ATLANTIC OCEAN

body of salt water covering approximately one-fifth of the Earth's surface and separating the continents of Europe and Africa to the east from the Americas to the west. The Atlantic Ocean and its marginal seas constitute the world's second largest ocean after the Pacific and have an area of 41,100,000 square miles (106,460,000 square km); the Atlantic proper has an area of 31,830,000 square miles (82,439,700 square km). The average depth (with marginal seas) of 10,925 feet (3,330 m) is somewhat less than that of the Pacific and Indian oceans because of extensive continental shelves in the north and the shallowness of the marginal seas. These seas include the Baltic, North, Black, and Mediterranean seas to the east and Baffin Bay, Hudson Bay, the Gulf of St. Lawrence, the Gulf of Mexico, and the Caribbean Sea to the west. The Atlantic becomes broader south of the Equator and is bordered by simple coasts almost without islands. Topographically the Atlantic floor is dominated by the tectonically and volcanically active Mid-Atlantic Ridge, which extends down the centre of the ocean from north to south and divides the ocean into two principal structural troughs. These two troughs comprise a number of smaller basins, usually separated from each other by continental shelves, oceanic rises or ridges, or other submarine relief features. The basins east of the Mid-Atlantic Ridge include (north to south) the Lofoten, Norwegian, West European, Canary, Cape Verde, Guinea, Angola, Cape, and Agulhas basins. Those west of the ridge include the Labrador, Newfoundland, North American, Guiana, Ceara, Brazil, and Argentina basins. Most mid-Atlantic islands are volcanic in origin because of the influence of the Mid-Atlantic Ridge; these include Iceland, the Azores, Ascension, St. Helena, Tristan de Cunha, Gough, and Bouvet, all adjoining the Mid-Atlantic Ridge. Purely continental islands are Svalbard (including Spitsbergen), the British Isles, Newfoundland, and the Falkland Islands. The Atlantic has relatively few seamounts, and long stretches of its coasts are devoid of fringing reefs. The continental slope around the Atlantic is cut by submarine canyons that funnel sediments from continental sources to the continental rise. Most of the bottom of the Atlantic is covered with foraminiferal ooze, a calcareous deposit consisting mainly of the shells of dead unicellular organisms. Calcareous deposits give way to red clay at depths below 16,400 feet (5,000 m). Airborne material from the deserts of Africa accumulates off the western coast of Africa, and detritus borne on ice is an important component of sediments in high latitudes. As a result of excess evaporation, salinity is highest in the surface waters of the North Atlantic and lowest in the Baltic Sea and other areas where precipitation is high and where admixtures of fresh water from large rivers are substantial. The surface currents of the Atlantic correspond to the system of prevailing winds and are modified by such factors as bottom and tidal friction, the Earth's rotation, regional excesses of evaporation or precipitation, and regional differences in cooling or heating. Trade winds in the North Atlantic maintain a fairly steady equatorial current from east to west. Much of the water carried by this current continues northward into the Caribbean and through the Strait of Yucatn into the Gulf of Mexico, from which it emerges as a warm and swift current to form the Gulf Stream off the eastern coast of the United States. The North Atlantic Current is a direct extension of the Gulf Stream that branches into the Irminger Current south of Iceland, the East Greenland Current, and the Canary Current between the Azores and Spain. The Canary Current flows southwest and joins the North Equatorial Current. Southeast trade winds in the South Atlantic maintain the South Equatorial Current, much of which is diverted northward by the coast of South America. No current in the South Atlantic is as powerful as the Gulf Stream. body of salt water covering approximately one-fifth of the Earth's surface and separating the continents of Europe and Africa to the east from those of North and South America to the west. The ocean's name, derived from Greek mythology, means the Sea of Atlas. It is second in size only to the Pacific Ocean. The Atlantic is, generally speaking, S-shaped and narrow in relation to its length. The area of the Atlantic without its dependent seas is approximately 31,830,000 square miles (82,440,000 square kilometres), and with them 41,100,000 square miles (106,460,000 square kilometres). It has an average depth (with its seas) of 10,925 feet (3,300 metres) and a maximum depth of 27,493 feet (8,380 metres) in the Puerto Rico Trench, north of the island of Puerto Rico. From east to west the ocean's breadth varies considerably. Between Newfoundland and Ireland it is about 2,060 