Indian Ocean
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The Indian Ocean is the third-largest of the world's five
ocean The ocean (also the sea or the world ocean) is the body of Saline water, salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Water distribution on Earth, Earth's water. An ocean can also refer to any of the ...
ic divisions, covering or ~19.8% of the
water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
on
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large list of largest lakes and seas in the Solar System, volumes of water can be found throughout the Solar System, only water distributi ...
's surface. It is bounded by
Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa Africa is ...
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 ...
to the west and
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
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 60th parallel south, 60° S latitude and encircling Antarctica. With a size of , it is regarded ...
or
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
, 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, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel a ...
,
Laccadive Sea The Laccadive Sea or Lakshadweep Sea is a body of water bordering India (including its Lakshadweep islands), the Maldives, and Sri Lanka. It is located to the southwest of Karnataka, to the west of Kerala and to the south of Tamil Nadu. This war ...
,
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...
, and
Andaman Sea The Andaman Sea (historically also known as the Burma Sea) is a marginal sea of the 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 ...
.


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 after
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
, 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'' (
Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
) before the
Pacific 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 continen ...
was surmised. Conversely, Chinese explorers in the Indian Ocean during the 15th century called it the Western Oceans. In
Ancient Greek geography ;Pre-Hellenistic Classical Greece *Homer *Anaximander *Hecataeus of Miletus *Massaliote Periplus *Scylax of Caryanda (6th century BC) *Herodotus ;Hellenistic period *Pytheas (died c. 310 BC) *''Periplus of Pseudo-Scylax'' (3rd or 4th century BC) ...
, 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. Original ...
.


Geography


Extent and data

The borders of the Indian Ocean, as delineated by the
International Hydrographic Organization The International Hydrographic Organization (IHO) is an intergovernmental organisation representing hydrography. , the IHO comprised 98 Member States. A principal aim of the IHO is to ensure that the world's seas, oceans and navigable waters a ...
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 60th parallel south, 60° S latitude and encircling Antarctica. With a size of , it is regarded ...
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. Meridionally, the Indian Ocean is delimited from the
Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa ...
by the 20° east meridian, running south from
Cape Agulhas Cape Agulhas (; pt, Cabo das Agulhas , "Cape of the Needles") is a rocky headland in Western Cape, South Africa. It is the geographic extreme points of Africa, southern tip of the Africa, African continent and the beginning of the dividing lin ...
, 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 continen ...
by the meridian of 146°49'E, running south from the southernmost point of
Tasmania ) , nickname = , image_map = Tasmania in Australia.svg , map_caption = Location of Tasmania in AustraliaCoordinates: , subdivision_type = Country , subdi ...
. 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 Persis, Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a Mediterranean sea (oceanography), me ...
. The Indian Ocean covers , including the
Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic language, Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''P ...
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 The Eastern Hemisphere is the half of the planet Earth which is east of the prime meridian (Greenwich), prime meridian (which crosses Greenwich, London, United Kingdom) and west of the 180th meridian, antimeridian (which crosses the Pacific Ocean ...
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 east, 90th meridian at the center of the Eastern Hemisphe ...
.


