ATLANTIC OCEAN. An ocean so named from Atlas (q.v.), probably because it was the sea beyond Mount Atlas. in northwestern Africa. It lies to the west of the great land masses of the Old World and to the east of those of the New World, and extends from the Arctic to the Antarctic regions. It is bounded on the east by Europe and Africa, and on the west by the two Americas. On the north it freely connects with the Arctic Ocean by a channel which is as broad as the narrower parts of the main body of the ocean, but which is obstructed by islands, of which Greenland is the largest. Greenland lies to the west of the main connecting channel, which is itself obstructed by Iceland. On the south no natural line of demarcation separates the Atlantic from the Antarctic Ocean, and the waters of the Atlantic mingle with those of the Pacific at the southern end of South America, and with those of the Indian Ocean at the southern end of Africa.
The northern and southern boundaries of the Atlantic are therefore not fixed by any natural harrier, but it is the custom to assume the Arc tic and Antarctic circles to be the limits on these two sides respectively, although the peculiar influences of the polar oceans extend considerably toward the equator from these limits. The length of the Atlantic between these north and south boundaries is over 9000 miles; the breadth averages perhaps something over 3000 miles, being only about 1900 miles in the narrowest place in the middle Atlantic between Cape Palmas, on the west coast of Africa, and Cape Silo Roque. on the east coast of South America.
By the protrusion of the two continents in the equatorial zone the Atlantie is divided into two basins, the North and the South Atlantic.
The area of the Atlantic is about 30,000.000 square miles, without counting the seas which are branches of it: including these the area is not far from 35,000.000 square miles. The east ern and western borders are irregular in outline, but are peculiarly parallel. The main groups of islands in the Atlantic are the Arctic group, Iceland and Greenland at the north, the British Isles at the northeast, Newfoundland at the northwest, and the West Indies in the west central part. Two pairs of great inland seas projecting from the North Atlantic cut into the two continents on either side—the Baltic and the Mediterranean on the eastern side, and Hudson Bay and the Gulf of Mexico on the western side.
The only great embayment along the shores of the South Atlantic is the Gulf of Guinea. The Atlantic, including all its connecting inland seas, receives most of the drainage of north eastern, central. and southern North America. practically the whole of South America, most of Europe, except the eastern portion ( Volga), end most of Africa except the southeastern part (Zambezi).
Tun ATLANTIC BASIN. The Atlantic Basin deepens to a depth of about 13,000 feet, usually within a distance of 200 or 300 miles from the eoast-line, and this may he taken as the average depth of the ocean floor beneath the water sur face between latitude 50° N. and 50° S. To the northward of latitude 50° N. the depth of the floor is much less, ranging from only about 6500 to 13,000 feet, and this same highland ex tends southward, mainly as a comparatively narrow ridge, along the whole length of the ocean floor. approximately midway between the Eastern and Western continents. On either side the bottom sinks to depths of about 16,000 feet. In the South Atlantic this submarine plateau is known as the Challenger Ridge. There are a number of depressions in the ocean floor, the chief of which are those eastward of the United States, approximately in the longi tude of Newfoundland. with a depth of 20,000 feet; northward of Porto Rieo, 19,700 to 27,300 feet; and one eastward of Cape Sao Roque, 19,700 to 20,700 feet. The temperature on the ocean floors is about 35° F. in the North At lantic, to 37° in the equatorial regions, 32° to 34° in the western part of the South Atlantic, and 34° to 36°' in the eastern part. The average temperatures of the ocean surface decrease in general from 80°-82° in the equatorial region to 52° in latitude 50°-60° N., and 32° in latitude 75° N., and 41° in latitude 47° S., and 32° in latitude 55° S. The surface temperatures follow the changes in atmospheric temperature. but vary much less in amount. The decrease in temperature with the depth of the water is, in lower latitudes, very rapid for a short distance below the surface; but below a depth of from 1800 to 2400 feet the change in temperature is slight.