The Indian Ocean is the third-largest of the world's five ocean
The ocean (also the or the world ocean) is the body of that covers approximately 70.8% of the surface of and contains 97% of . Another definition is "any of the large bodies of water into which the great ocean is divided".
ic divisions, covering or 19.8% of the water
Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for all known forms of , even though it provide ...
on Earth
Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wit ...
's surface. It is bounded by Asia
Asia () is 's largest and most populous , located primarily in the and . It shares the continental of with the continent of and the continental landmass of with both Europe and . Asia covers an area of , about 30% of Earth's total lan ...
to the north, Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area and 20% of i ...
to the west and Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
to the east. To the south it is bounded by the Southern Ocean
The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. As such, it is regarded as the second-smallest of t ...
or Antarctica
Antarctica ( or ) is 's southernmost . It contains the geographic and is situated in the region of the , almost entirely south of the , and is surrounded by the . At , it is the fifth-largest continent and nearly twice the size of . At 0.00 ...
, depending on the definition in use. Along its core, the Indian Ocean has some large marginal or regional seas such as the Arabian Sea
The Arabian Sea ( ar, بحر العرب ''Bahr al-Arab'') is a region of the northern Indian Ocean
The Indian Ocean is the third-largest of the world's oceanic divisions, covering or 19.8% of the water
Water is an Inorganic co ...
, the Laccadive Sea
The Laccadive Sea or Lakshadweep Sea is a body of water bordering India
India (Hindi: ), officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by population, second-most populo ...
, the Somali Sea, Bay of Bengal
The Bay of Bengal is the northeastern part of the Indian Ocean
The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or 19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to th ...
, and the Andaman Sea
The Andaman Sea (historically also known as the Burma Sea) is a marginal sea of northeastern Indian Ocean bounded by the coastlines of Myanmar and Thailand along the Gulf of Martaban and west side of the Malay Peninsula, and separated from the B ...
.
Etymology
The Indian Ocean has been known by its present name since at least 1515 when the Latin form ''Oceanus Orientalis Indicus'' ("Indian Eastern Ocean") is attested, named for India, which projects into it. It was earlier known as the ''Eastern Ocean'', a term that was still in use during the mid-18th century (see map), as opposed to the ''Western Ocean'' () before the
Pacific
The Pacific Ocean is the largest and deepest of Earth
Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. T ...
was surmised.
Conversely, Chinese explorers in the Indian Ocean during the 15th century called it the Indian Oceans. The ocean has also been known as the Hind Mahasagar and Indic Ocean in various languages.
In Ancient Greek geography
;Pre-Hellenistic Classical Greece
*Homer
Homer (; grc, Ὅμηρος , ''Hómēros'') was the presumed author of the ''Iliad'' and the ''Odyssey'', two epic poems that are the foundational works of ancient Greek literature. The ''Iliad'' i ...
, the Indian Ocean region known to the Greeks was called the Erythraean Sea
The Erythraean Sea ( grc-gre, Ἐρυθρὰ Θάλασσα, ''Erythrà Thálassa'', ."Red Sea") was a former maritime designation that always included the Gulf of Aden and at times other seas between Arabia Felix and the Horn of Africa. Origina ...
. In ancient Indian texts it was called "Ratnakara".
Geography
Extent and data
The , as delineated by the
International Hydrographic Organization
The International Hydrographic Organization (IHO) is an intergovernmental organisation
An intergovernmental organization (IGO) is an organization composed primarily of sovereign states (referred to as ''member states''), or of other organiza ...
in 1953 included the Southern Ocean
The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. As such, it is regarded as the second-smallest of t ...
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. ly, the Indian Ocean is delimited from the by the 20° east meridian, running south from 
Cape Agulhas
and Indian
Indian or Indians refers to people or things related to India, or to the indigenous people of the Americas, or Aboriginal Australians until the 19th century.
People South Asia
* Indian people, people of Indian nationality, or p ...
, and from the Pacific Ocean
The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south and is bounded by the continents o ...
by the meridian of 146°49'E, running south from the southernmost point of Tasmania
Tasmania (), abbreviated as TAS, is an island
An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atol ...
. The northernmost extent of the Indian Ocean (including marginal seas) is approximately 30° north in the Persian Gulf
The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of , ) is a in . The body of water is an extension of the () through the and lies between to the northeast and the to the southwest.United Nations Group of Exper ...
