The Indian Ocean is the third largest of the world's oceanic divisions, covering 70,560,000 km2 (27,240,000 sq mi) (approximately 20% of the water on the Earth's surface).[3] 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.[4]

Indian Ocean
Indian Ocean-CIA WFB Map.png
Extent of the Indian Ocean according to The World Factbook
Indian Ocean bathymetry srtm.png
The ocean-floor of the Indian Ocean is divided by spreading ridges and crisscrossed by aseismic structures
LocationIndian subcontinent, Southeast Asia, Western Asia, Northeast Africa, East Africa, Southern Africa and Australia
Coordinates20°S 80°E / 20°S 80°E / -20; 80Coordinates: 20°S 80°E / 20°S 80°E / -20; 80
Max. length9,600 km (6,000 mi) (Antarctica to Bay of Bengal)[1]
Max. width7,600 km (4,700 mi) (Africa to Australia)[1]
Surface area68,556,000 km2 (26,470,000 sq mi)
Average depth3,741 m (12,274 ft)
Max. depth7,258 m (23,812 ft)
SettlementsDurban, Mumbai, Perth, Colombo, Padang, Maputo

Scientifically, the Indian Ocean remained poorly explored before the International Indian Ocean Expedition in the early 1960s. The Challenger expedition 1872–1876 only reported from south of the polar front. The Valdivia expedition 1898-1899 made deep samples in the Indian Ocean. In the 1930s, the John Murray Expedition mainly studied shallow-water habitats. The Swedish Deep Sea Expedition 1947–1948 also sampled the Indian Ocean on its global tour and the Danish Galathea sampled deep-water fauna from Sri Lanka to South Africa on its second expedition 1950–1952. The Soviet research vessel Vityaz also did research in the Indian Ocean.[1]



A 1747 map of Africa with the Indian Ocean referred to as the Eastern Ocean
A 1658 naval map by Janssonius depicting the Indian Ocean, India and Arabia.

The Indian Ocean is named after India (Oceanus Orientalis Indicus) since at least 1515. India, then, is the Greek/Roman name for the "region of the Indus River".[5]

Called the Sindhu Mahasagara or the great sea of the Sindhu by the Ancient Indians, this ocean has been variously called Hindu Ocean, Indic Ocean, etc. in various languages. The Indian Ocean was also known earlier as the Eastern Ocean.[5] The term was still in use during the mid-18th century. Consequently, when China explored the Indian Ocean in the 15th century they called it the "Western Oceans".[6]

In Ancient Greek geography the region of the Indian Ocean known to them was called the Erythraean Sea.[7]


The borders of the Indian Ocean, as delineated by the International Hydrographic Organization in 1953 included the Southern Ocean but not the marginal seas along the northern rim, but in 2000 the IHO delimited the Southern Ocean separately, which removed waters south of 60°S from the Indian Ocean, but included the northern marginal seas. [8][9] Meridionally, the Indian Ocean is delimited from the Atlantic Ocean by the 20° east meridian, running south from Cape Agulhas, and from the Pacific Ocean by the meridian of 146°49'E, running south from the southernmost point of Tasmania. The northernmost extent of the Indian Ocean (including marginal seas) is approximately 30° north in the Persian Gulf.[9]

The Indian Ocean covers 70,560,000 km2 (27,240,000 sq mi), including the Red Sea and the Persian Gulf but excluding the Southern Ocean, or 19.5% of the world's oceans; its volume is 264,000,000 km3 (63,000,000 cu mi) or 19.8% of the world's oceans' volume; it has an average depth of 3,741 m (12,274 ft) and a maximum depth of 7,906 m (25,938 ft).[10]

The ocean's continental shelves are narrow, averaging 200 kilometres (120 mi) in width. An exception is found off Australia's western coast, where the shelf width exceeds 1,000 kilometres (620 mi). The average depth of the ocean is 3,890 m (12,762 ft). Its deepest point is Sunda Trench at a depth of 7,450 m (24,442 ft); Diamantina Deep has a depth of 7,079 m (23,225 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.[11]

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. All of the Indian Ocean is in the Eastern Hemisphere and the centre of the Eastern Hemisphere, the 90th meridian east, passes through the Ninety East Ridge.

