- or 10- fathom depth contour) to sand-and-mud, with mud at the outer margins. The elevated mounds on some outer parts of the northwestern shelf have nodular algal limestone on their tops and possibly some coral. Subsectors, alluvial coast: terraced detaic plain. — Sector 1.2, Alabama, Mississippi, and western Florida (fig. 14), has a fairly steep coastal plain," with two Pleistocene-and-Recent deltas (Apala- chicola, Pascagoula, and Pearl), a minor amount of embayment of drowned stream valleys and a reported series of low, parallel elevated shoreline scarps (Carlston 1950). In places, the younger two of these have roughly parallel Pleistocene barrier islands and coastal lagoons (MacNeil 1950) in part entrenched by drainage and embayed. This coast is like that of the southern Atlantic coastal plain of the United States, with which it has a common geologic history. These similari- ties exist because of the position of the old (Pale- ozic), almost entirely quiescent Appalachian mountains fairly close (90 to 150 miles) to the coast hut not in a bordering position. Drainage basins extending from the mountain front across the coastal plain are small in relation to those of the deltaic 1.12 alluvial coast. The large cuspate Pleistocene-Recent Apalachicola delta and the long, broad, and shallow Mobile Bay are striking features of this coast • Eight feet per mile nenr the coast in some places. Broadly embayed deltaic coastal plain. — ^Sector 1.12 (fig. 14), the coast of Louisiana, Texas, and part of Tamaulipas, receives the drainage of some ten major rivers. Three major Recent deltas now reach the Gulf; the Mississippi-Red, Brazos- Colorado, and Rio Grande deltas. A very broad, gently sloping deltaic coastal plain (Barton 1930) has been built, forming a fully concordant coast (Suess 1888). Coastal plain deposits form a new structiu'al (monoclinal) trend in front of the abrupt southwestern ends of Appalachian folds once projected into the broad Mississippi embayment. Sector 1.12 (fig. 14) is deltaic except between arcuate delta fronts where the active barrier and the Pleistocene Ingleside barrier island (Price 1933) with their parallel, active and entrenched coastal lagoons form a diversified inner coast tran- sected by many broadly drowned and embayed stream valleys (Price 1947). There are, thus, intermittent terraced riverine plains between ad- jacent protuberant Recent deltas. Behind the terraced belt are continuously overlapping and coalescing Pleistocene deltas with their surfaces slightly up-warped inland. The great protuber- ant Mississippi-Red delta (Russell 1936; 1940; Bates 1953) dominates the eastern part of this sector both at the shoreline and on the shelf where large shoals seem to indicate submerged deltas. A minor feature of the deltaic coast is the saline marsh (paralic) environment described on a later page with the biogenous environments. Saline plain of Rio Grande delta. — A broad, treeless, saline plain, the Jackass Prairie of Cameron County, dominated in the native state by coarse, bunchy Spartina salt grass (sacahuista), stretches inland across the Recent delta north of the natural levees of the present Rio Grande course for a maximum distance of 10 miles. The Gulf ward edge of the plain is honeycombed by saline lagoons lined on their lee (N., NW., W., and SW.) sides by clay dunes (Coffey 1909, Price 1933, Huffman and Price 1949). The soil of the low deltaic plain is made heavily saline by wind- blown (cyclic) salt contained in clay pellets and dust blown from the saline tidal flats of the la- goons. These flats undergo strong deflation dur- ing the warm months. Sand-sized pellets of flocculated saline clay accumulate on lee shores to build the dunes, while saline dust passes over the 30-foot-high dunes under the strong steady hot winds of the warm months. 48 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE From detailed topographic data it is estimated that about one-fifth of the wind-blown clay ex- cavated from playa lake basins is caught on the dunes as sand-sized pellets and the remainder passes inland as dust. The saline plain is nar- rower in Willacy County to the north where the Recent delta and the zone of playas and dunes is narrower than to the south near the Rio Grande. Unentrenched deltaic sector. — Sector 1.11, the coast of Tabasco and parts of Veracruz and Cam- peche, Mexico (figs. 12, 14), is a simple deltaic coast with a tropical rain-forest and fairly wide tidal streams that are not embayed. The large Laguna de Terminos is a delta-margin depression, a feature which Bates (1953) thinks is normally a nondepositional basin. Sinking by compaction, former entrenchment and enlargement by wave and current scour are factors that aid in shaping some of the delta-margin basins. This sector has a broad, gentle deltaic plain, abundantlj' crossed by innumerable courses of the Tonala, Seco, Grijalva, Teapao, Usumacinta, San Pedro Y San Pablo, and Palizada Rivers. These courses are grouped into two main deltas; the Seco-Grijalva delta at the west, with a broadly and symmetrically bowed shorehne, and the asymmetrically bowed Grijalva-San Pedro Y San Pablo delta at the east. The latter has a small cuspate mouth. DROWNED LIMESTONE-PLATEAU COASTAL PLAINS Continental or insular shelves may exist off the above-water parts of oceanic shoals appearing as island groups or as peninsulas attached to coa- tinents. Very broad shelves, upwards of 100 miles wide, border the peninsulas of Florida and Yuca- tan in the Gulf (fig. 13 and No. 2 Sectors, fig. 14). These low peninsulas are great uplifted limestone shoals, now partly drowned limestone plateaus. Their origins have been discussed elsewhere (Price 1951b). The surfaces of these plateaus, both above and below water, show a young rolling karst topography of limestone solution with solution-basins and sinkholes. Surface drainage is locally absent and is supplemented by under- ground water circulation moving tlirough solution channels. The Florida limestone is abundantly fissured, at least at the northwest (Vernon 1951). The plateau peninsulas are terraced limestone coastal plains. They have delivered a minimum of land-derived detrital sediment to the shelves, so that, under tropical climates, these shelves in places abound and probably have long so abounded in great coral reefs (F. G. W. Smith, p. 291) and some reef-like bars and sand keys of shell detritus. The sinkhole topography of the limestone plateaus is of subaerial origin, now modified in a broad belt near the shoreline, both above and below water, by coastal deposits (Vernon 1951)'^ and an undetermined amount of solutional activ- ity (Fairbridge 1948). There are a few relatively narrow, submerged stream valleys. Submerged subaerial karst basins are, so far as known, only shallowly filled with a foot or two of sediment, yielding poor anchorage for ships. Offshore bot- tom slopes of the inner half or more of the conti- nental shelf are very gentle (fig. 15, curve 6) to moderately gentle (fig. 15, curve 4), ranging from about 1.5 to 2.5 feet per statute mile. For a few miles offshore, there are many, irregular, shifting bars of shelly sand. The limestone-plateau coasts have three types of subsectors: slightly elevated drowned karst salients of a low marshy coast (2.1), beach-bor- dered (2.2), and mangrove-ridge (4.1) shorelines. These show shoreline modification and smoothing ranging from a virtual zero modification through incipient planation to nearly completely smooth beach-bordered coasts. Coastal marsh and swamp of the limestone plateaus are abundantly chan- neled perpendicular to the shoreline by tidal scour. The tides are higher on the peninsula coast of Florida (range 2 to 4.5 feet) than on any other part of the Gulf shoreline. Inshore on the drowned karst coast, and offshore on it and on the other subsectors of the limestone plateaus, we have the so-called carbonate environment of the continental shelf (Trask 1937). DROWNED KARST SHORELINE SUBSECTOR Subsector 2.1 (fig. 14), along the northern coast of peninsular Florida north of Anclote Keys, near Tampa, has a new type, the drowned karst shore- line. Short convex areas have an intricate, cren- ulate shoreline with many small shoreline basins and archipelagoes of stony islets. Much of this karst shows, on the scale of the navigation charts, no modification by marine agencies. This entire subsector lacks embayed drowned stream valleys " Zones of submerged bars and their uplifted counterparts on elevated terraces. GULF OF MEXICO 49 and sandy beaches (Martens 1931) except short, elevated stormbeach ridges and sandy beaches on some of the Cedar Keys archipelago at 29° 10' N. Lat. These latter beaches (Martens 1931) are somewhat muddy and unlike those of glaringly white sand on the front of the Apalachicola delta, Sector 1.2, and westward from it in Florida. With this drowned karst coast of Sector 2.1, there are areas of transversely channeled marsh 2 to 3 miles wide occupied by grassy vegetation and forested swamp. This swamp is probably mostly saline. Patches of mangrove swamp occur in the southern part of this Sector. The scattered mangrove swamps with offshore oyster reefs to be described mark a minor exten- sion of the biogenous environment (Sector 4, fig. 14). The drowned karst coast is conspicuous for its many and unique marine oyster reefs, located along a shallow-water zone extending outward to a distance of a mile or two from shore. Crassos- trea virginica, the North American oyster of commerce, is notably lagoonal and estuarine, commonly being confined to brackish water en- vironments by its marine-water foes. Only along parts of the Gulf coast are living reefs of this species known in oceanic waters in North America. On Sector 2.1, the highly fractured and channeled limestones of Florida are filled inland with fresh water to a considerable height above sea level. The slope of the groundwater surface (piezomet- ric) toward the coast indicates a movement of underground water in that direction. Also, along much of the coast of Sector 2.1 there is an artesian groundwater head of about 10 feet near and at the shoreline (Cooper and Stringfield 1950, fig. 14). This pressure-head forms springs in the stream mouths and stream beds, as well as offshore. '^ The absence of land-derived sedi- ment in these streams during most of the year and the protected nature of the shelf waters leave the water of the Gulf brackish here. Off the mouth of Atchafalaya Baj', Louisiana, oj'ster reefs also grow in the Gulf out to a distance of 3 to 5 miles, with the fresh water of the river mixing with Gulf water to produce a brackish environment. Beach-bordered karst subsector. — Sector 2.2 (fig. 14) is represented both on the central coast of " Data on charts and reports of aviators via V. T. Stringfield, letter of 1862. peninsular Florida and on the coast of the Yucatiin Peninsula. On Florida, the sector has fairly continuous sandy barrier islands and barrier spits with some mainland beaches. This sector ex- tends from Anclotc Keys near Tampa at the north to Cape Romano at the south. The drowTied karst lies behind the beaches and the coastal lagoons of the sandy barriers. The lagoons are bordered by mangrove swamp and with the karst depressions more or less filled with sediment and marshy growths. The beaches of this sector (Martens 1931) have much shell material but also quartz sand. The quartz is derived from elevated sandy Pleistocene beach deposits of the elongated dome-shaped summit (300 feet or more) of the peninsula, which lies immediately inland, and from a sandy limestone formation that has been almost removed by embayment of several streams to form the broadly embayed harbors of Tampa Bay and Charlotte Harbor. These harbors are the only embayed, drowned, stream valleys of the Gulf coast of the peninsula, except the mod- erately widened tidal portion of Caloosahatchee River, nearby. The shelf-bottom slopes more steeply off this sector (2.2 feet per mile, fig. 15, curve 4) than it does farther north on Sector 2.1. Cape Sable (fig. 12) protrudes into the Gulf where Florida Bay extends eastward at the end of the mainland of the peninsula. This major shoreline bend produces a convergence zone for waves, swell and currents with the local wave attack necessary to develop a beach, keeping the shore free of mangroves. The beach plain has cuspate points and encloses narrow lagoons behind it. The beach sand is presumably mainly shelly. The oval area of plain behind the sandy beaches and the lagoons of the Cape is somewhat marshy. The origin of the broad, irregular lagoon known as Whitewater Bay, lying several miles inland from the beach is linked with the deliverj'^ of a concen- tration of drainage to a marsh. The bay is heavily fringed with mangrove swamp. The beach-bordered subsectors (2.2) on the Yucatdn Peninsula include the northern coast and the short Campeche-Champoton sector at the west. The northern coast has barrier islands and a number of slightly disconnected barrier spits which extend westward from moderate pro- jections of the shoreline. Pinnacles of limestone 50 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE several feet high protrude thi'ough the beach in places (Sapper 1937). Marshy, swampy, and partly mud-filled coastal lagoons lie behind the barriers. They are extensively occupied by man- grove swamp forest. These lagoons are called "rivers" on some maps. They were formerly thought to form a continuous inner waterway across the north end of the Peninsula. The short beach-bearing sector in the Campeche coast between the towns of Campeche and Champton (fig. 12), seems from air photographs and ground-elevation figures (20 feet to the north against 400 to 500 feet in the block) to be an uplifted fault block of limestone with entrenched stream valleys floored by narrow alluvial plains. The Gulf ends of these alluvial deposits have sandy-to-cobbly pocket beaches. Observers re- port seeing large blocks of limestone on some of them. One report, probably, erroneous, calls some of these blocks and a nearby outcrop "igneous" rock. BIOGENOUS ENVIRONMENT Where, on the coasts of the Gulf, land-derived sediments have been and are now scarce, sediments of organic origin with large marine organic struc- tures become conspicuous. Such a biogenous environment (fig. 14, Sector 4) (Fleming and Elliott 1950) may vary, here and there, from a brackish lagoonal and inshore enviroimient to a marine environment with waters of normal salinity or salinities somewhat above average (Trask 1937) . Where the water is now, or has lately been, warm, tropical and of at least normal marine salinity, coral reefs thrive. The physical limita- tions of this environment have been long and widely discussed. The biogenous environment is an oceano- graphic condition existing as an overlay on the basic geological coastal structures. It may occur on any type of shoreline where, and so long as, the requisite sedimentary and oceanographic conditions previously mentioned occur. The biog- enous environment includes the carbonate en- vironment, where MoUusca and corals are con- spicuous among the sedentary organisms, and the paralic or marine swamp and marsh environ- ments, such as those of the mangrove and salt- water grasses and reeds. It may be that, with further analysis, a funda- mental geological coastal type of biogenous nature may be recognized. Thus, the limestone peninsulas of Florida and Yucatdn may, from the historical point of view, be considered geologically biogenous, since the limestones have been built up for millions of years under dominantly cal- careous biogenous conditions. The Cuban coast, and the Gulf coast of Mexico west of the Yucatdn Peninsula, are today only superficially biogenous, as the organic growths and sediments form a mere patchwork skin on the rock folds. Limestone series several thousands of feet thick among the folded and faulted rocks of Cuba, however, show that the site of the island was biogenous for millions of years. Deposits of argillaceous (clayey) shales and the great earth-deforming (tectonic) events, were major interruptions in the carbonate type of biogenous environment in Cuba. The structural conditions of Cuba today overshadow, for geologists, the biogenous history. Carbonate subdivisional environment. — Subsec- tors of the biogenous coasts (Sectors 4) present a variety of structures and bottom types. Coral reefs and the carbonate environment in general occur on both broad (fig. 14, 4.1) and narrow (4.2) shelves. Large shelf areas have a conspicuous bottom-dwelling population. Among these, sponges are conspicuous. Actively growing coral reefs (Smith, p. 292) include fringing and barrier reefs on Cuba and a barrier reef along the outer side of the Florida Keys. This coral barrier runs along the edge of the shelf facing the Straits of Florida at the far southern end of the peninsula. Fringing reefs are also found here and there on other coastal sectors, as near the mouths of streams on the Mexican coast (Sectors 1.11, 3.1, 3.2) and on 4.1 on the Yucatan Peninsula. The great Colorados Barrier Reef of northwestern Cuba is fringing at its eastern end but encloses a 15-mile- wide lagoon to the west. Atolls and atoll-like coral reefs of more or less tabular form occur west of the Florida Keys (Dry Tortugas atoll) and others form a great, dis- continuous, barrier range along the northern and northwestern margins of the Yucatdn shelf, called the Campeche Banks (Smith, fig. 62, p. 292). The best known of these is the large Alacran atoll. The Marquesas detrital atoll off Florida (Vaughan 1914; Cooke 1939, fig. 31) is not known to have coralline growth, the reef being a group of sand keys of shell detritus formed on the shelf by the strong westward currents and winds. The Mar- GULF OF MEXICO 51 qiiesas is a great lunate key partly closed at the southwest by a series of smaller lunate keys curved oppositely to the major key and built by sec- ondary currents from the west-southwest. The living barrier reef of southern Florida in front of the main Florida Keys stands in about 5 to 7 fathoms of water. The Colorados Barrier Reef of western Cuba stands in about 5 to 6 fathoms. The barrier range off northern Yucatdn, however, stands in 20 to 30 fathoms, nearer to the edge of the shelf than to the mainland. The Florida Keys are partly coralline, partly of other origin (Cooke 1945, pi. 1, and 1939, pp. 68-72). The main eastern Key range is con- sidered to be a former barrier coral reef of the elevated Pleistocene Pamlico (25-foot) shoreline, now emerged and dead. Its highest present natural ground elevations are said to be about 18 feet above present mean sea level. This Key range ends to the southwest in the Boot, Mara- thon, and Vaca group of Keys. Westward along the line of the Keys, there is a large emergence of the Miami oolite limestone stratum to the present intertidal zone, somewhat built up, in places, by mangrove peat and marl. Marine carbonate and paralic deposits combine to form the Pine Island group of Keys. This low island mass has been broadly and abundantly channeled in a northwest- southeast direction by the strong tidal currents produced by the regularly recurring tidal differ- ence of 2 to 3 feet between the Gulf and Florida Straits. Key West is the western terminus of this group of channeled-shoal Keys. West of Key West and the Pine Islands lie the small Sand Keys (Davis 1942) where the main Miami oolite shoal lies below or mainly below low tide. These Sand Keys only sparingly fill the gap between the Pine Island Keys and the large Mar- quesas atoll. Scattered coral patches. — The scattered patches of coral growth mapped by various agencies and persons along the northern coast of the Gulf (fig. 14, Sector 4.3), far out on the shelf are not \vell known. These notations may refer to growths on the tops of small salt-dome-like seamounts found along the edge of the shelf here. Studies by H. C. Stetson show that nodular algal lime- stone balls are common on the tops of some of these small seamounts. Specimens of solitary corals, possibly from the sea areas, are found sparingly upon the beaches. Coral patches occur widely 259534 0—54 5 as bottom growths off the central peninsula coast of Florida. Paralic, or marine marsh and swamp subdivisional eninronment. — In the biogenous environment, as here defined, grassy to reedy marsh is dominant between the convex areas of drowned karst shore- line (fig. 14, Sector 2.1). It is also scattered among the mangrove swamps. The mangrove swamp forests (Davis 1940, 1942) form a conspicuous marginal coastal belt on the inshore sectors noted (4.1, fig. 14), and occur prominently in thelagoonal habitat on 4.1 and 4.2 Sectors. Fresh-water marsh (paludal environment) has some of its most extensive known developments on the broad, very gently sloping coastal plain of southern Florida inland from the marine man- grove shoreline. The paludal areas include the famous Everglades and the almost as well known Big Cypress Swamp. Marine marshes (paralic) are conspicuous in places in a relatively narrow zone along the coast of Louisiana in the deltaic alluvial environment. Here salt grasses {Spartina) and reeds have pioneered on deltaic and other shoals. Garden Island Bay, between two mouths of the Mis- sissippi's active bird-foot delta, is reported (Russell 1936) to have extended its shoreline materially by the aid of paralic vegetation. Here, again, extensive fresh-water marshes lie inland in a very gently sloping coast from the more notable saline marshes. On the steeper deltaic coast of the western Gulf, shore and coastal marsh are narrow and relatively inconspicuous. Mangrove swamp growth. — Charts of the near- tropical coast of Florida (4.1, fig. 14) south of Cape Romano (1113, 1253, 1254) and north of the Bay of Florida, and air photographs of a part of the west coast of the Yucatdn Peninsula (4.1), show a broad, belted disposition of saline man- grove swamp forest with an irregular brackish lagoon or line of lagoons landward from it. This arrangement seems to be unique for North America and for those parts of the Antilles which have been studied by the writer. It depends upon the presence of a broad, shoal continental shelf in a tropical or near-tropical sea. Lesser mangrove growths on lagoonal shores seem to be incomplete approaches to this disposition of the swamp. Mangrove swamp forests extend along the coasts of the biogenous sectors (4, fig. 14) with an extension on the drowned karst (2.1), and on the 52 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE southwestern Gulf coast (1.11 and 3). The swamps occur either in lagoons or on outer coasts that lack beaches or cliffs. It is along the beach- less and cliffless coasts, in quiet shallow waters, that the unique mangrove ridge and lagoon are found. Davis (1940) reports the growth on Florida as one of the greatest known. The tropical and near- tropical mangrove forests of the main biogenous environment are dominated by the red mangrove {Rhizophora mangle) and the white buttonwood or white mangrove (Laguncularia racemosa) . Inland from the widely flooded zone, the black or honey mangrove {Avicennia nitida) grows. The latter outruns the other mangroves into the marginal tropical regions north of the main biogenous environment. The black mangrove grows as far northwest as the Chandeleur Islands of Louisiana off the eastern part of Mississippi delta and in spots in the Laguna Madre near the mouth of Rio Grande. In the mangrove forests of southern Florida numerous other trees and plants grow with the mangroves (Davis 1940). The fact that red mangroves build out the shores on which they grow has long been known to geologists (Vaughan 1909). The abundant roots and the manner of seeding on shoals by the floating of well-sheathed seedlings aids these trees in occupying marginal marine and lagoonal areas in protected waters (Davis 1940). The black man- grove, however, seeds immediately under its branches, and tends to grow toward land from a shoreline fringe, rather than outward. The mangrove barrier ridge and coastal lagoon. — Chart 1113 shows an extremely irregular outer shoreline beginning at the north with the Ten Thousand Islands archipelago. This belt of islands starts at the northwest in the coastal lagoon behind the Cape Romano barrier spit. It then curves to the southeast to end at Lopez River. From Lopez River southeastward to Cape Sable the mangrove swamp of the outer coast is mapped as being much more compact than in the Ten Thousand Islands, and is smoother, but far from regular. It is broken by transverse marshy channels and has, in the northwestern part, an outer line of islets and small peninsulas. From 3 to 8 miles inland, there is a zone of highly irregular, more or less intercommunicating swampy lagoons and channels running roughly parallel with the outer coast. Between the inner lagoons and the outer coast, there is a broad belt of man- grove swamp which is the ridge. Davis shows that the height of the ridge should be a function of both tidal range and the slope of the bottom and adjacent land surface across which the man- grove belt originally spread. The entire coast southeast of Cape Romano (4.1) is composed of mangrove swamps and la- goons except for the sandy barrier islands, spits and beaches of the Cape Romano barrier at the northwest and of Cape Sable at the southeast. The delineation of shorelines for the mangrove forest is difficult (McCurdy 1947) because of the indefiniteness of shoreline position for a marine swamp, especially where the tidal range, as here, varies from about 2 to 4 feet. East of Cape Sable, there is a mangrove belt along the north side of Florida Bay. The mangrove peat rests on limestone rock, marl, or shell beds (Davis 1940). The peat sec- tion varies from about 5 to 14 feet. Except where it descends into depressions in the karst, Davis thinks that the general average thickness is about 7.5 feet below mean low water. This would place the base of the peat at an average of 8 feet, or slightly more, below mean sea level. The red mangrove seats itself in as much as 2 feet of water, the roots spreading outward somewhat. The seedlings float and ground in a few inches of water. There was in many cores taken by Davis through the peat, an alternation of peat and marl, with an upper marl bed a foot or two thick present in most of the area. The roots of the present swamp trees penetrate this upper marl but without peaty development in it as yet. Alternations of marl and peat in a core may or may not indicate a ver- tical oscillation of sea level, as they, certainly in some cases, have been due to compaction or minor horizontal shoreline changes under essential still- stand of the sea. The history of the formation of the mangrove barrier ridge and lagoon may be somewhat as follows: On a broad, well-protected tropical to subtropical shoal coast, especially, as m Florida, where the wind is dominantly offshore but swell and some on-shore wave movement is present, ad- vance of the mangrove forest is assured. The elongated, winged, pod-shaped seedlings ground and take root at any depth down to 6 to 8 inches of water. Root growth may extend as far offshore as a 2-foot depth at low tide (Davis 1940). The dense growth of roots, trunks, and associated veg- GULF OF MEXICO 53 etation, slowly advances seaward by the consoli- dation of peaty growth and by trapping fine- grained inorganic sediment (Vaughan 1909). Shells are added by the accumulation of small species of Mollusca on the roots (Davis 1940). It may be assumed that the maximum of accumula- tion of marl, clay, and silt takes place always somewhat forward, that is, gulfward, in the slowly advancing swamp. Storm waters and tidal os- cillations combine to permit the up-building of the accumulating swamp materials by those inor- ganic sediments which, in turn, may promote, at and above high tide levels, a denser undergrowth of the less aquatic plants. As the zone of maximum arrest and accumula- tion of inorganic sediment advances Gulfward, lack of accretion or a decrease in rate of accretion in the zone nearer the original mainland permits normal compaction of peat and marl to show in an invasion of groundwater and brackish marine waters. The swamp is abundantly penetrated all along the western peninsula coast by transverse tidal scour channels, permitting Gulf waters to enter the rear zone. If the foregoing processes and results depict the true history of the formation of the mangrove barrier ridge and lagoon on the western coast of peninsular Florida during the stillstand for the 3,000 to 5,000 years of Fisk's (1944) determin- ations, then the considerable width of 5 to 10 nautical miles of the mangrove belt is a product of the extended period of time during which ap- proximate stillstand has persisted. If minor oscillations have occurred during this period, then some of the alternations of peat and of peat marl and in the types of peat reported by Davis may have been related to changes of sea level. An end condition of seaward advance may be found where the bottom slopes too steeply, or the growth has finally reached a zone where the processes outlined no longer produce bottom offshore that I is sufficiently shoal to support mangroves. Under I this hypothesis, we may understand why the man- i grove growth on the southern part of the Gulf i shore of Florida is exceptionally wide, as the ! combination of conditions required for the full I formation of a mangrove ridge and lagoon are exceptional. Under this hypothesis the rate of Gulfward advance is the ratio between the width of the ridge, 30,000 to 50,000 feet, and the dura- tion of stillstand, 3,000 to 5,000 years. Using the figure 5,000 from Fisk's estimate, we find that the net outward advance of the mangrove forest has been between 6 and 10 feet per year. This is a measurable quantity- It has been said that Davis (1940) finds the present swamp forest to be resting on and rooted through a surficial zone of marl a few feet thick without appreciable peat deposition in it. Hence, his interpretation that the