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. The
active 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 diss ...
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 margin. A passive margin forms by sedimentation Sedimentation is the deposition of sediments. It takes place when particle (ecol ...
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 ...
of the continental shelves are for active and passive margins respectively, with a maximum depth of . In correspondence of the
Shelf break A continental shelf is a portion of a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarde ...
, also known as Hinge zone, the Bouguer gravity ranges from 0 to 30 mGals that is unusual for a continental 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 India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
from
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
." 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 Ocean
drainage basin A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter ...
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. Its drainage basin covers ...
,
Ganges The Ganges ( ) (in India: Ganga ( ); in Bangladesh: 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 states." is ...
-
Brahmaputra The Brahmaputra is a trans-boundary river which flows through Tibet, northeast India, and Bangladesh. It is also known as the Yarlung Tsangpo in Lhasa Tibetan, Tibetan, the Siang/Dihang River in Arunachal languages, Arunachali, Luit in Assamese ...
,
Indus The Indus ( ) is a transboundary river of Asia and a trans-Himalayan river of South Asia, South and Central Asia. The river rises in mountain springs northeast of Mount Kailash in Western Tibet, flows northwest through the disputed region ...
, Jubba, and Murray rivers and (order 4) the
Shatt al-Arab The Shatt al-Arab ( ar, شط العرب, lit=River of the Arabs; fa, اروندرود, Arvand Rud, lit=Swift River) is a river of some in length that is formed at the confluence of the Tigris–Euphrates river system, Euphrates and Tigris riv ...
, Wadi Ad Dawasir (a dried-out river system on the Arabian Peninsula) and
Limpopo Limpopo is the northernmost Provinces of South Africa, province of South Africa. It is named after the Limpopo River, which forms the province's western and northern borders. The capital and largest city in the province is Polokwane, while th ...
rivers. After the breakup of East
Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic, Jurassic period (about 180 million years ago). The fi ...
and the formation of the Himalayas, the Ganges-Brahmaputra rivers flow into the world's largest delta known as the Bengal delta or Sunderbans.