miles; farther south it widens to more than 3,000 miles before narrowing again so that the distance from Cape So Roque, Braz., to Cape Palmas, Liberia, is only some 1,770 miles. Southward it again becomes broader and is bordered by simple coasts almost without islands; between Cape Horn and the Cape of Good Hope the ocean approaches Antarctica on a broad front nearly 4,000 miles wide. Although not the largest of the world's oceans, the Atlantic has by far the largest drainage area. The continents on both sides of the Atlantic tend to slope toward it, so that it receives the waters of a large proportion of the great rivers of the world; these include the St. Lawrence, the Mississippi, the Orinoco, the Amazon, the Ro de la Plata, the Congo, the Niger, the Loire, the Rhine, the Elbe, and the great rivers draining into the Mediterranean, Black, and Baltic seas. In contrast to the South Atlantic, the North Atlantic is rich in islands, in the variety of its coastline, and in tributary seas. The latter include the Caribbean Sea, the Gulfs of Mexico and St. Lawrence, and Hudson and Baffin bays on the west and the Baltic, North, Mediterranean, and Black seas on the east. This article treats the physical and human geography of the Atlantic Ocean as a whole. For detailed discussion of the physical and chemical oceanography and marine geology of the Atlantic Ocean, see ocean. Additional reading General works Useful atlases containing maps and other information about the Atlantic Ocean and its marginal seas are Alastair Couper (ed.), The Times Atlas and Encyclopedia of the Sea (1989); and Martyn Bramwell (ed.), The Rand McNally Atlas of the Oceans (also published as Mitchell Beazley Atlas of the Oceans and The Macmillan Atlas of the Oceans, 1977, reissued 1987). K.O. Emery and Elazar Uchupi, The Geology of the Atlantic Ocean (1984), is a well-illustrated technical work. Two excellent texts on oceanic processes, with numerous examples from Atlantic study, are the classic by H.U. Sverdrup, Martin W. Johnson, and Richard H. Fleming, The Oceans: Their Physics, Chemistry, and General Biology (1942, reissued 1970); and M. Grant Gross, Oceanography, 5th ed. (1990). Rhodes W. Fairbridge (ed.), The Encyclopedia of Oceanography (1966), contains technical articles on all aspects of oceanography. Physical and human geography Physical environment Francis P. Shepard, Submarine Geology, 3rd ed. (1973), discusses ocean sediments, deposition and transport processes, and continental shelf structures. A scholarly treatment of geologic and tectonic processes can be found in F.J. Vine and H.H. Hess, Sea Floor Spreading, in A.E. Maxwell (ed.), The Sea, vol. 4 (1970). Ocean-continent boundaries are the focus of a special issue of Oceanus, vol. 22, no. 3 (1979), which includes articles on passive (Atlantic-type) continental margins. Alan E.M. Nairn and Francis G. Stehli (eds.), The Ocean Basins and Margins, vol. 14 (197378), examines the geology of the South and North Atlantic, the Gulf of Mexico and the Caribbean, and the eastern and western Mediterranean. R.C.H. Russell and D.H. Macmillan, Waves and Tides (1952, reissued 1970), offers a basic understanding of wave physics and cites numerous Atlantic phenomena. Henry Stommel, The Gulf Stream (1965, reprinted 1976), is the authoritative text on this current. The physiography of the northern Atlantic is described in Burton G. Hurdle (ed.), The Nordic Seas (1986). Economic aspects P.J.P. Whitehead et al. (eds.), Fishes of the North-eastern Atlantic and the Mediterranean (1984 ), is a comprehensive list for these regions. Additional information on the entire basin is available in Food and Agriculture Organization of the United Nations, Fisheries Dept., Atlas of the Living Resources of the Sea, 4th ed. (1981). D.H. Cushing, Marine Ecology and Fisheries (1975), is an intermediate-level treatment of marine biology and food-web dynamics. Historical perspectives on and descriptions of key commercial fisheries are contained in Georg Borgstrom and Arthur J. Heighway, Atlantic Ocean Fisheries (1961). Edward L. Miles (ed.), Management of World Fisheries (1989), analyzes policy conflicts surrounding the trend toward fishing restrictions in the Atlantic and elsewhere. Fillmore C.F. Earney, Marine Mineral Resources (1990), provides in-depth information on the location of Atlantic offshore resources, reserve and value estimates, and the geopolitics of their exploitation. The journal Maritime Policy and Management (quarterly) includes frequent articles on transatlantic shipping. A comprehensive report on marine pollution, with data on the Atlantic and Gulf of Mexico, is United Nations Environment Programme, GESAMP: The State of the Marine Environment (1990); and an examination of the effects of offshore production is provided in J.P. Hartley and R.B. Clark (eds.), Environmental Effects of North Sea Oil and Gas Developments (1987). Study and exploration The work by Emery and Uchupi cited above includes a comprehensive chapter on ancient and European exploratory voyages of the Atlantic Ocean. D.W. Meinig, The Shaping of America, vol. 1, Atlantic America, 14921800 (1986), supplies contemporary perspectives on the settlement of the New World. Margaret Deacon, Scientists and the Sea, 16501900 (1971), chronicles the history of oceanographic exploration through the 19th century, with extensive discussions of Atlantic discoveries; and M. Sears and D. Merriman (eds.), Oceanography: The Past (1980), is a compilation of articles on significant historical events and developments in marine science. John G. Weihaupt, Exploration of the Oceans (1979), offers technical treatments of exploration activities. Oceanus (quarterly), published by the Woods Hole Oceanographic Institution, contains brief articles on current research activities in the Atlantic. James M. Broadus Matthew J. LaMourie The Editors of the Encyclopdia Britannica Economic aspects Biological resources The great north-south extent, relatively broad areas of continental shelf, proportionally large runoff from land, and circulation patterns are all factors that have given the Atlantic a proliferation of plant (i.e., algae) and animal species that is second only to that of the Pacific among the world's oceans. A large variety of seaweeds inhabit the shallower continental margins and coastal areas, particularly in the North Atlantic. Algae of commercial value include the kelp genus Laminaria a source of iodine, potassium, and algin; Irish moss (Chondrus crispus), from which carrageen is derived; and such edible varieties as dulse (Rhodymenia palmata) and laver (Porphyra ). Also of note in the North Atlantic are the huge masses of gulfweed (Sargassum natans) in the Sargasso Sea that support large communities of crustaceans and fish normally associated with coastal regions and that are the spawning grounds for the American and European freshwater eels of the genus Anguilla. The areas of coastal upwelling of cold, nutrient-rich deep waterespecially off western Africa, in the Grand Banks of Newfoundland and the waters surrounding Iceland, and off the coasts of southeastern South America and southern Africaare the sites of large plankton blooms, which, in turn, are the basis of much of the Atlantic's rich fish life. The greatest concentrations of plankton are found in the North Atlantic. In tropical regions, plankton production is fairly constant throughout the year, whereas with increasing latitude it becomes tied to the availability of sunlight and results in explosive and relatively short-lived blooms. In addition to fish, the Atlantic is home to a variety of sponges, sea anemones, horseshoe crabs, mollusks, and sea turtles. Coral reefs are confined largely to the Caribbean and do not approach those of the Pacific in the diversity of their reef life. Marine mammals consist primarily of dolphins and dwindling numbers of manatees in tropical regions and harp seals in the northwest of the basin. Whales generally are restricted to the cool-temperate and Antarctic regions of the South Atlantic, although many species migrate to tropical waters to breed. Fisheries The Atlantic's major fishing groundsrepresenting more than half the world's totallong have been the most productive and most heavily utilized of all the oceans. For some time, many Atlantic species have been intensively fished, and some key populations are thought to be at or near collapse. Thus, while the total global marine catch has been increasing steadily, that for the Atlantic has remained fairly constant; and the Atlantic's share of the overall marine catch has dropped from more than half in the mid-1950s to less than a third. Lobster fishing off the coast of Cape Breton, Nova Scotia, Can. The Atlantic continues to provide millions of tons of fish annually for human consumption and industrial purposes. Nearly all of the Atlantic fish catch is taken from waters of the continental shelf, primarily from the nutrient-rich areas, where upwellings occur. Among the important commercial fish taken in the North Atlantic are the demersal (deep-dwelling) members of the Gadidae (cod) familynotably haddock and codand such pelagic (free-swimming) species as lobster, mackerel, and menhaden. In the Gulf of Mexico and in equatorial regions, shrimp, shellfish, and eels are harvested in quantities. Hake, tuna, and pilchard are key commercial species in the South Atlantic, despite severe depletion of the latter two stocks. Many Atlantic countries have been attempting to protectwith limited successtheir living resources by managing the level of fishing activity in their territorial waters and 200-nautical-mile (370-kilometre) exclusive economic zones. Methods used have included area closures, permits, catch limits and quotas, and time and season restrictions.