accumulation of the average of 7.5 feet of buried peat and marl took place mainly during a rise of sea level seems not to conflict with the present writer's hypothesis for forward growth during stillstand. Accumulating datings by the deterioration of radiocarbon may permit a rate of upward growth, less compaction, to be made, Davis having found no means of doing so. The mangrove barrier ridge and coastal lagoon are similar, in accomplishing appreciable shoreline prograding, to the other barriers known, the barrier island of sand, the barrier coraline reef and the rare barrier oyster reef, noted in the Gulf of Mexico where a large reef of Crassosfrea virginica forms a bay barrier 25 miles long across the mouth of Atchafalaya Bay. EMERGENT AND SUBMERGENT SHORELINES OF THE GULF USE OF TERMS Johnson (1919) laid much stress, in his shoreline studies, on the determination of whether the features of a shoreline were dominantly those of the relative submergence of a land surface or the relative emergence of a sea bottom. His interest centered in the immediate history of sea level and its effect on shorelines. Others have found it impracticable to discriminate entirely on many coasts between the exact form of the present shoreline and the topography of the coastal zone which has determined major features of both coast and shoreline (Shepard 1937a, Price 1939). This distinction involves the difficulty in deter- mining for each sector whether the several sub- mergences or emergences of the coasts during the Pleistocene have produced its dominant features. A major shortcoming of the Johnson classifica- tion or the way in which it came to be applied was its use of the common and widely developed barrier island as either a major criterion or a 54 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE positive indicator (Price 1939, Johnson 1938) of emergence. Later work, here discussed, seems to invahdate this criterion entirely as an indicator of sea-level movement except where it may be found wholly emerged or submerged. While not finding the concepts of submergence and emergence as valuable for shoreline classifica- tion as some others, we may well inquire what features plainly indicate such items of shoreline history. SUBMERGENT SHORELINE FEATURES Pleistocene entrenchment oj stream valleys. — It is well established that the accumulation of lai-ge amounts of ice in the arctic and circumarctic regions several times during the Pleistocene, or Great Ice Age, caused strong lowerings of sea level. The latest well-established major lowering occurred in the late Wisconsin or Wiirm glaciation and amounted to about 450 feet in the Gulf of Mexico (Fisk 1944, 1952) and the Gulf of Paria, south of Trinidad, Venezuela." In some regions the figure is set at between 240 and 350 feet (Flint 1947). Fisk (1944, 1948, 1952) has shown by borings cited in various reports of the Corps of Engineers that the northwestern Gulf coast had a large number of entrenched Pleistocene stream valleys that have now been filled with sediments. Configurations of branch estuaries show that entrenchment was general in the Gulf. Only on the hard shelf off peninsular Florida are such valleys found submerged and fairly well outlined by depressions. These valleys are marked by depths of as much as 10 to 15 feet on the coast charts off northern peninsular Florida. Embayed drowned valleys. — Incompletely filled drowned valleys in the Gulf take at least two forms, those in which the branching, dendritic pattern of drowned tributaries is still prominent (Baffin Bay in Texas) and those in which waves and currents have broadened the valley at shallow depth, producing oval, rounded or other equidi- mensional shapes. The writer (Price 1947) has shown that on the northwestern Gulf coast elon- gated drowned valleys tend to become segmented by spits and other obstructions, separately em- bayed by segments and the bay bottoms made flat under a dynamic equilibrium between erosion and deposition. This equilibrium of basin shape » Personal communication, T. H. Van Andel. is actually the result of the formation of equilib- rium bottom-profiles along most bay radii. Embayment of drowned streams is most prominent in the Gulf on the compound Pleisto- cene-to-Recent deltaic coast of Texas and south- western Louisiana. There, the rivers are large and the gradient of the Beaumont is not steep (1 to 3 feet per mile). On the steeper plain of Sector 1.2 (fig. 14), only one large, transverse valley bay (Mobile Bay) occurs. Where the plain is composed dominantly of active deltas or hard rocks or has only relatively minor streams, Sectors 1.11, 2.0 and 3.0, long broadly embayed stream valleys are absent. The writer has further considered local meteorological influences in the shaping of the bays of the northwestern coast (Price 1952). The harbor of Matanzas, Cuba, is thought to be a drowned valley cut in a structural depression or in a structurally weak zone. Submerged base of mangrove peat. — Davis' (1940) conclusion that the mangrove swamps and peat of Florida formed during a gradual, more or less uninterrupted rise of sea level from about —8 feet relative to mean sea level has been mentioned. Drowned lacustrine plain oj Florida Bay. — Anaylsis of this unusual type of marine area needs somewhat extended exposition. The entire water area (Trask 1939, pp. 292, 293) is a honeycomb of shallow, rimmed basins individually upwards of 10 miles wide and 11 feet deep, the bottoms bare with a cover of soft marl or shell sand. The narrow rims are of marl and mangrove peat (Davis 1940). The writer's interpretation is that a rising sea moving up and across a very gently sloping shoal surface carried with it a transgres- sive shoreline zone of mangrove swamp. This coastal swamp belt, the mangrove ridge, moved slowly north and northeastward and is now present along the north shore. This ridge is of irregular shape and the marsh and swamp back of it to the north are now and were probably at all times honeycombed with lakes. Such lakes tend to become enlarged by wind scour if the banks are not encroached on too strongly by marsh and swamp growth. The result is that some large lakes occur among the innumerable small ones. It is further postulated that, as the Gulf waters invaded the swamp, more and more deeply, vegetation was slowly killed, and the lakes gradually widened by drowning and wave erosion. p GULF OF MEXICO 55 The outlines of the lakes and rimmed basins of Florida Bay today show the characteristic coa- lescing of small basins with each other and with large ones, the intervening rims being removed. The lacustrine plain, the so-called bay, with its network of marl ridges prevents the development of appreciable tidal flow and scour in and be- tween basins except along the border of the bay at the south. Here tidal channels have been scoured through breaks in the line of the Florida Keys, locally deepening the rimmed basins. Statistical study of the relation between width and depth in the rimmed basins shows a rough approximation to the progressive deepening with increasing size characteristic of the bays of the northwestern Gulf (Price 1947). In the Bay of Florida this relation is modified on the southeast by the limiting depth of the hard Miami oolite and at the extreme west by an excess of sandy or marly deposition in the relatively large basins that there border the Gulf. Some of the western basins are completely filled with sediment. Partly submerged eolian sand plain of Rio Grande delta region. — Stretching inland across the Pleistocene plains of this delta in Tamaulipas and Texas to their inner erosional scarp is a plain of eolian sand, or erg, with scattered dune fields. All, except small blowout fans of bare sand (about 1 by 3 miles in size) and their fields of bare dunes, is stabilized by grassy vegetation, thorny brush and live oaks. The coastal lagoons now form traps for eolian sand blowing inland from the beaches of the barrier islands. Only in droughts is some of this sand able to cross to the maiidand over narrow flats that locally close the coastal lagoon. This immense sand plain must have come on shore before the barrier island was formed. The simplest explanation follows that of Daly (1934, pp. 197-201) that large amounts of sand probably blew on some shores when the sea level was low during one or more of the glacial periods. Other possible explanations are that the sand has come from the reworking of successive barrier island sands and other beach deposits or from sandy sediments in the walls and on the floors of entrenched valleys. EMERGENT SHORELINE FEATURES Pocket harbors (emergent rimmed basins) of Northwestern Cuba. — Several writers on Cuba (as Hayes, Vaughan, and Spencer 1901) have referred to the purse-shaped or pocket harbors of Cuba. Tliose of the sector from Havana to Bahia Honda (fig. 12) on tiie northwest coast are of an unusual, petal-shaped type. They lie in a plain from 3 to 5 feet above sea being upwards of 6 miles long. A small stream usually enters one or more of the several marginal indentations of the small rounded-to-oval basin, not always in the axial position. Other similar marginal indenta- tions have either no appreciable inflowing drainage or receive very slight drainage. Yet well-formed submerged channels converge from all these in- dentations toward a central channel of tidal type. This channel may be as deep as 8 fathoms. Such harbors do not seem to the writer to be explicable as normal embayments of drowned stream courses or of stream confluences, as some have suggested. If the coast of Cuba west of Bahia Honda (3.1, fig. 14) is examined on the navigation charts, basins similar to the pocket harbors and the rimmed basins of the Bay of Florida, lying in swampy terrain, will be seen here and there be- hind the Colorados Barrier Reef, mostly clustering toward the mainland shore. These basins have axial or radial tidal channels draining to the Gulf below sea through passes or breaches in the reef. These small, rounded and rimmed basins of the Colorados lagoon seem to be features of a present mangrove-lined shoreline like those along the north shore of Florida Bay. The writer inter- prets the pocket harbors of the Havana type, surrounded by a slightly elevated plain (Palmer 1945), as similar mangrove lakes scoured out at sea level in the midst of a saline swamp and then slightly elevated on the unstable young orogenic coast (Sector 3) of Cuba. Barrier Island not an indicator of long-period sea-level change. — Johnson (1919, 1925) thought that his offshore bar, called barrier island by the writer (Price 1951a, Shepard 1952), was a feature predominantly of an emergent shoreline. He be- lieved that the structure was formed by a semi- permanent sea level change, a slight worldwide lowering of sea level or an upwarping of the crust, along an offshore bar formed originally as a sub- marine feature. Fenneman (1938, p. 4), following some early writers, believed, however, that a barrier island was formed merely as an equilibrium structure produced on a shallow shelving coast by the balance between wave attack and bottom re- sistance regardless of any history of sea level 56 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE change. The writer's study of bottom profiles in the Gulf (fig. 15) indicates that barrier islands are (1) associated with well-developed equilibrium profiles, (2) on a shallow coast where the bottom is now at least 15 to 45 feet deep within one to two miles of shore and (3) thereafter slopes out- ward between about 2.0 and 5.0 feet per mile, (4) where sand, gravel or cobble are abundant along shore, and (5) where onshore wave attack is strong. These observations tend to confirm Fenneman's interpretation. Other observations, briefly stated, indicate that the barrier island does not require a worldwide or other semipermanent fall of sea level to bring it above sea, but that the only change in level needed is a local, short-period change be- tween storm levels and normal sea levels taking place during periods of a few hours or days. A series of aerial photographs taken at intervals of several years over the period 1934 to 1949 (Bates 1953) shows that a bar formed just below the intertidal zone off a new mouth of Brazos River remained submerged until a hurricane had occurred, after which it became a typical emergent barrier island of cuspate outline. A second bar then formed off a breach in this bar- rier, after which other hurricanes occurred before the second bar was, in turn, raised above sea to form a second line of emergent barriers. The inference is strong that, in each case, a pre-existing submarine bar was built higher during a hurricane, so that during the storm it bore the same height relation to the elevated storm sea level as it had formerly borne to the normal level of the Gulf. The bars emerged as barrier islands after the subsidence of the temporarily high sea levels. On October 3, 1948, a hurricane passed about 100 miles off the coast of southwestern Texas, causing a high sea level or storm tide of some 3 or 4 feet for two days or more along the barrier islands. A week later, the writer found that the summit of the beach, the beach ridge, in front of the shore dunes had been built up and remade by the storm and was slightly farther inland than its former alignment. The shift in position was evi- denced by erosion of dune faces. The convexly rounded beach ridge then rested where the front part of the dunes had been. The raising of the beach ridge, previously described, to an elevation above its position during normal times was shown by the rapid mass-wasting that had affected it in a single week. The beach ridge on this island formerly had, in places, a fairly well developed pavement of shell, but now the pavement had just begun to be formed on the newly made ridge. The pavement was formed from disseminated shell by the washing and blowing away of sand, according to a well-established process. It was evident that this ridge had lost some 6 inches of its height and would lose another foot or a foot-and-a-half before a pavement would be formed to protect it. The former paved beach ridges had evidently lost similar heights. Reports and illustrations of hmricane damage to New England beaches (Brown 1939, Howard 1939) show that the beach ridges were remade at higher levels, moved inland from their forvier positions and their axes rotated slightly by the « hurricane waters. These observations indicate clearly that the summit ridge of a barrier island functions briefly during storm tides as an underwater offshore bar and thereafter emerges as a barrier island. Evans (1942) found that waves operating at a steady sea level tend to modify the slopes and positions of underwater bars, but not to build them up above water. The great development of active barrier islands on the Gulf coast, dominating the shorelines of the alluvial sectors (1, fig. 14), does not then, in the writer's opinion, tell a story of permanent or semipermanent sea level change, or mark either a submergent or an emergent shoreline condition. The question of the source of the supply of material for the barrier, long thought to be a critical factor, is found to be secondary. Thus, barriers occur in the Gulf where longshore sedi- ment drift is prominent (Sectors 1.12, 1.2, fig. 14) the sand derived largely from rivers (Bullard 1942), also where a longshore drift from a land connec- tion (Chandeleur Islands, La.) is absent and where no land-derived sediment is present but onshore waves are strong and the barrier is built of broken shells from the adjacent bottoms, as on the north shore of Yucatan (2.2, fig. 14). Emergent shoreline terraces and notches. — The lowest well-established elevated shoreline is that of the Pamlico of the Atlantic coast and Florida, standing at about 25 feet above mean sea level. This shoreline is marked in many regions by a well-cut and well-preserved terrace or by a broad elevated lagoon flat with a barrier island. Less GULF OF MEXICO 57 well-developed and somewhat controversial shore- lines are reported from manj- places in the interval from about +3 to +10 feet. However, carefully selected, stable, protected, inner shoreline sectors on North Pacific Islands (Stearns 1941, 1945) and in Australia (Fairbridge 1948) exhibit shoreline cliffs in even-grained limestones with solution notches at about +3, +5 and +8 feet. These seem to represent worldwide stillstands of the sea (eustatic shorelines). Shorelines reported at + 16 and +20 feet (Daly 1934 and others), are not as yet substantiated by data of unquestioned accuracy. In places around the shores of the Gulf, there are definite indications of shoreline terraces that seem to indicate stillstands at about +5 and +8 feet. An elevated barrier island and coastal lagoon caught by the 10-foot contour has been mapped in Florida by MacNeil (1950) as the "Silver BluflF shoreline" (Parker and Cooke, 1944, pi. 4, fig. B). He did not follow it across southern Florida or on the west side of the peninsula. Low shoreline flats appear in many places around the Gulf, but have not been critically studied in the field. Such a low bench shows in air photo- graphs along the base of the high bluffs of the Champoton-Campeche limestone fault-block sali- ent (fig. 12; Sector 2.2, fig. 14). It seems to have a gray, sandy soil. A flat along the front of the elevated Ingleside shoreline between the Rio Grande and Brazos-Colorado deltas (fig. 12) lying at irom about 1 to about 5 feet above mean sea level has low, subdued spits and bars on its sur- face '* and seems to be an emergent marine plain. It is about 0.3 mile wide. This flat may be a nondeltaic part of the original Pleistocene surface in front of this barrier. Deltaic deposits appear along the Gulf side of this barrier east of Galveston Bay. Marsh borders the Pleistocene delta of Brazos River in Texas to an elevation of 2 to 3 feet above mean sea level. Just behind the marsh is a bench 1.0 to 1.5 mile wide at 3.0 to 4.5 feet with a low nip or wall between 4.0 and 6.5 feet above sea. This bench may be a low Silver Bluff representa- tive. At Buhler, a few miles northwest of Lake Charles, Louisiana, the Ingleside barrier and lagoon clays are well preserved. The top-of-clays, " Obscured by mima (pimple) mounds higher and wider than the spits (Price 1949). representing the approximate shoreline position, lies between 22 and 25 feet above sea. This shore- line and the associated features are well defined running at the same elevation from near Lake Charles west to Beaumont and thence southwest through Fannette, Jefferson County, Texas. Where the shoreline comes within about 10 miles of Anahauc, Chambers County, it is sloping down to the southwest at about 1.5 feet per mile and reaches sea level at Smith Point on the shore of Galveston Bay. Before the formation of the bay, it was formerly tied there to the Brazos delta. The Ingleside shoreline seems to correlate with the Pamlico through the emergent barrier of Gulfport and Biloxi, Mississippi. The deltaic plain lying south of the Ingleside in southwestern Louisiana and in Jefferson and Chambers counties, Texas, is of the same age as that immediately to the north of it, Prairie or Beaumont (Hayes and Kennedy 1903, pp. 27-38; Deussen 1924, p. 110). Along the shore of Jeffer- son and Chambers counties, it is a partly sub- merged deltaic plain. The Ingleside appears again south of the Brazos-Colorado delta along the coastal lagoon that opens from Matagorda Bay at its southeast extremity and runs from there to the north flank of Rio Grande delta, the shoreline (top of clay) being at approximate^ 5 to 10 feet above sea. The disagreements in the shoreline data for the northern Gulf coast would be removed if the coast from Florida to the Mississippi delta had been stable since Pamlico time, but a slight amount of gulfward downwarping had occurred between the vicinity of Galveston Bay and the coast of Mexico at some point north of Tampico. The post-Pleistocene gulfward downwarp of the Beaumont Pleistocene plain (Doering 1935) in- creases in amount from about 1 foot per mile in southeastern Texas to 2 feet per mile southwest of Matagorda Bay. This downwarp seems to mark the influence of the young orogenic coast of Mexico, which it is approaching.'^ This interpre- tation suggests that the emergent shoreline flat on the Gulfward flank of the Ingleside barrier may be either of Ingleside age, down warped some 15 feet, or a younger post- warping shoreline, possibly of Silver Bluff age. Against a Recent age for the low bench is the seeming absence of marine fossils '" Corpus Christi lies 175 miles east of folded Cretaceous rocks at the surface iu Meiico and 125 miles northwest of submerged mountains in the Gulf. 58 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE above present sea level in the much cored and studied post-Pleistocene alluvial fill of Mississippi River in the Atchafalaya river basin, Louisiana (Fisk 1952). No unquestionable evidence seems yet to have been offered that elevated, unwarped (eustatic) shorelines below +25 feet are of Recent or post- Glacial age, despite continued statements by many geologists that they "seem to be Recent." R. W. Fairbridge and E. D. Gill of Australia " think th at the materials of the shorelines of Australia below +10 feet are not sufficiently weathered and leached to have been formed before the last major sea level lowering. On Chesapeake Bay, G. F. Carter '* finds no post-Pleistocene deposits above a maturely developed soil, supposedly of post- Pleistocene age, which dips beneath bay sediments and has been cored into off-shore. We do not know that the shores of the Chesapeake have been down warped. The Pamlico terrace is reported as running level along this coast from Maryland to Florida. The only dated shoreline deposits above sea level that are thought to be of historical or earlier Recent Age of which the writer has been able to learn, come from young orogenic coasts, as that of Tripoli '° in Lebanon (Wetzel and Haller 1945) and on the Pacific coast of South America. These coasts must be suspected of having had crustal movements going on at any time, even in recent millenia. Thus, Jerico, 175 miles southwest of Tripoli, was once destroyed by an earthquake and 200 historical shocks are reported for the area of Israel (Ball and Ball, 1953). SHORELINE CHANGES AND PROCESSES SHORELINE SIMPLIFICATION Terminology.— Shep&rd (1937a; 1948, pp. 70-73) says that "as numerous coasts and shorelines have undergone little modification since the sea level and the land came to rest, it seemed logical to re- fer to these as Primary . . . and to . . . those which have been considerably modified by the waves and currents as Secondary ..." In his tables he calls "primary" shorelines youthful and "secondary" coasts mature. Following this con- cept, we find that mature marine coasts have in " Letters of 1952. " Letters of 1952. '• At 2 to 3 meters above sea 600 m. inland and possibly 3,000 to 4,000 years old. general become simplified in contour, with their irregularities reduced by erosion, solution or sedi- mentation, or a combination of processes. Hence, the end I'esult of marine action on most types of coasts is smoothing, though not always straighten- ing, as smooth coasts may be curved. Processes. — Simplification of a coast may con- sist of the reduction of projections by erosion, and the deposition of beach and other deposits in re- entrants. It may also be brought about by the formation offshore in shallow water of a barrier island or barrier spits (Price 1951a, Shepard 1952). Such inorganic barriers tend to follow along a bot- tom contour, crossing the sites of entrenched valleys on postentrenchment fill, while the main- land shoreline is deeply indented by the shallow embayments of the former valleys. Thus, the new marine shoreline is smooth and shorter than the mainland shoreline off which it is built. Examples. — Simplification of Gulf shorelines is shown by (1) extensive development of sandy bar- riers where there are or were irregularities of the mainland shoreline, chiefly between the convexities of deltas (Sector 1), (2) the gradual filling of coastal lagoons (as east of Galveston Bay, sector 1.2), (3) the incipient smoothing of projections along some sectors of the drowned karst coast (2.1), (4) seem- ingly some smoothing of the front of parts of the mangrove ridge (Sector 4.1) facing the Gulf, in contrast with a possibly irregular original con- figuration such as that of the Ten Thousand Is- lands or the north shore of the Bay of Florida, (5) smoothing of the karst irregularities of the elevated Champoton-Campeche fault-block (Sector 2.2, Yucatdn peninsula) so that only small cuspate points remain, (6) reduction by erosion of project- ing folded limestone rock (northern Sector 3.1) and of the ends of narrow tongues of lava solidified to rock extending into the Gulf from the active volcanic salients of the young orogenic coast of Mexico (southern Sector 3.1). Signijicance . — The several degrees of shoreline simplification evident in the preceding list, sug- gest a considerable quantitative range in the effective application of marine energy to shoreline modification during the 3,000 to 5,000 years of essential stillstand of the Gulf. Just as we find variation in simplification related to the hardness and resistance of the shoreline materials, rocks or soft sediments, so we may suspect that there have been differences in the amounts of energy available GULF OF MEXICO 59 for shoreline work. This supposition is justified by (1) the consideration that erosion at the shore- line has a vertical as well as a horizontal com- ponent, (2) comparison of variations in the form and offshore gradients of the bottom of the continental shelf on various sectors of tlie Gulf, and (3) inspection of the charts of resultant winds along: the shorelines of the Gulf (U. S. Weather Bureau, 1938). These factors indicate that it may be feasible, from the partly quantitative, partly qualitative data presented or referred to here, to set up a preliminary energy classification of the coasts and shorelines of the Gulf of Mexico. This is attempted in the tabulation. Extensive Marine Modification of Coasts of Gulf. — A summarj' of prominent shoreline condi- tions that indicate the degree of coastal modifica- tion is shown in tabular form below. The simpli- fied coasts (the secondary or mature coasts of Shepard) greatly dominate in linear distribution, indicating that the sea has been at about the same level for a substantial period of time in relation to the resistance of most of the coastal materials to shoreline modification. Percenfage Approximate of marine length in shoreline /-, ,r J . . statute miles length (juIi and major parts: Marine shoreline 3,000 100 Coastal plains 2,500 *3l Volcanic and other sectors 500 17J Secondary shorelines: Simplified (smooth) 2,250 75] Moderately smooth 250 SflOO Little modified 500 17] Sandy beach 1,553 52 Barrier islands and bay bar- riers 1,370 46 Inactive and elevated beach plains 810-1- 27 + Beach ridges, average of 10 (?) ridges per beach 20,000+ 667 + EQUILIBRIUM PROFILE OF CONTINENTAL SHELF BOTTOM Definitions. — Figure 15 shows bottom profiles for sectors of the continental shelf having different steepness of curvature. Only for the broad shelves off the alluvial and limestone plateau coasts (fig. 14, Sectors 1 and 2) of the Gulf of Mexico are there enough data for analysis. On the shelf sectors studied, the profile of the bottom is concave in the first mile or two, this section being the shoreface, an extension of the beach or other shore. The shoreface grades into a nearly smooth plain, here called the ramp, the gradient of which flattens slowly in an offshore direction for varj'ing dis- tances, commonly to 30 fathoms or more. The profiles drawn on this section of the shelf are math- ematically of the hyperbolic or asymptotic type, the so-called logarithmic or exponential curves. The ramp grades, usually far offshore, into a usually smooth convex section, here called the "camber," the gradient of which usually increases rapidly to the top of the irregular, steep, conti- nental shelf slope. The sparse soundings available for the shelf of the young orogenic coast of Mexico (3, fig. 14), suggest that, except where a beach or barrier is present, this coast may lack a ramp, the camber beginning at or near the base of whatever shore cliff or shoreface is present. The so-called shelf break (Dietz and Menard, 1951) should be the junction between ramp and camber. Data showing the locations and ramp slopes of the profiles (curves) of figure 15 and the sectors on which the curves are located are given in a tabulation following the illustration. Location of profiles in figure 15. — All profiles measured perpendicular to shoreline from naviga- tion charts U. S. Coast and Geodetic Survey. (1) Off old Corpus Christi Pass and Padre Island barrier island 27°35' N. Lat., 97°13' W. Long. Chart 1286, 1922 edition. A profile at same place from original survey sheet (1880) shows only minor irregularities and smoothly asymptotic curvature to 90-foot depth. Beach. Sand and clay bottom. (2) Off Padre Island at Baffin Bay mouth, 27°I8' and 97°20'. Chart 1286, beach sector: "Little Shell." Beach. Sand and clay bottom. (3) Off Matagorda Peninsula barrier island, off mouth Trespalacious Bay, 28°00', 96°10'. Chart 1284, 1945 edition. Beach. Sand and clay bottom. Fathogram off Galveston shows ramp as smooth as curves 1-3. (4) Off barrier island on Florida peninsula 10 miles north of Cape Romano, 26°03' and 81°48'. Chart 1254, 1931 edition. Beach. Sand inshore. Rock bottom (limestone) with some sand and shells. (5) Off Pine Islands-Key West shoals (Miami oolite with mangrove swamp deposits above), Florida, at Johnson Keys, 24°42', 81°36'. Chart 1251, 1940 edition. Profile begins at -8 feet. Add 8 to all depths for this curve in figure 15. 