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The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded by Asia on the north, on the west by Africa, on the east by Australia, and on the south by the Southern Ocean (or, depending on definition, by Antarctica). Although generally assumed to be named for India, early European writers referred to the "East Indian" Ocean, the East Indies being the name given by European travellers collectively to India, South East Asia and the Indonesian archipelago.
As one component of the 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 Ocean by the meridian of 146°55' east. The northernmost extent of the Indian Ocean is approximately 30° north in the Persian Gulf. The ocean is nearly 10,000 km (6200 mi) wide at the southern tips of Africa and Australia, and its area is 73,556,000 km² (28,350,000 mi²), including the Red Sea and the Persian Gulf.
The Indian Ocean's volume is estimated to be 292,131,000 km³ (70,086,000 mi³). Small islands dot the continental rims. Island nations within the ocean are Madagascar (the world's fourth largest island), Bahrain, Comoros, Maldives, Mauritius, Seychelles and Sri Lanka. The archipelago of Indonesia and the island nation of Timor-Leste border the ocean on the east.
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 kilometres (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 m (12,762 ft). Its deepest point is Diamantina Deep in Diamantina Trench, at 8,047 m (26,401 ft) deep; also sometimes considered is Sunda Trench, at a depth of 7,258–7,725 m (23,812–25,344 ft). 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.
The major choke points include Bab el Mandeb, Strait of Hormuz, the Lombok Strait, the Strait of Malacca and the Palk Strait. Seas include the 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. The Indian Ocean is artificially connected to the Mediterranean Sea through the Suez Canal, which is accessible via the Red Sea.
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.
Among the few large rivers flowing into the Indian Ocean are the Zambezi, Shatt al-Arab, Indus, Narmada, Ganges, Brahmaputra, Jubba and Irrawaddy River. The ocean's 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.
The Kerguelen Plateau is a small, submerged continent of volcanic origin in the southern Indian Ocean.
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, Pakistan, 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, because 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.
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, 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's relatively calmer waters opened the areas bordering it 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 2nd or 1st 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 1st and 2nd centuries AD 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, as well as the commodities that were traded along various commercial ports on the coasts of the Horn of Africa and India circa 1 AD. Among these trading settlements were Mosylon and Opone on the Red Sea littoral.
In 1497, Portuguese navigator Vasco da Gama rounded the Cape of Good Hope and became the first European to sail to India and later the Far East. The European ships, armed with heavy cannon, quickly dominated trade. Portugal attempted to achieve pre-eminence by setting up forts at the important straits and ports. They dominated trade and discovery along the coasts of Africa, and Asia until the mid 17th century. Later the Portuguese were challenged 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. Spain established a major trading operation in the Philippines and the Pacific. By 1815, Britain became the principal power in the Indian Ocean.
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 was forced to withdraw from the area, to be 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. The United Kingdom and United States maintain a military base on Diego Garcia atoll in the middle of the Indian Ocean.
On 26 December 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.
In the late 2000s, the ocean evolved into a hub of pirate activity. By 2013, attacks off the Horn region's coast had steadily declined due to active private security and international navy patrols.
The Indian Ocean is known as Ratnakara in the ancient Sanskrit literature. Ratnakara means "the mine of gems". It is also called Hind Mahasagar in Hindi and other Indian languages.
Heading roughly clockwise, the states and territories (in italics) with a coastline on the Indian Ocean (including the Red Sea and Persian Gulf) are:
Egypt (Sinai Peninsula), Israel, Jordan, Saudi Arabia, Yemen, Oman, United Arab Emirates, Qatar, Bahrain, Kuwait, Iraq, Iran, Pakistan, India, Maldives, British Indian Ocean Territory, Sri Lanka, Bangladesh, Burma, Thailand, Malaysia, Singapore Indonesia, Cocos (Keeling) Islands,
The Port of Singapore is the busiest port in the Indian Ocean, located in the Strait of Malacca where it meets the Pacific. Mumbai Port is the chief trading port in India on the coast of the Indian Ocean, often known as "The Gateway of India". Chennai Port is the second largest port in India and the busiest on the east coast. Mormugao Port, Panambur, Kochi, Kolkata, Port Blair, Visakhapatnam, Paradip, Ennore, Tuticorin and Nagapattinam are the other major ports in India. South Asian ports include Chittagong in Bangladesh, Colombo, Hambantota and Galle in Sri Lanka, and ports of Karachi, Sindh province and Gwadar, Balochistan province in Pakistan. Aden is a major port in Yemen and controls ships entering the Red Sea. Major African ports on the shores of the Indian Ocean include: Mombasa (Kenya), Dar es Salaam, Zanzibar (Tanzania), Durban, East London, Richard's Bay (South Africa), Beira (Mozambique), and Port Louis (Mauritius). Zanzibar is especially famous for its spice export. Other major ports in the Indian Ocean include Muscat (Oman), Yangon (Burma), Jakarta, Medan (Indonesia), Fremantle (port servicing Perth, Australia) and Dubai (UAE).
Chinese companies are making investments in several Indian Ocean ports, including Gwadar, Hambantota, Colombo and Sonadia. This has sparked a debate about the strategic implications of these investments.
Marginal seas, gulfs, bays and straits of the Indian Ocean include:
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