Atlantic Ocean (so called either from Mount Atlas or from the fabulous island of Atlantis), separating the Old from the New World, Europe and Africa being on the E., and North and South America on the W. Its greatest width is about 5000 miles, but between Brazil and the African coast the distance is only about 1600 miles. It is in open communication with both the Arctic Ocean and Antarctic or Southern Ocean. The North Atlantic, stretching from 70° N. to the equator, has an area of 14,000,000 sq. m. It communicates with many inclosed or partially inclosed seas, such as the Caribbean Sea, Gulf of Mexico, and Hudson Bay on the west, the Baltic, North Sea, Mediterranean, and Black Sea on the east. The South Atlantic from the equator to 40° S. has an area of 10,100,000 sq. m.; if it be supposed to extend through the great Southern Ocean as far as the Antarctic circle, its area is 16,700,000 sq. m.
Towards the centre of the North Atlantic, between Africa and North America, and in the centre of the South Atlantic, between Africa and South America, there are anticyclonic areas of high atmospheric pressure (over 30 inches), out of which winds blow in all directions to surrounding regions where the pressure is less. The positions of these high-pressure areas and the winds that blow out from them, determine the great oceanic currents and the positions of the Sargasso seas, for the winds everywhere determine and control the movements of the surface waters. The SE. and NE. trades drive the heated surface waters of the tropics before them, and eventually produce the Equatorial current, which on reaching Cape St Roque bifurcates, one branch becoming the Brazil current of the South Atlantic, the other and larger branch passing on to the Caribbean Sea and Gulf of Mexico, finally issuing from the latter by the Strait of Florida, forming the Gulf Stream (q.v.), the greatest and most important of all oceanic currents. A cold Arctic current passes southward along the shores of Greenland, and unites off Cape Farewell with the Davis Strait current, forming the Labrador current, which passes along the west coast of America, and passes beneath the Gulf Stream to the south of the banks of Newfoundland. Icebergs are carried as far south as 40° N. in the northern and as far north as 38° S. in the southern hemisphere. In the equatorial regions, the surface water has generally a temperature ranging from 70° to 84° F.; the temperature decreases as the depth increases. The warm water is a relatively thin stratum, the greater part of ocean water having a temperature below 40° F. It is ice-cold in the Atlantic at the bottom even beneath the equator. The water of the Atlantic contains the least salt towards the poles and in the equatorial belt of calms. The saltest water (density over 1.0275) is found in the centre of the trade-wind regions. The salinity of the deeper waters is considerably below the average of the surface. The average depth of the Atlantic is between 2 and 3 miles (2200 fathoms). A low submarine ridge runs clown the centre, from north to south, with an average depth of about 1700 fathoms over it. On either side of this ridge there are, both in the North and South Atlantic, depths of between 3000 and 4000 fathoms. The greatest depth yet met with is just north of the Virgin Islands (4561 fathoms). The surface waters from equator to poles swarm with all kinds of pelagic plants and animals, many of which emit phosphorescent light, producing what is known as luminosity of the sea. In the centre of the North Atlantic, in the so-called Sargasso Sea, there are enormous floating banks of gulf weed (Sargassum bucciferum), on which a large number of peculiar animals live. Life has been found to exist at all depths in the Atlantic, but it becomes less abundant as greater depths and a greater distance from continental shores are reached. There are relatively few oceanic islands. Iceland, the Azores, St Paul's Rocks, Ascension, and the Tristan da Cunha group all rise from the central elevation, and are all of volcanic origin. Jan Mayen rises from the deep water of the Norwegian Sea. The coral group of Bermudas rises from the deep water of the Western North Atlantic. Off the west coast of Africa are the Canaries, Cape Verds, and Madeira. In the South Atlantic, to the west of the central ridge, are Fernando Noronha and Trinidad, and to the east of the central ridge, St Helena. There are numerous continental islands, such as the British Isles, Newfoundland, the West Indies, the Falklands, and others. The most civilised nations of the world inhabit the shores of the Atlantic, and it is the great commercial highway of the world. It has been sounded in all directions, and the nature of its bed is so well known that telegraph cables can be laid across it with great certainty of success. In the neighbourhood of some continental shores, and around some of the volcanic cones which rise from the floor of the ocean, there are occasionally very steep slopes; but as a rule, the bed of the ocean is a widespread, gently undulating plain.