Marginal seas

Marginal seas, gulfs, bays and straits of the Indian Ocean include:[9]


During summer, warm continental masses draw moist air from the Indian Ocean hence producing heavy rainfall. The process is reversed during winter, resulting in dry conditions.

Several features make the Indian Ocean unique. It constitutes the core of the large-scale Tropical Warm Pool which, when interacting with the atmosphere, affects the climate both regionally and globally. Asia blocks heat export and prevents the ventilation of the Indian Ocean thermocline. That continent also drives the Indian Ocean monsoon, the strongest on Earth, which causes large-scale seasonal variations in ocean currents, including the reversal of the Somali Current and Indian Monsoon Current. Because of the Indian Ocean Walker circulation there is no continuous equatorial easterlies. Upwelling occurs near the Horn of Africa and the Arabian Peninsula in the Northern Hemisphere and north of the trade winds in the Southern Hemisphere. The Indonesian Throughflow is a unique Equatorial connection to the Pacific.[12]

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.[11] Some 80% of the total annual rainfall in India occurs during summer and the region is so dependent of this rainfall that many civilisations perished when the Monsoon failed in the past. Huge variability in the Indian Summer Monsoon has also occurred pre-historically, with a strong, wet phase 33,500–32,500 BP; a weak, dry phase 26,000–23,500 BC; and a very weak phase 17,000–15,000 BP, corresponding to a series of dramatic global events: Bølling-Allerød, Heinrich, and Younger Dryas.[13]

The Indian Ocean is the warmest ocean in the world.[14] Long-term ocean temperature records show a rapid, continuous warming in the Indian Ocean, at about 1.2 °C (34.2 °F) (compared to 0.7 °C (33.3 °F) for the warm pool region) during 1901–2012.[15] Research indicates that human induced greenhouse warming, and changes in the frequency and magnitude of El Niño (or the Indian Ocean Dipole), events are a trigger to this strong warming in the Indian Ocean.[15]

South of the Equator (20-5°S) the Indian Ocean is gaining heat from June to October, during the austral winter, while it is losing heat from November to March, during the austral summer.[16]


The ocean's currents are mainly controlled by the monsoon. Two large gyres, one in the northern hemisphere flowing clockwise and one south of the equator moving anticlockwise (including the Agulhas Current and Agulhas Return Current), constitute the dominant flow pattern. During the winter monsoon (November–February), however, circulation is reversed north of 30°S and winds are weakened during winter and the transitional periods between the monsoons.[17]

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.[11]

Water circulation in the Indian Ocean is dominated by the Subtropical Anticyclonic Gyre, the eastern extension of which is blocked by the Southeast Indian Ridge and the 90°E Ridge. Madagascar and the Southwest Indian Ridge separates three cells south of Madagascar and off South Africa. North Atlantic Deep Water reaches into the Indian Ocean south of Africa at a depth of 2,000–3,000 m (6,600–9,800 ft) and flows north along the eastern continental slope of Africa. Deeper than NADW, Antarctic Bottom Water flows from Enderby Basin to Agulhas Basin across deep channels (<4,000 m (13,000 ft)) in the Southwest Indian Ridge, from where it continues into the Mozambique Channel and Prince Edward Fracture Zone.[18]

The Indian Ocean drainage basin covers 21,100,000 km2 (8,100,000 sq mi), virtually identical to that of the Pacific Ocean and half that of the Atlantic basin, or 30% of its ocean surface (compared to 15% for the Pacific). The Indian Ocean drainage basin is divided into roughly 800 individual basins, half that of the Pacific, of which 50% are located in Asia, 30% in Africa, and 20% in Australasia. The rivers of the Indian Ocean are shorter in average (740 km (460 mi)) than those the other major oceans. The largest rivers are (order 5) the Zambezi, Ganges-Brahmaputra, Indus, Jubba, and Murray rivers and (order 4) the Shatt al-Arab, Wadi Ad Dawasir (a dried out river system on the Arabian Peninsula) and Limpopo rivers.[19]