60 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 20 UJ 40 UJ 60 80 90 10 20 en t-ioo UJ 200 STATUTE MILES 4 6 8 10 12 ^ 1 1 5 THEORETICAL. SECTOR I ^ 1 7 6 ^i!:^i^ ^ ^ ^ 5 "'^^^'^--~^^:^ 5 5 ^ -^ 2 SECTOR "4~~ ^^^^==^t:r--^ SECTOR m~P' 3 ^ P=::^^r^^ 1 _ ^~-*-~^r^^ 1^^--- 2 20 40 60 80 90 STATUTE MILES 10 15 20 ^ ^^ -<.^ ^rrs^_ \ X THEORETICAL-" 7 ^ \ ~o - V 1 --,-._ ^ SECTOR I^^*^ \6 50 KILOMETERS IC )0 25 10 20 30 40 Figure 15. — Characteristic bottom profiles of inshore zone, continental shelf, north half, Gulf of Mexico. Steepening and progressive smoothing of bottom from profile to profile correlates with increasing energy of water, decreasing resistance of bottom, and increasing steepness of initial drowned surfaces. The theoretical low-energy, breakerless profile of Keulegan and Krumbein (curve 7) is compared with a beachless sector of drowned karst coast off Florida (curve 6). Profiles are listed on pages 59 and 60. Sectors are described in tabulation, pages 61 and 62. The shore- face extends 1 to 4 miles offshore. The ramp extends out from the shoreface as far as the profile continues to flatten. The outer parts of profiles 1 and 2 are averaged between the points shown. Bottom "hard," mostly oolite limestone. Little sand reported in region. Beachless. (6) Off rocky coast of Florida at Net Spread Key between Chassahowitzka and Weekiwachee Rivers, 28°38', 82°40'. Chart 1258, 1944 edition. Beachless. Hard bottom (limestone). Very few notes of sand in region. (7) Theoretical mathematical curve of Keulegan and Krumbein (1949) for the steepest bottom across which waves will move with the maximum height without breaking. A wave 3 m. high enters the shelf-sea on a bottom 4 m. deep 40 km. from shore. Depth equals the 4/7 power of the distance from shore. A hyperbolic curve. GULF OF MEXICO 61 Table 1. — Gradients of ramp shown in figure 15 Proaie Oradi- ent Statute miles from shore Depth in ^t Sector of Oulf 7 . 2.0 1.7 0.6 0.4 0.3 1.5 I.O 2.0 2.4 2.2 6.0 3.0 2.7 5.0 4.3 3.5 3.6 0. 1- 0. 6 .6- 2.2 2. 2- 7. 4 7. 4-15. 15. 0-25. 0-4.0 -13.0 13. 0-27. 0. 7-12. 0.9-11.0 1.0- 4.0 4. 0- 8. 5 4. 0-12. 1.8-12.2 4.4-12.2 1. 8-12. 2 3. 6-12. 2 0.5- 1.6 1.6-3.3 3. 3- 6. 6 6. 6- 9. 8 9. 8-13. 1.0-7.0 1.0-10.0 10. 0^0. 7. 0-21. 20.0-40.0 25.0-44.0 44. 0-57. 44.0-67.0 41.0-87.0 54.0-87.0 45. 0-83. 51.0-83.0 6 bottom profile, Kcu- legan and Krumbein. I 5 4 V 3 2 VII. VII 1 VII Sedimentation and the profiles. — The shoreface, ramp and camber of the normal coastal plain shelf, as exhibited on the Gulf of Mexico, seem to have specific characteristics as to sedimentation (map, fig. 16, p. 79) and erosion. From meager data, it seems that sand and shifting bars characterize the shoreface. Contemporary sands, relict deltas and barriers of former sea levels, with some contemp- orary clay deposition, characterize the ramp. Ex- cept when the entire profile is migrating landward, transportation probably dominates the ramp after any rehct elevations have been removed from the part under consideration. Fine-grained sedi- ments, mostly land-derived clays, and presumably the process of deposition, characterize the camber. Off the mouths of large deltas, little or no coarse sand reaches the Gulf and the charts show "mud" beginning near shore. Where sand is present it usually extends to 5 to 10 fathoms (Bates 1953; Lohse 1952). Dietz and Menard (1951) have lately advanced evidence and argument for the belief that, at the level of the passage of the shelf from the steep concavity into the gentler slope, in present ter- minology, where the shoreface joins the ramp, is found the depth of maximum wave action on the bottom. They term it the depth of maximum abrasion, replacing the older concept of "wave base." If the Gulf has remained essentially at the same level for the past 3,000 to 5,000 years, as pre- viously suggested, it is evident that, on bottoms closely approximating the hj^perbolic curve the shelf bottom must be in equilibrium. This should be true especially in coastal materials of slight resistance and where large amounts of marine energy have been effectively applied. That the topography of the bottom is a simple mathematical surface with a hyperbolic bottom profile, is be- lieved to indicate that the forces are in equilibrium. Wliere the bottoms are of hard rock and largely retain a subaerial topography, it may be concluded that the marine forces have inherited a surface produced under different conditions which they have been unable to destroy or to which they happen to be more or less adjusted. The equilibrium profile of the coastal plain shelf is in a state of dynamic, not static, equilibrium. In dynamic equilibrium, variations of temporary, short-term value are to be expected. Thus, heavy storm waves are known to shift offshore bars ^^ temporarily as much as a half-mile from their previous positions on the shoreface. Varia- tion of the equilibrium will be about the mean. Marked departures from the mean are caused only by forces external to those in equUibrium. The shift of a river mouth, the coming of a lava flow, or the warping of the earth's crust, would be external forces or conditions which might upset a previously existing equilibrium on the shelf. Usefulness of equilibrium profile. — Despite some pessimism (Kuenen 1950, p. 302) as to the value of the profile in geologic studies and much mis- conception on the part of writers as to the differ- ence between static and dynamic equilibria in nature, the present writer finds that the profile of equilibrium is a suitable index of the response of a continental shelf bottom to the application of marine energy for a significant period of time. If, as some think, there have been several oscilla- tions of sea level of as much as 10 to 20 feet during the past 4,000 years or so, a proposition that re- mains unproved, then the interpretation of the modification of the shorelines and shelf by marine energy is less clear than as here tentatively presented. Theoretical breakerless curve fits Florida. — Keu- legan and Krumbein (1949) made a theoretical study of the critical steepest bottom slope in shallow water on a shelf across which waves from deep oceanic waters may move but be constantly deformed and constantly lose energy so that they arrive at and near shore without enough height or energy to break or to develop shore structures, such as beaches or cliffs. The absence of such " The true underwater feature, not the barrier island. This occured at Galveston, Teias. 62 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE shore structure along much of the western shores of the limestone peninsulas of Florida and Yuca- tan, and the low gradients prevailing there off- shore, led the writer to investigate these regions for examples of the beachless and breakerless coasts. More information is available for Florida than for Yucatan. It was found that the requisite combination of (1) unmodified or little-modified shorelines, (2) gentle offshore slope and (3) essential absence of breakers (Corps of Engineers, U. S. Army 1940) exists on long stretches (Sectors 2 . 1 and 4 . 1 , fig. 14) of the Gulf shoreline of peninsular Florida.^' By analogy, similar conditions are believed to exist on more than half the lengths of the western peninsular coasts of Florida and Yucatan, where the bottom gradient is low and the shoreline and bottom essentially unmodified by marine forces. Comparison of the theoretical "breakerless bot- tom" curve of Keulegan and Krumbein (1949), described as profile 7 (p. 60 and fig. 15) with the actual rolHng bottom profile of the drowned karst shelf of peninsular Florida (profile 6, fig. 15), shows that the two curves closely superimpose and are identical in over-all gradient. But the drowned karst profile has not been fully smoothed by ero- sion and deposition and is not yet a marine profile or equilibrium, although slight modifications of it indicate that such a development is going on. DIRECTIONS OF LONGSHORE DRIFT In the northwestern Gulf of Mexico, where a strong longshore sediment drift occurs, and wherever a barrier spit terminates, the dominant drift of the year is in the direction of the elongated, pointed barrier ends." These criteria agree there with the known histories of inlet migration, although there is a weaker summer drift to the northeast. Using spit criteria, the dominant longshore drift is seen to be westward and south- westward, that is, counterclockwise,^ from Apa- lachicola delta, Florida, to the poorly mapped volcanic sectors (Sector 3, fig. 14). Where sandy beaches and barriers occur on peninsular Florida, " The data on waves and swell are being studied at the Agricultural and Mechanical College of Texas by Charles Bretschneider (Bretschneider and Reid 1953), w The so-called Gulliver's rule (Johnson 1919, p. 376) cannot be applied here successfully in all cases from chart data and is of doubtful validity in any case. See Bullard (1942) and Price (1952). ^ With reference to the center of the Gulf. longshore drift occurs. A northward drift exists for 20 nautical miles from the headland at Indian Rocks (27G°52' N. Lat.) to Anclote Keys. A much stronger south-southeastward drift exists from Indian Rocks to Cape Romano and its large underwater bars, a distance of 75 nautical miles. Southeastward drift again appears south of Cape Sable, where fine-grained sediments have been carried into the northwestern part of Florida Bay. Colorados barrier reef at the western end of Cuba diverges from the shoreline to the west, suggesting a clockwise drift. ^^ Split ends indicate a clockwise drift (to the west) on the north and northwest coasts of Yucatan to the Laguna de Terminos (Sector 1.11, fig. 14). The unmodified and slightly modified drowned karst and mangrove ridge shorelines do not show appreciable longshore drift, judging by their irregular shorelines and dominantly transverse tidal channels. Convergence areas exist at the cuspate delta of the Apalachicola and the cuspate foreland of Cape Sable, Florida. The cuspate foreland of Cabo Rojo (fig. 12; Sector 3, fig. 14), is asymmetrical, showing that the counterclockwise drift persists across it despite convergence. Bates (1953) shows from photographs and ocean- ographic data that there is a Coriolis effect ^' turning Mississippi River water westward along shore. This coincides in direction with a weak, westward-moving wind-powered drift. Together there is formed a dominant counterclockwise drift (to the right). Distribution of sediments along the delta front agrees well with this drift. Air photographs show that the Coriolis drift oc- curs also at the mouths of the other rivers of the northwestern Gulf coast. It is not operative, however, in equatorial and near-equatorial waters such as the southern Gulf of Mexico. REFERENCES Ball, M. W., and Douglas, Ball. 1953. Oil prospects of Israel. Bull. Am. Assn. Petrol. Geols. 37 (1): 1-113. Barton, D. C. 1930. Deltaic coastal plain of southeastern Texas. Bull. Geol. Soc. Am. 41 (3) : 359-382. " Observations of drift in this direction have been recorded. The drift seems to be powered by a clockwise eddy developing off the right flank of the Yucatin current (N. to NNE. through Yucatan Channel; Leipper p. 121, fig. 34). >* Relative right hand turning of flows because of the rotating coordinates of the revolving earth. The turn is to the left in the southern hemisphere. 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Ground water in Florida. Inf. Circ. No. 3, Florida State Geol. Surv., 7 pp. Daly, R. A. 1934. The changing world of the Ice Age. xxi, 271 pp. Yale Univ. Press, New Haven, Conn. Davis, J. H., Jr. 1940. The ecology and geologic role of mangroves in Florida. Carnegie Inst. Washington Pub. No. 517, Papers Tortugas Lab. 32 (16): 303-412. 1942. The ecology of the vegetation and topography of the sand keys of Florida. Carnegie Inst, of Wash- inton Pub. No. 524, Papers Tortugas Lab. 33: 113- 195. Deussen, Alex. 1924. Geology of the coastal plain of Texas west of Brazos river. U. S. Geol. Surv. Prof. Paper 126, xii, 139 pp. DiETZ, R. S., and H. W. Menard. 1951. Origin of abrupt change in slope at continental shelf margin. Bull. Am. Assn. Petrol. Geols. 35 (9) : 1994-2016. DoERiNG, John. 1935. Post-Fleming surface formations of coastal south- east Texas and south Louisiana. Bull. Am. Assn. Petrol. Geols. 19 (5): 651-688. Emery, K. O. 1952. Continental shelf sediments of southern Cali- fornia. 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T. 1937. Mittelamerika. Handbiich der regionalen Geol- ogic. Steinmann and Wilckens, eds. Band 8, Abt. 4, Heft 29. 160 pp. Carl Winter, Heidelberg. Shepard, F. p. 1937a. Revised classification of marine shorelines. Jour. Geol. 45(6): 602-624. 1937b. "Salt" domes related to Mississippi submarine trough. Bull. Geol. Soc. Am., 48(9): 1349-1361. 1948. Submarine geology, xvi, 348 pp. Harper & Bros., New York. 1952. Revised nomenclature for depositional coastal features. Bull. Am. Assn. Petrol. Geols. 36(10): 1902-12. Steers, J. A. 1946. The coastline of England and Wales, xix, 644 pp. Univ. Press, Cambridge, England. 1952. The coastline of Scotland. Geogr. Jour. 118, pt. 2: 180-190. Stearns, H. T. 1941. Shore benches on North Pacific islands. Bull. Geol. Soc. Am. 52(6): 773-780. 1945. Eustatic shore lines in the Pacific. Bull. Geol. Soc. Am. 56(11): 1071-1078. SuEss, Eduard. 1888. Das Antlitz der Erde. Vol. 2, iv, 704 pp. Tempsky & Freytag, Leipzig. Tamato, J. L. 1949. Geografia general de Mexico (Geografia Fisica). Vol. I, viii, 628 pp. Vol. II, 583 pp. Publ. by Author (printer Talleres Graficos de la Nacion) ; Atlas, 24 maps. Trask, p. D. 1937. Relation of salinity to the calcium carbonate con- tent of marine sediments. U. S. Geol. Surv., Prof. Paper No. 186-(N): 273-299. 1939. Additional note (to) Florida and Bahama marine calcareous deposits, by E. M. Thorp, pp. 292-293, Recent Marine Sediments, Am. Assn. Petrol. Geols., 736 pp. Umbgrove, J. H. F. 1947. The pulse of the earth. Martinius NijhoflF, The Hague, 2d ed, xx, 358 pp. U. S. Army, Corps of Engineers. 1940. Report on survey of intracoastal waterway, Caloosahatchee River to Apalachicola Bay, Florida (Anclote River to St. Marks) and Barge Canal across Florida. U. S. Engr. Off., Jacksonville, Fla., Nov. 1940. U. S. Weather Bureaxj. 1938. Atlas of climatic charts of the oceans. Supp. Pub, No. 1247. Vaughan, T. W. 1909. The geologic work of mangroves in southern Florida. Smithsonian Misc. Coll, 52(5): 461-464. 1914. The building of the Marquesas and Tortugas atolls and a sketch of the geologic history of the Florida reef tract. Carnegie Inst. Washington, Pub. No. 182, Papers Tortugas Lab. 5: 55-67. GULF OF MEXICO 65 Vaughan, T. W., and Others. Weaver, P. 1937. International aspects of oceanography, oceano- 1950. Variations in history of continental shelves. graphic data and provisions for oceanographic re- Bull. Am. Assn. Petrol. Geols. 34(3): 351-360. search. Nat. Acad. Sci., Washington, xvii, 255 pp. Wetzel, Rene, and Jean Haller. Vernon, R. O. 1945. Le Quaternarie de la rdgion de Tripoli (Liban). 1951. Geology of Citrus and Levy counties, Florida. Delegation G6n6rale de France au Levant, Section Florida State Geol. Surv. Bull. No. 33. xii, 256 pp. Geologique. Notes et Memoirs. 4:1-48. Beyrouth. GEOLOGY OF THE GULF OF MEXICO By S. A. Lynch,^ Agricultural and Mechanical College of Texas The lower Gulf coast and the inner continental shelf of the Gulf of Mexico are the sites of oil fields in Veracruz, Tamaulipas, Texas, Louisiana, and Florida. Therefore, hundreds of geologists, geophysicists, and engineers are engaged in inves- tigations of the structure, geologic history, and sedimentology of the fringe of the Gulf of Mexico. Due to the economic necessity for research to discover new trends and new provinces of petro- leum accumulation and to the many data contin- uously being furnished by the drill and geophysics, great strides have been made in the knowledge of the continental shelf and the adjacent Coastal Plain of the United States. Even though these economic studies were of the coastal area and con- tinental shelf, they have encouraged thought con- cerning the origin and geologic history of the Gulf of Mexico. A modern study of the Gulf Stream was initi- ated by the United States Coast Survey in 1846, and some work in the Gulf of Mexico was started soon thereafter. During the last century, many capable students of geology have studied the geo- logical history of the Gulf of Mexico, but there is still much diversity of opinion concerning its origin and manner of development. EARLY CONCEPTS Early European writers initiated the idea of North and South America being tied together by a continuous mountain sj'stem, and this century- old concept is still popular in Europe. Suess (1885, pp. 283-285) described the Gulf of Mexico bottom as an elevated "plate" and considered this plate the foreland of the Antillean chain. He believed the present deep Gulf did not exist in Paleozoic time, but an old metamorphosed and deformed basement formed a somewhat flat platform that continued southward the low-lying ' Contribution from the Department of Geology of the Agricultural and Mechanical College of Texas, Oceanographic Series No. 18. ' Head, Department of Geology, Agricultural and Mechanical College of Texas, College Station, Texas. 259534 O— 54 6 central area of the United States. The present Gulf of Mexico was formed by the collapse of the plate during Cretaceous and later time, and the general outline of the Gulf was "not influenced by the course of the mountainfolds unless perhaps in the west by the approach of the Mexican ranges to the coast of Vera Cruz" (1885, p. 551). The plate of Suess has influenced geologic thought con- cerning the origin of the Gulf for the past three- score years. Spencer (1895, pp. 103-140) not only believed that the whole tract of the Caribbean Sea, the Antilles, and the Gulf of Mexico constituted an ancient continental region, but he attempted to restore the topography of the submerged conti- nent. Using available soundings, Spencer found drowned valleys which he considered of prime importance in establishing the existence of a continental region which ever since the Miocene had executed vertical fluctuations of an amplitude of many thousands of meters. In discussing the area, he stated, "the Gulf of Mexico appears to have been a plain, with the fjords and embayments reaching nearly to its greatest depths" (1895, p. 119). Thus, Spencer agreed with Suess, at least in part, and postulated a Gulf floor more than 12,000 feet above its present deepest position. Hill (1898, pp. 3-5) believed the Gulf of Mexico is more closely related to North America than to Central or South America. He declined to con- sider most of the Antilles as other than true oceanic formations and refused to believe that there is any connection between the northern Antilles and Barbados-Trinidad, the latter being by him assigned to the South American mainland. He saw that the Gulf is nearly surrounded by low plains composed of nearly horizontal, uncon- solidated sediments deposited in an enlarged Gulf of Mexico. This border of plains is in direct contrast to the Caribbean and its mountainous periphery. Willis (1929, p. 328) held that basins are per- manent, and he did not believe the Gulf of Mexico 67 68 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE was ever an area of shallow seas over a flat "plate." This is shown by his statement that The isostatic equilibrium of the Gulf is inconsistent with the conditions that should result if a continental mass had sunk ... I, myself, regard the Gulf as representing a mass of basalt which was erupted in Pre-Canibrian time, either before or soon after the eruptions of the granitic nuclei of North America. If so, it has been a basin ever since . . . The Caribbean, Yucatan Deep, and the Gulf of Mexico are, from the point of view of actual isostatic equilibrium, all of the same nature. They are, I think, all of them basins of great antiquity. Van der Gracht (1931, p. 121) discussed the origin of the Gulf of Mexico and the downbreaking of Llanoria. He believed the coastal plain "represents a sunken basin over old central chains" and that both the Caribbean Sea and the Gulf of Mexico were part of a great geosyncline and a "very complicated system of anticlinoria, ridges and chains . . . must now fill the original geosyn- cline, generated by its late-Paleozoic compression stage. Since then, complete abrasion and renewed sedimentation . . . have obscured the original structure." Fifty years after Suess, Schuchert (1935, p. 340) confirmed the conclusion of Suess as to the Gulf of Mexico "plate" and described it as extending from Tabasco northward so as to include part of Texas, Ai-kansas, the southern tip of Illinois, Alabama, the peninsula of Florida, and the northern Bahama Banks, as well as other Mis- sissippi embayment States. The Gulf of Mexico and the Caribbean were separated, according to Schuchert, by a Central American-Antillean anticlinorium until Jurassic time. By mid-Cretaceous, the Gulf of Mexico area responded to crustal movements in Mexico and the Antillean geanticline and began to sub- side; this downward movement continued until great depths were reached. Thus, the Gulf of Mexico was a shallow sea probably from Pro- terozoic to mid-Mesozoic time, and by late Cenozoic time the depth had changed from possibly less than 1,000 to over 12,000 feet. Schuchert believed the cause of the inbreaking of the "plate" and the subsequent subsidence was related to "the geologic structures of the Central American-Antillean region, those of northern South America, and those of the present Caribbean sea bottom" and that all were "due to subcrustal flowage, to the rising of plutonic masses into the various arches, and to the subsequent cooling of these masses." He also believed that — The present depth of 12,000 feet was surely exceeded during Cenozoic time, since in the course of this era sedi- ments thought to be many thousands of feet thick ac- cumulated upon it ... In the latitude of South Lou- isiana, the ancient Gulf bottom has subsided over 25,000 feet, about twice the depth of the present Mexican Basin (Sigsbee Deep). Therefore we may say that the greater part of the Gulf of Mexico has sunk since Middle Cretaceous time at least 20,000 feet. These are striking facts, in- dicating slow, but in the end enormous, loading and isostatic adjustment, accompanied by subcrustal move- ments and rock fiowage toward the rising geanticlines of Mexico and the Central American-Antillean arch, a move- ment that is not yet completed. GULF COAST GEOSYNCLINE Barton, Ritz, and Hickey (1933, pp. 1446- 1458) were among the first to publish concerning the Gulf coast geosyncline, and they presented both stratigraphic and geophysical evidence for the existence of a geosyncline in the Gulf coast of Texas and Louisiana. They showed geophysical calculations to indicate a horizontal increase in density of the basement rocks from the Sabine uplift to near the middle of the Gulf of Mexico, and they concluded that a geosyncline must occur in the basement surface with its trough axes slightly landward from the present coast line (op. cit., p. 1456). They also showed the great thickening of the Upper Cretaceous and Tertiary beds as they dip Gulf ward, with the Tertiary beds reaching a stratigraphic thickness of more than 25,000 feet near the coast. Knowing that the deepest part of the Gulf of Mexico is 12,500 feet and assuming that the thickness of the Upper Cretaceous-Tertiary sedimentary deposits in the great depths of the Gulf are 10 percent or less of their thickness in the Gidf coast, it was concluded that "the basement of the Upper Cretaceous- Tertiary beds must be down-warped 6,000 to 16,000 feet in reference to the depth of that basement under the Sigsbee Deep." The geosynclinal trough is a well-marked feature indicating considerable subsidence. Its westward limit is not definitely known, but some thinning of formations is noted in the longitude of Mata- gorda County, Texas. It is further complicated by transverse structures such as the Rio Grande syncline, the San Marcos arch, the Houston syncline, the Sabine uplift, and the Mississippi River syncline. GULF OF MEXICO 69 Howe (1936, p. 82) called attention to the great sinking in the rou;ion of the Mississippi Delta which he believed amounted to about 30,000 feet since the beginning of the Tertiary. He believed the Gulf coast is an active geosyncline resulting from the weight of the sediments brought down by the Mississippi River. Evidence of the sinking of the Mississippi Delta was also presented by Russell (1936, pp. 167-169) in his study of the physiography of the region. Russell and Fisk (1942, pp. 56-59) questioned the "strength" of the earth's crust and concluded that the crust appeared "weak" as it jnelded and subsided "at essentially the same rate that the deposits thickened." Meyer (1939, p. 206) did not subscribe to the sedimentary -load theory and among various ob- jections stated that the "epochs of reversal of movement in the geosyncline, indicated by un- conformities, shoreline migrations, entrenched streams, submarine canyons, and the elevated beach at Corpus Christi, are opposed to the basic tenets of the sedimentary-load theory." Meyer also used the argument that the ocean deeps, which are structural troughs, could not have been caused by the weight of accumulating sedi- ments. He suggested that the Mexican Basin and the Gulf coast geosyncline may be related structures and that the Gulf coast geosyncline was a "similar structural and topographic basin in early Tertiary time when the strand-line was far inland. After this basin had come into existence, it offered an opportunity for the accumulation of thousands of feet of sediments. The weight of the first several thousand feet of Tertiary deposits may have been sufficient to overcome the in- herent strength of the crust and to cause further sinking" (op. cit., p. 206). Storm (1945, p. 1330) considered the Gulf coast geosynclinal trough as a well-marked feature indicating considerable subsidence. He believed that, if subsidence continued at a fixed position and if sediment filled this trough and passed over it, there should be some sign of sinking inland and drainage should have caused deposition over the axis of the syncline. Such indications were lack- ing, and he therefore believed that the shape of the trough was a composite of past and present. He showed that sediments are accumulating prin- cipally on the seaward flank of the trough which pushes the bottom of the flank downward while the landward flank rises slightly. Thus, the trough tends to move seaward with continued sedimentation. Glaessner and Teichert (1947, p. 586) thoroughly reviewed the subject of gcosynclines and con- cluded that the origin of gcosynclines is still unknown. Observed facts are too often over- shadowed by an author's "attitude to one or the other of the current and mutually exclusive hypotheses of mountain building and of the origin of continents on which no finality has yet been reached. Concerning the actual mechanism of the formation of gcosynclines it would seem that the school of Gulf coast geologists has produced such weighty arguments in favor of subsidence under load that the operation of the factor can no longer be doubted. On the other hand, there is evidence for 'autonomous' uplift and subsidence of parts of the crust which would make it possible for sedimentary accumulations to be formed as a result of active subsidence and uplift rather than of passive depression under the load of shifting products of erosion." Bornhauser (1947, pp. 706-711) observed that, since the Tertiary transgressions affected the whole northern border of the Gulf of Mexico, diastrophic movements must have been the primary cause of the transgressions. He agreed that the subsidence of the Mississippi embayment and the Gulf coast geosyncline caused the Ter- tiary transgressions of those areas, and the sub- sidence was due to diastrophic movements. Bornhauser "has not found clear evidence to support the idea that the weight of the sedi- mentary column is the deciding factor for subsi- dence. On the contrary, all facts and evidences seem to point toward the conclusion that the formation of the Mississippi embayment is a tectonic incident closely related to the structural history of the Gulf of Mexico which underwent considerable epeirogenic movements during the Tertiary." The idea of a Gulf of Mexico neutral plate was introduced by Suess and substantiated by Schu- chert who considered it to be the foreland of the Antdles. Bornhauser accepted this neutral plate and suggested that the northern border of the plate may have formed the submarine plateau of southeast Mississippi, at least during earlier Ter- tiary. Deeper synclines separated this plateau 70 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE from the land masses on the northwest and north, particularly during Midway-Wilcox time. Bornhauser (op. cit., p. 709) stated: In order to explain the progressive enlargement of the southeast Mississippi plateau and the corresponding shifting toward the north and northwest of its frontal synclinal zones during the Eocene, the theory is advanced that this plateau, together with the Gulf of Mexico "plate," drifted in successive stages to the north as a result of Tertiary orogenic movements in the Antilles. A maximum penetration of the' plateau into the Missis- sippi embayment was reached at the close of the Eocene and early Oligocene periods, when it touched the northern land masses. A breakdown of the southern part of this plateau and a large part of the Gulf of Mexico followed during the Oligocene and Miocene, forming the present Gulf of Mexico. This downbreaking in connection with the emergence of the embayment probably caused a change in direction of the Gulf Coast geosyncline in south Loui- siana. During the Eocene, the axis of this syncline followed a southwest-northeast trend, with the Missis- sippi embayment syncline forming its northeastern extension. With the formation of the present Gulf of Mexico during Oligocene and Miocene time, this axis was diverted to a west-east trend. Trask, Phlcger, and