Marginal seas

Marginal seas, gulfs, bays and straits of the Indian Ocean include: Along the east coast of Africa, the
Mozambique Channel The Mozambique Channel (french: Canal du Mozambique, mg, Lakandranon'i Mozambika, pt, Canal de Moçambique) is an arm (geography), arm of the Indian Ocean located between the Southeast African countries of Madagascar and Mozambique. The channe ...
separates
Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Afric ...
from mainland Africa, while the Sea of Zanj is located north of Madagascar. On the northern coast of the
Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel a ...
,
Gulf of Aden The Gulf of Aden ( ar, خليج عدن, so, Gacanka Cadmeed 𐒅𐒖𐒐𐒕𐒌 𐒋𐒖𐒆𐒗𐒒) is a deepwater gulf of the Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% o ...
is connected to the
Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic language, Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''P ...
by the strait of
Bab-el-Mandeb The Bab-el-Mandeb (Arabic Arabic (, ' ; , ' or ) is a Semitic languages, Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Kh ...
. In the Gulf of Aden, the Gulf of Tadjoura is located in Djibouti and the
Guardafui Channel The Guardafui Channel ( so, Marinka Gardafuul) is an oceanic strait off the tip of the Horn of Africa that lies between the Puntland region of Somalia and Socotra to the west of the Arabian Sea. It connects the Gulf of Aden to the north with the ...
separates Socotra island from the Horn of Africa. The northern end of the Red Sea terminates in the
Gulf of Aqaba The Gulf of Aqaba ( ar, خَلِيجُ ٱلْعَقَبَةِ, Khalīj al-ʿAqabah) or Gulf of Eilat ( he, מפרץ אילת, Mifrátz Eilát) is a large gulf at the northern tip of the Red Sea The Red Sea ( ar, البحر الأحمر - ...
and
Gulf of Suez The Gulf of Suez ( ar, خليج السويس, khalīǧ as-suwais; formerly , ', "Sea of Calm") is a gulf at the northern end of the Red Sea, to the west of the Sinai Peninsula. Situated to the east of the Sinai Peninsula is the smaller Gulf of ...
. The Indian Ocean is artificially connected to the
Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...
without ship lock through the
Suez Canal The Suez Canal ( arz, قَنَاةُ ٱلسُّوَيْسِ, ') is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea to the Red Sea through the Isthmus of Suez and dividing Africa and Asia. The long canal is a popular ...
, which is accessible via the Red Sea. The Arabian Sea is connected to the
Persian Gulf The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Persis, Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a Mediterranean sea (oceanography), me ...
by the
Gulf of Oman The Gulf of Oman or Sea of Oman ( ar, خليج عمان ''khalīj ʿumān''; fa, دریای عمان ''daryâ-ye omân''), also known as Gulf of Makran or Sea of Makran ( ar, خلیج مکران ''khalīj makrān''; fa, دریای مکرا ...
and the
Strait of Hormuz The Strait of Hormuz ( fa, تنگه هرمز ''Tangeh-ye Hormoz'' ar, مَضيق هُرمُز ''Maḍīq Hurmuz'') is a strait between the Persian Gulf and the Gulf of Oman. It provides the only sea passage from the Persian Gulf to the o ...
. In the Persian Gulf, the Gulf of Bahrain separates Qatar from the Arabic Peninsula. Along the west coast of India, the
Gulf of Kutch The Gulf of Kutch is located between the peninsula regions of Kutch district, Kutch and Saurashtra (region), Saurashtra, bounded in the state of Gujarat that borders Pakistan. It opens towards the Arabian Sea facing the Osman Gulf. It is about ...
and
Gulf of Khambat The Gulf of Khambhat, historically known as the Gulf of Cambay, is a bay on the Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the n ...
are located in Gujarat in the northern end while the
Laccadive Sea The Laccadive Sea or Lakshadweep Sea is a body of water bordering India (including its Lakshadweep islands), the Maldives, and Sri Lanka. It is located to the southwest of Karnataka, to the west of Kerala and to the south of Tamil Nadu. This war ...
separates the Maldives from the southern tip of India. The
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...
is off the east coast of India. The
Gulf of Mannar The Gulf of Mannar ( ) is a large shallow bay forming part of the Laccadive Sea in the Indian Ocean with an average depth of .
and the
Palk Strait The Palk Strait ( ta, பாக்கு நீரிணை ''Pākku Nīriṇai'', si, පෝක් සමුද්‍ර සන්ධිය ''Pok Samudra Sandhiya'') is a strait between the Tamil Nadu States and territories of India, state ...
separates Sri Lanka from India, while the
Adam's Bridge Adam's Bridge, '; ta, ஆதாம் பாலம் ' also known as Rama's Bridge or ''Rama Setu'', '; ta, ராமர் பாலம் '; sa, रामसेतु ' is a chain of natural limestone shoals, between Pamban Island, al ...
separates the two. The