.
The Indian Ocean covers , including the Red Sea
The Red Sea ( ar, البحر الأحمر, translit=al-Baḥr al-ʾAḥmar; or ; Coptic
Coptic may refer to:
Afro-Asia
* Copts, an ethnoreligious group mainly in the area of modern Egypt but also in Sudan and Libya
* Coptic language, a Northe ...
and the Persian Gulf but excluding the Southern Ocean, or 19.5% of the world's oceans; its volume is or 19.8% of the world's oceans' volume; it has an average depth of and a maximum depth of .
All of the Indian Ocean is in the Eastern Hemisphere
250px, Eastern Hemisphere
The Eastern Hemisphere is a geographical term for the half of Earth which is east of the prime meridian
A prime meridian is the meridian (geography), meridian (a line of longitude) in a geographic coordinate system ...
and the centre of the Eastern Hemisphere, the 90th meridian east, passes through the Ninety East Ridge
The Ninety East Ridge (also rendered as Ninetyeast Ridge, 90E Ridge or 90°E Ridge) is a mid-ocean ridge on the Indian Ocean floor named for its near-parallel strike along the 90th meridian at the center of the Eastern Hemisphere. It is approxima ...
.
Coasts and shelves
In contrast to the Atlantic and Pacific, the Indian Ocean is enclosed by major landmasses and an archipelago on three sides and does not stretch from pole to pole, and can be likened to an embayed ocean. It is centered on the Indian Peninsula. Although this subcontinent has played a significant role in its history, the Indian Ocean has foremostly been a cosmopolitan stage, interlinking diverse regions by innovations, trade, and religion since early in human history. Theactive margin
Active may refer to:
Music
* ''Active'' (album), a 1992 album by Casiopea
* Active Records
Active Records was a record label, record sublabel of RCA Records founded in 1980. The label focused mainly on heavy metal music. The label was dissol ...
s of the Indian Ocean have an average depth (land to shelf break) of with a maximum depth of . The passive margin
A passive margin is the transition between oceanic and continental lithosphere that is not an active plate Continental margin, margin. A passive margin forms by sedimentation above an ancient rift, now marked by transitional lithosphere. Contin ...
s have an average depth of .
The average width of the slopes
In mathematics, the slope or gradient of a Line (mathematics), line is a number that describes both the ''direction'' and the ''steepness'' of the line. Slope is often denoted by the letter ''m''; there is no clear answer to the question why the l ...
of the continental shelves are for active and passive margins respectively, with a maximum depth of .
In correspondance of the Shelf break, also known as Hinge zone, the Bouguer gravity ranges from 0 to 30 mGals that is unusual for a continantal region of around 16 km thick sediments. It has been hypothesized that the "Hinge zone may represent the relict of continental and proto-oceanic crustal boundary formed during the rifting of India from Antarctica
Antarctica ( or ) is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Oc ...
."
Australia, Indonesia, and India are the three countries with the longest shorelines and exclusive economic zones. The continental shelf makes up 15% of the Indian Ocean.
More than two billion people live in countries bordering the Indian Ocean, compared to 1.7 billion for the Atlantic and 2.7 billion for the Pacific (some countries border more than one ocean).
Rivers
The Indian Oceandrainage basin
A drainage basin is any area of land where precipitation collects and drains off into a common outlet, such as into a river, bay, or other body of water. The drainage basin includes all the surface water from surface runoff, rain runoff, snowm ...
covers , 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 on average () than those of the other major oceans. The largest rivers are ( order 5) the Zambezi
The Zambezi River (also spelled Zambeze and Zambesi) is the List of rivers by length, fourth-longest river in Africa, the longest east-flowing river in Africa and the largest flowing into the Indian Ocean from Africa. The area of its drainage ba ...
, Ganges
The Ganges ( ) (in India: Ganga ( ); in Bangladesh: Padma River, Padma ( )). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international river to which India, Bangladesh, Nepal and China are the riparian ...
-Brahmaputra
The Brahmaputra (), called Yarlung Tsangpo
The Yarlung Tsangpo, also called Yarlung Zangbo () or Yalu Zangbu () is the upper stream of the Brahmaputra River
The Brahmaputra (), called Yarlung Tsangpo in Tibet, Siang/Dihang River in Aruna ...
