Indian Ocean

The Indian Ocean, not including the Antarctic region.

The Indian Ocean is the third largest of the world's oceanic divisions, covering about 20% of the water on the Earth's surface.^[1] It is bounded on the north by the Indian subcontinent; on the west by East Africa; on the east by Indochina, the Sunda Islands, and Australia; and on the south by the Southern Ocean (or, depending on definition, by Antarctica). It is the only ocean to be named after a country, i.e., India.^[2][3][4]

As one component of the interconnected global 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 meridian of 146°55' east^[5]. 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).^[6] Small islands dot the continental rims. Island nations within the ocean are Madagascar, the world's fourth largest island; Reunion Island; Comoros; Seychelles; Maldives; Mauritius; and Sri Lanka. The archipelago of Indonesia borders the ocean on the east.

Geography

Bathymetric map of the Indian Ocean

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 metres (12,760 ft). Its deepest point, 7258 meters deep, is in the Java Trench^[7]. 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 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.

Limits

The Indian Ocean is bounded by India's Lakshadweep Islands to the north.

The 3rd edition of the International Hydrographic Organization's (IHO) Limits of Oceans and Seas defines the limits of the Indian Ocean as follows:^[8]

On the North. The Southern limits of the Arabian Sea and the Lakshadweep Sea, the Southern limit of the Bay of Bengal, the Southern limits of the East Indian Archipelago, and the Southern limit of the Great Australian Bight.

On the West. From Cape Agulhas in 20° long. East, Southward along this meridian to the Antarctic Continent.

On the East. From South East Cape, the Southern point of Tasmania down the meridian 146°55'E to the Antarctic Continent.

On the South. The Antarctic Continent.

Note that this definition excludes any marginal waterbodies that are separately defined by the International Hydrographic Organization (such as the Bay of Bengal and Arabian Sea), though these are usually considered to be part of the Indian Ocean.

In 2000 the IHO redefined the Indian Ocean, moving its southern limit to 60°S, with the waters south of that line identified as the Southern Ocean. This new definition has not yet been ratified (a reservation has been lodged by Australia^[9]) though it is in use by the IHO and others. If and when adopted, the 2000 definition will be published in the 4th edition of Limits of Oceans and Seas, restoring the Southern Ocean as originally outlined in the 2nd edition and subsequently omitted from the 3rd edition.

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 ^[10] it has active spreading ridges that are part of the worldwide system of mid-ocean ridges :-

• Carlsberg Ridge
• Southwest Indian Ridge
• Southeast Indian Ridge
• Central Indian Ridge

The Ninety East Ridge runs north-south at meridian 90°E, 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 small 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.

Due to the relatively high traffic of petroleum tankers, piracy off the Somali coast has been rising. This has been a threat to international shipping since the second phase of the Somali Civil War in the early 21st century.

Marine Life

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 gems". It's also called Hindu Mahasagara(m) in Indian languages.

See Culture of the Indian Ocean Islands and Indian Ocean literature.

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 of the Arabian Sea". It is the finest natural harbour of India. Kolkata, Visakhapatnam and Chennai are other important ports of India. They control the Indian goods flowing towards the east. Aden is the important Arabian port controlled by the country of Yemen. Perth is the important Australian port. Karachi is the major seaport in Pakistan.

Port Louis, Mauritius is the largest container handling facility in the Indian Ocean and can accommodate fourth and fifth generation container vessels. At present, only Cape Town and Port Louis can achieve that in Sub-Saharan Africa.^[11]

See also

• List of islands in the Indian Ocean
• List of island countries and territories in the Indian Ocean
• Piracy in Somalia

Oceans:

• Arctic Ocean
• Atlantic Ocean
• Pacific Ocean
• Southern Ocean
• Seven Seas

References

External links

• NOAA In-situ Ocean Data Viewer Plot and download ocean observations
• The Indian Ocean in World History: Educational Website Interactive resource from the Sultan Qaboos Cultural Center
• The Regional Tuna Tagging Project-Indian Ocean with details of the importance of Tuna in the Indian Ocean..
• Detailed maps of the Indian Ocean
• The Indian Ocean Trade: A Classroom Simulation

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