The Bay of Bengal contributes more than half (2,950 km3 (710 cu mi)) of the runoff water to the Indian Ocean. Mainly in summer, this runoff flows into the Arabian Sea but also south across the Equator where it mixes with fresher sea water from the Indonesian Throughflow. This mixed freshwater joins the South Equatorial Current in the southern tropical Indian Ocean.[20] 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.[11]

There are two amphidromes of opposite rotation in the Indian Ocean, probably caused by Rossby wave propagation.[21]

Icebergs drift as far north as 55° south latitude, similar to the Pacific but less than in the Atlantic where icebergs reach up to 45°S. The volume of iceberg loss in the Indian Ocean between 2004 and 2012 was 24 Gt.[22]

Since the 1960s, anthropogenic warming of the global ocean combined with contributions of freshwater from retreating land ice causes a global rise in sea level. Sea level increases in the Indian Ocean too, except in the south tropical Indian Ocean where it decreases, a pattern most likely caused by rising levels of greenhouse gases.[23]


Left: The oldest ocean floor of the Indian Ocean formed c. 150 Ma when the Indian Subcontinent and Madagascar broke-up from Africa. Right: The India–Asia collision c. 40 Ma completed the closure of the Tethys Ocean (grey areas north of India). Geologically, the Indian Ocean is the ocean floor that opened up south of India.

As the youngest of the major oceans,[24] the Indian Ocean has active spreading ridges that are part of the worldwide system of mid-ocean ridges. In the Indian Ocean these spreading ridges meet at the Rodrigues Triple Point with the Central Indian Ridge, including the Carlsberg Ridge, separating the African Plate from the Indian Plate; the Southwest Indian Ridge separating the African Plate from the Antarctic Plate; and the Southeast Indian Ridge separating the Australian Plate from the Antarctic Plate. The Central Indian Ridge is intercepted by the Owen Fracture Zone.[25]

There are only two trenches in the Indian Ocean: the 6,000 km (3,700 mi)-long Java Trench between Java and the Sunda Trench and the 900 km (560 mi)-long Makran Trench south of Iran and Pakistan.[25]

A series of ridges and seamount chains produced by hotspots pass over the Indian Ocean. The Réunion hotspot (active 70–40 million years ago) connects Réunion and the Mascarene Plateau to the Chagos-Laccadive Ridge and the Deccan Traps in north-western India; the Kerguelen hotspot (100–35 million years ago) connects the Kerguelen Islands and Kerguelen Plateau to the Ninety East Ridge and the Rajmahal Traps in north-eastern India; the Marion hotspot (100–70 million years ago) possibly connects Prince Edward Islands to the Eighty Five East Ridge.[26] These hotspot tracks have been broken by the still active spreading ridges mentioned above.[25]

There are fewer seamounts in the Indian Ocean than in the Atlantic and Pacific. These are typically deeper than 3,000 m (9,800 ft) and located north of 55°S and west of 80°W. Most originated at spreading ridges but some are now located in basins far away from these ridges. The ridges of the Indian Ocean form ranges of seamounts, sometimes very long, including the Carlsberg Ridge, Madagascar Ridge, Central Indian Ridge, Southwest Indian Ridge, Chagos-Laccadive Ridge, 85°E Ridge, 90°E Ridge, Southeast Indian Ridge, Broken Ridge, and East Indiaman Ridge. The Agulhas Plateau and Mascarene Plateau are the two major shallow areas.[18]

The opening of the Indian Ocean began c. 156 Ma when Africa separated from East Gondwana. The Indian Subcontinent began to separate from Australia-Antarctica 135-125 Ma and as the Tethys Ocean north of India began to close 118-84 Ma the Indian Ocean opened behind it.[25]

Marine life

Among the tropical oceans, the western Indian Ocean hosts one of the largest concentration of phytoplankton blooms in summer, due to the strong monsoon winds. The monsoonal wind forcing leads to a strong coastal and open ocean upwelling, which introduces nutrients into the upper zones where sufficient light is available for photosynthesis and phytoplankton production. These phytoplankton blooms support the marine ecosystem, as the base of the marine food web, and eventually the larger fish species. The Indian Ocean accounts for the second largest share of the most economically valuable tuna catch.[27] 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.[2]