, Indus#REDIRECT Indus River
{{Redirect category shell,
{{R from move
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...
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 
* Madagascar and the islands of the western Indian Ocean (Comoros, Réunion, Mauritius, Rodrigues, the Seychelles, and Socotra), includes 13,000 (11,600 endemic) species of plants; 313 (183) birds; reptiles 381 (367); 164 (97) freshwater fishes; 250 (249) amphibians; and 200 (192) mammals.
This area, one of the only two hotspots that are entirely arid, includes the Ethiopian Highlands, the East African Rift, East African Rift valley, the Socotra islands, as well as some small islands in the Red Sea and areas on the southern Arabic Peninsula. Endemic and threatened mammals include the dibatag (''Ammodorcas clarkei'') and Speke's gazelle (''Gazella spekei''); the Somali wild ass (''Equus africanus somaliensis'') and hamadryas baboon (''Papio hamadryas''). It also contains many reptiles.
In Somalia, the centre of the hotspot, the landscape is dominated by Acacia-Commiphora deciduous bushland, but also includes the Yeheb nut (''Cordeauxia edulus'') and species discovered more recently such as the Somali cyclamen (''Cyclamen somalense''), the only cyclamen outside the Mediterranean. Warsangli linnet (''Carduelis johannis'') is an endemic bird found only in northern Somalia. An unstable political regime has resulted in overgrazing which has produced one of the most degraded hotspots where only c. 5 % of the original habitat remains.
* The Western Ghats–Sri Lanka; 5,916 (3,049 endemic) species of plants; 457 (35) birds; 265 (176) reptiles; 191 (139) freshwater fishes; 204 (156) amphibians; and 143 (27) mammals.
Pleistocene fossils of ''Homo erectus'' and other pre-''H. sapiens'' hominid fossils, similar to ''Homo heidelbergensis, H. heidelbergensis'' in Europe, have been found in India. According to the Toba catastrophe theory, a supereruption c. 74000 years ago at Lake Toba, Sumatra, covered India with volcanic ashes and wiped out one or more lineages of such archaic humans in India and Southeast Asia.
The Recent African origin of modern humans, ''Out of Africa'' theory states that ''Homo sapiens'' spread from Africa into mainland Eurasia. The more recent ''Southern Dispersal'' or ''Coastal hypothesis'' instead advocates that modern humans spread along the coasts of the Arabic Peninsula and southern Asia. This hypothesis is supported by Mitochondrial DNA, mtDNA research which reveals a rapid dispersal event during the Late Pleistocene (11,000 years ago). This coastal dispersal, however, began in East Africa 75,000 years ago and occurred intermittently from estuary to estuary along the northern perimeter of the Indian Ocean at a rate of per year. It eventually resulted in modern humans migrating from Sundaland, Sunda over Wallacea to Australia (continent), Sahul (Southeast Asia to Australia).
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.
Food globalisation began on the Indian Ocean littoral c. 4.000 years ago. Five African crops — Sorghum bicolor, sorghum, Pennisetum glaucum, pearl millet, Eleusine coracana, finger millet, Vigna unguiculata, cowpea, and Lablab purpureus, hyacinth bean — somehow found their way to Gujarat in India during the Late Harappan (2000–1700 BCE). Gujarati merchants evolved into the first explorers of the Indian Ocean as they traded African goods such as ivory, tortoise shells, and slaves. Panicum miliaceum, Broomcorn millet found its way from Central Asia to Africa, together with chicken and zebu cattle, although the exact timing is disputed. Around 2000 BCE Piper nigrum, black pepper and Sesamum indicum, sesame, both native to Asia, appear in Egypt, albeit in small quantities. Around the same time the Rattus rattus, black rat and the Mus musculus, house mouse emigrate from Asia to Egypt. Banana reached Africa around 3000 years ago.
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.