Stetson (1947, pp. 460-461) obtained sediments from the northwestern part of the Gulf of Mexico during the 1946 expedition of the Atlantis. In the central part of the Gulf, where the depth of water exceeds 11,000 feet, two distinctly different layers of sediment were found. A thin top zone of globigerina was underlain, in most cores, abruptly, by alternating clay and very fine, well-sorted silt containing a cold water fauna. In other cores, from the same depth, ripple marks and crossbedding were found. Such conditions suggest shallow-water deposition; and, to get such conditions, it is necessary to assume either a rather recent great depressing of the Gulf floor or an equally great lowering of sea level. The other alternate is to assume sufficient currents at depth to cause sorting, ripple marks, and crossbedding. Lowman (1949, pp. 1986-1993) believed that the central part of the Gulf of Mexico might have been epicontinental in character during Eocene time. The evidence cited includes the wide extent of the Eocene into the transverse embayments, the gentle depositional slopes, the dominance of con- tinental shelf faunas, and the character of the sediments of the southeast Mississippi platform. In contrast to the Eocene, the Upper Tertiary is absent from the transverse embayments and has continental-slope facies on relatively steep deposi- tional slopes. Therefore, the Upper Tertiary sup- ports a deep hole in the central part of the Gulf of Mexico, as it is today, though not necessarily in the same location. Lowman did not believe the stratigraphic evi- dence was conclusive that the Mississippi River syncline subsided in response to load. He believed some workers have used facies criteria instead of planes of stratification in the isopach maps which find "maxima under the delta in the Quaternary and the Pliocene-Miocene" (op. cit., p. 1991). Weaver (1950, p. 359) studied the continental shelves of the Gulf of Mexico and decided that a significant tectonic zone is at the outer edge of the continental shelf. He concluded that the topo- graphic contours on the continental slope are really structural contours and that they exist in sufficient number to indicate active tectonic regional features. He proposed "the theory that the Gulf of Mexico as a deep sea is young, and that its present central great depth is due to downfaulting." The most intense faulting is indicated along the outer margin of the continental shelf west of Florida and near Yucatan, but even the more gentle continental slopes are considered fault zones. No definite time of faulting was given by Weaver. Moody (1950) favored a single salt mass as the source of the Gulf coast and Mexican domes and suggested that it may extend across the Gulf of Mexico into the Isthmus of Tehuantepec. If this is true, the Gulf of Mexico was shallow enough to allow salt deposition beyond the present continent during the time of the deposition of the Eagle Mills salt, which is Jurassic in the opinion of Moody, although some writers place it in the Triassic or Permian. He believed the Gulf of Mexico had some downwarping during Upper Cretaceous ; that it began to take shape at the end of the Laramide Revolution; and that it subsided, and maybe formed the Mexican Basin, in post-Reynosa (Pliocene) diastrophic movements. The finding of Reynosa gravels in Florida at an elevation of 360 feet suggests a great change in sea level to allow these gravels to be transported there. This means a great post-Reynosa diastrophic movement during which the west Florida shelf scarp and possibly the Mexican Basin came into existence. Eardley (1951b, p. 2236) stated that "the Gulf of Mexico came into existence after the Appa- lachian orogeny by subsidence. ' ' Much of the Gulf is surrounded by the belt of late Paleozoic orogenj^. GULF OF MEXICO 71 and sediments dating back to at least the Permian are found in its niar<;inal areas. Eardley believed that the margins of the Gulf have had a near balance between subsidence and deposition, while subsidence has exceeded deposition in the central Mexican Basin. King (1951, p. 175) stated his i)elief that the origin of the Gulf coast geosyncline was uncertain, but he believed "that the geosyncline represents an independent tectonic feature and perhaps a new mobile belt in its early stage of development." The theory of Weaver that fault scarps bound the present central great deep of the Gulf received additional support by Jordan (1951, p. 1991) who described the escarpment off the panliandle of Florida. This escarpment occurs in 700 to 900 fathoms of water, and the sea floor is offset 6,000 feet or more in some places. Comments on Jor- dan's paper by Stetson (1951, p. 1993) confirmed the findings of Jordan and noted that the escarp- ment maintains about the same height and slope southward along the west Florida shelf. Stetson further commented that "from the overall picture of the whole area, one gets the impression that the bottom of the Gulf has foundered and that at least this continental slope is due to a normal fault" (idem.). To date little exploration in the Gulf of Mexico has had as its objective the determination of major tectonic features. The cost of marine geo- physical surveying and the drilling of offshore wells are such that the tectonics of the Gulf must be approached indirectly by using soundings and bottom samples together with observations of the shore features. GEOMORPHOLOGY OF GULF OF MEXICO The topography of the Gulf of Mexico is too scantily mapped to show the degree of develop- ment of the different types of topography so far known there. As early as 1878 Agassiz (1878-79, p. 1) noted two of the striking topographic features of the Gulf, the great limestone banks: one west of Florida and the other northward from the penin- sula of Yucatdn. In both cases the 100-fathom line is somewhat parallel to the shore and forms the inner edge of the steep slopes descending to the Mexican Basin, which is another major fea- ture of the Gulf. The varying development of continental shelves and the irregular continental slope with its escarpments, basins, knobs, and trougiis are also striking features of the Gulf of Mexico. GENERAL CHARACTERISTICS The continental shelf forms an almost con- tinuous terrace around the margin of the Gulf of Mexico. The major breaks occur in the Straits of Florida and the Yucatdn Channel which form outlets from the Gulf to the Atlantic Ocean and Caribbean Sea, respectively. The shelf is not an expressionless plain lacking in interesting physiographic features as may be suggested by some maps with a contour interval too great to properly present the smaller features. This terrace or shelf has numerous depressions, troughs, ridges, minor knobs, coral heads, escarp- ments, and two known submarine canyons. The widest parts of the continental shelf in the Gulf of Mexico lie off Texas and the peninsulas of Yucatan and Florida. The shelf width varies from 8 to 117 miles in the northern Gulf, the maximum width being off western Florida. Other shelf widths include: 40 miles off the southern tip of Florida, 52 miles off the Isles of Dernieres, Louisiana, 110 miles off the Sabine River mouth, 40 miles off the Rio Grande outlet, and 135 miles off western and northern Yucatdn. The continental slope differs from place to place not only in width and steepness but also in physiographic features associated with it. The continental slope, in general, constitutes one of the great relief features of the earth. The edge of the continental shelf is only very roughly paral- lel to the shore line as is shown by the varying width of the shelf. The continental slope varies greatly in width with a minimum width west of Florida and west and northwest of the Yucatan Peninsula. ORIGIN OF MAJOR FEATURES The continental shelves of the Gulf of Mexico seem to have a close geologic and physiographic relationship with the adjacent land. Broad shelves lie in front of broad coastal plains, and narrow shelves lie between steep continental slopes and rugged near-shore terrain. There is no simple explanation of the origin of the shelves and slopes, or of some of the features of these provinces, that has gained wide accept- ance. 72 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE In discussing continental shelves, Pratt (1947, p. 661) observed that "modern investigations have also confirmed Nansen's pioneer observation that the inland portion of the continental shelf is a surface of degradation." Umbgrove (1946, p. 249) stated, "it appears that the history of the shelf was rather complicated. Sedimentation, abrasion, and denudation played their role. The area was subjected to changes of sea-level and movements of the bottom. Wind-waves and tidal currents acted upon the sediments of the shelf. The influence of each of these and still more factors in the building of the submerged part of the continental margin is still an open question." He also believed that the landward part of the shelf may have resulted from plana- tion when the sea was some 300 feet lower than at present. Many workers believed that the topography of the shelves resulted from subaerial erosion. Dana (1863, p. 441) stated this was accomplished by the elevating of the land. Long coast lines would have to be uniformly elevated to such heights that most geologists agree the hypothesis has too many difficulties to be acceptable. The lowering of sea level could also produce conditions for subaerial erosion. Shepard and Emery (1941, p. 154) found that the formation of Pleistocene ice could account for lowering sea level 2,200 feet; Veatch and Smith (1939, p. 41) believed sea level was lowered 12,000 feet and restored in the last 25,000 years; Fisk (1944, p. 68) found evidence for a drop of sea level of 400 to 450 feet; and Carsey (1950, p. 375) suggested that if sea level was lowered 420 to 480 feet "the origin of the shelves could be attributed' largely to wave planation." The irregularities of the bottom of the shelves and the great valley-like notches along the out- ward slopes of the shelves are also unsolved prob- lems. Umbgrove (1946, p. 249) believed "the phenomena of the continental margin are corre- lated with other periodic events occurring in the earth's crust and its substratum." Daly (1936, p. 401) introduced the idea of density currents or "bottom streams of sea water containing mud in suspension and therefore tem- porarily endowed with density greater than that normal to the clean water overlying the respective continental terraces. It is further supposed that the conditions for the formation of such bottom currents were specially developed at certain stages of the Glacial Period ..." This heavy mass of mud and water would naturally move into the depressions on the continental shelf, and in places it would flow over the margin of the shelf and down the continental slope with accelerated mo- tion and force. A new hypothesis for the origin of continental slopes and submarine canyons has been suggested by Emery (1950, pp. 102-104). He proposed that "thrusting along a shear plane at the con- tinental margins may result in a temporary up- bulging of the margins above sea level. During the time of exposure erosion by streams should have incised canyons which now, after isostatic readjustment of the margins, constitute the widely distributed submarine canyons. Known down- warped peneplains below the surface of con- tinental shelves may have been developed on the bulged margins by long-continued erosion. The margins may, thus, have served as sources of some sediments now found on land and believed to have been derived from a seaward direction." Kuenen (1950, p. 497) adhered to the beUef that "the action of turbidity currents, especially during the ice ages" cut the submarine canyons along the edge of the shelf and slope of the continents. An examination of the maps of the topography of the outer shelf and slope of the northern Gulf of Mexico shows many features which suggest an origin due to density currents and the deposition of the mass of mud. Also, continental shelf fauna dredged from the Mexican Basin may have been transported from the shelf by turbidity currents. Furthermore, these currents may have carried sediment to the central Gulf and, therefore, aided in developing the rather flat floor of the Mexican Basin. GEOMORPHOLOGY BY AREAS Soundings in only a few areas of the Gulf are adequate to permit the drawing of accurate maps of the surface of the continental slope. More information is available concerning the northern Gulf; therefore, this area is discussed in some detail starting with the Straits of Florida and progressing in a counterclockwise direction. GULF OF MEXICO 73 EASTERN GULF AREA The Florida Plateau includes not only the State of Florida but an equally great or greater area that lies submerged beneath water less than 50 fathoms deep and forms the Florida shelf (H. Gunter, 1929, p. 41). This plateau has been in existence since ancient time and is a part of the Gulf of Mexico "plate" of Suess and Schuchert. Its history includes submergence during Upper Cretaceous, part of Oligocene, and Upper Miocene. Since Miocene time uplift has continued, and erosion has removed much of the once continuous cover of Miocene sandy limestone. The Florida Peninsula now has very little relief. It has a wide continental shelf off its west coast, thus demonstrating the physiographic similarity be- tween the coastal plain and the adjacent con- tinental shelf. The 1947 expedition of the United States Coast and Geodetic Survey ship Hydrographer in the waters on the continental slope southwest of the Apalachicola River, Florida, has been reported, in part, by Jordan (1951, pp. 1978-1993). Many new and interesting data have been secured in the 25,000-square-mile area of this report. The greater part of the continental shelf west of the peninsula of Florida is covered by about 40 fathoms of water, and the slope out to the 100-fathom contour is for the most part gradual. The westward slope varies from 1° at the north to 5° at the south end of the shelf. In the 25- to 80-fathom depths, domes, ridges, and troughs were discovered; escarpments and knobs with a relief of more than 300 feet were found in the 70- to 90-fathom depths. Most of these features occur along the shelf margin. Within the 400- to 1,760-fathom zone the con- tinental slope contains a deep escarpment, faults, and the terminus of the De Soto Canyon, as well as domes and depressed areas. The continental slope escarpment is of special interest since it may materially aid in the ultimate solution of the origin of the Gulf of Mexico. Jordan (op. cit., p. 1991) noted a 35° gi-adient on a 4,000-foot drop, contrasting with 1° gradients or less above and below the escarpment. A ridge 30 miles long parallels the escarpment at 700 to 800 fathoms, and ridges and troughs with relief up to 600 feet occur along the bottom of the escarpment. The main escarpment undoubtedly represents faulting, and some of the minor troughs and ridges may have a like origin. There can be little doubt that the Florida Plateau has been faulted along its western edge, but the faulting is difficult to date. Schuchert believed this faulting was due to the inbreaking of the Gulf of Mexico "plate" and that it probably began in the Upper Cretaceous. However, Weaver (1950, p. 359) beheved "that the Gulf of Mexico as a deep sea is young" and therefore the faulting must have occurred at a much more recent date. MISSISSIPPI DELTA AREA The Mississippi River brings to its mouth a daily load of sediment in the order of 2 million tons. This material has permitted the Mississippi to build its delta out on the continental shelf with the overlapping delta reaching within some 10 miles of the landward edge of the continental slope. It might be expected that a deep trough would exist in the outer edge of the continental shelf in front of the Mississippi River, but such is not the case. An ancient, deeply buried channel is found about 30 miles southwest of the passes of the Mississippi River. Shepard (1948, p. 213) stated that this trough, which has a depth of 1,800 feet, is the only major indentation in the shelf margin in the Gulf of Mexico and that the trough-head penetrates the shelf for nearly 30 miles. The sides are steep, and the flat floor is filled with loosely consolidated sediments. The canyon has been traced out on the continental slope to a depth of 900 fathoms before it becomes merged in the irregularities of the slope. A second trough, called De Soto Canyon, has been discovered off the Apalachicola River of southwestern Florida. Shepard (1948, p. 179, fig. 65) reproduced a map of this trough or canyon as contoured by H. W. Murray of the United States Coast and Geodetic Survey. This map shows a series of depressions, some with relief exceeding 20 fathoms, along the bottom of the trough and a few depressions along the sides of the trough. This canyon is shown in Jordan's map (1951, p. 1982, fig. 2) of the continental slope. The canyon has a relief of about 600 feet, heads near the 240-fathom contour, and terminates near the 500-fathom contour. Stetson (1951, p. 1993) stated that cores of the steepest walls of the canyon showed sediment and no bed rock. 74 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE Upwellings of clay, locally known as mud- lumps, occur near the mouths of the Mississippi River passes and have never been reported from any other delta. These mudlumps have been the subject of written discussion for more than a century, but only a few writers have attempted a scientific explanation of them. The most recent study has been made by Morgan (1951) in conjunction with the Corps of Engineers at New Orleans. Mudlumps and mudlump islands have at- tracted much attention since they may have mud cliiFs with a relief of up to 10 feet in an area where the average relief is usually 2 feet or less. Most mudlumps have central cores of fine- grained plastic clay surrounded and sometimes capped by irregularly stratified layers of clay and silt. The upwelling of the clay core usually produces fissures and faults with vertical dis- placements resulting in central grabens. The stratified layers dip away from the islands, often forming doubly plunging anticlinal structures. Local cones along the faults and fissures are formed by the discharge of mud, gas, and salt water. Morgan (ibid.) believed that the "formation of new lumps and rejuvenation of old lumps occurs as a direct result of excessive sedimentation at the river mouths" and "the deforming force which caused mudlump uplift is the static pressure of the sedimentary mass continually being dumped beyond the mouths of the passes." NORTHERN GULF OF MEXICO The continental shelf off Louisiana and Texas is somewhat uniform and has a gentle slope to about the 50-fathom contour. From this point the slope increases to the 70-fathom line where it has an increase in gradient to the 100-fathom depth. Some increase in slope is noted beyond the 100-fathom line, but the bottom becomes so irregular that the true slope becomes obscure. Probably the chief characteristic of the con- tinental slope of the northern Gulf is the hum- mocky topography. Shepard (1937, p. 1350) found 26 topographic features off the coast of Louisiana some of which had a relief of several hundred feet. Charts revealed that the belt of domes can be traced definitely for 180 miles west and southwest of the Mississippi submarine trough. More recent data show that some of the depressions are 2,000 feet deep, and some of the hills have a relief of at least 2,500 feet. Carsey (1950, p. 376) found 164 topographic features along the shelf off the coast of Louisiana and Texas. An area of apparent concentration of these features is shown in figure 16. However, it is probable that there are many somewhat similar features elsewhere on the continental shelf and slope. They seem to be most prevalent in the area between the 100- and 750-fathom con- tours. It is particularly interesting to note that no stream patterns have been found other than the troughs on the margins of the slope off the Mis- sissippi Delta and the Apalachicola River (Shepard 1948, p. 178). Price (1951, p. 32) observed that the "rugged topography of the northwestern shelf-margia or slope seems to contain dislocated segmeats of submarine canyons" which differ in late history from the canyons along the less rugged slope to the east. This suggests that the front edge of the shelf was faulted down in slices as it was built out into the Gulf. Available maps of the topography of the Gulf bottom vary widely in their representation of the physiographic features. The amount of time as well as the number of soundings available influence the choice of the contour interval. Thus, the Treadwell (1949) map of the continental slope of the northwestern Gulf of Mexico, contour interval of 50 fathoms, shows a great number of closed basins and knobs between 91° and 95° W. Long, and 27° to 28° N. Lat. Also, there are suggestions of drainage patterns that are not evident in the map by Shepard (1948, p. 178, fig. 64) with a con- tour interval of 100 fathoms. Some of these differences may be due to the contour interval, but some may also be the result of additional data and the choice of the cartographer when more than one interpretation of the data exists. All available maps of the continental slope of this region show the same general characteristics of the Gulf bottom: a very irregular, hummocky, knob and basin topography. Minor near-shore features of ridge and trough were noted by Kindle (1936, pp. 866-867) along the Louisiana coast. He waded across a 1,500- foot traverse and found ridges whose crests were 10 feet wide and separated by troughs from 60 to 90 feet wide. The same traverse was repeated GULF OF MEXICO 75 2 days later, and while the ridges were free of mud, the depressions were filled with several inches of mud. Therefore, the whole character of the local bottom was changed in 48 hours. This shows the futility of making sweeping conclusions from only a few data, especially in the shore zone. MEXICO Too few data are available on the topography adjacent to Mexico to make a detailed study of either the continental shelf or slope of this region. However, some generalizations may be made from the scanty sounding data and geological maps of the adjacent land. Mountain ranges, trending northeast-southwest, have been mapped 90 and 110 miles east of the mouth of the Rio Grande. The range nearer the coast has a known relief of 2,750 feet with a summit reached at a depth of 540 fathoms and the other range has a known relief of 3,810 feet with a summit at a depth of 839 fathoms. Due east of Tampico a mountain i-ange, with a bearing of N. 65°-70° E., extends some 40 miles and has a relief of 5,800 feet with a summit rising to within 33 feet of the surface. Along the extreme western edge of the Gulf of Mexico, south of Tampico, the continental shelf is narrow, and the adjacent coastal plain is also narrow, being locally practically absent. Tertiary and later igneous rocks occur in the Misantla- Japala area, northwest of Veracruz, and in the Alvarado-El Paso area, south of Veracruz. Some of the highest peaks of Mexico occur just northwest of Veracruz. Lava flows cover much of the near-shore land area and locally form 1,000-foot cliffs at or very near the shore. South of Vera- cruz other smaller cones are very near the coast. While local narrow beaches are formed and break the surface continuity of igneous rocks, undoubt- edly the offshore irregular topography is due to underwater outcropping of these igneous rocks. Practically all of the Yucatan Peninsula forms a broad coastal plain. This peninsula tilts north- westward and passes under the Gulf to form a continental shelf averaging over 125 miles in width. The shelf terminates abruptly to the west and north, and the topographic contours along its edge are undoubtedly also structural contours and represent faulting. MEXICAN BASIN There is within the Gulf of Mexico, but not centrally situated, a large triangular area with deeps exceeding 2,000 fathoms. It lies north- west of the Campeche Banks approximately between 22° and 25° N. Lat. and 89° and 95° W. Long. Regarding this area, Hilgard is quoted by Agassiz (1888, p. 101) as follows: "The large sub- marine plateau below the depth of 12,000 feet has received the name of the 'Sigsbee Deep', in honour of its discoverer." Since the "depth of the basin does not attain 3,000 fathoms, it is not a 'deep' in the Murray sense, but it is an enclosed, distinctive basin, for which Sigsbee's name may appropriately be retained" (Vaughan 1940, p. 66). More recently, however, the name "Sigsbee Deep" has been restricted to the deepest measure- ment in the basin, and the name "Mexican Basin" is used here for the broad, enclosed basin. The bottom of the Mexican Basin is very flat, especially when contrasted with the continental slope of the Gulf. The depths range from 2,000 to 2,070 fathoms over the deepest part of the basin. The bottom rises rather uniformly to the shore in the west in a distance of 180 miles, but the northern slope is more gentle and apparently more irregular in its distance of 300 miles. The slopes toward Florida and the Yucatdn Peninsula are broken by abrupt changes which undoubtedly represent faults in the bottom. One of the most prominent mounds in the Gulf is found in the northeast portion of the Mexican Basin. It has a relief exceeding 890 fathoms, a possible width of 60 miles, and its top is encoun- tered at a depth of 916 fathoms. SEDIMENTS OF GULF OF MEXICO SOURCE OF SEDIMENTS The near-shore sediments, at least, should be expected to be closely related to the sediments of the adjacent coastal plain except near the mouths of major rivers. Much study has been given samples obtained from wells and outcrops in the area surrounding the Gulf of Mexico. Such studies have shown that each formation varies widely in its composition as it curves around the Gulf from Florida to Mexico. 