Research indicates that increasing ocean temperatures are taking a toll on the marine ecosystem. A study on the phytoplankton changes in the Indian Ocean indicates a decline of up to 20% in the marine plankton in the Indian Ocean, during the past six decades. The tuna catch rates have also declined 50–90% during the past half century, mostly due to increased industrial fisheries, with the ocean warming adding further stress to the fish species.[28]

An Indian Ocean garbage patch was discovered in 2010 covering at least 5 million square kilometres (1.9 million square miles). Riding the southern Indian Ocean Gyre, this vortex of plastic garbage constantly circulates the ocean from Australia to Africa, down the Mozambique Channel, and back to Australia in a period of six years, except for debris that get indefinitely stuck in the centre of the gyre.[29] The garbage patch in the Indian Ocean will, according to a 2012 study, decrease in size after several decades to vanish completely over centuries. Over several millennia, however, the global system of garbage patches will accumulate in the North Pacific.[30]

Endangered marine species include the dugong, seals, turtles, and whales.[2] Coral reefs, sea grass beds, and mangrove forests are the most productive ecosystems of the Indian Ocean — coastal areas produce 20 tones/km² of fish. These areas, however, are also being urbanised with populations often exceeding several thousand people/km² and fishing techniques become more effective and often destructive beyond sustainable levels while increase in sea surface temperature spreads coral bleaching.[31]

In 2016 six new animal species were identified at hydrothermal vents in the Southwest Indian Ridge: a "Hoff" crab, a "giant peltospirid" snail, a whelk-like snail, a limpet, a scaleworm and a polychaete worm.[32]


The Indian Ocean, together with the Mediterranean, has connected people since ancient times, whereas the Atlantic and Pacific have had the roles of barriers or mare incognitum. The written history of the Indian Ocean, however, has been Eurocentric and largely dependent of the availability of written sources from the colonial era. This history is often divided into an ancient period followed by an Islamic period; the subsequent early modern and colonial/modern periods are often subdivided into Portuguese, Dutch, and British periods.[33]

A concept of an "Indian Ocean World" (IOW), similar to that of the "Atlantic World", exists but emerged recently and is not well established. The IOW, nevertheless, is sometimes referred to as the "first global economy" and was based on the monsoon which linked Asia, China, India, and Mesopotamia. It developed independently from the European global trade in the Mediterranean and Atlantic and remained largely independent until European dominance in the 19th century.[34]

With its diverse history, the Indian Ocean is a unique mix of cultures and etnical groups, natural resources and shipping routes. It grew in importance beginning in the 1960s and 1970s and after the Cold War it has undergone periods of political instability, most recently with the emergence of India and China as regional powers.[35]

First settlements

Homo sapiens evolved inland from the western shores of the Indian Ocean and had settled in Australia c. 50,000 years ago. Since then, waves of migration have resettled people and, clearly, the Indian Ocean littoral had been inhabited long before the first civilisations emerged. 5000-6000 years ago six distinct cultural centres had evolved around the Indian Ocean: East Africa, the Middle East, the Indian Subcontinent, South East Asia, the Malay World, and Australia; each interlinked to its neighbours.[36]

At least eleven prehistoric tsunamis have struck the Indian Ocean coast of Indonesia between 7400 and 2900 years ago. Analysing sand beds in caves in the Aceh region, scientists concluded that the intervals between these tsunamis have varied from series of minor tsunamis over a century to dormant periods of more than 2000 years preceding megathrusts in the Sunda Trench. Although the risk for future tsunamis is high, a major megathrust such as the one in 2004 is likely to be followed by a long dormant period.[37]

A group of scientists have argued that two large-scale impact events have occurred in the Indian Ocean: the Burckle Crater in the southern Indian Ocean in 2800 BCE and the Kanmare and Tabban craters in the Gulf of Carpentaria in northern Australia in 536 CE. Evidences for these impacts, the team argue, are micro-ejecta and Chevron dunes in southern Madagascar and in the Australian gulf. Geological evidences suggest the tsunamis caused by these impacts reached 205 m (673 ft) above sea level and 45 km (28 mi) inland. They must have disrupted human settlements and possibly caused major climate changes (see extreme weather events of 535–536).[38]

