Introduction to The Atlantic Ocean
Atlantic Ocean, the world's second largest body of water. Its area, including all connecting seas and gulfs, is about 33,420,000 square miles (86,557,000 km2), almost 24 per cent of the world's oceanic area. The main body has an area of nearly 32,000,000 square miles (82,880,000 km2).
The Atlantic is bounded on the east by Europe and Africa, and on the west by the Americas. To the north, it merges with the Arctic Ocean; to the south, it extends to Antarctica. The Equator is the dividing line between the North and South Atlantic.
Among the principal bodies of water adjoining the Atlantic are the Gulf of St. Lawrence, the Gulf of Mexico, and the Caribbean Sea on the west and the Baltic, North, and Mediterranean seas on the east.
The Ocean Floor
Like all ocean bottoms, the Atlantic's is extremely uneven, with submarine ridges, deep basins and canyons, and isolated underwater peaks, or seamounts. The Mid-Atlantic Ridge, longest of the underwater ranges, runs in an S-shaped curve for about 10,000 miles (16,000 km), approximately midway between the continents on the east and the west. The ridge lies generally one to two miles (1,600 to 3,200 m) beneath the ocean's surface.
On both sides of the Mid-Atlantic Ridge are broad, deep basins. Among those west of the ridge are the Labrador, North American, Guiana, Brazilian, and Argentine basins. Those east of the ridge include the Norwegian, West European, Canary, Cape Verde, Guinea, Angola, and Cape basins.
Between the principal basins are prominent submarine ridges, or rises. Though shorter and less prominent than the Mid-Atlantic Ridge, they nevertheless have pronounced relief. For example, the Rio Grande Rise off southern Brazil lies some 2,000 to 12,000 feet (600 to 3,600 m) beneath the water's surface and separates the Brazilian and Argentine basins, which are each about 18,000 feet (5,500 m) deep.
The Puerto Rico Trench, deepest of the Atlantic's trenches, stretches in a narrow arc north of Hispaniola and Puerto Rico. It reaches a depth of 28,232 feet (8,605 m). The South Sandwich Trench, just north of the South Sandwich Islands, has a maximum depth of 27,313 feet (8,325 m).
About three-fourths of the ocean floor is covered with deep-sea sediments. Most of these are oozes, soft sediments made up of shells and skeletons of various microorganisms. In the basins on the American side of the Mid-Atlantic Ridge are also large bottom areas of red clay.
The continental shelf, the shallow underwater extension of the continents, reaches seaward about 250 miles (400 km) southwest of England, 300 miles (480 km) southeast of Newfoundland, and 400 miles (640 km) off southern Argentina. Along Africa, however, the shelf is much narrower.
Beyond the continental shelf is the continental slope, where the ocean floor drops steeply. In some areas deep, narrow canyons cut into the continental shelf and slope. One of these is the Hudson Canyon, which leads to New York City.
Currents and Tides
Circulation of surface waters is generally clockwise in the North Atlantic and counterclockwise in the South Atlantic. There are, however, many exceptions to the general circulation, particularly along the coasts.
In the North Atlantic, the strongest current is the warm Gulf Stream, which forms in the Gulf of Mexico. It flows northeastward off the United States coast, encounters the cold Labrador Current from the north, and continues across the Atlantic as the North Atlantic Current, or Drift. It continues northward as the Irminger and Norwegian currents.
West of Spain, part of the North Atlantic Current turns southward, flows along the "bulge" of Africa as the Canaries Current, then turns westward as the North Equatorial Current. This current crosses the ocean; part of its water reaches the Gulf of Mexico. South of the North Equatorial Current, running in the opposite direction, is the Equatorial Countercurrent. In the western North Atlantic, around Bermuda, is the Sargasso Sea, a calm area named for its masses of floating sargassum weed.
In the South Atlantic, the cold Benguela Current flows northward up to the coast of Africa, turns west near the Equator, and flows westward as the warm South Equatorial Current. Near the South American coast, part of the current swings southward to become the Brazil Current, which runs down the coast of South America to about 40° South latitude. Here, it meets the cold Falkland Current. Flowing eastward across the South Atlantic in a broad belt around 50° S. is the West Wind Drift.
Most areas bordering the Atlantic have relatively high tides. Occurring with the tides in some narrow river mouths, particularly those with shallow estuaries, are tidal bores—advancing walls of water. The highest tides in the world are in the Bay of Fundy, Canada. Here, the range between high tide and low tide is as much as 60 feet (18 m).
Fisheries
The Atlantic is rich in food fish, particularly in the shallow waters of the continental shelf. Here, conditions are favorable to the growth of plankton, the microorganisms that form the basic food of marine life.
The northeast Atlantic Ocean is by far the leading fishery. Especially important are the North and Norwegian seas. Species taken in large amounts here include herring, cod, mackerel, whiting, pollock, and capelin. Overfishing has depleted some formerly abundant Atlantic fisheries, including the Grand Banks, off Newfoundland.
Whaling was formerly important in far North Atlantic and adjacent Arctic waters. As the supply here became depleted, the industry shifted to South Atlantic and other Antarctic waters.
Islands
The Atlantic has large stretches of open water without islands. There are no archipelagoes consisting of thousands of islands, such as those found in the Pacific. Most of the large islands, such as the British Isles, Greenland, Newfoundland, and the main islands of the Greater Antilles, were once connected with the continents.
Other islands, especially those far out at sea, were formed by successive eruptions of volcanic material far below the water's surface. Only the tops of these underwater mountains and high plateaus are exposed as islands. Examples of such islands in the North Atlantic are the Faeroe Islands, the Azores, Madeira, the Canary Islands, the Cape Verde Islands, and São Tomé. Volcanic islands of the South Atlantic include St. Helena, Ascension, the Tristan da Cunha group, and the South Sandwich Islands. In contrast to these usually high-peaked islands, Bermuda and some of the West Indies are flat coral islands.
The world's largest volcanic island is Iceland. It has many signs of continuing volcanic activity, such as hot springs, geysers, and active volcanoes. Another volcanic island, Surtsey, emerged off the coast of Iceland in 1963.