The
Indian Ocean is the third largest of the world's
oceanic divisions, covering about 20% of the
water on the
Earth's surface.
It is bounded on the north by
South Asia (including
India, after which it is named); on the west by
Africa; on the east by
Indochina, the
Sunda Islands, and
Australia; and on the south by the
Southern Ocean (or, traditionally, by
Antarctica). One component of the all-encompassing
World Ocean, the Indian Ocean is delineated from the
Atlantic Ocean by the
20° east meridian running south from
Cape Agulhas, and from the
Pacific by the
147° east meridian. The northernmost extent of the Indian Ocean is approximately
30° north in the
Persian Gulf. The Indian Ocean has asymmetric
ocean circulation. This ocean is nearly 10,000 kilometres (6,200 mi) wide at the southern tips of Africa and Australia; its area is 73,556,000 square kilometres (28,400,000 mi²), including the
Red Sea and the
Persian Gulf.
The ocean's volume is estimated to be 292,131,000 cubic kilometres (70,086,000 mi³).
Small islands dot the continental rims.
Island nations within the ocean are
Madagascar, the world's fourth largest island;
Comoros;
Seychelles;
Maldives;
Mauritius; and
Sri Lanka. The archipelago of
Indonesia borders the ocean on the east. 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 successfully dominated most of it until the early 1800s when the
United Kingdom controlled much of the surrounding land.
The Indian Ocean, not including the
Antarctic region.
Geography
The African, Indian, and Antarctic crustal
plates converge in the Indian Ocean at the
Rodrigues Triple Point. 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 kilometres (600 mi). The average depth of the ocean is 3,890 metres (12,760 ft). Its deepest point, is in the
Java Trench. 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 Organisation 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. In Australia the Southern Ocean is considered to comprise all of the ocean south of the continent. This is obviously out of step with prevailing views in the rest of the world. The Indian Ocean remains the third-largest of the world's five oceans.
Major choke points include
Bab el Mandeb,
Strait of Hormuz, the
Lombok Strait, the
Strait of Malacca and the
Palk Strait. Seas include
Gulf of Aden,
Andaman Sea,
Arabian Sea,
Bay of Bengal,
Great Australian Bight,
Laccadive Sea,
Gulf of Mannar,
Mozambique Channel,
Gulf of Oman,
Persian Gulf,
Red Sea, and other tributary water bodies. It is artificially connected to the
Mediterranean Sea via the
Suez Canal, accessible via the Red Sea.
Climate
The climate north of the
equator is affected by a
Monsoon climate. Strong north-east 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 are generally 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. The Indian Ocean is the warmest ocean in the world.
Hydrology
Among the few large rivers flowing into the Indian Ocean are the
Zambezi,
Shatt al-Arab,
Indus,
Ganges,
Brahmaputra,
Jubba 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 anticlockwise, constitute the dominant flow pattern. During the winter monsoon, however, currents in the north are reversed. Deep water 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 south-western 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.
Sub surface features
As the youngest of the major oceans it has active spreading ridges that are part of the worldwide system of
mid-ocean ridges :-
The
Ninety East Ridge runs north-south at
meridian 90E, dissecting the Indian Ocean into eastern and western halves. Another submerged mountain range runs approximately north-south between the
Atolls of the Maldives and the
Chagos Archipelago.
The
Kerguelen Plateau is a large submerged continent, of volcanic origin, in the southern Indian Ocean.
The
Mascarene Plateau is 2000 km long undersea plateau that lies east of
Madagascar.
Economy
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 oil fields 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 fringe 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 and ship
pollution threatens the
Arabian Sea,
Persian Gulf, and
Red Sea,
History
The world's earliest civilizations in
Mesopotamia (beginning with
Sumer),
ancient Egypt, and the
Indian subcontinent (beginning with the
Indus Valley civilization), which began along the valleys of the
Tigris-
Euphrates,
Nile and
Indus rivers respectively, had all developed around the Indian Ocean. Civilizations soon arose in
Persia (beginning with
Elam) and later in
Southeast Asia (beginning with
Funan). 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 AD 70.
From 1405 to 1433, Admiral
Zheng He led large fleets of the
Ming Dynasty on several voyages to the Western Ocean (
Chinese name for the Indian Ocean) and reached the coastal country of
East Africa (see
Zheng He for reference).
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 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 people were left homeless.
Culture and literature
The Indian Ocean is known as
Ratnakara in the ancient
Sanskrit literature. Ratnakara means
"the maker(creator) of pearls".
Major ports and harbours
Mumbai is the chief Indian trading port on the coast of Indian Ocean. It is often known as "The Gateway of India". The port of Kochi from the Southern Indian is known as "The Queen Arabian Sea". It is the finest natural harbour of India. Kolkata and Chennai are other important ports of India. They control the Indian goods flowing towards the east. Aden is the important Arabian port controled by the country of Yemen. Perth is the important Australian port.
See also