The history of the Indian Ocean is marked by maritime trade; cultural and commercial exchange probably date back at least seven thousand years.[39] Human culture spread early on the shores of the Indian Ocean and was always linked to the cultures of the Mediterranean and Persian Gulf. Before c. 2000 BCE, however, cultures on its shores were only loosely tied to each other; bronze, for example, was developed in Mesopotamia c. 3000 BCE but remained uncommon in Egypt before 1800 BCE.[40] During this period, independent, short-distance oversea communications along its littoral margins evolved into an all-embracing network. The début of this network was not the achievement of a centralised or advanced civilisation but of local and regional exchange in the Persian Gulf, the Red Sea, and Arabian Sea. Sherds of Ubaid (2500–500 BCE) pottery have been found in the western Gulf at Dilmun, present-day Bahrain; traces of exchange between this trading centre and Mesopotamia. The Sumerians traded grain, pottery, and bitumen (used for reed boats) for copper, stone, timber, tin, dates, onions, and pearls.[41] Coast-bound vessels transported goods between the Indus Valley Civilisation (2600–1900 BCE) in the Indian subcontinent (modern-day Pakistan and Northwest India) and the Persian Gulf and Egypt.[39]

During Egypt's first dynasty (c. 3000 BCE), sailors were sent out onto the Indian Ocean, journeying to Punt, thought to be part of present-day Somalia. Returning ships brought gold and slaves. The earliest known maritime trade between Mesopotamia and the Indus Valley (c. 2500 BCE) was conducted along the Indian Ocean. Phoenicians of the late 3rd millennium BCE may have entered the area, but no settlements resulted.[11]


The Rub' al Khali desert isolates the southern parts of the Arabic Peninsula and the Indian Ocean from the Arabic world. This encouraged the development of maritime trade in the region linking the Red Sea and the Persian Gulf to East Africa and India. The monsoon (from mawsim, the Arabic word for season), however, was used by sailors long before being "discovered" by Hippalus in the 1st century. Indian wood have been found in Sumerian cities, there is evidence of Akkad coastal trade in the region, and contacts between India and the Red Sea dates back to the 2300 B.C.. The archipelagoes of the central Indian Ocean, the Laccadive and Maldive islands, were probably populated during the 2nd century B.C. from the Indian mainland. They appear in written history in the account of merchant Sulaiman al-Tajir in the 9th century but the treacherous reefs of the islands were most likely cursed by the sailors of Aden long before the islands were even settled.[42]

Periplus of the Erythraean Sea, an Alexandrian guide to the world beyond the Red Sea — including Africa and India — from the first century CE, not only gives insights into trade in the region but also shows that Roman and Greek sailors had already gained knowledge about the monsoon winds.[39] The contemporaneous settlement of Madagascar by Austronesian sailors shows that the littoral margins of the Indian Ocean were being both well-populated and regularly traversed at least by this time. Albeit the monsoon must have been common knowledge in the Indian Ocean for centuries.[39]

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 ancient Indonesian peoples to cross the Indian Ocean to settle in Madagascar around 1 CE.[43]

Age of Discovery

The economically important Silk Road was blocked from Europe by the Ottoman Empire in c. 1453 with the fall of the Byzantine Empire. This spurred exploration, and a new sea route around Africa was found, triggering the Age of Discovery.

In the 2nd or 1st century BCE, Eudoxus of Cyzicus was the first Greek to cross the Indian Ocean. The probably fictitious sailor Hippalus is said to have learnt the direct route from Arabia to India around this time.[44] 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 people 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 CE. Among these trading settlements were Mosylon and Opone on the Red Sea littoral.[45]

Unlike the Pacific Ocean where the civilization of the Polynesians reached most of the far flung islands and atolls and populated them, almost all the islands, archipelagos and atolls of the Indian Ocean were uninhabited until colonial times. Although there were numerous ancient civilizations in the coastal states of Asia and parts of Africa, the Maldives were the only island group in the Central Indian Ocean region where an ancient civilization flourished.[46] Maldivians, on their annual trade trip, took their oceangoing trade ships to Sri Lanka rather than mainland India, which is much closer, because their ships were dependent of the Indian Monsoon Current.[47]