Andaman Sea The Andaman Sea (historically also known as the Burma Sea) is a marginal sea of the 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 ...
is located between the Bay of Bengal and the Andaman Islands. In Indonesia, the so-called Indonesian Seaway is composed of the
Malacca Malacca ( ms, Melaka) is a state in Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal terr ...
, Sunda and
Torres Strait The Torres Strait (), also known as Zenadh Kes, is a strait between Australia and the Melanesian island of New Guinea. It is wide at its narrowest extent. To the south is Cape York Peninsula, the northernmost extremity of the Australian mai ...
s. The
Gulf of Carpentaria The Gulf of Carpentaria (, ) is a large, shallow sea enclosed on three sides by northern Australia and bounded on the north by the eastern Arafura Sea (the body of water that lies between Australia and New Guinea). The northern boundary is ...
of located on the Australian north coast while the
Great Australian Bight The Great Australian Bight is a large oceanic bight (geography), bight, or open bay, off the central and western portions of the southern coastline of mainland Australia. Extent Two definitions of the extent are in use – one used by the In ...
constitutes a large part of its southern coast. #
Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel a ...
- 3.862 million km2 #
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...
- 2.172 million km2 #
Andaman Sea The Andaman Sea (historically also known as the Burma Sea) is a marginal sea of the 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 ...
- 797,700 km2 #
Laccadive Sea The Laccadive Sea or Lakshadweep Sea is a body of water bordering India (including its Lakshadweep islands), the Maldives, and Sri Lanka. It is located to the southwest of Karnataka, to the west of Kerala and to the south of Tamil Nadu. This war ...
- 786,000 km2 #
Mozambique Channel The Mozambique Channel (french: Canal du Mozambique, mg, Lakandranon'i Mozambika, pt, Canal de Moçambique) is an arm (geography), arm of the Indian Ocean located between the Southeast African countries of Madagascar and Mozambique. The channe ...
- 700,000 km2 #
Timor Sea The Timor Sea ( id, Laut Timor, pt, Mar de Timor, tet, Tasi Mane or ) is a relatively shallow sea bounded to the north by the island of Timor, to the east by the Arafura Sea, and to the south by Australia. The sea contains a number of reef ...
- 610,000 km2 #
Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic language, Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''P ...
- 438,000 km2 #
Gulf of Aden The Gulf of Aden ( ar, خليج عدن, so, Gacanka Cadmeed 𐒅𐒖𐒐𐒕𐒌 𐒋𐒖𐒆𐒗𐒒) is a deepwater gulf of the Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% o ...
- 410,000 km2 #
Persian Gulf The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Persis, Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a Mediterranean sea (oceanography), me ...
- 251,000 km2 #
Flores Sea The Flores Sea covers of water in Indonesia. The sea is bounded on the north by the island of Celebes and on the south by Sunda Islands of Flores and Sumbawa. Geography The seas that border the Flores Sea are the Bali Sea (to the west), Java ...
- 240,000 km2 #
Molucca Sea The Molucca Sea (Indonesian language, Indonesian: ''Laut Maluku'') is located in the western Pacific Ocean, around the vicinity of Indonesia, specifically bordered by the Indonesian Islands of Sulawesi, Celebes (Sulawesi) to the west, Halmahera t ...
- 200,000 km2 # Oman Sea - 181,000 km2 #
Great Australian Bight The Great Australian Bight is a large oceanic bight (geography), bight, or open bay, off the central and western portions of the southern coastline of mainland Australia. Extent Two definitions of the extent are in use – one used by the In ...
- 45,926 km2 #
Gulf of Aqaba The Gulf of Aqaba ( ar, خَلِيجُ ٱلْعَقَبَةِ, Khalīj al-ʿAqabah) or Gulf of Eilat ( he, מפרץ אילת, Mifrátz Eilát) is a large gulf at the northern tip of the Red Sea The Red Sea ( ar, البحر الأحمر - ...
- 239 km2 #
Gulf of Khambhat The Gulf of Khambhat, historically known as the Gulf of Cambay, is a bay on the Arabian Sea coast of India, bordering the state of Gujarat just north of Mumbai and Diu Island. The Gulf of Khambhat is about long, about wide in the north and up ...
#
Gulf of Kutch The Gulf of Kutch is located between the peninsula regions of Kutch district, Kutch and Saurashtra (region), Saurashtra, bounded in the state of Gujarat that borders Pakistan. It opens towards the Arabian Sea facing the Osman Gulf. It is about ...
#
Gulf of Suez The Gulf of Suez ( ar, خليج السويس, khalīǧ as-suwais; formerly , ', "Sea of Calm") is a gulf at the northern end of the Red Sea, to the west of the Sinai Peninsula. Situated to the east of the Sinai Peninsula is the smaller Gulf of ...


