Atlantic Ocean

V

Currents

The circulatory system of the surface waters of the Atlantic can be depicted as two large gyres, or circular current systems, one in the North Atlantic and one in the South Atlantic. These currents are primarily wind driven, but are also affected by the rotation of the Earth. The currents of the North Atlantic, which include the North Equatorial Current, the Canaries Current, and the Gulf Stream, flow in a clockwise direction. The currents in the South Atlantic, among which are the Brazil, Benguela, and South Equatorial currents, travel in an anticlockwise direction. Each gyre extends from near the equator to about latitude 45°; closer to the poles are the less completely defined counterrotating gyres, one rotating anticlockwise in the Arctic regions of the North Atlantic and one rotating clockwise near Antarctica in the South Atlantic. Areas of comparatively still water, such as the Sargasso Sea, lie within the gyres. The Gulf Stream brings warm water into the Arctic Ocean, while the East Greenland and Labrador currents bring cold Arctic water into the Atlantic.

The Atlantic receives the waters of many of the principal rivers of the world, among them the St Lawrence, Mississippi, Orinoco, Amazon, Paraná, Congo, Niger, and Loire, and the rivers emptying into the North, Baltic, and Mediterranean seas. Nevertheless, primarily because of the high salinity of outflow from the Mediterranean, the Atlantic is slightly more saline than the Pacific or Indian oceans.

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Temperatures

The Atlantic Ocean may be described as a bed of water colder than 9° C (48° F) —the cold-water sphere—within which lies a bubble of water warmer than 9° C—the warm-water sphere. The warm-water sphere extends between latitude 50° north and latitude 50° south and has an average depth of about 600 m (2,000 ft) from the surface. The most active circulation is found in the uppermost layer of warm water. Below this, circulation becomes increasingly sluggish as the temperature decreases.

Surface temperatures range from 0° C (32° F), found year-round at the Arctic and Antarctic margins, to 27° C (81° F) in the broad belt at the equator. At depths below 2,000 m (6,600 ft), temperatures of 2° C (36° F) are prevalent; in bottom waters, below 4,000 m (13,200 ft), temperatures of -1° C (30° F) are common.

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Marine Resources

The Atlantic Ocean contains some of the world's most productive fisheries, located on the continental shelves and marine ridges off the British Isles, Iceland, Canada (especially the Grand Banks off Newfoundland), and the north-eastern United States. Upwelling areas, in which the nutrient-rich waters of the ocean depths flow up to the surface, as in the vicinity of Walvis Bay off south-western Africa, also have abundant sea life. Herring, anchovy, sardine, cod, flounder, and perch are the most important commercial species. Tuna is taken off north-western Africa and north-eastern South America in increasing numbers. The catch per unit area is much higher in the Atlantic than in the other oceans.

A remarkable example of plant life is found in the Sargasso Sea, an oval section of the North Atlantic lying between the islands of the Caribbean and the Azores and bounded on the west and north by the Gulf Stream. Here extensive patches of brown gulfweed (Sargassum) are found on the relatively still surface waters.

Actively mined mineral resources in the Atlantic include titanium, zircon, and monazite (phosphates of the cerium metals), off the eastern coast of Florida, and tin and iron ore, off the equatorial coast of Africa. The continental shelves and slopes of the Atlantic are potentially very rich in fossil fuels. Large amounts of petroleum are already being extracted in the North Sea and in the Gulf of Mexico-Caribbean Sea region; lesser amounts are extracted off the coast of Africa in the Gulf of Guinea.

See also Ocean and Oceanography: Ocean Currents.