Arabic missionaries and merchants began to spread Islam along the western shores of the Indian Ocean from the 8th century, if not earlier. A Swahili stone mosque dating to the 8th-15th centuries have been found in Shanga, Kenya. Trade across the Indian Ocean gradually introduced Arabic script and rice as a staple in Eastern Africa.[48]

From 1405 to 1433 admiral Zheng He said to have led large fleets of the Ming Dynasty on several treasure voyages through the Indian Ocean, ultimately reaching the coastal countries of East Africa.[49]

In 1497 Portuguese navigator Vasco da Gama rounded the Cape of Good Hope and became the first European to sail to India (with the help of an Indian sailor) and later the Far East. The European ships, armed with heavy cannon, quickly dominated trade. Portugal achieved pre-eminence by setting up forts at the important straits and ports. Their hegemony along the coasts of Africa and Asia lasted until the mid 17th century. Later, the Portuguese were challenged by other European powers.

The Ottoman Empire began its expansion into the Indian Ocean in 1517 with the conquest of Egypt under Sultan Selim I. Although the Ottomans shared the same religion as the trading communities in the Indian Ocean the region was unexplored by them. Maps that included the Indian Ocean had been produced by Muslim geographers centuries before the Ottoman conquests; Muslim scholars, such as Ibn Battuta in the 14th Century, had visited most parts of the known world; contemporarily with Vasco da Gama, Arab navigator Ahmad ibn Mājid had compiled a guide to navigation in the Indian Ocean; the Ottomans, neverhteless, began their own parallel era of discovery which rivaled the European expansion.[50]

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. From 1565 Spain established a major trading operation with the Manila Galleons in the Philippines and the Pacific. Spanish trading ships purposely avoided the Indian Ocean, following the Treaty of Tordesillas with Portugal. By 1815, Britain became the principal power in the Indian Ocean.[11]

Modern era

The Suez Canal opened in 1869 when the Industrial Revolution dramatically changed global shipping — the sailing ship declined in importance as did the importance of European trade in favour of trade in East Asia and Australia.[51] The construction of the canal introduced many non-indigenous species into the Mediterranean. For example, the goldband goatfish (Upeneus moluccensis) has replaced the red mullet (Mullus barbatus); since the 1980s huge swarms of scyphozoan jellyfish (Rhopilema nomadica) have affected tourism and fisheries along the Levantian coast and clogged power and desalination plants. Plans announced in 2014 to build a new, much larger Suez Canal parallel to the 19th century canal will most likely boost economy in the region but also cause ecological damage in a much wider area.[52]

An unnamed Chagossian on Diego Garcia in 1971 shortly before the British expelled the islanders when the island became a U.S. military base. The man spoke a French-based creole language and his ancestors were brought to the inhabited island as slaves in the 19th century.

Throughout the colonial era, islands such as Mauritius were important shipping nodes for the Dutch, French, and British. Mauritius, an inhabited island, became populated by slaves from Africa and indenture labour from India. The end of World War II marked the end of the colonial era. The British left Mauritius in 1974 and with 70% of the population of Indian descent, Mauritius became a close ally of India. In the 1980s, during the Cold War, the South African regime acted to destabilise several island nations in the Indian Ocean, including the Seychelles, Comoros, and Madagascar. India intervened in Mauritius to prevent a coup d'état, backed-up by the United States who feared the Soviet Union could gain access to Port Louis and threaten the U.S. base on Diego Garcia.[53]Iranrud is an unrealised plan by Iran and the Soviet Union to build a canal between the Caspian Sea and Persian Gulf.