76 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE The Tertiary outcrops in the Gulf Coastal Plain include thick continental sandy and lignitic deposits and thinner marine sands and clays. Down-dip from the outcrops, drilling has shown that the Tertiary continental deposits pass into brackish water and near-shore marine deposits. According to Lowman (1949, p. 1941), rapid transgressions and slow regressions produced cyclical effects in the sediments with most of the sediments deposited during the regressive phases of the cycles. Farther down-dip or seaward the sediments change to a succession of offshore marine clays. In general, the Gulf coastal area may be di- vided into intergrading depositional areas as fol- lows: Rio Grande Embayment, East Texas Basin, Mississippi Embayment, the Gulf coastal region of Alabama, Georgia, and North Florida, and South Florida. The amount of rainfall on the land area surrounding the ancient Gulf may have been the chief factor in determining the contem- poraneous deposition of many sedimentary de- posits ranging from anhydrite and salt to shales and limestones. Rolshausen (1947, p. 5) sug- gested that during pre-Eagle Ford Cretaceous time, west of the Appalachian Mountains, rivers entering the Gulf from the north and northeast supplied the major load of sediments. East of the mountains the rivers entered the Gulf from the northwest and west. After Eagle Ford time, rivers entering the Gulf from the west, and prob- ably draining the western part of the present Mississippi basin, were the chief source of sedi- ments. The Rio Grande may have been the major source of sediments from the late Cretaceous through early Miocene time with the Mississippi River contributing little sediment during that time. PLACE OF DEPOSITION The sediments brought to the Gulf of Mexico are probably not carried far from shore. Parr (1935, p. 62) showed that at a point only 70 miles out in front of the mouth of the Mississippi River the water has "transparency practically equal to the clearest ocean water known." It is a gen- erally accepted fact that water discharged from the Mississippi River is carried almost entirely to the west and that it stays relatively close to the shore. Clarke (1938, p. 91) found that measure- ments of transparency supported this conclusion. Geyer (1950b, p. 100) noted that the salinity of the offshore coastal waters of Louisiana west of the delta was largely controlled by the discharge of fresh water from the Mississippi River and the westward moving littoral current. The observa- tions of the writer between 1948 and 1951 confirm the westward movement of the fresh water enter- ing the Gulf from the Mississippi River. Cogen (1940, p. 2101) examined samples of sed- iments taken from the bottom of the Gulf near the mouth of the Rio Grande and concluded that the present bottom sediments of this region were carried into the Gulf by the Rio Grande. Bullard (1942, pp. 1021-1043) showed that each of the principal rivers carries a distinct suite of heavy minerals. The Rio Grande sand shows its primary source by the predominance of basaltic hornblende and pyroxene and only 30 percent of the stable minerals such as garnet, rutile, zircon, tourmaline, and staurolite in the heavy mineral residue. The Nueces, San Antonio, Brazos, Trinity, and Sabine Rivers, draining areas of sed- imentary rocks, have little hornblende and pyrox- ene and a high content of stable minerals. Since the Colorado River derives its load from both primary and secondary rocks, its suite of heavy minerals is over half green hornblende. North- ward from the Rio Grande the beach of Padre Island contains the Rio Grande suite of heavy minerals, but the influence of the other rivers is clearly shown by an increased ratio of more stable minerals in the samples farther north in Texas. The sediments of the Coastal Plain do not end at the shore but extend out under the sea, and "if the basement surface on which they rest con- tinues to slope uniformly, the mass of sediments must increase in thickness at least as far as the edge of the continental shelf, beyond which they should thin out rapidly as they merge into the oozes of the ocean depths" (Stephenson 1926, p. 463). Land derived sediments are not being moved in a "continuous sheet of detritus all the way from the beach to the continental slope" (Daly 1942, p. 100). If this were true, much of the con- tinental shelf would be some fathoms shallower than at present. With continuing deposition the sea would become more shallow, and wave and current action would push the sediments nearer the edge of the shelf. When the sediments reached the edge of the continental shelf and a profile of equilibrium was attained, the shelf sur- GULF OF MEXICO 77 face would have been raised several fathoms. Therefore, it appears that a profile of equilibrium does xiot exist on the outer part of broad Gulf of Mexico continental shelves. Sediments carried to the Gulf of Mexico largely remain in that body of water rather than being carried into the Atlantic. The Gulf of Mexico is of no importance to the deep-water circulation of the Atlantic Ocean (Kuenen 1950, p. 44). The unnamed current that becomes the Florida cur- rent is the major current of the Gulf, and "it is essentially a direct continuation of the current through the Yucatan Channel" (Sverdrup, John- son, and Fleming, 1942, p. 642). The waters of the Gulf mainly form independent eddies and are only to a small extent drawn into the Straits of Florida. These eddies appear to be semiper- manent features with their locations determined by the contours of the coast and the configuration of the bottom (idem., p. 641).' EARLY STUDIES OF SUBMARINE DEPOSITS The Coast Survey instituted a series of investi- gations on physical problems of the deep sea in 1846, with emphasis on the Gulf Stream. In 1850, L. Agassiz made an extended biological sur- vey of the Florida reefs, and in 1867, Pourtal6s and Mitchell began a more systematic deep-sea exploration. Dredging between Florida and Cuba in 1868 reached depths of 850 fathoms, and the bottom samples obtained showed a closer relation- ship to the cretaceous fauna rather than to or- ganisms of the adjacent shores. Commander Howell, U. S. N., began a system- atic exploration of the Gulf of Mexico in 1872, starting in the shallow waters along the west coast of Florida, and the work was continued by Lieutenant Commander Sigsbee in 1875-78, using the United States Coast Survey steamer Blake. The specimens of bottom deposits were sent to John Murray of the Challenger for examination, and he published the results in 1885 (Murray, pp. 51-61). Excerpts from his original description are as follows: In all the deeper deposits in the Gulf of Mexico and Strait of Florida, the crystalline mineral particles are very small, rarely exceeding one-tenth of a millimeter in diam- eter. They consist principally of small rounded grains of quartz, with fragments of felspars, mica, hornblende, ' For a detailed discussion of circulation of water in the Oulf of Mexico see article hy D. F. Leippcr, Physical Oceanography of the Gulf of Mexico, in this book. pp. 119-137. augite, magnetite, and rarely tourmaline. In a few places there were fragments of pumice, and glauconitic particles were occasionally noticed. The mineral particles and fine clayey matter appear to be almost wholly derived from North American rivers. The carbonate of lime in the deposits of these regions is mostly made up of the shells of pelagic Foraminifera and MoUusks. In depths greater than 2,000 fathoms the Pteropod and Heteropod shells appear to be nearly, if not quite, absent — the carbonate of lime then consisting of the shells of pelagic Foraminifera; in less depths the Ptero- pod and Heteropod shells are present, and in depths vary- ing from 200 to 500 fathoms they make up the bulk of the deposits in many places. In several of the deposits, where the percentage of carbonate of lime is very high, the whole has a very chalk-like appearance; it appears, indeed, as if it were in the process of transformation to true chalk. The siliceous organisms consist of Radiolarians and Sponge spicules, with a few Diatoms, but these seldom make up more than three or four percent of the whole deposit. A study of the United States Coast and Geo- detic Survey maps of the continental shelf ad- jacent to Louisiana shows many different mate- rials forming the Gulf bottom such as sands, muds, clays, shells, and local reefs. These represent the surface of the Gulf floor, and little is known about the material even immediately below the surface. Some borings have been made in the erection of the platforms required for petroleum exploration, but these platforms are all located approximately within the first 30 miles off shore. The wells drilled from these offshore structures have yielded no known information of the surface formations. Likewise, crews making geophysical surveys in the Gulf are not interested in the surface or near- surface formations (Willey 1948, p. 3). Trowbridge (1927, p. 148) stated that the United States Coast and Geodetic Survey obtained 600 bottom samples in 1921 and that their map of 1926 included the results of this work. RECENT STUDIES OF SUBMARINE DEPOSITS According to Trask, Phleger, and Stetson (1947, p. 460) sediments in the Gulf of Mexico have changed in relatively recent time. During the 1947 expedition of the Atlantis, more than 600 cores were taken along 19 lines perpendicular to the Texas and Louisiana coast, crossing both the continental platform and the continental slope and continuing into the depths of the Gulf. The complete results of this expedition have not been published to date, but some data were discussed by Phleger (1950). It was found 78 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE that sediments off shore were remarkably uni- form. Out to a distance of some 40 miles from shore a combination of fine sand and coarse silt with an average diameter of 100 microns was found; this material was extremely well sorted. On the outer shelf the sediments were much finer, the average diameter being about 1 micron, and they were poorly sorted. In water over 11,000 feet deep in the central part of the Gulf foramini- feral ooze at the surface was underlain, beginning at 2 feet depth, by alternating clay, silt, and sand, the silt and sand being extremely well sorted. A core taken in the Mexican Basin in 1947 is of unusual interest. Trask, Phleger, and Stetson (1947, p. 461) reported that: The upper foraminiferal zone, 50 cm. in thickness, is characterized by a subtropical planktonic fauna . . . Between depths of 50 and 68 cm. in a zone of red clay or red mud, the fauna is transitional between cold and warm water faunas. Between depths of 74 and 78.5 cm., at the top of the zone of banded clay and silt, the fauna is definitely sub-Arctic . . . Between 78.5 cm. and 125 cm., the fauna is cold-water in type but is warmer than that between 74 and 78.5 cm.; and from 125 to 128 cm., at the bottom of the core, the fauna is definitely sub- Arctic. Trask (1948, p. 683) mentioned that ice-age deposits showing crossbedding or ripple marks were found in the coarse elastics of two cores taken in the central Gulf of Mexico. In other cores "well-sorted sand zones, one and three feet, respectively, were encountered at depths of more than three feet beneath the surface of the sedi- ments. Such deposits, if hardened into rock and formed in a geosyncline, would be taken as compatible with the idea of shallow-water depo- sition. Yet they were encountered in 11,000 feet of water." The Fish and Wildlife Service of the United States Department of the Interior, cooperating with the Agricultural and Mechanical College of Texas, is making a systematic survey of the Gulf of Mexico. Much of the physical ocean- ography is being done by the Texas A. and M. Department of Oceanography, and the Depart- ment of Geology is cooperating in the study of Gulf problems of marine geology. Samples of sediments obtained early in 1952 are now being studied. SEDIMENTARY PROVINCES The major sedimentary provinces of the Gulf are shown on the map in figure 16. The basic data for this map were collected from many sources, including the publications of Agassiz, Carsey, Gunter, Kindle, Lowman, Murray, Phleg- er, Price, Shepard, .Stetson, Trask, and Weaver, and by personal communications from individuals principally W. A. Price, Department of Ocean- ography, Agricultural and Mechanical College of Texas. Unfortunately, the data resulting from some 600 cores taken from the Atlantis in 1946 are not yet available. Also, the systematic exploration of the Gulf now in progress will provide many bottom samples from the whole Gulf area, and these data will make possible more detailed sediment maps in the future. The recent sediments are divided into lithologi- cal units which form somewhat indefinite zones parallel to the coast and extending outward on the continental shelf. In general, sands and shales predominate from Florida west and south to Cabo Rojo, Mexico, while limestone forms a wide platform west and north of the Yucatdn Peninsula and west of Florida. EASTERN GULF Modern calcareous sediments were thought by Agassiz (1888, p. 286) to cover the continental shelf on the west side of Florida. The charts of this area show "sand and shells" and are therefore deceiving. Samples from this region that were examined by Shepard (1932, p. 1021) "were lacking in quartz-sand and the use of sand as a textural term seemed questionable." Little sediment goes to the Gulf in streams from the Florida Peninsula, and the shore deposits consist largely of calcium carbonate secreted by organisms. Even the Apalachicola River does not discharge an appre- ciable amount of clay and silt. However, some quartz sand is found relatively near shore from Mississippi eastward across Alabama and the panhandle and near shore along the northern part of the west coast of Florida. Also, recently, num- erous sand bars have been found on the northern part of the continental shelf west of the Florida Peninsula. The area off shore from Alabama and the pan- handle of Florida has detrital sediments which show the influence of the southern Appalachians. These sediments contain an abundance of ilmenite, staurolite, kyanite, zircon, tourmaline, and silli- manite, and only minor amounts of magnetite, GULF OF MEXICO 79 80 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE amphiboles, pyroxenes, leucoxene, and hematite (Goldstein 1942, p. 81). Most of the continental shelf west of the penin- sula of Florida is hard rock, chiefly limestone, but a thin veneer of detrital sediment is present in local areas and fills some of the shelf depressions. Stetson (1951, p. 1993) obtained two specimens of hard limestone and a specimen of soft, chalky limestone from this shelf by using a steel rock dredge after core tubes were damaged by the hard rock. The Florida Keys include a 200-mile chain of islands curving southwestward along the edge of the Florida Straits from Biscajme Key to Key West and the Dry Tortugas. The northeastern keys are old coral reefs, but the ones to the south- west are remnants of a former island. Vaughan (1910, p. 119) stated that silica, as sand, is abun- dant in Biscayne Bay but decreases to the south- west as calcium carbonate becomes more abundant near the living coral reefs. The calcium carbonate occurs "as a flocculent sediment or ooze over practically the entire region from the lower portion of Biscayne Bay to the gulf end of Florida Bay." However, Trask (1932, pp. 166-172) found that the basins in Florida Bay have coarser sediments than the compact marl rims. The basin sediments are "shell breccia embedded in a matrix of marl." The recent work of Lowman (1951, pp. 234-235) provided the basis of division of the limestone banks west of Florida. He found that the white sands of the Pensacola beaches extended seaward to the depth of 20 fathoms and that the sands were free of mud and were highly fossiliferous, with Mollusca and Foraminifera being the most common forms. A second zone, extending out to 40 fathoms, was found to contain many algae, forams, pelecypods, brachiopods, bryozoans, and cup corals. The Foraminifera showed a definite faunal break at about 75 fathoms which Lowman (idem., p. 235) suggested may be the result of changes in turbidity and light penetration in the clear water. In the more turbid waters west of the Mississippi Delta a faunal break was noted at 45 to 50 fathoms. Bush (1951, pp. 102, 106) reported on a rock specimen obtained by dredging in the Straits of Florida, south of the American Shoals, at a depth of 375 fathoms. This rock, apparently broken from the ocean floor, was very fossiliferous and was correlated with the Chipola formation (lower Miocene) of northern Florida. This suggests "the dip and continuance of the lower Miocene strata from the Florida Peninsula under the Straits of Florida toward Cuba" (idem., p. 106). Between the Florida Straits and Cuba and also west of the continental shelf the bottom sediments are calcareous muds, and westward they grade into blue mud and Globigerina ooze. MISSISSIPPI DELTA Most of the coarse sediment of the Mississippi River is deposited near its mouth, but Trowbridge (1930, p. 892) noted that outside the Southwest Pass of the river, coarser sediment occurred oa knolls in 30 fathoms of water. This coarser sedi- ment apparently was not derived from the present Mississippi River under present conditions. The concentration of coarse sediments may have resulted from the removal of the finer sediments by winnowing due to stronger currents over the knolls. Shaw (1916, p. 107) stated that fine sand, sUt, and clay were accumulating on the Gulf of Mexico floor immediately beyond the mouth of the Mis- sissippi River very near where they were dropped by the river. He contrasted this with conditions on the west Gulf coast where the sediments brought to the Gulf by streams were being re- worked by waves and currents yet not carried far from the mouths of the streams. Mud and sand are recorded on many maps on either side and adjacent to the Mississippi River, but sampling by the writer shows silt and "mud" to be greatly in excess of sand. Westward from the delta there is a clay-silt zone with some sand and shells. Dark gray to black "mud" is present in most of the lagoons. Kellogg (1905, p. 34) and many others, including the writer, have observed the hard crust that develops during the winter. This crust is only an inch or two thick and is underlain by soft silt and "mud." The clay and finest particles have probably been removed by winnowing during the winter when the Mississippi River is in a low stage and therefore carrying a minimum sediment load. The very high ratios of organic matter to chlorophyll which occur near the mouth of the Mississippi River "indicate large quantities of organic detritus. The ratios fall so rapidly as one proceeds out in the Gulf that it seems likely that practically all the organic detritus of fresh water origin is removed from the surface water GULF OF MEXICO 81 before it gets more than ten or fifteen miles from the mouth of the river" (Riley 1937, p. 91). It is noted in figure 16 that the blue mud province extends northward to near the mouths of the Mississippi River. Since the front of the delta overlaps the continental shelf nearly to its outer edge, the sediments of the deeper Gulf approach the tip of the delta. Likewise, the Globigerina zone lies close to the land at the delta. LOUISIANA SHELF The numerous submerged hills rising above the sea floor near the outer edge of the continental shelf materially influence the local sediments. Trask, PUeger, and Stetson (1947, p. 461) noted that the slopes of these hills are covered with "silty, calcareous sand, and the tops by round Lithothamnium balls and little or no sandy material . . . while the adjacent flat continental shelf is underlain by sandy silt." The Lithothamnium balls, diameters up to 10 cm., must have been moved by the water since they seemed to be alive on all sides. Corals, similar to those common in the West Indies, were dredged with the Litho- thamnium balls. These areas are included in figure 16 in the patches of coral lying along 28° N. lat. between 91° and 95° W. long. The dominant sediment on the continental shelf along the Louisiana coast west of the Mis- issippi Delta is mud and sand. Locally, near shore, sand predominates to form a sand beach and shore zone. The common, heavy minerals of these sediments are amphiboles, epidote, dolomite, pyroxene, ilmenite, and biotite. Near the outer edge of the shelf and particularly on the continental slope there are many topo- graphic features of considerable relief. Carsey (1950, pp. 377-379) noted 164 such topographic features along the Louisiana-Texas slope and made a study of their density distribution accord- ing to their degree of relief. This study showed that two-thirds of these features have a relief of less than 300 feet, while some rise 600 feet above the floor of the Gulf. The sediments on the tops and flanks of topo- graphic features, having a relief in hundreds of feet, may be greatly different from those on the ocean floor only a short horizontal distance away. Corals have been dredged from the tops of a few of these knobs or domes, but little is known con- cerning the deposits on the flanks. The finer sediments may have been washed from the tops of these knobs to settle on the Gulf floor around the base. More detailed sounding and dredging in this area are needed to adequately study the sedimentology of the area. Over a 50-year period numerous "oil spots" or "seeps" have been reported as having been ob- served in the northwest Gulf of Mexico. The locations of these seeps are noted on the map (fig. 16), and it is seen that they are concentrated between 91°-93° W. and 26°30'-27°30' N. Since several of these "oil spots" were said to be several scores of miles long, their origin, although un- known, is of interest. WESTERN GULF The rivers of Texas are not heavily laden with sediment, except during flood stages, and for this reason it can be assumed that the Recent alluvial deposits found on the continental shelf will not be of great thickness. Also, these streams have little velocity as they cross the wide coastal plain, and only fine-grained mechanical sediments are carried to the Gulf. This has been shown by Storm (1945, p. 1313) in a series of samples col- lected in the Gulf out from Corpus Christi, Texas. Beyond the near-shore fine material sands with 0.21 millimeter average diameter occurred in a narrow belt about 12 miles from shore. Twenty miles from shore the grain size had decreased to an average of 0.03 millimeter, while 30 miles from shore it had increased to an average of 0.18 milli- meter. From 30 to 40 miles off shore the grain size remained about the same, but beyond 40 miles it decreased again. These variations seem to be closely associated with the currents. In 1948 Mattison (p. 77-78) found a string of coral heads off the Brazos River mouth about 8 miles off shore. They occur in 6 to 8 fathoms of water and have a relief of 2 to 3 fathoms. They have been seen by fishermen who describe them as having the appearance of sunken icebergs but having sea fans and other marine growth forming solid coral or white limestone in an area of black mud. Coral heads occur approximately along the 40-fathom line in front of Corpus Christi, Texas, and Smith (1948, p. 82) noted that six of these heads were reached within a foot or two of 31 fathoms of water. Along most of the east coast of Mexico from Texas to the Gulf of Campeche the charts show 82 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE "sand" near shore and "mud" off shore, showing an outward gradation of sediments. Agassiz (1878, p. 1) found the fauna of the Yucatan Bank to be identical with that of the Florida Bank, being characterized by the same species of echinoderms, mollusks, crustaceans, corals, and fishes. From Tampico southward beyond Veracruz volcanic rocks are found near shore, and possibly igneous rocks will be found in the adjacent Gulf waters. Therefore, the sediments in this area should be somewhat different from those off southern coastal Texas and from those associated with the limestone of the Campeche Banks to the east. The coastal plain is exceedingly narrow locally, and the beach sands give way to near- shore patches of coral. In many places mud extends out on the shelf beyond the coral. YUCATAN PENINSULA The beach sands along the west and north shores of the Yucatan Peninsula do not spread far from shore except locally where sand and mud are found out to the edge of the shelf. To the southwest of the peninsula the sand becomes mixed with near-shore coral patches. Numerous local patches of coral occur over the Campeche Banks, and in other places the bottom is very similar to the Florida Bank. The hard limestone is locally covered with a thin veneer of detrital sediments. The Globigerina ooze prov- ince joins the Campeche Banks apparently with the blue mud absent between these calcareous sediments. CUBA Corals are common at the outer edge of the narrow shelf off the northern coast of Cuba. Beyond these corals the Florida Straits contain calcareous mud with the exception of a local area to the northwest of Cuba where pteropod ooze has been found. A bottom sample taken in 20 fathoms of water at 24°25' N. lat. and 82°26' W. long, was sub- jected to a chemical and spectrographic analysis. Also, use was made of electrolytic separation in a mercury cathode cell to concentrate the trace elements. No unusual trace elements were found, and the common elements were in approximately the same abundance as has been determined by others who analyzed the skeletal material of organisms which contribute to sediment formation. MEXICAN BASIN The upper surface of the floor in the deepest part of the Gulf consists of foraminiferal ooze. The few available cores show the underlying sedi- ment to be clay, silt, and sand, which is cross- bedded and ripple-marked in some cores. The origin of this detrital material is unknown as is also the origin of the basin forming the Gulf. Turbidity currents may have brought much sedi- ment to the central Gulf. Such an origin is further suggested by the presence of continental- shelf Foraminifera in the Mexican Basin sediments. Agassiz (1888, pp. 280-282) quoted Murray who observed that the globigerine and pteropod ooze found in the central Gulf of Mexico differed materially from that found in the oceanic basins. Diatoms, radiolarians, and sponge spicules com- prise the siliceous organisms but represent only a small percentage of the bottom deposits. Fish oto- liths were found at depths from 392 to 1,568 fath- oms. The globigerine ooze was found to extend northward to the Mississippi River slope where it was replaced by dark, rich muds containing "a number of interesting forms of annelids, mollusks, ophiurous and sea-urchins, characteristic of the continental Gulf slope, and typical of mud deposits" (idem., p. 282). CONCLUSIONS The Gulf of Mexico, with a surface area of 615,000 square miles, offers many rewards for research in geology, biology, and oceanography. Continued drilling at the extreme margins of the Gulf may produce new local data as greater depths are reached by the drill, but much of the search must be made far from shore. To date most of the geophysical prospecting has been in the very shoal areas where present methods of development may apply. The use of geophysics to study the tec- tonics of the Gulf largely lies in the future. Therefore, it seems that present aid in solving the many problems of the Gulf of Mexico must come from the oceanographer who can give other scientists new data from soundings, bottom samples, and the physical characteristics of the water. While the time and manner of the origin of the Gulf basin are still undetermined, present evidence favors the existence of a shallow Gulf, the "plate" of Suess and Schuchert. Assuming that Llanoria GULF OF MEXICO 83 extended into the Gulf, its submergence may have been completed by late Jurassic time, thus pro- viding for the uivasion by the Cretaceous seas. Post-Cretaceous downwarping tilted the Creta- ceous deposits Gulfward, but, in general, the Gulf remained a shallow sea during most of the early Tertiary. During late Tertiary the basin of the Gulf further subsided, possibly both by down- warping and faulting along the basin margins. The escarpment along the west edge of the Florida shelf (Jordan 1951, pp. 1978-1993) un- doubtedly has its origin in faulting, and similar conditions seem to e.xist at the outer edge of the Campeche Banks. Other areas along the con- tinental slope suggest fault scarps. The basin of the Gulf may well have been deeper than the present 12,425 feet, with post-mid-Tertiary sedi- ments filling the basin to its present depth. 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Submarine topography of continental slope of northwest Gulf of Mexico. Submarine Geol. Rept. No. 7, Scripps Inst. Oceanog., Univ. Calif., 7 pp. Trowbridge, A. C. 1927. Disposal of .sediments carried to the Gulf of Mexico by Southwest Pass, Mississippi River. (Ab- stract) Bull. Geol. Soc. Am. 38 (1): 148. 1930. Building of the Mississippi Delta. Bull. Am. Assn. Petrol. Geols. 14: 867-901. Turner, H. J. 1903. Examination of mud from the Gulf of Mexico. U. S. Geol. Surv. Bull. 212: 107-112. Umbgrove, J. H. F. 1946. Origin of continental shelves. Bull. Am. Assn. Petrol. Geols. 30 (2) : 249-253. 1947. The pulse of the earth. 358 pp. Nijhoff, The Hague. Van Der Gracht, W. A. J. v. W. 1931. The Permo-Carboniferous orogeny in the south- central United States. K. Akad. Wetens., Amster- dam, Verh., Afd. Natuurk., 2d Sect., 27 (3): 121. Vaughan, T. W. 1902. Evidence of recent elevation of the Gulf coast along the westward extension of Florida. Science, n. s., 16: 514. 1909. Geology of the Florida Keys and the marine bot- tom deposits and recent corals of southern Florida. Carnegie Inst. Washington Year Book 7, pp. 131-136. 1910. A contribution to the geologic history of the Floridian plateau. Carnegie Inst. Washington Pub. 133, pp. 99-185. Vaughan, T. W. 1914. The building of the Marquesas and Tortugas atolls and a sketch of the geologic history of the Florida reef tract. Carnegie Inst. Washington Pub. 182: 55-67. 1918. Geologic history of Central America and the West Indies during Cenozoic time. Bull. Geol. Soc. Am. 29: 615-620. 1940. The classification and nomenclature of the sub- marine features of the Gulf of Mexico and the Carib- bean Sea. D'Oceanographie Physique, Union Geo- desique et Geophysique Internationale, Pub. Scien- tifique No. 8. Vaughan, T. W., and E. W. Shaw. 1915. Geologic investigations of the Florida coral reef tract. Carnegie Inst. Washington Year Book 14: 232-238. Veatch, a. C, and Smith, P. A. 1939. Atlantic submarine valleys of the United States and the Congo submarine valley. Geol. Soc. Am., Spl. Paper No. 7, 101 pp. Weaver, Paul. 1950. Variations in history of continental shelves. Bull. Am. Assn. Petrol. Geols. 34 (3): 351-360. Willey, M. B 1948. Engineering characteristics of the Gulf coast con- tinental shelf (La.). Am. Inst. Min. Engrs., Tech. Pub. 2323, Petr. Tech. 11 (2): 1-11. Williams, H. F. 1950. The Gulf of Mexico adjacent to Texas. Texas Jour. Sci. 3 (2) : 237-250. Willis, B. T. 1929. Continental genesis. Bull. Geol. Soc. Am. 40: 281-336. WOLLARD, G. P. 1936. An Interpretation of gravity anomalies in terms of local and regional geologic structures. Trans. Am. Geophys. Union, Pt. 1, pp. 70-73. CHAPTER III MARINE METEOROLOGY OF THE GULF OF MEXICO MARINE METEOROLOGY OF THE GULF OF MEXICO, A BRIEF REVIEW By Dale F. Leipper, Department of Oceanography, Agricultural and Mechanical College of Texas The best general summary of the weather over the Gulf of Mexico in nontechnical langjuage is probably that prepared by the United States Weather Bureau for the United States Coast Pilot (1949). There are a number of articles on the general circulation of the atmosphere and on meteorological processes without specific reference to the Gulf of Mexico which, nevertheless, pertain to this region as well as to all similar regions. It will not be attempted to review such articles in the present summary. Two references of this type are Holmboe, Forsythe, and Gustin (1948), and Byers (1944). In addition, there are some publi- cations such as Riehl (1947) which deal with the general weather in the low latitudes and are helpful in understanding the Gulf of Mexico weather more completely. EXTRATROPICAL CYCLONES Saucier (1949) has analyzed the frequency and behavior of extratropical cyclones originating on or near the northwestern coast of the Gulf of Mexico over a 40-year period. These cyclones have marked effect upon the weather of the Gulf as well as upon that of much of the eastern United States. They occur on the average about 10 times per year with a maximum number of 19 occurring in 1899 and a minimum of 2 in 1916. The high frequency of these storms appears to result from the influence on the general circulation of the warm moist surface provided by the Gulf of Mexico, the cold continental air to the north, and the mountains to the west. It was found that the cyclones seldom occurred immediately after a deep cold air mass penetrated the entire Gulf of Mexico but were most common when it remained north of the Gulf coast. The storms may begin as early as October. The maximum number occurs in January. Very few occur later in the ' Contribution from the Department of Oceanography of the Agricultural and Mt'chanieal College of Texas, Oceanographic Series No. 20. Based in part upon work done under the sponsorship of the Office of Naval Research and the .\ir Force Cambridge Research Center. 