ATLANTIC OCEAN, the body of water lying between the eastern coasts of the Amer icas and the western coasts of Europe and Africa, and extending from the Arctic Basin to the Great Southern Ocean. Its greatest breadth, attained in lat. 25° N., is 4,500 miles; but between Cape S. Roque in Brazil and Cape Palmas its breadth is only 1,600 miles. Its superficial extent, not including the inland seas, is approximately 23,215,000 square miles, or 10, 588,000 square miles in the north Atlantic Ocean and 12,627,000 square miles in the south Atlantic. The mean depth of the north Atlan tic is 2,047 fathoms; of the south Atlantic 2,067 fathoms.
Chief Distinguishing A preliminary and strictly condensed statement may serve, in some slight degree, to character ize this ocean and to differentiate it from the others. In the following respects, then, if we limit the number of particulars to a dozen, the Atlantic seems to be most clearly differentia ted: (1) It has a much larger drainage area than either the Indian Ocean or the Pacific Ocean. (2) That portion of the Atlantic Ocean lying north of the equator and known as the north Atlantic has been more carefully studied than the other main divisions of the hydrosphere; and the interest manifested in this way is partly due to the number and ex ceptional importance of the enclosed seas con nected with it. (3) The Atlantic Basin has, as the dominant feature of its relief, a sub marine ridge that extends, approximately, from lat. 50° N. to lat. 40° S. and divides the basin into the eastern and western submarine valleys or troughs. (4) The number of islands in the Atlantic is relatively small particularly small in the south Atlantic. (5) The basin of the Atlantic Ocean was formed in comparatively recent geologic time. It dates probably from the Mesozoic age, whereas the Pacific Ocean's basin is of truly great antiquity. (6) The salinity of the Atlantic far exceeds that of the other great oceans; it is especially marked in its great inland sea, the Mediterranean, and increases as we proceed toward the eastern part of that sea. (7) As compared with the wind circulation over the other great oceans, that over the Atlantic has a very definite character. (We shall refer to this subject again in con nection with the formation of drifts and cur rents). (8) The Atlantic contains the Gulf stream, which probably exceeds in volume and in rapidity all other stream currents in the world. (9) Between lat. 20° N. and 35° N. and long. 40° W. and 75° W. there is a dis tinctively Atlantic area in which there is prac tically no surface circulation and which— owing to the circumstance that it is covered by enormous banks of gulf-weed (Sargassum buccifemos — has received the name Sargasso Sea. (10) Between South America and Africa, a secondary tidal-wave moves north ward; and this is produced by, or perhaps de flected from, the east-to-west tidal-wave of the Southern Ocean. (11) Ice formations of the north Atlantic are noticeably different in character from those of the north Pacific. (12) The entire Atlantic, vast though it is, may be called simply the greatest of inland seas, rather than a true ocean. (The reasons for this will be mentioned in the paragraph Fauna).
Islands and Enclosed The principal oceanic islands are the Canaries, Azores, Cape Verde Islands, Madeira, Ascension, Saint Helena, Bouvet Island and Tristan da Cunha; while those classed as continental groups are the British Isles, West Indies, Iceland, Newfound land and the Falklands. Connected with the Atlantic are, on the eastern side, the Mediter ranean and the Black Sea, the North Sea and the Baltic ; on the western side are the Gulf of Mexico and the Caribbean Sea (together form ing the American Mediterranean), Hudson Bay and the Gulf of Saint Lawrence.
Winds and Of the winds of the Atlantic, the most remarkable are (1) the perennial or trade winds which blow con stantly in one direction, or nearly so — from east to west, southeast to northwest, or north east to southwest, and (2) the so-called ((roar ing forties.* The region of the trade winds
north of the equator is known as the zone of the northeast trades; that south of the equa tor as the region of the southeast trades. The northeast trade wind blows with less steadiness than the southeast; in the West Indies, how ever, the former seldom forsakes its regular course. Both are found to be most constant when the observations are taken far out at sea; less steady on the land or near it. Com mander W. W. Campbell Hepworth has written (in the Geographical Journal, November 1914, Vol. XLIV, No. 5) : northeast and southeast drift-currents, following the course of the wind, gradually turn more and more to the eastward [as the source, not the direction of their movement], and increase in volume, in breadth and depth as they flow toward the equator until they unite and form the Equa torial Current. For convenience, the northern portion of this great ocean river, which owes its origin mainly to the northeast trade wind, is called the North Equatorial Current, while the southern portion, which is derived mainly from the southeast trade wind drift-current, is called the South Equatorial Current; but there is in fact no definite dividing line, except that during the six months of the year, June to November, the heaped-up waters of the two currents overflow between the third and 13th parallels of north latitude, east of about the 50th meridian, and turn to the eastward, thus becoming a counter current, which subse quently joins a southeastward setting branch of the northeast trade wind drift-current and a northeastward setting branch of the southeast trade wind drift-current, when the combined current flows eastward, immediately south of and parallel to the Guinea Coast.* The Gulf Stream is a continuation, partly of the main and partly of the north equatorial currents, which pass across the Atlantic to the South American coast. That portion of the ocean river deflected northward then runs along the coast until it enters the American Mediter ranean; receiving later the name of Gulf Stream when (and because) it issues, between Florida and Cuba, from the Gulf of Mexico. It afterward flows nearly parallel to the coast of the United States, separated from it by a belt of cold water. Off Cape Hatteras it attains a width of 167 miles and com prises three warm sections with two cold belts interposed. On passing Sandy Hook it turns eastward and continues to be recognizable, partly by its characteristic blue color, until it reaches long. 30° W., where, with diminished temperature, it is found flowing nearly due east. The warm drift from it that reaches the coasts of the British Isles represents, not the Gulf Stream proper, but a side branch, which derives its impetus from the southwest winds of those latitudes. There is, none the less, a real connection between the two. The Brazil Current is formed by that portion of the equa torial ocean river which is turned southward from Cape S. Roque in South America. The South African current originates near the Cape of Good Hope and flows in a north westerly direction, eventually uniting with the equatorial currents. The Cape Horn current flows from the Southern into the Atlantic Ocean, its general directidn being east-north east. Rennel current, a drift from the Gulf Stream, enters the Bay of Biscay from the west. The Arctic current runs along the east coast of Greenland and continues along the coast of the United States, from which it separates the Gulf Stream by a band of cold water. An Antarctic current of cold water not at the surface, like the foregoing, but at a great depth—flows from Antarctic regions toward the equator.