Atlantic Ocean

The atlantic ocean forms a broad s-shape from the Arctic Sea to the north and from Antarctica to the south. North America and South America are to the west; Europe and Africa are to the east. It is about half the size of the Pacific Ocean and slightly larger than the Indian Ocean. It covers 31,800,000 square miles (36,000,000 square kilometers) or 16 percent of the Earth's surface. If marginal seas are included, the coverage is nearly 20 percent. The ocean's principle marginal seas are the Caribbean Sea, the Gulf of Mexico, and the Hudson and Baffin bays to the west; the Arctic, Greenland, and Norwegian seas to the North; the Baltic, North, Mediterranean, and Black Seas to the east; and the Weddell Sea to the south. The Atlantic Ocean proper refers to the ocean minus its marginal seas.

The equator divides the Atlantic Ocean into the North Atlantic and the South Atlantic. Drake Passage (between the island of Tierra del Fuego and Antarctica) and the Magellan Strait (between Tierra del Fuego and South America) connects the South Atlantic to the Pacific Ocean. A broad stretch of water separating Africa and Antarctica connects the South Atlantic to the Indian Ocean. The North Atlantic's connection to the Pacific Ocean follows a circuitous series of straits among the northern Canadian islands to the Arctic Sea and thence to the Bering Strait.

Plate tectonics have given rise to the general topography of the seafloor. The gigantic north-south trending Mid-Atlantic spreading ridge makes up about one-third of the sea bottom and divides the Atlantic Ocean rather evenly into western and eastern halves. The ridge in most places rises to within about 1.5 miles (2.5 kilometers) of the surface and occasionally breaches the surface to form prominent oceanic islands: Iceland, the Azores, Ascension, St. Helena, and Tristan da Cuhna. On either side of the ridge are abyssal plains. The plains extend from the base of the mid-ocean ridge to the base of adjoining continents. The name “plain” implies that this part of the seafloor is a monotonous, uninteresting place. Actually, abyssal plains are remarkable for their deep sediments and life forms. On the landward sides of the plains, the sea bottom rises gently landward as continental shelves (submerged portions of continents). The average depth of abyssal plains is about 4 miles (6.5 kilometers). The ocean's average depth (without its marginal seas) is about 2.5 miles (4 kilometers), owing mainly to the Atlantic Ocean's broad, shallow continental shelves, which make up 13 percent of the Atlantic Ocean proper. The greatest depth (28,224 feet or 8,605 meters) is Milwaukee Deep, in the Puerto Rico Trench, north of Puerto Rico.

South Georgia is an island in the South Atlantic Ocean, about 1,300 kilometers east of the Falkland Islands.

Available solar energy, which decreases with increasing latitude, affects the ocean's climate as well as its temperature and salinity levels. The high sun [Page 80]angles of the equatorial latitudes create warm tropical waters, a belt of low surface pressure, convergent trade winds, and convective thunderstorms. Salinity levels in this zone are especially low where large rivers—such as the Amazon, Orinoco, Niger and Congo Rivers—empty freshwater from the heavy rains into the sea. Moreover, the broad extent of tropical waters in the North Atlantic serve as the repository of heat energy that feeds an annual supply of tropical storms and hurricanes there.

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