2 References are listed at the end of the chapter. spring than April. The regions of formation, directions of motion, and the characteristics of the intensification of the 388 cyclones studied are discussed. THE GENERAL AIR CIRCULATION AND SOME OF ITS CONSEQUENCES The Bermuda atmospheric high pressure cell dominates the circulation over the Gulf, partic- ularly during the spring and summer months. In the late summer there is a general northward shift of the circulation and, as shown in figure 17, the Gulf comes under the more direct influence of the equatorial low pl-essure belt. The constancy of the Bermuda high tends to maintain steady circulation and to govern the climate during the summer. Summer conditions are illustrated in figure 18. No isotherms appear for average water temperature (sea surface temperature) since the waters are nearly uniform at about 84° F. as illustrated in the chapter on physical oceanog- raphy.' The air temperatures on the average are also quite uniform and high. The southerly posi- tion of the Bermuda cell brings about the south- east-northwest orientation of isobars across the Gulf and leads to a predominance of southeasterly winds, as shown by wind arrows. The winds tend to become more soullu>rly in the northern part of the Gulf. In this region there are prac- tically no northerly winds in summer and only a relatively few from the east or the west. In the more southern parts of the area the predomi- nance of the easterly and southeasterly flow is even more marked. With a typical summer circulation in the Gulf and the uniform average sea surface temperature, there would be expected only a minimum lunnber of local weather features over the water which are the type caused within the Gulf by air flow toward successively warmer or cooler water sur- faces. However, on a larger scale the relatively I See Physical Oceanography of the Gulf of Mexico, p. 119. 89 90 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE Figure 17. — Normal sea level pressure, October. high temperature of the Gulf of Mexico waters compared to those of other water surfaces in the same latitudes brings about such a great warming and increase in the moisture content of the over- lying air masses that weather patterns of the area are markedly affected. (The mean annual sur- face temperature of the Gulf is 78° F., while that of a comparable region at the same latitude in the western Atlantic is 76°, in the eastern Atlantic 73°, and in the eastern Pacific 68°). Typical features of the winter circulation are shown in figure 19. Here the winds are more from the easterly directions with fewer southerlies but more northerlies. There are very few winds from the west or the southwest. The sea surface tem- perature pattern shows a variation from more than 75° F. in the southeastern portion to less than 65° in the northwest. Southeasterly winds bring warm, moist air from lower latitudes and carry it from warmer toward colder water in the Gulf. When this flow is slow and sustained, the cooling by the ocean surface leads to condensation and fog and stratus formation in the northern Gulf. A discussion of the upper air circulation for the Gulf and Caribbean area is given by Erna and Rudolf Penndorf (1944). AVERAGE CONDITIONS Average sea-level atmospheric pressures in the Gulf vary from 30.00 to 30.15 inches of mercury. There a>"e wide deviations from these averages in individual synoptic situations. Worthy of note is the diurnal pressure variation with a lesser early morning minimum followed by a greater late morning maximum and evening minimum and a lesser nocturnal maximum. The Atlas of Climatic Charts of the Oceans, published by the United States Weather Bureau, and the Pilot Chart of Central American Waters, published by the Hydrographic Office of the United States Navy, issued monthly, give further information about the winds, pressures, tempera- GULF OF MEXICO 91 tines, and other weathei- features of the Gulf of Mexieo, The average wind velocity varies fioni ti to 8 knots in the summer, with the stronj^er winds in the southeast portion, to 10 to 12 knots with considerable variability in the winter, the higher averages being in the northeastern portions. P^og is most frequent in midwinter when as high, as U) percent of all observations record light or dense fog in the north central part of the Gulf. In this season fogs occur less than 1 percent of the time in the soutiieastern portion. For the year-round the average cloud-cover over the Gulf is Yio to %o of the sky obscured. In winter and sjjring the areas most obscured are in the north and northwest, while in the summer and fall the southern and southwest portions have the highest average cloud cover. The most commonly reported low type clouds are cumulus . AVERAGE SEA LEVEL PRESSURt (INCHES) AVERAGE AIR TEMPERATURE CFl WIND: Arrows flv with the wind Lenoth of 4Rrow oivE9 percent of total observations to SIXTEEN points OF THE COMPASS. BARBS SHOW FORCE ON BEAUFORT SCALE. FlOuRE IN CEHTCR OF CIRCLE GIVES PERCENTAQE OF lIOHT, VARIABLE WINDS 10 20 30 40 50 60 TO BO 90 100 SCAUE OF WINO PERCENTASES Figure 18. — Average sea level pressure (inches) and average air temperature (°F.), July. 92 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE JANUARY AVERAGE SEA LEVEL PRESSURE (INCHES) AVERAGE AIR TEMPERATURE (" F) OVERAGE WATER TEMPERATURE CF) WIND; Arrows flt with tke wind Length of arrow aivES percent of total observations to sixteen POINTS OF THE COMPASS BarBS SHOW FORCE ON BEAUFORT SCALE. FlQURE IN CENTER OF CIRCLE GIVES percentage of light, variable winds. to 20 SO 40 50 60 70 80 90 lOO Scale of Wind Percentages Figure 19. — Average sea level pressure (inches), average air temperature (°F.), and average water temperature (°F.) January. which have the greatest frequency — greater than 30 percent of all observations — in the summer and fall in a band extending from the Yucatan Channel northwestward across the Gulf. Altostratus and altocumulus are common the year-round, their average frequency being from 10 to 20 percent throughout the Gulf. In the summer and fall cumulonimbi are observed about 10 percent of the time in the western and northwestern regions. The period of lowest occurrence of rainfall over the open water is in the spring when less than 5 percent of the observations show rain according to the Atlas of Climatic Charts of the Oceans. The remainder of the year the frequency is 5 to 10 percent over most of the Gulf except for an area around the Yucatln Peninsula where fre- quencies drop below 5 percent in the winter and summer. A study by Kloster reported in the GULF OF MEXICO 93 Coast Pilot shows rain in from 13 to 21 percent of the hourly observations available for the entire year between 22^2° to 27 K° N. latitude and 80° to 90° W. longitude. Rainfall was most fre- quently reported in the mid afternoon — 19 percent versus 15 to 17 percent at other times of the day. The average depression of the wet bulb is 3° F. for the fall quarter — September, October, and November. During the remainder of the year it is 2° for the western Gulf and 3° for the eastern. In the summertime the air and the sea surface differ in temperature by less than 1°, the sea temperature being higher according to the Atlas of Climatic Charts of the Oceans. In the fall and winter differences increase, with the sea temperature being as much as 5° higher than the air temperature in the area just west of the Florida Peninsula. This leads to heating from below on the average and explains the high fre- quency of cumulus-type clouds over the Gulf. Monthly average sea surface and air temperatures are tabulated in the chapter on physical ocean- ography (p. 119). WEATHER OBSERVING STATIONS It is the purpose of this summary to discuss weather over the water in the Gulf. Since the observations here are sparse, some of the conclu- sions are drawn from observations made on the surrounding land areas. The weather observing stations in these areas are shown in figure 20. Those on the coast are listed in table 1. A par- ticularly interesting feature of the Gulf is that Table 1. — Weather observing stations along the coast of the Gulf of Mexico I Station number Location Station number Location 201 Key West, Fla. (NAS). 642 - Nautla, Verarcuz. 2n Tampa. Fla. (Interna- 692 Veracruz, Veracruz. tional Airport). 741 Coatzacoalcos, Veracruz. 214 Tallahassee, Fla. (Dale 743_ Villa Hermosa. Tabasco . Mabry Field). 746 Ciudad GbreRon, Ta- 220 Apalachieola, Fla. basco. 222 Pensacola. Fla. 749 Ciudad del Carmen, 223 Mobile, Ala. Campeche. 231 New Orleans, La. 695 Campeche, Campeche. 232 Burrwood, La. 643. Merida. Yucat4n. 240 Lake Charles, La. 648 Cozumel, Quintana Roo. 241 Port Arthur. Tex. 7.')1 Chctumal, Quintana Roo. 242 Qalveston, Tex. 601 Swan Island, West Indies. 243 Houston, Tex. 395 Vemam Field, Jamaica. 255 Vietoria, Tex. 397 Kingston, Jamaica. 251 Corpus Christi. Tex. 325 Havana, Havana (Casa 250 Brownsville, Tex. Blanca). 491 Ciudad Victoria, Tamau- 244 Cienfuepos, Santa Clara. lipas. 355 Camaguey, Camaguey. 349 Ciudad Camargo, Tam- 367. Guantanamo, Oriente. aulipas. 265 Antilla, Oriente. 639 Tuxpan, Veracruz. although it covers some 700,000 square miles, it is more than 90 percent surrounded by land. The rather complete coverage of weather information around its perimeter makes it an unusual natural laboratory in which to study changes in the character of air masses as they pass across the large body of water. TYPICAL UPPER AIR SOUNDINGS A comparison of the upper air soundings from Swan Island, south of the Gulf, with those of New Orleans and Brownsville, on the north and northwestern coasts, illustrates the modifying effects of the water surface. Monthly average radiosonde observations for a summer month and a winter month at each of these stations are shown in figure 21. It will be noted that the an- nual change in structure at Swan Island, which is almost completely controlled by oceanic factors, is very small, the most noticeable change being the higher relative humidities in the summer. At Brownsville and New Orleans the sea surface is cooler in winter, but, also, the continental influence tends to make winter temperatures definitely lower than those in summer. A rather complete discussion of the tropical Gulf air mass is given by Willett (1943). He states that the uniformity of the water tempera- ture in the source regions of tropical maritime air masses has proved to be of more importance in fixing the properties of the masses at all levels than has the previous life history of the individual air masses. Evidence is given demonstrating that the structure of the lower stratum of the air mass results from the turbulent mixing of saturated air. The air masses are characterized by marked potential instability, implying that all convective or mechanical turbulence up to at least 5 kilo- meters elevation must effect an upward transport of latent heat. The high relative humidities indicate that active convection extending above this level can be initiated by very little vertical displacement. Summer thunderstorms are more likely along the eastern part of the northern Gulf coast than along the western. There are higher relative humidities in the eastern area. Using a series of atmospheric temperature and moisture soundings to 45 feet elevation made at 4-hour intervals in March 1949 from an oil platform in the northwestern Gulf, Gerhardt 94 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 05 O o 3 O c '> y reference to the above standard stations. The Coast aiid Geodetic Survey also issues, in looseleaf form, descriptions and elevations of the tidal bench marks it has established in various places along the United States coast of the Gulf. These describe the location of each bench mark and its elevation above mean low water. For each 118 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE locality there is given, in addition, a table listing the highest and lowest tides observed or inferred, and the heights of mean high water, half tide level, and mean low water. At the present time, there are in operation by the Coast and Geodetic Survey 10 primary tide stations located as follows: in Florida, at Key West, St. Petersburg, Cedar Keys, and Pensacola; in Louisiana, at New Orleans, Bayou Rigaud, and Eugene Island; in Texas, at Galveston, Rockport, and Port Isabel. Most of these stations have been in operation for a number of years, at Galveston, for example, since 1909. For each of these sta- tions there are available, in the files of the Coast and Geodetic Survey at Washington, tabulations giving the hourly heights of the tide and the times and heights of high and low waters. There are also available summaries giving the monthly and yearly heights of high water, low water, and sea level. Tide stations have also been operated in recent years by the governments of Mexico and Cuba. LITERATURE CITED Cline, Isaac M. 1920. Relation of changes in storm tides on the coast of the Gulf of Mexico to the center and movement of hurricanes. Monthly Weather Review, March, pp. 127-146. Courtier, A. 1938. Marees. Service Hydrographique de la Marine, Paris, p. 149. Grace, S. F. 1932. The principal constituent of the tidal motion in the Gulf of Mexico. Monthly Notices Roy. A.str. Soc. Geophysic. Sup., May, pp. 70-83. Mar.mer, H. a. 1949. Sea level changes along the coasts of the United States in recent years. Trans. Am. Geophys. U., 30 (2): 201-204. Schureman, Paul 1940. Manual of harmonic analysis and predictions of tides. Coast and Geodetic Survey Spec. Pub. 98, rev. ed. U. S. Coast and Geodetic Survey. 1952. Manual of harmonic constant reductions. Sp. Pub. 260. Van Der Stok, J. P. 1897. Wind, weather, currents, tides and tidal streams in the East Indian Archipelago. Batavia. PHYSICAL OCEANOGRAPHY OF THE GULF OF MEXICO By Dale F. Leipper, Agricultural and Mechanical College of Texas Oceanography may be defined as the study of the oceans in all their aspects, including the interrelationships betweea the seas and their boundaries — the atmosphere, the shoreline, and the sea bottom. Physical oceanography consists of the analysis of the physical properties of sea water, the study of motions in the oceans such as those associated with ocean waves, tides, and winds, and examinations of the various mecha- nisms for the transfer and interchange of energy. The nature of physical oceanography differs from that of the other aspects of the subject in that certain mvestigations may be conducted somewhat independently. The other generally recognized aspects of oceanography are the bio- logical, the chemical, the geological, and the meteor- ological. Investigations in these are usually dependent upon physical oceanography and upon each other. It is desirable that work in the physical aspect be planned jointly with that in the other aspects in order that maximum utilization may be made of results which are obtained. The physical oceanograplier must pay particular attention to the problems in the other branches of the work since one of the primary objectives of his own researches is the development of information needed for the solution of some of these problems. There are many unique opportunities in the study of physical oceanography in the Gulf of Mexico. There is an offshore oil industry facing many problems related to construction and opera- tion in the shallow waters over the wide conti- nental shelf, there is a huge chemical industry which has an output depending heavily upon the varying longshore currents which alter the salt content of the water at the position where it is taken into the plants, and there are many characteristic weather features such as hurricanes. ' Contribution from the Department of Oceanography of the Agricultural and Mechanical College of Texas, Oceanographic Series No. 16; based in part on investigations conducted for the Texas A. and M. Research Founda- tion, through the sponsorship of the U. S. Navy Office of Naval Research. squalls, and fog which result from effects of the oceans upon the atmosphere. Further, the large oyster and shrimp fisheries are markedly affected by currents, turbulence and the physical charac- teristics of the sea water. Also, in reduction of beach contamination, prevention of beach erosion, reduction of dredging costs in marine channels, increasing the efficiency of marine transportation, development of recreational areas on the beaches, and in providing oceanographic information critical to the defense of our coastline, physical oceanog- raphy plays a most important role in the Gulf of Mexico. The Gulf, being nearly enclosed, provides a model ocean in which much may be learned about processes operating in the larger oceans which are not so readily adaptable to comprehensive and systematic analysis. The presence of fixed plat- forms far from shore may make it possible for the first time to make such determinations as that of the effect of the wind in changing the slope of the sea surface in the open sea. Such information is needed for further development of the theories of wind stress upon the sea surface and for the more complete understanding of the manner in which the winds drive the ocean currents and set up ocean waves. Despite the need for physical information in the Gulf, relatively little has as yet been done to survey the region systematically and to provide information in a form which is generally available. Recently there have been increased efforts in this direction, and within the near future it may be expected that knowledge of this highly important oceanic region will be greatly increased. OCEAN CURRENTS The primary problem in the physical ocean- ography of any region is the determination of the ocean cuiTents. In the Gulf of Mexico it is par- ticularly difficult. To provide a background for a discussion of this problem it is well to consider 119 120 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE briefly the general nature of the currents which may be expected in such a region. The general nature of currents in the Gulf of Mexico Sverdrup (1942) ^ lists three different groups of currents each of which is represented in the Gulf of Mexico. These are: (1) currents that are related to the distribu- tion of density in the sea, (2) currents that are caused directly by the stress that the wind exerts on the sea surface, and i'.i) tidal currents and currents associated , with internal waves. Tidal currents ' are caused by the tide-producing forces. These forces result from differences between the constant centrifugal force which acts on any particle on the earth and the varying gravitational attractions between the earth, the moon, and the sun. These attractions are pro- portional to the masses of the bodies and inversely proportional to the squares of the distances between them. Because of its very short dis- tance from the earth the attraction of the moon is large. The sun, on the other hand, although it is at a much greater distance from the earth, is so large that a tide-producing force results which is as much as 46 percent of that of the moon. The direct result of tide-producing forces acting upon the rotating earth is to raise and lower peri- odically the level of the ocean's surface, i. e., to create tides. Water which is required to raise sea level at a particular location must be furnished by horizontal movements within the ocean. These are the tidal currents. Since the sun and moon change their position with respect to a given part of the earth's surface in a periodic fashion, the tides and tidal currents are periodic. Because the rotation of the earth affects movements of water the tidal currents do not oscillate back and forth on a straight Ime bu^ rotate. In the Northern Hemisphere this rotation usually is in a clockwise direction except where modified by other factors. At times, interference i)et\veen tidal waves or the influence of other forces is such that the rotation may be counterclockwise. Along the Gulf coast there are many bays and lagoons which have relatively restricted outlets to ' References are listed ;it the end of the chapter. 3 Tides in the (Julf of Mexico are discussed separately in the article by H. A. Marmer, pp. 101-118. the sea. If the water level in these bays is to be raised by tidal action, all of the water required for the change in level must flow into the bay through these restricted channels. Therefore, the tidal currents in such channels may be quite large, particularly at certain stages of the tide. The great width of the shallow continental shelf along the Gulf coast results in tidal current veloc- ities which are relatively high considering the small range of tide. This is because the change of water level of this large area over the shelf must be brought about by flow across the shallow shelf. Since the depth of the moving water is small, its velocity must be relatively great to provide the volume needed for change in sea level. The high velocities and the changing di- rection and speed of these tidal currents may lead to considerable turbulence and stirring in certain localities. Oscillating currents related to internal waves may be important in this region, but little infor- mation now is available on this subject. Currents caused by tiie stress of the wind upon the sea surface are particularly important on the Gulf coast. The most widely known phenom- enon which results from the action of such cur- rents is the storm tide or general rise in water level which precedes winds of hurricane velocities. Storm tides are discussed by Cline (1920) and Tannehill (1927). Some of their results are sum- marized in the chapter on meteorological phe- nomena. Wlien a wind starts to blow over the ocean it exerts a frictional force or drag upon the sea surface. If the wind persists the surface layers of the water start to move and they in turn act upon the deeper layers and set these in motion also. The two forces which are involved in setting up such cm-rents are the frictional force, and the Coriolis force which is the apparent force due to the rotation of the earth. If the wind blows long enough for a state of equilibrium to be reached, the surface waters away from tlie influence of the coast will be moving in a direction approximately 45° to the riglit of the wind direction in the North- ern Hemisphere. A north wind sets up a surface current toward the southwest. The surface veloc- ities may reach 1 to 2 percent of the wind velocity. Currents at greater deptlis will flow at greater angles to the wind and at speeds which decrease with depth. GULF OF MEXICO 121 Fku're 34. — Surface ocean currents in the Gulf of Mexico in June. Conclusions concerning currents sot up by the wind are mostly based upon theoretical consider- ations. A few observations have been made in landlocked bays to show the piling up of water by the wind. However, in the open ocean no sys- tematic data are available. The drilling plat- forms off the Gulf coast permit the accumulation of data which will make possible a practical analysis". The ciuTents related to the distribution of density are the major semipermanent currents of the oceans. Little is known about these currents in the Gulf of Mexico. The chief source of infor- mation is the pilot charts of the United States Navy Hydrographic Office (figs. 34 and 35) . These are based upon the navigation reconis of the ships sailing in the Gulf over many jears. 'i'hev do indicate the general drift in various regions, but the individual observations upon which they are based are subject to many errors. For example. the deviation of a ship from its course may be caused by the wind rather than by the current. Also, it is difficult to determine positions at sea accurately. A survey of the pilot charts for the Gulf indicates that these may not describe all of the cm-rents present. They show waters flowing into the western part of the area at all latitudes but no water flowing out. This situation cannot exist unless theic is a submarine return current of equal nuignitude,»which seems unlikely. In the deep waters, direct observation of current velocities has been almost impossible until recently because of difficulty in anchoring vessels. Ac- cordingly, few such observations have been made. Instead, oceanographers have developed a method based upon principles of [ihysics. By use of this method the ocean currents present may be inferred fnun the (listril)ution of density as deter- mined l)y relatively simple observations of tem- perature, salinity, and pressure. Two forces again 122 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 94° 92* 90* 88° 86° 84° 8 2° Figure 35. — Surface ocean currents in the Gulf of Mexico in December. 80° 78° are involved, one of these being the CorioHs force and the other the "pressure force" which is a force that depends upon the water density distribution in the earth's gravitational field. The pressure force tends to make water flow from a region of high pressure toward a region of low pressure just as water poured into less dense oil will flow outward from the point at which it is poured. When the movement related to the pressure gradient has begun, the Coriolis force acts toward the right of the movement in the Northern Hemisphere and the resulting equili- brium between the two forces is associated with a steady current flowing almost perpendicular to a line connecting the regions of high pressure and low pressure. This flow is such that in the Northern Hemisphere the more dense water is on the left of a person standing with his back to the current and the less dense water is on his right. Since temperature is one of the major factors influencing density, it may be inferred that the cold water is on the observer's left and the warm is on his right when he is standing as described above with relation to the current. Thus, he can tell something about the currents if he knows the distribution of temperature, or he can tell something about the temperature if he knows the distribution of currents. There are a number of difficulties which arise in applying the current computation method. These occur partly because the basic assumptions under- lying the theory are not always fulfilled. How- ever, despite these difficulties the method has been found to be the one which provides the most infoimation for a reasonable amount of work. It is not known how accurately the Gulf currents in deep water may be determined by this method, but there is reason to believe it to be the most GULF OF MEXICO 123 accurate of the methods now in use. Used in conjunction witli the geomagnetic electrokineto- graph, it probably provides the best complete picture of the current patterns in the open Gulf. Determination of the flow over the broad, shallow continental shelf remains a diflicult problem. vSome processes by which the distribution of density is caused to change are evaporation, conduction, and the movement of masses of water by the winds. Since the total transport of water due to the winds in this hemisphere is toward the right of the wind, and since this trans- port consists of waters in the surface layers which are warm and of low density, the low density waters are piled up at the right of the wind flow, which is in the center of anticyclones, regions of good clear weather. The warm waters are removed from the low pressure storm areas at the left by the wind action. These movements are called the wind-driven currents. Their primary effect is to pile up water of small density in areas of anticj'clonic winds and to leave waters of greater density in areas of cyclonic winds. This leads to a secondary effect, namely, the mainte- nance of a different ocean current related to this distribution of density. Since such currents flow nearly perpendicular to a line connecting the regions having the different water densities, the associated currents form a pattern quite similar to the pattern of the winds. This may readily be recognized on charts showing the distribution of ocean currents with prevailing winds super- imposed. Investigations of ocean currents in the Gulf of Mexico There is probably no part of the oceans of the world of comparable size to the Gulf of Mexico where there is such a wide difference of opinion concerning the specific current regime. This difference is brought out by Sweitzer (1898). He quotes Isaac Vassius who, writing about the year 1663, tells how the currents through the Yucatan Channel "turn obliquely" and pass through the Straits of Florida. The issue of the Encyclopedia Britannica available in 1898 states that "a portion of it (the current — DFL) passes directly to the northeast along the shore of Cuba; but by far the larger part sweeps around the Gulf." Sweitzer himself concludes that, at times "the channel of Yucatan pours its waters into the Gulf so that they spread out in all directions moving on its center," while at other times the currents flow "in a northeasterly direction around the extreme west coast of Cuba." These last results were based upon studies of the distribution of specific gravity of the surface waters. United States Coast and Geodetic Survey, Lindenkohl (1896), and upon modification of currents by the prevailing winds. Sweitzer also reported considerable agitation of the waters covering an area of about 100 square miles occurring off the coast of Texas about 40 miles south and 20 miles east of Aransas Pass which could only be accounted for by the meeting of two opposing currents. Other evidence of converging currents has since been found, and this area has become known as the graveyard of ships. Measurements made in the years 1885 to 1889 by the United States Coast and Geodetic Survey vessel Blake, commanded by Pillsbury (1889), determined the currents in the Straits of Florida. Since the ship was anchored, direct current ob- servations could be compared to computed values, and the comparison provided one of the best examples illustrating the validity of the method for computing relative currents which is now so widely used. Agassiz (1888) published temperature and salinity data collected by the Blake in 1878. These data, together with others collected by the Bache, Bigelow (1917), were used by Wvist to compute the transport of the water through the Florida Straits as 26 million m^second. As- sociated with this transport is a water level difference of 19 cm. between the southeastern Gulf and the Atlantic at St. Augustine, Florida, which is discussed by Montgomery (1938). A