Atlantic Ocean

Ocean lying between Europe and Africa to the east and the Americas to the west; area of basin 81,500,000 sq km/31,500,000 sq mi; including the Arctic Ocean and Antarctic seas, 106,200,000 sq km/41,000,000 sq mi. It is generally divided by the Equator into the North Atlantic and South Atlantic. It was probably named after the legendary island continent of Atlantis. The average depth is 3 km/2 mi; greatest depth is at the Milwaukee Depth in the Puerto Rico Trench 8,648 m/28,374 ft. The Mid-Atlantic Ridge, of which the Azores, Ascension, St Helena, and Tristan da Cunha form part, divides it from north to south. Lava welling up from this central area annually increases the distance between South America and Africa. The North Atlantic is the saltiest of the main oceans and has the largest tidal range.

Currents The trade winds, which determine the course of the ocean currents, have their origin in high-pressure areas in the centre of both the North and South Atlantic. They produce a warm equatorial current which divides and flows south as the Brazil current, and north through the Caribbean Sea and Gulf of Mexico, emerging as the Gulf Stream, which has an enormous warming influence on the climate of northwest Europe. A cold current flows south from the Arctic Ocean and, as the Labrador current, passes beneath the Gulf Stream off the Newfoundland Grand Banks. Between 40° and 80° west, and 25° and 30° north, there is an area of calm occupied by the Sargasso Sea, in which float extensive banks of weed.

Fishing Herring- and cod-fishing form important industries on both the American and European shores of the North Atlantic, particularly in the shallow waters of sandbanks such as Grand Banks off Newfoundland. However, the Newfoundland cod fishery was halted in 1992 because of diminishing cod stocks attributed to overfishing.

Islands and drainage Continental islands are numerous, including the British Isles, the West Indies, Newfoundland, and the Falklands; among the comparatively few oceanic islands are Iceland, the Azores, Ascension, Tristan da Cunha, Bermuda, the Canaries, the Cape Verde Islands, Madeira, Fernando Noronha, Trindade, Gough Island, and St Helena. The Atlantic Ocean receives the drainage of almost all Western Europe, most of Africa, North America east of the Rocky Mountains, and South America east of the Andes. The chief river systems flowing into it are those of the Loire, Tagus, Senegal, Niger, Congo, St Lawrence, Mississippi, Orinoco, Amazon, and Río de La Plata.

Temperature and salinity The lower waters to the west of the Mid-Atlantic Ridge are at a temperature of 1°C whereas to the east they are 2.5°C. The continental shelf all round the Atlantic Ocean is narrow and falls away in a steep slope. The surface temperature varies from about 30°C at the Equator to 4°C in the north and south temperate regions, and the lower water temperatures average about 1-2°C. The water is saltiest in the trade-wind regions, decreasing in the belt of equatorial calms, always increasing in salinity below the surface.

Navigation The Atlantic is heavily used by shipping, and the chief danger to navigation is the presence of floating ice, which is carried north from the Antarctic to 38° south, and south from the Arctic to 40° north, thus interfering with the route between northern Europe and North America. There are now numerous submarine cables which span the Atlantic.