Climate

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 A thermocline (also known as the thermal layer or the metalimnion in lakes) is a thin but distinct layer in a large body of fluid (e.g. water column, water, as in an ocean or lake; or air, e.g. an atmosphere) in which temperature changes more dra ...
. That continent also drives the Indian Ocean
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in Atmosphere of Earth, atmospheric circulation and precipitation associated with annu ...
, the strongest on Earth, which causes large-scale seasonal variations in ocean currents, including the reversal of the
Somali Current The Somali Current is a warm ocean boundary current that runs along the coast of Somalia and Oman in the Western Indian Ocean and is analogous to the Gulf Stream in the Atlantic Ocean. This current is heavily influenced by the monsoons and is th ...
and Indian Monsoon Current. Because of the Indian Ocean Walker circulation there are no continuous equatorial easterlies.
Upwelling Upwelling is an physical oceanography, oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted ...
occurs near the
Horn of Africa The Horn of Africa (HoA), also known as the Somali Peninsula, is a large peninsula and Geopolitics, geopolitical region in East Africa.Robert Stock, ''Africa South of the Sahara, Second Edition: A Geographical Interpretation'', (The Guilford P ...
and the
Arabian Peninsula The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa Africa is t ...
in the
Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's North ...
and north of the trade winds in the Southern Hemisphere. The Indonesian Throughflow is a unique Equatorial connection to the Pacific. The climate north of the
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the ...
is affected by a
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in Atmosphere of Earth, atmospheric circulation and precipitation associated with annu ...
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 The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel a ...
and the
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...
. Some 80% of the total annual rainfall in India occurs during summer and the region is so dependent on this rainfall that many civilisations perished when the Monsoon failed in the past. The 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 The Younger Dryas (c. 12,900 to 11,700 years Before Present, BP) was a return to glacial conditions which temporarily reversed the gradual climate, climatic warming after the Last Glacial Maximum (LGM, c. 27,000 to 20,000 years BP). The Younger ...
. The Indian Ocean is the warmest ocean in the world. Long-term ocean temperature records show a rapid, continuous warming in the Indian Ocean, at about (compared to for the warm pool region) during 1901–2012. Research indicates that human induced greenhouse warming, and changes in the frequency and magnitude of El Niño (or the
Indian Ocean Dipole The Indian Ocean Dipole (IOD), also known as the Indian Niño, is an irregular oscillation of sea surface temperatures in which the western Indian Ocean becomes alternately warmer (positive phase) and then colder (negative phase) than the eastern ...
), events are a trigger to this strong warming in the Indian Ocean. 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. In 1999, the Indian Ocean Experiment showed that fossil fuel and biomass burning in South and Southeast Asia caused air pollution (also known as the
Asian brown cloud The Indian Ocean brown cloud or Asian brown cloud is a layer of air pollution that recurrently covers parts of South Asia, namely the northern Indian Ocean, India, and Pakistan. Viewed from satellite photos, the cloud appears as a giant brown sta ...
) that reach as far as the
Intertropical Convergence Zone The Intertropical Convergence Zone (ITCZ ), known by sailors as the doldrums or the calms because of its monotonous windless weather, is the area where the northeast and the southeast trade winds converge. It encircles Earth near the thermal e ...
at 60°S. This pollution has implications on both a local and global scale.