theory of piling up water in the "Bay of Mexico" was advocated by Benjamin Franklin about 1770. In 1922, the Dana made some observations in the Yucatan Channel and in the Florida Straits, as shown in figure 36. These observations, as well as those of the Mabel Taylor in 1932, were sum- marized by Parr (1935) who concluded that "evidence thus obtained from the Gulf itself, although directly opposed to some of his premises, nevertheless serves to confirm the theory already advanced by Nielsen on the basis of observations in the Straits alone, that the so-called Gulf Stream only takes the shortest possible path from its entrance through the Yucatan Channel to its 124 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE GULF OF MEXICO 125 exit through the Straits of Florida, without de- viating on the way, or dilTusing any to itself significant amount into the Gulf of Mexico |)roi)er, or receiving any predominant contribution from the Gulf in return." This statement on the one hand and the current pattern shown in figures 34 and 35 on the other hand summarize the present divergence of opinion. The Mahtl Taylor cruise was made without unprotected thermometers or other reliable means of determining depth of observations. Parr cautions that particularly in the Yucatan Channel and Florida Straits there is sufficient uncertainty of the depths of the Mabd Taylor operations "to make it seem inadvisable to subject them to a form of analysis and comparison in which depth is an essential consideration." Similarly, the Atlantis cruise of 1934, Parr (1937), lacks sub- surface data since the hydrographic cable was lost early in the survey. Thus, the oceanographic data available to Parr were meager. Dietrich (1939) reviewed the currents of the Gulf, and his conclusions, although based upon essentially the same data as used by Parr, show considerably more influence by the Gulf Stream upon the general circulation in the Gulf. He discussed the sill depths showing that the Gulf circulation cannot affect the deep water circulation of the Atlantic below about 800 meters. However, the Florida current, which is shallower than this, has considerable effect. In 1947 the Atlantis conducted a survey of the northwestern Gulf making 27 hydrographic sta- tions (fig. 36) and 473 bathythermograph observa- tions of temperature. These data have been analyzed by Fred B. Phleger (1951), now of the Scripps Institution of Oceanography of the Uni- versity of California, and have been published by the Geological Society of America. The first cruises of the Alaska, oceanographic research vessel of the Fish and Wildlife Service operating on a survey of the Gulf of Mexico with the cooperation of the Department of Oceanog- raphy of Te.xas Agricultural and Mechanical College and the United States Navy, Office of Naval Research, were completed in October 1951 (fig. 37). These provide the first complete coverage of the Gulf with information needed to compute the deep water currents. The data from these cruises have been distributed and prelimary anal- yses indicate that they support the main fea- tures of llie current pattern shown in figure 34, A i)rief description of the currents of the Gulf of Mexico is provided in the United States Coast Pilot (1949): Under noriual coiiditioii.s, at all seasons of the year, the great volume of water passing northward through Yucatdn Channel into the Gulf of Mexico, spreads out in various directions. Surface flows set westward across Cainpeche Bank, the (iulf of Canipeche, and the Sigsbee Deep; northwestward toward tlalveston and Port Arthur; north-northwestward toward the Mississippi Passes; and eastward into the Straits of Florida. A straight line drawn from Buenavista Key, Western Cuba, to the Mississippi Pas.ses forms an approximate boundary between movements having different directions. West of this line the drift is generally northward or west- ward, while east of it the drift is eastward or southeast- ward toward the Straits of Florida. There are northward flows along the west side of the Gulf between Tampico and Corpus Christi in the vicinity of the 100-fathom and 1,000-fathom curves, north of the Sigsbee Deep between the 2,000-fathom and the 100- fathom curves, and along the west coast of Florida. In general, the surface circulation is the same at all seasons. There is, however, some .seasonal change in velocity, the flow being generally stronger in spring and summer than in the autumn and winter. The current near the Florida Keys is variable and uncertain. This description is apparently taken from the Pilot Chart series of the Hydrographic Office (H. O. No. 3500, issued monthly). Another series, H. O. No. 10,690, 1 to 12, Current Charts of the Central American Waters, give resultant direction and velocity for each 1° quadrangle of latitude and longitude. This series has been used by Smith, et al. (1951), to show zones where seasonal convergence or divergence occur. Many of the references cited above contain bibliographies pertinent to the Gulf of xMexico. Also, Geyer (1950) lists many useful works. In summary, the currents of the Gulf of Mexico and their variations are not specifically known. Studies completed in the past indicate some unusual and interesting features and provide incentive and justification for continued intensive investigation. SEA SURFACE TEMPERATURES A large number of sea surface temperature ob- servations have been collected at shore stations. Some of these data from locations shown in figure 126 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE o OS - a ■0 c 03 fa ad o C a O GULF OF MEXICO 127 128 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE be 3 J3 be GULF OF MEXICO 129 130 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 38 have been made available through the Fish and Wildlife Service of the United States Department of the Interior and are on file in the Department of Oceanography at Texas Agricultural and Me- chanical College where a file-report has been pre- pared. The key in figure 38 shows the period of years in which observations were made and sent in from each station. The study of these shore station data is continuing, and references to addi- tional information of this kind are sought. It is hoped that they may provide a clue to general changes which are occurring offshore where ob- servations are not so readily obtainable. Studies of sea surface temperatures in the Gulf of Mexico have been based on some 200,000 ob- servations taken on ships in this area over a period of more than 50 years. The majority of these observations were made with the instruments carried as a regular part of each ship's equipment. Due to the possibility of error in the individual thermometers and to errors in reading, the results must be interpreted with care. However, with such a large number of observations the non- systematic errors tend to cancel each other, with resulting averages being not far from the true mean. The Weather Bureau of the United States De- partment of Commei'ce has computed average sea surface temperatures in the Gulf of Mexico using the above observations. Table 1 shows the aver- Table I. — Monthly average sea surface and air temperatures in the Gulf of Mexico (in degrees Fahrenheit) [Figures in italics are averages of dry bulb thermometer readings observed as a rule on the ship's bridge. Figures in roman are mean sea surface temperatures, obtained mainly from bucket sampling] Area 100-95 W30-2SN 95-90W 30-25N 90-85W 30-25N 85-80W 30-25N 100-95W 25-20N 95-90W 25-20N 90-85W 25-20N 85-80W 25-20N January 66.8 66.9 67.5 73. S 75.6 80.3 83.1 8S.9 81.8 77.2 77. « 69. S 67.7 68.3 68.8 72.6 76.3 80.6 82.6 83.3 83.3 80.2 76.3 70.7 63. 5 63.7 66.3 71.1 75.9 80. S 82.5 83.0 81.5 76. i 70. i 66. i 67.9 67.3 68.5 71.6 76.0 80.6 83.1 S.3.9 82.8 79.4 74.7 70.7 68. 1 68.3 69.8 73. S 77.3 80.8 82. i 82.9 81.8 77.8 72.8 69.8 72.5 72.1 72.6 74.6 77.7 81.0 82.9 83.7 82.9 80.3 76.7 74.2 69.3 69.2 70.9 710 77.5 80.6 82.3 82.6 81.9 78.5 710 70.9 73.2 72 7 73.2 75.2 77.9 80.8 82.6 83.4 82.9 80.7 77.5 75.0 70.7 70. i 72.7 75.1, 78.6 80.8 81.7 82.5 81.6 79.1 76.1 71.7 73.0 72 6 73.3 75.4 78.5 81.1 82.5 83.3 83.1 81.3 77.9 74.5 72.5 72.7 73.9 76.2 78.8 81.0 82.1 82. i 82.1 80.2 76.5 73.8 74.3 73.9 74.6 76.1 78.6 81.2 82.4 83.2 83.2 81.6 78.5 75.9 711 71 1 76. S 77.1 7.9. y, 81. i 82.2 82.5 82. 2 80.1 76.9 75.2 76.3 76.0 76.4 77.7 79.5 81.6 82.6 83.2 83, 1 81.8 79.5 77.7 71.9 7S.1 73.3 76.9 78.7 81.3 82.7 &10 82.3 79.6 75.8 7S. 3 . 75.0 74.7 75.3 April 76.8 May _. 79.0 June 81.5 July - 83.0 August 83.8 83.4 October 81.5 78.8 76.5 Note.— From Charts 115-126, Atlas of Climatic Charts of the Oceans, U. S. Department of Commerce, Weather Bureau. age sea surface and air temperatures for the 12 months of the year, the Gulf being divided into eight 5° quadrangles. This information was taken from charts 115 to 126 of the Weather Bureau's Atlas of Climatic Charts of the Oceans. Probably the most recently prepared charts showing average sea surface temperatures in the Gulf are those of Fuglister (1947). Isotherms reproduced from his work for the winter month of February and the summer month of August are shown in figures 39 and 40. The main feature of the average winter pattern is a gradual drop from approximately 75° F. in the south to 65° F. in the north in all parts of the Gulf, the gradient being larger in the east portion. In the summer- time the average temperatures are very nearly uniform at 84° F. throughout the region. Cruises of the Alaska indicate that considerable deviation from these average isotherms may occur at cer- tain times. The annual range of normal sea surface tem- perature varies from 15° to 20° F. in the northern portion of the Gulf, while m the central and southern portions the range is about 10° F. February is normally the coolest month of the year, though January is the coolest month for that portion of the Gulf adjacent to Texas and Mexico. Except for a few scattered areas, August is normally the warmest month of the year. In regard to diurnal variation of surface tem- perature in the Gulf, a study by Stommel and Woodcock (1951) presents some data and dis- cusses various methods of computation. It makes recommendations for future investigation of this problem. According to Storey (Gunter 1947), there were nine freezes along the west coast of Florida be- tween 1886 and 1936 which killed fishes in large numbers. Intense cold spells, sufficiently severe to kill large numbers of fishes, occurred along the Texas coast on an average of one every 14 years between 1856 and 1940, with less damaging spells coming at shorter intervals. Similar data for other parts of the Gulf coast are not available. GULF OF MEXICO 131 Slocum (1934-36) lias made a comparative study of sea surface temperatures for various regions of tlie Gulf in different years. This study is based on temperature observations taken from 1912 to 1933. The year-to-year changes are summarized in table 2 for the regions shown by Table 2. — Some variatiotis of mean annual sea surface temperatures for 1912-33 ' in various regions of the Gulf {° F.) [After SlocumJ Variation High Dif Mean Dif Low High-Low Dif.. (1) 25-26° N. 84-86° W. 79.5 78.4 76.8 1.1 1.6 2.7 (2) 27-29° N. 90-93° W. 77.0 75.5 73.9 1.5 1.6 3.1 (3) 26-28° N. 86-89° W. 78.7 77.8 76.6 0.9 1.2 2.1 (4) 21-25° N. 90-94° W. 79.7 78.5 77.6 1.2 0.9 2.1 (5) 23-24° N. 82-84° W. 1.0 2.1 3.1 (6) 21-22° N., 8.')-87° \V. 22-23° N.. 84-87° W. 81.1 80.3 79.3 0.8 1.0 1.8 I The number of observations varies from year to year. Few observations were made in 1917-19. In other years, the number ranged from 100 to over a thousand in each region. Locations are shown in figure 41. encircled numbers in figure 41. The mean tem- perature for each year has been computed. It is of interest to note that in one case the minimum mean yearly temperature for a given region for this period of years differed from the overall mean temperature for the region by 2.1° F. Moreover, the maximum and minimum mean yearly tem- peratures differ by 3.1° F. m two localities. For one of these extreme examples, in the region 27-29° N., 90-93° W., the lowest mean yearly temperature recorded was for the year 1915 which showed a mean temperature of 73.9° F. In 1922 and 1927, the highest mean temperatures were recorded here, being 77.0° F. For the other example, the low was 77.8° F., the high 80.9° F. Siocum's stud}' also iacluded consideration of the means for the different months of the year. SEA TEMPERATURE VARIATIONS WITH DEPTH The sea temperatures obtained by the Mabel Taylor below the surface have been -published by Parr (1935). Although the depths of these obser- vations are not known accurately, they do give considerable information about vertical tempera- ture distribution. An average temperature-salinity correlation in the Gulf of Mexico proper as woi'ked out by Parr for the months February-April is given as table 3. In the early 1940's the United States Navy developed the bathythermograph for making observations of sea temperature continuously from the surface to depths as great as 900 feet. To date, some 10,000 observations or bathy thermo- grams have been made in the Gulf. Copies of 259534 O— 54 10 these are now filed at the Woods Hole Oceano- graphic Institution where they are processed and in the Department of Oceanographv at Texas Agricultural and Mechanical College. Their dis- tribution b}' 1° quadrangles is shown in figure 42. Table 3. — An average temperature-salinity correlation for the Gulf of Mexico proper lAfter Parr] Average tem- Average Weighted aver- perature salinity age depth °C. °/» m. 24.74 36.19 5 23.06 36.06 15 21.03 36.14 58 19.25 36.28 94 17.09 36.22 125 14.85 35.95 192 13.00 35.68 237 10.89 35.35 321 9.60 35.16 380 8.57 35.04 432 7.42 34.93 562 6.39 34.88 647 Two bathy thermograms, one for summer and the other for winter, were chosen from each of four parts of the Gulf within the 1 ,000-fathom line. These locations are indicated by encircled crosses in figure 41. The bathythermograms were chosen as being typical after considering range of tempera- ture variation, general shape of temperature-depth curve, depth of thermoclinc, and other features. Unfortunately, due to the paucity of observations it was not possible at any one of the four positions to obtain "typical" summer and winter bathy- thermograms from the same year. However, by plotting a typical summer and a typical winter bathy thermogram for each position on the same coordinates it was possible to show in a general 132 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE ■a C9 e T3 3 01 & tn C o GULF OF MEXICO 133 134 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 24n47 xrF) -^ 25*26H93*44'W 75m 43 25'04'Na3*59'W bo a z 18 I 47 rrF)— 27*05'N,e9'40'W 27 68 70 72 74 ' 76 78 80 82 8 71014 •|8'n| D(H.) 40 80 120 160 200 • /■ .r 7 .iwu- / i / ' 7- / -a. J .'^ J 4^ f / / I y / / / 400 440 480 l|*43'W II I 45 l2Sm43 TCF)^ 24"0I'N,89*I7'W 24*0I'N,89*48'W P(,,) 70 7;2 74 ^ Ve 77 QO 8? 84^ ^6 , ^8 i" 40 T( F)— 24°08'N,85°59'W — ~ -- 76 ^- 25 Vm 45 24°I3'N,85°56'W 8,4 ^ 86 as Figure 43. — Typical summer and winter bathythermograms from different areas in the Gulf of Mexico. GULF OF MEXICO 135 way the seasonal difForences. These curves are presented in fio;ure 43 which gives the date and position of each observation. Typical curves properly selected are believed more representative of conditions than average ones, since certain characteristic features of temperature structure may be lost in the process of averaging. A report by Adams and Sorgnit (1951) gives similar infor- mation for each 1° quadrangle of the Gulf where data were available. It also shows the contours of the bottom of the mixed or isothermal layer in summer and winter insofar as can be determined. SALINITY Parr (1935) presents a chart of the distribution of average salinities in the upper 50 meters of the Gulf of Mexico. It shows the values to be typ- ically 36.00 parts per thousand over the entire central region. Water from the Mississippi River reaches to depths of 50 meters and extends beyond Mabel Taylor station 1106 (fig. 36), a distance of 150 miles, keeping salinities below 36.00 parts per thousand. Near stations 1201 and 1202 the river extends its influence on salinity only about 85 miles seaward. From the Yucatdn Channel a subsurface in- trusion of water having salinity over 36.50 parts per thousand extends north and bends westward to the central part of the Gulf. From February to April this tongue underwent a marked shift westward in position of some 120 miles according to the Mabel Taylor data. Above 50 meters waters of salinity greater than 36.25 parts per thousand are found over both the wide Campeche and Florida Banks indicating possible upwelling of the subsurface intrusion. Average variation of salinity with depth is shown in table 3. TEMPERATURE-SALINITY RELATIONSHIPS An average temperature-salinity relationship for the Gulf proper was shown in table 3. A single station tj'pical of what Parr defined as the Gulf Complex is Mabel Taylor station 705 (fig. 36). Another which he calls typical of the Caribbean Complex, divided from the Gulf Complex by a line extending from the northeast corner of Yuca- tan Bank to the southwest corner of the Florida Bank, is station 701 (fig. 36). Data for these sta- tions are listed in table 4. The primary difference l)etween these two distributions is that at temper- atures above 18° C. the Gulf Complex station has markedly lower salinities, being below 36.32 parts per thousand, while the Caribbean station has values as high as 36.73 parts per thousand. The T-S curves in the Yucatdn Channel do not seem to vary significantly from year to year, but those in the Straits of Florida are not so stable, particularly at temperatures above 20° C. Cruises in different years in the Straits have shown wide variations in the extent of Gulf water found in the upper 200 meters. Table 4. — Typical temperature and salinity data [After Parr) Qulf Complex Station 70\ Feb. 18, 27°42' N., 86'00' W. Caribbean Complex Station 701, Feb. 16, 23°28' N., 85°37' W. Depth Salinity Tempera- ture Depth Salinity Tempera- ture m. 30 100 150 200 300 500 700 900 1,200 1,500 2,000 2,500 3,000 °/oo 35.52 3B. 15 36.32 36.21 3.5.96 35.52 35.08 34.87 34.92 34.95 34.97 34.97 34.97 34.97 °C. 23.75 23.15 18.59 16.58 14.94 12, .■!0 7.88 5.91 4.94 4.21 4.21 4.16 4.22 4.24 m. 100 200 300 400 600 800 1,000 7oo 36.18 36. 32 36.73 36.44 35,94 35.08 34.86 °C. 25.34 25.28 21.88 18.21 14.96 9.12 6.86 5.15 Parr (1935) believes that since — The presence of Gulf waters in the Straits of Florida is ... identified with the location in which a counter- current running in the opposite direction of the Caribbean- Florida Current flow is usually indicated on the hydro- graphic charts. ... it seems reasonable to draw the tentative conclusion "the water masses of the Gulf of Me.xico proper should be considered part of the coastal water system of the North and Central American Atlantic seaboard and not as part of the oceanic- circulation system of the Caribbean and Florida Currents." Considerable further evidence is required to fully support this tentative conclusion. Below 800-1,200 meters depth observations of the Mabel Taylor showed hydrographic conditions in the Gulf so extremely uniform that it was not considered advisable to attempt to prepare verti- cal profiles for the deep layers. More accurate depth determinations on subsequent investigations may bring out significant variations at these depths. 136 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE OCEAN WIND WAVES AND SWELL A basic and easily obtainable reference for climatic data on waves in the Gulf is the Atlas of Sea and Swell Charts of the United States Navy Hydrographic Office (1943-50), Miscellaneous Publication No. 10,712, A through D. Certain uses of these data are discussed by Fleming and Bates (1951). Information concerning wave heights in some regions on certain specific days may be obtained by referring to wind data available through the United States Weather Bureau and applying a method of calculation described in United States Navy Hydrograpliic Office Publication No. 604, Techniques for Forecasting Wind Waves and Swell. The problem of wave action on structures is discussed by .\Iunk (1947). Considerable addi- tional research will be i-equired before knowledge of wave forces in the Gulf is complete. Such work has been underway at the University of California (La Jolla and Berkeley) and is being initiated at Texas Agricultural and .Mechanical College. SHALLOW WATER OCEANOGRAPHY Much of the marine interest on the Gulf coast tends to center on the shallow waters. There are many bays, lagoons, and inlets of gi'eat importance to fishing, navigation, recreation, oil recovery, and other activities. Each of these pri'sents its owTi peculiar problems, and extensive investiga- tions have been carried on in many of them. A recent publication indicating the nature of this work is that of Collier and Hfl Gulf Stream (16 to 20 miles olTshore) .067- ,047 East of Loggerhead Key ' .189-, 150 West end of Garden Key Cliannel 227- . 174 Clarke (1938) calculated the extinction coeffi- cients for a series of stations east of the Mississippi Delta. These values are indicated in table 1 as series 439 through 442. For security reasons, Hulburt's paper (1940) on transparency and visibility of submerged objects in the Key West sector has been classified. Bumpus and Clarke (1947) have connected equal points of known "K" values on a chart which includes the Gulf of Mexico. It must be remembered that these lines are based on very few observations, and considerable interpolation was necessary. The Special Scientific Reports, Fisheries No. 8, by Butler (1949), and \o. 14, by Butler and Engle (1950), of the United States Department of the Interior contain turbidity indices for selected points of the Mississippi Sound and Lake Pont- chartrain. Turbidity is expressed as the per- centage-transmission of light through the sample. No correlations with extinction coefficient values or (('(i to many mcmhers of llie stnfTs (if tlif \Vu(icls H.ilc ()c'('!Uii)ity of Miami Marine Ijaboraton , in particular to Dean F. Binnpiis and II. ]\. Moore for placing: tiicir files at my disposal. LITERATURE CITED UiMiMs, 1 1 K., and (i.arkk, G. L. H)47. Hydrography of tlir western Atlantic; trans- parency of the coastal and oceanic waters of the western Atlantic. Woods Hole Oceanographic Inst. Tech. Hept. No. 10. Submitted to the Oceanog. Div.. Hydrog. Off., under Contract \o. N6onr-277 with OtT. Xav. Res., Dec. HM7. BlTLER, I'niLIP A. 1949. An investigation of oyster producing areas in Louisiana and Mississippi damaged by flood wat<'rs in 1945. U. S. Dept. Int., Fish and Wildlife Service, Spec. Sci. Kept.: Fisheries 8: 1-29., App. I-VI. and E.NGLE, James H. 1950. The 1950 opening of the Bonnet Carre Spillway: its effect on oysters. V. S. Depl. Int., Fish and Wildlife Service, Spec. Sci. He[)f.: Fisheries 14: l-IO. ('l,.\HKi:, CiE<)R(;K I.. 19.S8. I.ighl penelration in the Caribbean Sea and in the Culf of .Me.\ico. Jonr. Mar. Hes. 1 (2): 85-93. 1941. Observations on transparency in the southwestern .section of the North Atlantic Ocean, .lour. .Mar. Res. 4 (.{): 221 2S0. HtLBERT, P. (). 1940. Tests at .s.-a in February 1940, in th" Key West area of visibility of submarines and transparency of navigable waters. Nav. Hes. I.al) Kept. NO. H-1598. (Classified.) Pooi,E, II. II., and Atkins. W , H. C. 1929. I'hoto-electric measurements of submarine il- lumination throughout the year. .lour. .Mar. Miol. Assn. I. K. Hi: 297-:i24. ScH.MIOT, .J. 1929, Introduction to the oceanographical reports in- cluding list of stations and hydrographical observa- tions. The Danish Dana i;x|)editions 1920-22 in the North .\tlaniic and (lulf of Panama, vol. 1, No. 1. T.WLOR, W .M. RaNUOI.I'H. 1928. The marine algae of Florida with special reference to the Dry Tortugas. Pap. Tortugas Lab., Carnegie lust. Washington 25: 1-219, M pis. DISTRIBUTION OF CHEMICAL CONSTITUENTS OF SEA WATER IN THE GULF OF MEXICO ' By ROBERT H. WILLIAMS, Marine Laboratory, University of Miami Earliest records of chemical analyses of Gulf of Mexico waters were published by biologists and biochemists who studied the sea water composi- tion as one ecological factor in the complex envi- ronment of the marine organisms with which they were concerned. Much of this early work was centered at the Carnegie Institution laboratory at the Dry Tortugas near the western end of the Florida Keys. First oceanographical studies of the chemistry of the water were confined to the system of currents flowing across the southeastern corner of the Gulf from the Yucatdn Channel to the Straits of Florida. Practically all analyses of offshore and subsurface waters of the Gulf were made in 1914, 1922, 1932, 1934-39, 1942, and since 1947. The chemical data are summarized here in order of the decreasing amount of published informa- tion: salinit}', oxygen, phosphorus, nitrate, nitrite, pH, alkalinity and carbon dioxide components, copper, and miscellaneous chemical constituents. SALINITY Salinity is defined as the total amount of dis- solved solid material in grams contained in 1 kilogram of sea water when all the carbonate has been converted to oxide, the bromine and iodine replaced by chlorine, and all organic matter com- pletely oxidized. In practice, it is calculated from the chlorinity which is determined by titra- tion with silver nitrate solution. Less accurate salinity values are calculated from densities determined with hydrometers. Both salinity and chlorinity are reported as parts per thousand by weight, using the symbol, "/co- in the shallow waters of the Dry Tortugas, in the years 1910 to 1913, Dole (1914) reported salinities ranging from 35.41°/oo to 36.11°/oo- Diurnal and tidal changes in salinity in the same ' Contribution No. 101, from the Marine Laboratory, University of Miami. area in 1919 indicated a wider range, 34.61 °/oo to 36.29°/oo (Wells 1922). In the bays along the coast of Texas the wide salinity variations cause recurring mass mortality of marine animals. This situation was reported by Johnson (1882), Rathbun (1895), and Higgins and Lord (1926). Results of detailed surveys of the salinity distribution in the Texas bays in 1926-27 were reported by Galtsoff (1931). Addi- tional studies of salinity along the Texas, Louisi- ana, and Mississippi coasts were published by Higgins (1931), Riley (1937), Lindner (1939, 1941), Gunter (1945, 1947, 1950), Wise, Winston, and Culli (1945), Price (1947), Geyer (1950), and Collier and Hedgpeth (1950). Alternating floods and droughts cause salinity changes from nearly fresh to 100°/oo, three times that of normal sea water. In connection with studies of the red tide along the west coast of Florida, salinity data were pub- lished by Galtsoff (1948), Gunter, WiUiams, Davis, and Smith (1948), and Ketchum and Keen (1948). In the open Gulf salinities ranged from 30.6°/oo to 37.0°/oo; in Estero Bay, 21.4°/oo; and near the mouth of the Caloosahatchee River, 12.2°/oo. In connection with plankton studies in 28 man- grove-bordered inland bodies of brackish water on the west and south coasts of Florida in 1947- 48, Davis and Williams (1950) reported salinities ranging from 0.6l7oo to 29.09°/oo. The present center of Florida's oyster industry, Apalachicola Bay in northwest Florida, was the subject of an 18-month survey of salinity (Ingle 1951; Ingle and Dawson 1951). Annual varia- tions ranged from fresh water to 42.5°/oo Daily, weekly, and tidal variations were considerable. Apparently the first published salinity records for offshore and subsurface Gulf of Mexico waters are those of Vaughan (1918) who reported salinity values for samples collected at five stations be- tween Havana and Key West from the surface to 143 144 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 1,700 meters by the United States Coast and Geodetic Survey steamer Bache in Marcii 1914. Salinities of two surface samples collected a little farther east in January and February 1919 were reported by Mayor (1922). Stations taken by the Danish research vessel Dana across the Hav'ana section in 1922 provided data for a salinity profile (Nielsen 1925; Schmidt 1929; Jacobsen 1929). Composition of two surface samples collected in July 1922 in the Gulf Stream south of the Dry Tortugas was reported by Lipman (1929). The Havana section was studied again in Feb- ruary 1932 on the Yale Oceanographic Expedition aboard the schooner Mabel Taylor (Parr 1935). Expeditions from the Woods Hole Oceanographic Institution aboard the research vessel Atlantis have made studies of the Havana section in March 1934 (Bulletin Hydrographique, 1935), February and April 1935 (Bulletin Hydrographique, 1936; Seiwell 1938), March 1938 (Montgomery 1941), and May 1939 (Riley 1939). The vertical distri- butions of salinities across the Havana sections in 1922, 1932, and 1934 were summarized in profiles by Parr (1935, pp. 42-44, 71). Below 100 meters the isohalines generally sloped downward toward the Cuban coast. In the middle of the Straits the salinity generally increased from 35.83°/oo at the surface to 36.68°/oo at 200 meters, then de- creased to a minimum of 34.87°/oo at 800 meters, and thereafter increased only slightly to 34.97°/oo at 1,600 meters. The next most thoroughly studied part of the Gulf of Mexico is the Yucatan Channel where the Caribbean Current enters the Gulf between west- ern Cuba and Mexico. This section was studied in 1922 from the Dana (Schmidt 1929; Jacobsen 1929), in February 1932 from the Mabel Taylor (Parr 1935), and from the Atlantis in May 1933 (Bulletin Hydrographique, 1934; Parr 1937; Rake- straw and Smith 1937) and March 1934 (Bulletin Hydrographique, 1935; Parr 1937). The vertical distributions of salinities across the Yucatan Channel in 1933 and 1934 were summarized in profiles by Parr (1937, pp. 42-43). Here, also, the isohalines generally sloped downward toward the Cuban coast. The vertical distribution of salinity was similar to that described above for the Havana section. Comparison of the average temperature-salinity correlation curves for the Yucatan Channel and the Havana section of the Straits of P'lorida led Parr (1935) to conclude'that the water mass entering the Straits of Florida is identical with that which passed through the Yucatan Channel except for a very small layer of "Gulf type" water at the surface on the left (Florida) side of the main current. Parr's (1935) report on the expedition of the Mabel Taylor, February to April 1932, included a map showing the locations of the 68 stations oc- cupied in the Gulf, complete temperature and salinity data, salinity profiles of 5 sections across the main parts of the Gulf, maps of salinity dis- tribution in upper 50 meters and at 200 meters, graphs of vertical distribution of salinity, and temperature-salinity correlation curves. The ex- pedition was not provided with unprotected re- versing thermometers and therefore had no means for accurate determination of the depths of observations. The highest salinities (above 36.25°/oo) in the upper 50 meters were found in the shallow waters off the west coast of Florida and the Campeche Bank. Most of the offshore water in this surface layer had salinities between 36.00°/oo and 36.25°/oo. Low salinities (below 33°/oo) were found along most of the northern regions of the Gulf, and very low (less than 24%©) salinities were found near the mouth of the Mississippi River and to the west from the delta region. At a typical station in the western Gulf (25°46' N., 92°3r W.) the salinity decreased slightly from 36.16°/oo at the surface to 36.12°/oo at 50 meters, then increased to the maximum of 36.31 °/oo at 100 meters, then decreased to the minimum of 34.87°/oo at 600 meters, then in- creased slightly to 34.92°/oo at 800 meters, below which it remained practically constant down to 3,000 meters. Dietrich (1939, p. 119) used the 1932 data from the Gulf of Mexico to prepare another map showing the distribution of the maximum salinities, regardless of depth. This showed a continuous layer of high salinity (above 36.7%o) water in most of the Caribbean Sea, the northern half of the Cayman Sea, and extending northward into the Guif to 26°0()' i\. and 89°20' W. The Atlantic occupied stations along several sections of the central and western Gulf in February to April 1935 (Bulletin Hydrograpliique, 1936). A map showing the locations of these stations was published by Vaughan (1937, p. 21). Vertical distribution of salinity at a typical station in April 1935 in the western Gulf (25°40' N., GULF OF MEXICO 145 94 °2:^' W.) was charted by Diotrich (1989, p. 117, fig. 33); it was similar to that describod above for the Mabel Taylor station about 100 miles farther east. The Atlantis occupied a series of nine stations in the northeast Gulf in March and .pril 1942 from which salinity data were publisi-ni (Bul- letin Hydrographique, 1950). The same vessel occupied a series of 24 stations in the north- western and central Gulf, January to March 1947 (Trask, Phleger. and Stetson, 1947).' The research vessel of the Fish and Wildlife Service laboratory at Sarasota, Florida, has occupied stations from Sarasota to Naples and to a distance of 120 miles off shore at appro.ximately monthly intervals since May 1949. Chemical analyses of the water were made for chlorinity, dissolved oxygen, inorganic phosphate, total phosphorus, nitrate, nitrite, and hydrogen ion concentration.