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Atlantic Ocean

The large body of sea water separating the continents of North and South America in the west from Europe and Africa in the east and extending south from the Arctic Ocean to the continent of Antarctica. The Atlantic is the second largest ocean water body and in area covers nearly one-fifth of the Earth's surface. The two major divisions, North and South Atlantic oceans, have the Equator as the common boundary. The North Atlantic, because of projecting land areas and island arcs, has numerous subdivisions. These include three large mediterranean-type seas, the Mediterranean Sea, the Gulf of Mexico plus Caribbean Sea, and the Arctic Ocean; two small mediterranean-type seas, the Baltic Sea and Hudson Bay; and four marginal seas, the North Sea, English Channel, Irish Sea, and Gulf of St. Lawrence. Parts of the Atlantic are given special names but lack precise boundaries, such as the Bahama Sea, Irminger Sea, Labrador Sea, and Sargasso Sea.

The mean depth of the Atlantic Ocean is 12,960 ft (3868 m), and its volume is 76,300,000 mi3 (318,000,000 km3). Broad shelves with depths less than 660 ft (200 m) are found in the region of the North Sea and the British Isles, on the Grand Banks of Newfoundland, and off the coasts of northeastern South America and Patagonia. The Mid-Atlantic Ridge, which extends from the Arctic Ocean to 55°S, is less than 9800 ft (3000 m) beneath the surface and is characterized by a pronounced relief. It separates the east and west Atlantic troughs, both of which have relatively uniform relief.

Three marked east-west ridges—the Greenland-Scotland Ridge in the North Atlantic and the Walvis and Rio Grande Ridges in the South Atlantic—and several less-conspicuous east-west rises separate the two Atlantic troughs into a series of basins including the West European, Canary, and Angola in the eastern Atlantic and the North American, Brazilian, and Argentine basins in the western Atlantic.

Islands in the Atlantic are mostly of volcanic origin. The Bermudas are the northernmost coral reefs, rising from an old submarine volcanic cone. Some islands, such as the British Isles, are continental in character. Oceanic islands

The primary circulation of surface winds over the Atlantic Ocean is characterized by a zonal distribution pattern oriented in an east-west direction. The greatest storm frequency, more than 30% in winter, is in the zone of the prevailing westerlies. Air temperatures also follow a zonal pattern of distribution. They are lower in the South Atlantic than in the North Atlantic, and lower in the tropics and subtropics over the eastern Atlantic, than they are in the same latitudes over the western Atlantic. Maximum precipitation occurs in the doldrum zone (80 in. or 2000 mm/year). Precipitation also is relatively great in the zone of westerlies but is low in the trade-wind zones.

Sea ice is formed in the northernmost and southernmost parts of the Atlantic Ocean. From these areas drift ice moves equatorward into neighboring regions where it becomes a hazard to sea traffic and limits fishing. Many icebergs drift southward into the sea lanes of the North Atlantic. Most of these have their origin in the valley glaciers of western Greenland. Icebergs generally drift south of the Grand Banks, and some are known to have drifted southeast of Bermuda. In the South Atlantic large, tabular icebergs separate from the Antarctic ice shelf and drift northward. Iceberg Sea ice

Surface currents in the Atlantic Ocean flow in much the same direction as the prevailing surface winds . Deflections from these directions are caused by the bottom topography and the latitude or increased effect of Coriolis forces. The fairly constant flow of the North and South Equatorial currents is sustained largely by the trade winds. As a result, warm water is piled up along the poleward borders of these currents and on the western sides of the Atlantic Ocean.Ocean Ocean circulation

The surface water in certain areas takes on a particularly high density in winter under the influence of climatic conditions. These water masses sink to a depth where the surrounding waters have a corresponding density and then spread out at that level. At the same time they are constantly mixing with the surrounding waters. In this way a multistoried stratification arises. Compared with that of the Indian and Pacific oceans, the deep circulation in the Atlantic Ocean is very vigorous, and the deeper water is therefore rich in oxygen. The abundance of nutrients permits a greater rate of organic production where the nutrient-rich waters nearly reach the surface, as in the Antarctic waters. Seawater Seawater fertility

The semidiurnal tidal form predominates in the Atlantic Ocean. The mean tidal range is about 3.3 ft (1 m) in the open ocean, but it decreases to 6.3 in. (16 cm) off Rio Grande do Sul in southern Brazil and to 3.5 in. (9 cm) off Puerto Rico. Tidal ranges increase beyond broad shelves under favorable physical conditions. The tides of the mediterranean and marginal seas are cooscillations of the tides of the Atlantic Ocean.

The Atlantic Ocean, especially the North Atlantic, is by far the most important bearer of the world's sea traffic. Favorable trend include increased transportation capacities for handling bulk goods, regular weather observations for the safety of air and sea traffic by weather ships in selected positions, and the observation and reporting of drifting icebergs by the International Ice Patrol. Communication facilities, including telegraph and telephone cables and radio stations, have been improved and increased in number.

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From McGraw-Hill Concise Encyclopedia of Environmental Science. The Content is a copyrighted work of McGraw-Hill and McGraw-Hill reserves all rights in and to the Content. The Work is © 2008 by The McGraw-Hill Companies, Inc.
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