Indian Ocean
This article is about the water body. For the Indian fusion music band, see Indian Ocean (band).The
Indian Ocean (
Hindi: हिन्द महासागर) is the third largest body of water in the world, covering about 20% of the Earth's water surface. It is bounded on the north by
Southern Asia (the
Indian subcontinent); on the west by the
Arabian Peninsula and
Africa; on the east by the
Malay Peninsula, the
Sunda Islands, and
Australia; and on the south by the
Southern Ocean. It is separated from the
Atlantic Ocean by the 20° east
meridian running south from
Cape Agulhas,
[Limits of Oceans and Seas. International Hydrographic Organization Special Publication No. 23, 1953.] and from the
Pacific by the 147° east meridian. The northernmost extent of the Indian Ocean is approximately 30°north
latitude in the
Persian Gulf. This ocean is nearly 10,000 kilometers (6,200 mi) wide at the southern tips of Africa and Australia; its area is 73,556,000 square kilometers (28,400,000 mi²), including the
Red Sea and the
Persian Gulf.
The ocean's volume is estimated to be
292,131,000 cubic kilometers (70,086,000 mi
3). Small islands dot the continental rims.
Island nations within the ocean are
Madagascar (formerly Malagasy Republic), the world's fourth largest island;
Comoros;
Seychelles;
Maldives;
Mauritius; and
Sri Lanka.
Indonesia borders it. The ocean's importance as a transit route between
Asia and Africa has made it a scene of conflict. Because of its size, however, no nation had successfully dominated most of it until the early 1800s when
Britain controlled much of the surrounding land. After
World War II, the ocean has been dominated by
India and Australia.
The African, Indian, and Antarctic crustal plates converge in the Indian Ocean. Their junctures are marked by branches of the Mid-Oceanic Ridge forming an inverted Y, with the stem running south from the edge of the continental shelf near
Mumbai,
India. The eastern, western, and southern basins thus formed are subdivided into smaller basins by ridges. The ocean's continental shelves are narrow, averaging 200 kilometers (125 mi) in width. An exception is found off Australia's western coast, where the shelf width exceeds 1,000 kilometers (600 mi). The average depth of the ocean is 3,890 meters (12,760 ft). Its deepest point, in the
Java Trench, is estimated to be 7,450 meters (24,442 ft) below sea level. North of 50° south latitude, 86% of the main basin is covered by
pelagic sediments, of which more than half is
globigerina ooze. The remaining 14% is layered with
terrigenous sediments. Glacial outwash dominates the extreme southern latitudes.
A spring 2000 decision by the
International Hydrographic Organization delimited a
fifth world ocean, stripping the southern portions of the Indian Ocean. The new ocean extends from the coast of Antarctica north to 60°south latitude which coincides with the Antarctic Treaty Limit. The Indian Ocean remains the third-largest of the world's five oceans.
Major chokepoints include
Bab el Mandeb,
Strait of Hormuz,
Strait of Malacca, southern access to the
Suez Canal, and the
Lombok Strait. Seas include
Andaman Sea,
Arabian Sea,
Bay of Bengal,
Great Australian Bight,
Gulf of Aden,
Gulf of Oman,
Laccadive Sea,
Mozambique Channel,
Persian Gulf,
Red Sea,
Strait of Malacca, and other tributary water bodies
Climate
The climate north of the
equator is affected by a
monsoon wind system. Strong northeast winds blow from October until April; from May until October south and west winds prevail. In the
Arabian Sea the violent monsoon brings rain to the Indian subcontinent. In the southern hemisphere the winds generally are milder, but summer storms near Mauritius can be severe. When the monsoon winds change, cyclones sometimes strike the shores of the Arabian Sea and the
Bay of Bengal.
Hydrology
|
Bathymetric map of the Indian Ocean |
Among the few large rivers flowing into the Indian Ocean are the
Zambezi,
Arvandrud/Shatt-al-Arab,
Indus,
Ganges,
Brahmaputra, and
Ayeyarwady River. Currents are mainly controlled by the monsoon. Two large circular currents, one in the northern hemisphere flowing clockwise and one south of the equator moving counterclockwise, constitute the dominant flow pattern. During the winter monsoon, however, currents in the north are reversed. Deepwater circulation is controlled primarily by inflows from the
Atlantic Ocean, the
Red Sea, and Antarctic currents. North of 20° south latitude the minimum surface temperature is 22 °C (72 °F), exceeding 28 °C (82 °F) to the east. Southward of 40° south latitude, temperatures drop quickly. Surface water
salinity ranges from 32 to 37 parts per 1000, the highest occurring in the Arabian Sea and in a belt between southern Africa and southwestern Australia. Pack ice and icebergs are found throughout the year south of about 65° south latitude. The average northern limit of icebergs is 45° south latitude.
The Indian Ocean provides major sea routes connecting the
Middle East, Africa, and
East Asia with
Europe and the
Americas. It carries a particularly heavy traffic of
petroleum and petroleum products from the oilfields of the Persian Gulf and Indonesia. Large reserves of hydrocarbons are being tapped in the offshore areas of
Saudi Arabia,
Iran, India, and western Australia. An estimated 40% of the world's offshore oil production comes from the Indian Ocean. Beach sands rich in heavy
minerals, and offshore placer deposits are actively exploited by bordering countries, particularly India,
South Africa, Indonesia,
Sri Lanka, and
Thailand.