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 
The Red Sea, one of the main trade routes in Antiquity, was explored by First Dynasty of Egypt, Egyptians and Phoenicians during the last two millennia BCE. In the 6th century, BCE Greek explorer Scylax of Caryanda made a journey to India, working for the Persian king Darius the Great, Darius, and his now-lost account put the Indian Ocean on the maps of Greek geographers. The Greeks began to explore the Indian Ocean following the conquests of Alexander the Great, who ordered a circumnavigation of the Arabian Peninsula in 323 BCE. During the two centuries that followed the reports of the explorers of Ptolemaic Kingdom, Ptolemaic Egypt resulted in the best maps of the region until the Portuguese era many centuries later. The main interest in the region for the Ptolemies was not commercial but military; they explored Africa to hunt for war elephants.
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 
''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 
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. Dhivehi people, 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.
Arabic missionaries and merchants began to Spread of Islam#East Africa, spread Islam along the western shores of the Indian Ocean from the 8th century, if not earlier. A Swahili culture, Swahili stone mosque dating to the 8th–15th centuries has been found in Shanga, Pate Island, Shanga, Kenya. Trade across the Indian Ocean gradually introduced Arabic script and rice as a Staple food, staple in Eastern Africa.
Muslim merchants traded an estimated 1000 African slaves annually between 800 and 1700, a number that grew to during the 18th century, and 3700 during the period 1800–1870. Slave trade also occurred in the eastern Indian Ocean before the Dutch settled there around 1600 but the volume of this trade is unknown.
The Portuguese navigator Vasco da Gama rounded the Cape of Good Hope during his first voyage in 1497 and became the first European to sail to India. The Swahili people he encountered along the African east coast lived in a series of cities and had established trade routes to India and to China. Among them, the Portuguese kidnapped most of their pilots in coastal raids and onboard ships. A few of the pilots, however, were gifts by local Swahili rulers, including the sailor from Gujarat, a gift by a Malindi ruler in Kenya, who helped the Portuguese to reach India. In expeditions after 1500, the Portuguese attacked and colonised cities along the African coast.
European slave trade in the Indian Ocean began when Portugal established Portuguese India, Estado da Índia in the early 16th century. From then until the 1830s, slaves were exported from Mozambique annually and similar figures has been estimated for slaves brought from Asia to the Philippines during the Iberian Union (1580–1640).
Scientifically, the Indian Ocean remained poorly explored before the International Indian Ocean Expedition in the early 1960s. However, the Challenger expedition, ''Challenger'' expedition 1872–1876 only reported from south of the polar front. The Valdivia Expedition, ''Valdivia'' expedition 1898–1899 made deep samples in the Indian Ocean. In the 1930s, the John Murray Expedition mainly studied shallow-water habitats. The Albatross expedition, Swedish Deep Sea Expedition 1947–1948 also sampled the Indian Ocean on its global tour and the Danish Galathea expeditions, ''Galathea'' sampled deep-water fauna from Sri Lanka to South Africa on its second expedition 1950–1952. The Soviet research vessel RV Vityaz (1939), ''Vityaz'' also did research in the Indian Ocean.
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 Indian indenture system, indenture labour from India. The end of Indian Ocean in World War II, 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.
Iranrud is an unrealised plan by Iran and the Soviet Union to build a canal between the Caspian Sea and the 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, such as 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.
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 , reached up to in height, and resulted in an estimated 236,000 deaths.
In the late 2000s, the ocean evolved into a hub of Piracy in Somalia, 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.
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 southern Indian Ocean about from the coast of southwest Western Australia. Despite an extensive search, the whereabouts of the remains of the aircraft is unknown.
The Sentinelese people of North Sentinel Island, which lies near South Andaman Island in the Bay of Bengal, have been called by experts the most Uncontacted peoples, isolated people in the world.
The sovereignty of the Chagos Archipelago in the Indian Ocean is Chagos Archipelago sovereignty dispute, disputed between the United Kingdom and Mauritius. In February 2019, the International Court of Justice in The Hague issued an advisory opinion Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965, stating that the UK must transfer the Chagos Archipelago to Mauritius.
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 the Indian Ocean and its vital chokepoints, 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.
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.
In particular, the maritime part of the Silk Road leads through the Indian Ocean on which a large part of the global container trade is carried out. The Silk Road runs with its connections from the Chinese coast and its large container ports to the south via Hanoi to Jakarta, Singapore and Kuala Lumpur through the Strait of Malacca via the Sri Lankan Colombo opposite the southern tip of India via Malé, the capital of the Maldives, to the East African Mombasa, from there to Djibouti, then through the Red Sea over the