Testimonies from the colonial era are stories of African slaves, Indian indentured labourers, and white settlers. But, while there was a clear racial line between free men and slaves in the Atlantic World, this delineation is less distinct in the Indian Ocean — there were Indian slaves and settlers as well as black indentured labourers. There were also a string of prison camps across the Indian Ocean, from Robben Island in South Africa to Cellular Jail in the Andamans, in which prisoners, exiles, POWs, forced labourers, merchants, and people of different faiths were forcefully united. On the islands of the Indian Ocean, therefore, a trend of creolisation emerged.[54]

On 26 December 2004 fourteen countries around the Indian Ocean were hit by a wave of tsunamis caused by the 2004 Indian Ocean earthquake. The waves radiated across the ocean at speeds exceeding 500 km/h (310 mph), reached up to 20 m (66 ft) in height, and resulted in an estimated 236,000 death.[55]

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, especially by the Indian Navy.[56]

Malaysian Airlines Flight 370, a Boeing 777 airliner with 239 persons on board, disappeared on 8 March 2014 and is alleged to have crashed into the southeastern Indian Ocean about 2,000 km (1,200 mi) from the coast of southwest Western Australia. Despite an extensive search, the whereabouts of the remains of the aircraft are unknown.[57]


Major ocean trade routes in the world includes the northern Indian Ocean.

The sea lanes in the Indian Ocean are considered among the most strategically important in the world with more than 80 percent of the world's seaborne trade in oil transits through Indian Ocean and its vital choke points, with 40 percent passing through the Strait of Hormuz, 35 percent through the Strait of Malacca and 8 percent through the Bab el-Mandab Strait.[58]

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.[2] 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.

Chinese companies have made investments in several Indian Ocean ports, including Gwadar, Hambantota, Colombo and Sonadia. This has sparked a debate about the strategic implications of these investments.[59] (See String of Pearls)

See also



  1. ^ a b c Demopoulos, Smith & Tyler 2003, Introduction, p. 219
  2. ^ a b c d CIA World Fact Book 2018
  3. ^ Rais 1986, p. 33
  4. ^ "'Indian Ocean' — Merriam-Webster Dictionary Online". Retrieved 7 July 2012. ocean E of Africa, S of Asia, W of Australia, & N of Antarctica area ab 73,427,795 square kilometres (28,350,630 sq mi)
  5. ^ a b Harper, Douglas. "Indian Ocean". Online Etymology Dictionary. Retrieved 18 January 2011.; Harper, Douglas. "India". Online Etymology Dictionary. Retrieved 8 July 2018.
  6. ^ Hui 2010, Abstract
  7. ^ Periplus of the Erythraean Sea
  8. ^ IHO 1953
  9. ^ a b c IHO 2002
  10. ^ Eakins & Sharman 2010
  11. ^ a b c d e f "U.S. Navy Oceanographer". Archived from the original on 2 August 2001. Retrieved 4 August 2001.
  12. ^ Schott, Xie & McCreary 2009, Introduction, pp. 1-2
  13. ^ Dutt et al. 2015, Abstract; Introduction, pp. 5526–5527
  14. ^ "Which Ocean is the Warmest?". Worldatlas. 17 September 2018. Retrieved 28 April 2019.
  15. ^ a b Roxy et al. 2014, Abstract
  16. ^ Carton, Chepurin & Cao 2000, p. 321
  17. ^ Shankar, Vinayachandran & Unnikrishnan 2002, Introduction, pp. 64–66
  18. ^ a b Rogers 2012, The Southern Indian Ocean and its Seamounts, pp. 5–6
  19. ^ Vörösmarty et al. 2000, Drainage basin area of each ocean, pp. 609-616; Table 5, p 614; Reconciling Continental and Oceanic Perspectives, pp. 616-617
  20. ^ Sengupta, Bharath Raj & Shenoi 2006, Abstract; p. 4
  21. ^ Chen & Quartly 2005, pp. 5–6
  22. ^ Matsumoto et al. 2014, p. 3454-3455
  23. ^ Han et al. 2010, Abstract
  24. ^ Stow 2006
  25. ^ a b c d Chatterjee, Goswami & Scotese 2013, Tectonic setting of the Indian Ocean, p. 246
  26. ^ Müller, Royer & Lawver 1993, Fig. 1, p. 275
  27. ^ FAO 2016
  28. ^ Roxy 2016, Discussion, pp. 831–832
  29. ^ Parker, Laura (4 April 2014). "Plane Search Shows World's Oceans Are Full of Trash". National Geographic News. Retrieved 30 December 2018.
  30. ^ Van Sebille, England & Froyland 2012
  31. ^ Lindén & Souter 2005, Foreword, pp. 5-6
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