The warmth of the Indian Ocean keeps
phytoplankton production low, except along the northern fringes and in a few scattered spots elsewhere; life in the ocean is thus limited.
Fishing is confined to subsistence levels. Its fish are of great and growing importance to the bordering countries for domestic consumption and export. Fishing fleets from
Russia,
Japan,
South Korea, and
Taiwan also exploit the Indian Ocean, mainly for
shrimp and
tuna.
Endangered marine species include the
dugong,
seals,
turtles, and
whales; oil
pollution in the Arabian Sea,
Persian Gulf, and
Red SeaThe three earliest civilizations of
Sumer,
ancient Egypt and the
Indus Valley civilization along the valleys of the
Tigris-
Euphrates,
Nile and
Indus rivers, as well as the civilizations in
Southeast Asia, had all developed around the Indian Ocean. During
Egypt's first dynasty (c. 3000 BC), sailors were sent out onto its waters, journeying to
Punt, thought to be part of present-day
Somalia. Returning ships brought gold and myrrh. The earliest known maritime trade between
Mesopotamia and the Indus Valley (c. 2500 BC) was conducted along the Indian Ocean.
Phoenicians of the late
3rd millennium BC may have entered the area, but no settlements resulted.
The Indian Ocean is far calmer and thus opened to trade earlier than the Atlantic or
Pacific Oceans. The powerful monsoons also meant ships could easily sail west early in the season, then wait a few months and return eastwards. This allowed Indonesian peoples to cross the Indian Ocean to settle in Madagascar.
In the second or first century BC Eudoxus of
Cyzicus was the first
Greek to cross the Indian Ocean.
Hippalus is said to have discovered the direct route from
Arabia to India around this time. During the first and second centuries intensive
trade relations developed between
Roman Egypt and the
Tamil kingdoms of the
Cheras,
Cholas and
Pandyas in
Southern India. Like the Indonesian peoples above, the western sailors used the monsoon to cross the ocean. The unknown author of the
Periplus of the Erythraean Sea describes this route and the ports and trade goods along the coasts of Africa and India around 70 AD.
In 1497,
Vasco da Gama rounded the
Cape of Good Hope, and became the first European to sail to India. The European ships, armed with heavy cannon, quickly dominated trade.
Portugal at first attempted to achieve pre-eminence by setting up forts at the important straits and ports. But the small nation was unable to support such a vast project, and they were replaced in the mid-17th century by other European powers. The
Dutch East India Company (1602-1798) sought control of trade with the East across the Indian Ocean.
France and Britain established trade companies for the area. Eventually Britain became the principal power and by 1815 dominated the area.
The opening of the
Suez Canal in 1869 revived European interest in the East, but no nation was successful in establishing trade dominance. Since World War II the United Kingdom has withdrawn from the area, to be only partially replaced by India, the
USSR, and the
United States. The last two have tried to establish hegemony by negotiating for naval base sites. Developing countries bordering the ocean, however, seek to have it made a "zone of peace" so that they may use its shipping lanes freely, though the United Kingdom and United States maintain a military base on
Diego Garcia atoll in the middle of the Indian Ocean.
On
December 26,
2004, the countries surrounding the Indian Ocean were hit by a
tsunami caused by the
2004 Indian Ocean earthquake. The waves resulted in more than 226,000 deaths and over 1 million were left homeless.
*
Calcutta,
India*
Chennai, India
*
Colombo,
Sri Lanka*
Durban,
South Africa*
Jakarta,
Indonesia*
Karachi,
Pakistan*
Fremantle, Western Australia*
Mumbai, India
*
Richards Bay, South Africa
*
Visakhapatnam, India
*
Kochi, India
*
Indian Ocean states
*Braun, D., The Indian Ocean (1983)
*Chandra, S., ed., The Indian Ocean (1987);
*Chaudhuri, K. N., Trade and Civilization in the Indian Ocean (1985);
*Cousteau, Jacques-Yves, and Diole, Philippe, Life and Death in a Coral Sea (1971);
*Cubitt, Gerald, Islands of the Indian Ocean (1975);
*Das Gupta, A., and Pearson, M.N., India and the Indian Ocean (1987);
*Dowdy, W. L., and Trood, R., eds., The Indian Ocean (1985);
*Kerr, A., ed., Resources and Development in the Indian Ocean Region (1981);
*Nairn, A. E., and Stehli, F. G., eds., The Ocean Basins and Margins, Vol. 6: The Indian Ocean (1982);
*Ostheimer, John M., ed., The Politics of the Western Indian Ocean Islands (1975); *Toussaint, Auguste, The History of the Indian Ocean, trans. by June Guicharnaud (1966).
Much of this text is based on public domain text by US Naval Oceanographer at: http://oceanographer.navy.mil/indian.html*
Oceanography Image of the Day , from the Woods Hole Oceanographic Institution
*
NOAA In-situ Ocean Data Viewer Plot and download ocean observations
