Water And Oceanography

Major Subdivisions of the Worlds Oceans



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There are five major subdivisions of the world's oceans; the ocean subdivisions are “basins” (with the exception of the Southern Ocean). Ocean basins cover 71 percent of Earth's surface, or 140 million square miles (361 million sq. kilometers). The saucer-shape of these subdivisions determined the name, basins.

The five main subdivisions are the Pacific Ocean Basin, Atlantic Ocean Basin, Indian Ocean Basin, Southern Ocean Basin and Arctic Ocean Basin. Scientists identify the Pacific, Atlantic, and Indian Oceans as conventional basins because continental masses, or ocean ridges and currents surround them.  The Southern (Antarctic Ocean) is in the Antartic Circumpolar current. The Arctic Ocean is almost landlocked, except between Greenland and Europe. Here's a closer look at the five principal subdivisions.

Pacific Ocean Basin

The Pacific ocean basin is the oldest and largest of the ocean basins. Scientists date the rocks to about 200 million years. Plate tectonics (the unifying theory of geology that describe and explains that all earthquakes, volcanic activity, and mountain-building processes are caused by the gradual motion of rigid slabs of rock, called plates) shaped the basin. The coastal shelf extends to 600 feet (180 meters) and is narrow along North and South America. Asia and Australia coastal shelf is wide.

The East Pacific Rise ranges from the Gulf of California to the southern tip of South America. This is a mid-ocean ridge that rises 7,000 feet (2130 meters) above the ocean floor. The importance of this ridge is magma (molten rock) comes up from Earth's mantle and adds crust to the plates on each side of the rise. Pressure forces the plates apart. This tremendous pressure causes the continental plates to fold into mountain ranges. The oceanic plates form deep trenches (subduction zones – the stresses cause earthquakes and volcano eruptions) This gives the Pacific Ocean the name, “Ring of Fire.”

Atlantic Ocean Basin

This is the second largest of the five oceans and claims 20% of the Earth's surface. It is the first most heavily traveled ocean. The ship traffic between Europe and North America makes it the most studied ocean of all. The name comes from Atlas, the Titan in Greek mythology.

The continental shelves of the Atlantic basin run along the American, African, and European coasts. The debris from the continents collects in these areas.

Submarine ridges and rises extend east-west between the shelves and the Mid-Atlantic Ridge divide the eastern and western ocean floors into basins (abyssal plains). These sub-basins on the American side of the Mid-Atlantic Ridge are 16,400 feet (5,000 meters) deep and cover the following sub=basins: North American Basin, Brazil Basin and the Argentina Basin. The European-African sub-basins are smaller but just as deep. They are the Iberia Basin, Canaries, Cape Verde, Sierra Leone, Guinea, Angola, Cape and Agulhas basins.

There is a break in the ridge at the equator called Romanche furrow. The furrow allows the deep-ocean water a place to flow. This furrow influences currents and temperature of the Atlantic Ocean.

Indian Ocean Basin

This is the third largest ocean of the five subdivisions. Africa is the west boundary; the north boundary is Asia; Australia and Australasian islands are the east boundary; the Southern Ocean constitutes the southern boundary. Unlike the Pacific and Atlantic Oceans, the Indian Ocean does not have a natural boundary that separates it from the Atlantic Ocean. An arbitrary line about 2500 miles (4,020 kilometers) long, connecting Cape Agulhas at the southern end of Africa with Antarctica is the boundary.

The marginal seas included with the Indian subdivision are Adaman Sea, Bay of Bengal, Great Australian Bight, Gulf of Aden, Gulf of Oman, Mozambique Channel, Persian Gulf, Red Sea, and the Strait of Malacca. The depth of the Indian Ocean is 13,800 feet (4,210 meters). The Indian Ocean basin is divided in half by the Mid-Ocean Ridge.

Southern Ocean

In 2000, the International Hydrographic Organization decided to (delimited) a fifth world ocean, the Southern Ocean. It is not a true ocean basin. It extends from the coast of Antarctica north to 60 degrees South latitude. It coincides with the Antarctic Treaty Limit. It is a circumpolar body of water. It encircles the Antarctica continent.

Arctic Ocean Basin

The smallest subdivision, the Arctic Ocean, has a broad shelf north of Eurasia and the narrower shelves of North America and Greenland. The continental shelf underlies the Arctic Ocean. The Arctic Ocean is subdivided further by three ridges, and four basins (deeps).

The Arctic Ocean is ice-covered. At lower latitudes, the ice melts during the summer. At the polar regions, ice cover is permanent.

Pacific, Atlantic, Indian, Southern and Arctic Oceans are the five subdivisions and are considered basins because they are saucer-shaped. The Southern Ocean, as the fifth designation of a subdivision, does not have a basin.

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