^ The phosphorus data have been published (Graham, Amison, and Marvin, 1954). The other data will be published later. ^ The Fish and Wildlife Service research vessel Alaska began a series of occanographic cruises in the Gulf of Mexico in 1951, Salinities collected on these cruises are being determined at Texas Agricultural and Mechanical College. They shortly will be made available in a mimeographed form.* DISSOLVED OXYGEN The first available data on dissolved oxygen content of Gulf of Mexico water seem to be on the results of analyses of water collected at the Dry Tortugas and published by McClendon (1918), Oxygen determinations were reported when the Atlantis occupied stations across the Yucatan Channel in May 1933, March 1934, and February 1935; across the Havana section of the Florida Straits in March 1934, February and April 1935, August 1938, and May 1939; and in the main part of the Gulf in February to Apnl 1935, The oxy- gen and other data from most of these stations were published in the Bulletin Hydrographique ' Salinity data from tlifse stations were kindly supplied by Fred B. Phleger on August 15, 1950. They are also available from data cards on file at the Woods Hole Oceanographic Institution and will probably be published in the Bulletin Hydrographique. 3 Personal communication from L, A. Walford, December 5, 1950. ' Personal communication from Herbert W. Qraham, January 3, 1952. * Temperature-salinity relationships are discussed in the article of D. F. Leipper. Physical Oceanography of the Gulf of Mexico, in this book. pp. 119-135. in 1934, 1935, and 1936. A graph of the vertical distribution of dissolved oxygen in the center of the Yucatan Channel in 1933 was given by Rake- straw and Smith (1937, p. 9), and a map showing the locations of the stations was published by Vaughan (1937, pi. 11). Seiwell summarized the oxygen data from the 1933-1935 Atlantis stations in the eastern half of the Gulf with profiles across the Straits of Florida and the Yucatan Channel (Seiwell 1938, figs. 6, 15) and gave charts of the horizontal distribution of oxygen at 100, 250, 500, 750, 1,000, 1,500, and 2,500 meters (Seiwell 1938, figs. 7, 8, 11, 14, 16, 17, 20). Vertical distribution of oxygen at a typ- ical station in the western Gulf (25°40' N., 94°23' W.) was charted by Dietrich (1939, p. 117, fig. 33): from about 4.8 cubic centimeters per liter at the surface, it increased slightly to about 4.9 cubic centimeters at 25 meters, then decreased to a minimum of 2.35 cubic centimeters at 300 meters, then increased gradually to about 5.0 cubic cen- timeters at 2,400 meters, and thereafter remained constant to 3,400 meters. Dietrich (1939, p. 120, fig. 35) also presented a chart showing the dis- tribution of minimum oxygen concentration, re- gardless of depth, in all but the southwest part of the Gulf. The lowest oxygen concentrations (be- low 2.5 cc, per liter) were found in the northwest corner; values below 2.7 cc. per liter were ob- served north of the Campeche Bank and off the central west coast of Florida. Riley (1938, 1939) reported oxygen concentra- tions in surface and subsurface samples in the summer of 1938 at two stations in the Dry Tor- tugas in depths of 3 and 19 meters, one station in the Florida Straits in the depth of 166 meters, and from two stations in the Havana section of the Florida Straits in May 1939. In presenting a detaded summary of oxygen in the Atlantic Ocean he omitted the Gulf of Mexico (Riley 1951). Scattered records of oxygen analyses made in connection with studies of animal mortality in- cluding the red tide have been published by Gunter (1942), Galtsoff (1948), Gunter, WUliams, Davis, and Smith (1948), Connell and Cross (1950), PHOSPHORUS The earliest published record of phosphorus content of Gulf of Mexico water is that of Lipman 146 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE (1929) who reported results of analyses of two samples of water collected at the Dry Tortugas in July 1922: 1.00 and 4.80 parts phosphate per million parts of water (10.5 and 50 microgram- atoms phosphate-phosphorus per liter). Information on the vertical distribution of phosphorus in the Gulf of Mexico is very limited. Determinations of phosphate were made on the 16 samples (surface to 1,732 meters) collected at Atlantis station 1606 in the middle of the Yucatdn Channel in May 1933 (Bulletin Hydrographique, 1934, p. 103). Graphs of the vertical distribution of phosphorus at this station were published by Rakestraw (1936, p. 160, fig. 11) and Rakestraw and Smith (1937, p. 9, fig. 7).^ The phosphate- phosphorus" remained nearly constant at 0.15 /ig-atoms/L from the surface to 97 meters, then in- creased to a maximum of 2.47 at 736 meters, then decreased to 1.71 at 1,732 meters. These data for Yucatan Channel water were used in the charts of horizontal distribution of phosphate at various depths (Rakestraw and Smith, 1937, figs. 10-12). Horizontal and vertical distribution of phos- phate near the mouth of the Mississippi River in March 1937 was reported in tables and a map by Riley (1937, pp. 74, 63). He found about 0.58 ^g-atoms/L in the low salinity surface water at the station at the mouth of the river. Phos- phate decreased in all directions to an average of 0.14 /ig-atoms/L at the stations in the Gulf. Distribution of phosphate at the Dry Tortugas and in the Florida Straits was reported by Riley (1938, 1939) and Riley, Stommel, and Bumpus (1949, p. 16). Near Loggerhead Key where the depth was 3 meters, the phosphate ranged from 0.015 to 0.10 Mg-atoms/L from July 18 to August 2, 1938. At his station midway between Loggerhead and Garden Keys where the depth was 19 meters the phosphate at depths of 1, 5, 10, and 15 meters varied quite differently with depth on 4 days in July 1938 from 0.02 to 0.16 Mg-atoms/L. His data from other stations are summarized in table 1 . Riley (1951) presented a detailed summary of phosphorus distribution in the Atlantic Ocean Table 1. — Vertical distribution of phosphate (yig-atoms ID in the Florida Straits Station depth (meters) Date Levels below surface at which samples were taken (in meters) 1 ig 45 90 100 153 200 300 166 1,719 722 Aug. 6, 1938 May 15. 1939 May 11,1939 0.11 .03 .21 0.02 0.12 0.12 "6.07' .10 1.07 Midway between Havana and Key West. Station number 3491. 0.33 .51 0.68 but omitted the Gulf of Mexico, except for his discussion (p. 15) of the tendency for the products of regeneration (phosphate and nitrate) to ac- ciunulate in the deep water of the Caribbean-Gulf of Mexico basins because the outflow through the Straits of Florida is shallower than the maximum depth of the inflowing water. » There appears to be some confusion regarding units in the three publica- tions dealing with this phosphorus data. The raw data in the Bulletin Hydrographique are reported in milligrams phosphate per cubic meter. When these figures are divided by 95, the corresponding unit is milligram- atoms per cubic meter or microgram-atoms per liter. The scale for fig. 11, p. 160 of Rakestraw (1936) indicates phosphate from to 1.5 microgram-atoms per liter, but the scale for fig. 7, p. 9 of Rakestraw and Smith (1937) indicates phosphate from to 3 milligram-atoms per liter. It is believed that the units in the last paper should be either microgram-atoms per liter or milli- gram-atoms per cubic meter, which are numerically equal. Later papers report this same data in microgram-btoms per liter (Sverdrup, Johnson, and Fleming, 1942, p. 241) or milligram-atoms per cubic meter (Riley, Stommel, and Bumpus, 1949; Riley, 1951). ' Phosphate data reported in this section have been corrected lor salt error by multiplying any uncorrected values by 1.15 (Cooper 1938, p. 177; Robinson and Thompson 1948, p. 36). Results of phosphate analyses at various in- shore stations in the Tampa Bay area and near the southern tip of the Florida peninsula in 1946, reported by Williams (1947) and Smith (1949), are summarized in table 2. Table 2. — Phosphate {ng-aloms/ L) along Gulf coast of Florida in 1946 Area Location of sampling station Date Phosphate ;ig-atoms/L Tampa Bay Do Green Key, Hillsboro Bay do Jan. .30. June 4.. do.... 8.4 12.0 Do 1 mile west of Green Key 8.4 Do Terra Ceia Bay Jan. 29. June 3.. ...do.... Mar. 9. . .do.... May 6. .84 Do Terra Ceia Bay (center) 3.60 Do... Terra Ceia Bay (north side) Yi mile southwest of Catfish Key, Florida Bay. Conchie Channel. Florida Bay.. East River, east of Whitewater Bay. 4.80 Cape Sable Do Do .03 .03 .03 In connection with studies of the red tide along the Gulf coast of Florida in 1947 made during and' OULF OF MEXICO 147 after the blooming of Gymnodinium brevis, the concentrations of inorganic phosplionis were fonnd as high as 7.4 ^g-atoms/L and total phosphorus (particulate organic, dissolved organic, and in- organic) up to 20.4 Mg-atoms/L in the amber colored water (Ketchum and Keen 1948, p. 18; Gunter, Williams, Davis, and Smith, 1948, p. 319: Galtsoff 1948, p. 20; Smith 1949, p. 5). These unusually high phosphorus concentra- tions suggested the need for more detailed informa- tion on horizontal, vertical, and seasonal dis- tribution of phosphorus compounds to clarify the fundamental causes of the red tide. Ac- cordingly, when the research program of the Fish and Wildlife Service laboratory in Sarasota, Florida, was planned studies of the distribution of total, inorganic, and organic phosphorus were given primary attention. Results of a detailed survey at 13 stations in the rivers, along the middle Florida coast, and 120 miles west to the 100-fathom line from May 1949 to August 1950 have been published (Graham, Amison, and Marvin, 1954). They show a gradual decrease in phosphorus content of the surface water with increase in distance from shore. The phosphorus- rich waters discharged from the Peace River did not affect, however, the local Gulf waters to any measurable degree. Beyond 14 miles from shore the concentration of total phosphorus in the sur- face water was usually below 0.25 fig-atoms/L and inorganic phosphorus was usually below 0.10 Mg-atoms/L. Larger quantities of phos- phorus, mostly inorganic, were found at depths below 50 meters. Occasional upwelling did not seem to influence the phosphorus content of the eu photic zone. There was no evidence of the bottom sediments contributing any appreciable quantities of phosphorus to the water. Local concentrations of the planktonic blue-green alga, Trichodesmium, appeared to be associated with high concentrations of total phosphorus. NITRATE-NITROGEN Studies of nitrate distribution in the Gulf have generally paralleled those of phosphate reviewed above. Vertical distribution of nitrate in the middle of the Yucatin Channel in May 1933 (Bulletin Hydrographique, 1934, p. 103) was indicated in a graph by Rakestraw (1936, p. 160, fig. 11) and Rakestraw and Smith (1937, p. 9, 259534 0—54 11 fig. 7).' The nitrate decreased from 2.4 Mg- atoms/L at the surface to 1.4 ^g-atoms/L at 49 meters, then increased regularly to a maximum of 37.1 Mg-atoms/L at 736 meters, then decreased to 24.2 Aig-atoms/L at 1,732 meters. These data for Yucatdn Channel water were used in the charts of horizontal distribution of nitrate at various depths (Rakestraw and Smith, 1937, figs. 14-16). Although no nitrate determinations were made on Gulf waters near the mouth of the Mississippi, Riley (1937, p. 69) reported the following data (supphed by A. A. Hirsch of the New Orleans Sewerage and Water Board Company) which are 1935 average values for the Mississippi River water at New Orleans: Ammonia nitrogen 20 mg/m' Albuminoid nitrogen 350 mg/m' Nitrite nitrogen 5 mg/m' Nitrate nitrogen 200 mg/m' Nitrate data for two stations in the Florida Straits reported by Riley (1939, p. 161) are sum- marized in table 3. Table 3. — Vertical distribulion of nitrate-nitrogen {ixg-atomsl L) in the Florida Straits Location Station depth (meters) Date Levels below surface at which samples were taken (in meters) 1 100 200 300 Midway between Ha- vana and Key West. Station No. 3491 Off Matanias, Cuba, Station No. 3486 1,719 722 May 15,1939 May 11,1939 1.70 1.00 0.31 .60 0.93 2.21 14.3 Riley, Stommel, and Bumpus (1949, p. 16, fig. 6) used these surface values for southeastern Gulf water in their summary chart and discussed the origin of Caribbean water from the nutrient-poor Equatorial and Antilles Currents. They ex- plained, however, that the Caribbean "also re- ceives a substantial draught of Antarctic inter- mediate water, which is very rich, particularly in nitrate. The maximum concentration of this substance at a depth of about 800 meters in the Caribbean (and possibly the Gulf of Mexico) ex- ceeds the amount found anywhere else in the western North Atlantic." Some of this may be accumulated products of regeneration, as sug- gested for phosphate (Riley 1951). ' There appears to be a confusion of units for expre.ssine these nitrate data parallel to that discussed for phosphate in footnote 5. 148 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE NITRITE-NITROGEN Distribution of nitrite-nitrogen in the Gulf of Mexico is almost unknown except for a single station in the Yucatan Channel and a few analyses of surface water along the Florida west coast made in 1946-47 by Williams (1947) and Gunter, Williams, Davis, and Smith (1948), (table 4). Table 4. — Nitrite-nitrogen along Gulf coast of Florida, 1946-4? [Observations by Williams, Ounter, Davis, and Smith] Area Location Date Nitrite- nitrogen Mg-atoms/L Tampa Bay... Do Oreen Key. Hillsborough Bay. ...do - - Jan. 30.1946 June 4, 1946 do Jan. 29,1946 June 3, 1946 do Mar. 9,1946 ...do May 6,1946 Apr. 12,1947 do Do Do Do Do.. Cape Sable Do Do .- Key West Do 1 mile west of Green Key, Hillsboro Bay. Terra Ceia Bay Terra Ceia Bay (center) Terra Ceia Bay (north side)... M mile southwest of Catfish Key. Florida Bay. Conchie Chamiel, Florida Bay. East River, east of White- water Bay. 2^^ miles north of Content Keys. 2 miles north of Barracuda Keys. ^1 2 .2 Vertical distribution of nitrite at Atlantis station 1606 in the middle of the Yucatdn Channel May 4, 1933, depth 1,911 m., reported in the Bulletin Hydrographique (1936, p. 103) and by Rakestraw (1936, p. 149, table 9)* is summarized in table 5. Table 5. — Nitrite-nitrogen in the Yucatdn Channel Depth (meters) Nitrite- nitrogen Mg-atoms/L Depth (meters) Nitrite- nitrogen Mg-atoms/L 0.135 .01 .01 .11 .035 .03 300 0.02 28 400 .01 50 500 .01 100 600..-. .01 150 800 .01 200 HYDROGEN ION CONCENTRATION (pH) The hydrogen ion concentration of sea water at the Dry Tortugas from the surface to 35 meters varied between the pH values of 8.1 and 8.28 (McClendon, 1916a, 1916b, 1918; IVIayor, 1922). Published data on vertical distribution of pH in deeper waters of the Gulf are limited to those taken at Atlantic station 1606 in the middle of the Yucatan Channel May 4, 1933. They were re- ported in the Bulletin Hydrographique (1936, • The graph of this nitrite distribution (Rakestraw, 1936, p. 160, flp. II) docs not correspond to the figures in the tables. p. 103), corrected for depth to represent condi- tions in situ, and diagrammed by Rakestraw and Smith (1937, figs. 7, 18-20). The pH increased slightly from 8.14 at the surface to 8.17 at 24 meters, then decreased to a minimum of about 7.9 at 736 meters, then increased to about 8.03 at 1,537 meters. Measurements of the pH of shallow waters of Galveston Bay were made by Wise, Winston, and CuUi (1945). Detailed studies of pH distribution at 26 stations in the coastal bays between New Orleans and Biloxi were reported by Gunter (1950) ; the pH values ranged from 6.66 in Pearl River entering Lake Borgne, to 8.35 in American Bay, off Breton Sound. Determinations of pH on the sea water col- lected during and after the red tide (Galtsoff, 1948, pp. 23-24; Gunter, Williams, Davis, and Smith, 1948, p. 319, table 9) indicated no abnormal hydrogen ion concentrations. ALKALINITY AND CARBON DIOXIDE The alkalinity or buffer capacity and con- centrations of carbonic acid (including the free carbon dioxide), bicarbonate, and carbonate have been studied in Gulf of Mexico water in the Dry Tortugas by Dole (1914), McClendon (1918), Mayor (1922), Wells (1922), and Lipman (1929), and in the Yucatin Channel by Mitchell and Rakestraw (1933), and Rakestraw and Smith (1937, p. 2, table 1; p. 9, fig. 7). COPPER According to Riley (1937) soluble copper and copper adsorbed on plankton and detritus is distributed horizontally and vertically in all direc- tions from the mouth of the Mississippi River as far as the 1 ,000-f athom line. All samples analyzed by him showed the concentrations of soluble copper from 1 to 25 mg/m ' and that of adsorbed copper from 0.3 to 7.2 mg/m.' The high copper values in the surface samples were generally found in waters of low salinity. At the 1,000-fathom station, soluble copper increased from 5 mg/m ' at the surface to 9, 10, 10, and 12 mg/m ' at 100, 300, 600, and 1,800 meters depth, respectively. MISCELLANEOUS CHEMICAL CONSTITU- ENTS Bromine content of the Gulf of Mexico water has been studied in connection with the commercial GULF OF MEXICO 149 extraction of this material at the plant constructed in 1940 at Freeport, Texas. Calcitini ran^inK ^rom 427 to 535 mg/kg was reported by iiipman (1929) in two samples collected at the Dry Tortugas in July 1922. Calcium carbonate precipitation in the water in the Marquesas lajioon when the pH was 8.46 was observed by McClendon (1928, p. 258). The mechanism of this process was studied by various chemists and bacteriologists at the Dry Tortugas and elsewhere (McClendon 1918, pp. 252-258; Gee 1934; Gee and Feltham 1934). Hydrogen sulfide was indicated in West Galves- ton Bay by blackening of the white lead paint on boats at a time of animal mortality (Gunter 1942). Tests for hydrogen sulfide were made on the red tide water, but no clearly positive results were found (Gunter, Williams, Davis, and Smith, 1938, p. 320). Iron ranging from 0.12 to 1.50 mg/kg was re- ported by Lipman (1929) in two samples from the Dry Tortugas. Magnesium content of 1,300 mg/kg was reported by Shiglcy in this book in the Gulf water at Freeport, Texas, where plants were erected for the com- mercial extraction of this metal from sea water.' Various organic compounds have been reported present in Gulf waters. Gunter (1942) concluded that the mortality of marine organisms in an inshore area was caused by oxygen deficiency as- sociated with decay of organic materials and the accumulation of toxic products of anaerobic decomposition. Riley (1937) reported from 0.23 to 20.60 mg/L of organic matter in the Gulf water in the area near the mouth of the Mississippi River. Both plankton and organic detritus ad- sorbed significant amounts of copper. Woodcock (1948) studied an unidentified human respiratory irritant, probably a product of the blooming Gymnodinium brevis which was carried ashore in minute droplets of sea water. A carbohydrate which showed some of the chemical properties of arabinose was found in concentrations from 2 to 25 mg/L in the natural sea water supply at the U. S. Fisheries Station at Pensacola, Florida (Collier, Ray, and Magnitzky, 1950). Products of industrial and sewage pollution have been reported in Texas coastal waters (Burr 1945a, b; Wise, Winston, and Culli, 1945). Potassium concentrations of 404 and 435 mg/kg were reported in two samples of sea water from the Dry Tortugas (jjipman 1929). Silicon concentrations of 9.80 and 11.10 mg. SiOj per kilogram were reported in the same samples (Lipman 1929). Solids reported by Lipman (1929) from analyses of the two samples of Dry Tortugas water are summarized in table 6. Table 6. — Solids, mg/kg, in Dry Tortugas sea water Sample No.l Sample No. 6 35891 34018 1873 37750 Nonvolatile solids 34580 Volatile solids 3170 Distribution of dissolved solids was studied at 26 stations in the coastal bays from New Orleans to Biloxi by Gunter (1950) who reported values ranging from 92 to 29,164 parts per million or milligrams per kilogram. SUMMARY Salinity distribution in the Gulf of Mexico is fairly well known except for the general absence of data on seasonal variations in offshore waters.'" The same could be said of oxygen distribution. Phosphorus distribution is known only for four small areas: Florida Straits, Yucatdn Channel, central west coast of Florida, and the Mississippi Delta region. Nitrate, nitrite, pH, alkalinity, carbon dioxide distributions are known only in the Yucatdn Channel-Florida Straits corner of the Gulf and there for only one or two seasons of the year. Other chemical data are scarce, scattered, or absent. It is expected that considerable information will soon become available with the publication of results of studies sponsored by the chemical and oil companies and of those being conducted by the research vessels and in the shore laboratories of the Fish and Wildlife Service. ' The extraction of bromine and magnesium from sea water is discussed in an article by C. M. Shiglcy, The Recovery of Minerals from Sea Water, p. 153. ■0 Seasonal and local variations of chlorinity and salinity in offshore waters of a portion of the Oulf of Mexico are being studied by the American Petro- leum Institute (Project 61) through Scripps Institution of Oceanography ol the University of California and the Department of Oceanography of the Agricultural and Mechanical College of Texas. Salinity data can be found in the Progress Reports of the Department of Oceanography, Agricultural and Mechanical College of Texas, Project 34, for October 1 to December 31, 1951. and January 1 to March 31, 1952. 150 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE LITERATURE CITED Burr, J. G. 1945a. Ferric salt deposits vs. fish and oysters. Texas Game and Fish 3 (2): 16-17. 1945b. Ferric salt deposits in Galveston Bay in relation to fish and oysters. Trans. Texas Acad. Sci. 28: 223-224. Collier, Albert, and Hedgpeth, J. W. 1950. An introduction to the hydrography of the tidal waters of Texas. Pub. Inst. Mar. Sci., Univ. Texas, 1 (2): 121-194. Ray, S., and Magnitzky, W. 1950. A preliminary note on naturally occurring organic substances in sea water affecting the feeding of oysters. Science 111 (2876): 151-152. CoNNELL, Cecil H., and Cross, J. B. 1950. Mass mortality of fish associated w-ith the proto- zoan Gonyaulax in the Gulf of Mexico. Science 112 (2909): 359-363. CoNSEiL Permanent International Pour l'Explora- TioN de la Mer. 1933-36, 1950. Bulletin Hydrographique pour les annees 1932, 1933, 1934, 1935, 1940-46, avec appendice: Atlantique-Florida, 1936-39. Copenhagen. Cooper, L. H. N. 1938. Salt error in determinations of phosphate in sea water. Jour. Mar. Biol. Assoc. U. K. 23 (1) : 171-178. Davis, Charles C, and Williams, Robert H. 1950. Brackish water plankton of mangrove areas in southern Florida. Ecology 31 (4): 519-531. Dietrich, Gijnter. 1939. Da,s Amerikanische Mittelmeer. Ein meeres- kundlicher tJberblick. Zeitschr. d. Gesellsch. f. Erd- kunde zu Berlin, 1939, Nr. 3/4, pp. 108-130. Dole, Richard B. 1914. Some chemical characteristics of sea water at Tortugas and around Biscayne Bay, Florida. Pap. Tortugas Lab., Carnegie Inst. Washington Pub. No. 182, 5: 69-78. Galtsoff, Paul S. 1931. Survey of oyster bottoms in Texas. U. S. Bur. Fish., Inv. Rept. No. 6, 30 pp. 1948. Red tide. Progress report on the investigations of the cause of the mortality of fish . . . U. S. Dept. Interior, Fish and Wildlife Service, Spec. Sci. Rept. No. 46, 44 pp. Gee, Haldane. 1934. Lime deposition and the bacteria. I. Estimate of bacterial activity at the Florida Keys. Pap. Tortugas Lab., Carnegie Inst. Washington Pub. No. 435, 28: 67-82. and Feltham, C. B. 1934. Lime deposition and the bacteria. II. Charac- teristics of aerobic bacteria from the Florida Keys. Pap. Tortugas Lab., Carnegie Inst. Washington Pub. No. 435, 28: 83-91. Geyer, Richard A. 1950. 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Although the salinities of the several seas vary somewhat, the average is approximately 35,000 parts of dissolved salts per million, equiv- alent to 165 million short tons per cubic mile. The oceans of the world thus represent a store- house of about 50 million billion tons of dissolved materials. The chloride ion represents 54.8 per- cent of the total salts, the sodium ion 30.4 percent, sulphate 7.5 percent, magnesium 3.7 percent, calcium 1.2 percent, potassium 1.1 percent, carbonate 0.3 percent, and bromide 0.2 percent. Although the sea is believed to contain at least traces of every clement, these eight ions account for over 99 percent of the sea water salts; all other elements total less thaa 1 percent. Since the sodium and chloride ions represent sLx-sevenths of the dissolved salts and are the most easily extracted, it is not surprising that they seem to have been involved in the first recovery on record. Sodium chloride, common salt, was undoubtedly the first compound to be removed from sea water and used by man. It is believed that salt was used by cave men at least 5,000 years ago. Salt from sea water is mentioned in Chinese writings about 2200 B. C. Aristotle in his Meteorologica wrote of the origin and usefulness of the salts of sea water and described a method of "unsalting" sea water. The ancient Greeks, Romans, and Egyptians were familiar with produc- tion of salt by solar evaporation of sea water. Such salt recovery has been common in China, India, and Japan for many centuries, and still continues. Salt from sea water was produced on the Atlantic coast of North America about 1680 and on the Pacific coast in 1852. The Atlantic coast industry was short lived, but that on the Pacific coast has thrived to this time. The production of crude soda and potash from the ashes of seaweeds was accomplished in Scotland as early as 1720. Iodine was recovered from seaweeds for the first time early in the nineteenth century; magnesia was first prepared on the Mediterranean coast at the end of the century. The records do not indicate any additional progress until 1923 when magnesium cliloride and gypsum were produced from the bitterns from solar evap- oration of the sea water of San Francisco Bay (Seaton 1931). These bitterns were first treated with calcium chloride, precipitating the sea water sulfate as calcium sulfate, which was settled and filtered. Concentration of the filtrate, cooling and separa- tion of the residual magnesium sulfate, potash, and other salts by settling and centrifuging, gave a fairly pure magnesium chloride solution which was further concentrated to salable form by boil- ing. The calcium sulfate resulting from the calcium chloride treatment was washed, dried, and sold as gypsum. In 1926, the first sea water bromine was recov- ered on a small commercial scale by chlorinating the S