Oceanography

Forty percent of the sediment of the Indian Ocean is found in the Indus and Ganges fans. The oceanic basins adjacent to the continental slopes mostly contain terrigenous sediments. The ocean south of the polar front (roughly 50° south latitude) is high in biologic productivity and dominated by non-stratified sediment composed mostly of siliceous oozes. Near the three major mid-ocean ridges the ocean floor is relatively young and therefore bare of sediment, except for the
Southwest Indian Ridge The Southwest Indian Ridge (SWIR) is a mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean. A divergent tectonic plate boundary separating the Somali Plate to the north from the Antarctic Plate t ...
due to its ultra-slow spreading rate. 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 The Agulhas Current () is the western boundary current of the southwest Indian Ocean. It flows south along the east coast of Africa from 27°S to 40°S. It is narrow, swift and strong. It is suggested that it is the largest western boundary curren ...
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. The Indian Ocean contains the largest submarine fans of the world, the Bengal Fan and Indus Fan, and the largest areas of slope terraces and
rift valley A rift valley is a linear shaped lowland between several Highland, highlands or mountain ranges created by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The ...
s. The inflow of deep water into the Indian Ocean is 11  Sv, most of which comes from the Circumpolar Deep Water (CDW). The CDW enters the Indian Ocean through the Crozet and
Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Afric ...
basins and crosses the
Southwest Indian Ridge The Southwest Indian Ridge (SWIR) is a mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean. A divergent tectonic plate boundary separating the Somali Plate to the north from the Antarctic Plate t ...
at 30°S. In the Mascarene Basin the CDW becomes a deep
western boundary current Boundary currents are ocean currents with dynamics determined by the presence of a coastline, and fall into two distinct categories: western boundary currents and eastern boundary currents. Eastern boundary currents Eastern boundary currents are ...
before it is met by a re-circulated branch of itself, the North Indian Deep Water. This mixed water partly flows north into the
Somali Basin Somali may refer to: Horn of Africa * Somalis, an inhabitant or ethnicity associated with Greater Somali Region ** Proto-Somali, the ancestors of modern Somalis ** Somali culture ** Somali cuisine ** Somali language, a Cushitic language ** Somali, ...
whilst most of it flows clockwise in the Mascarene Basin where an oscillating flow is produced by
Rossby waves Rossby waves, also known as planetary waves, are a type of inertial wave naturally occurring in rotating fluids. They were first identified by Sweden-born American meteorologist Carl-Gustaf Arvid Rossby. They are observed in the atmosphere ...
. 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 separate three cells south of Madagascar and off South Africa.
North Atlantic Deep Water North Atlantic Deep Water (NADW) is a deep water mass formed in the North Atlantic Ocean. Thermohaline circulation (properly described as meridional overturning circulation) of the world's oceans involves the flow of warm surface waters from the s ...
reaches into the Indian Ocean south of Africa at a depth of 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 (<) in the Southwest Indian Ridge, from where it continues into the
Mozambique Channel The Mozambique Channel (french: Canal du Mozambique, mg, Lakandranon'i Mozambika, pt, Canal de Moçambique) is an arm (geography), arm of the Indian Ocean located between the Southeast African countries of Madagascar and Mozambique. The channe ...
and Prince Edward Fracture Zone. North of 20° south latitude the minimum surface temperature is , exceeding to the east. Southward of 40° south latitude, temperatures drop quickly. The
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...
contributes more than half () 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 seawater from the Indonesian Throughflow. This mixed freshwater joins the South Equatorial Current in the southern tropical Indian Ocean. Sea surface salinity is highest (more than 36  PSU) in the Arabian Sea because evaporation exceeds precipitation there. In the Southeast Arabian Sea salinity drops to less than 34 PSU. It is the lowest (c. 33 PSU) in the Bay of Bengal because of river runoff and precipitation. The Indonesian Throughflow and precipitation results in lower salinity (34 PSU) along the Sumatran west coast. Monsoonal variation results in eastward transportation of saltier water from the Arabian Sea to the Bay of Bengal from June to September and in westerly transport by the East India Coastal Current to the Arabian Sea from January to April. It is found that Arabian Sea warming is in response to the reduction in lower monsoon circulation in recent decades. An Indian Ocean garbage patch was discovered in 2010 covering at least . Riding the southern
Indian Ocean Gyre The Indian Ocean gyre, located in the Indian Ocean, is one of the five major oceanic gyres, large systems of rotating ocean currents, which together form the backbone of the global conveyor belt. The Indian Ocean gyre is composed of two major curr ...
, this vortex of plastic garbage constantly circulates the ocean from Australia to Africa, down the
Mozambique Channel The Mozambique Channel (french: Canal du Mozambique, mg, Lakandranon'i Mozambika, pt, Canal de Moçambique) is an arm (geography), arm of the Indian Ocean located between the Southeast African countries of Madagascar and Mozambique. The channe ...
, and back to Australia in a period of six years, except for debris that gets indefinitely stuck in the centre of the gyre. 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. There are two amphidromes of opposite rotation in the Indian Ocean, probably caused by
Rossby wave Rossby waves, also known as planetary waves, are a type of inertial wave naturally occurring in rotating fluids. They were first identified by Sweden-born American meteorologist Carl-Gustaf Arvid Rossby. They are observed in the atmospheres and o ...
propagation.
Iceberg An iceberg is a piece of Fresh water, freshwater ice more than 15 m long that has broken off a glacier or an ice shelf and is floating freely in open (salt) water. Smaller chunks of floating glacially-derived ice are called "growlers" or "bergy ...
s 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. 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 also increases in the Indian Ocean, except in the south tropical Indian Ocean where it decreases, a pattern most likely caused by rising levels of
greenhouse gas A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
es.


Marine life

Among the
tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...
oceans, the western Indian Ocean hosts one of the largest concentrations of
phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), m ...
blooms in summer, due to the strong
monsoon A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in Atmosphere of Earth, atmospheric circulation and precipitation associated with annu ...
winds. The monsoonal wind forcing leads to a strong coastal and open ocean
upwelling Upwelling is an physical oceanography, oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted ...
, which introduces nutrients into the upper zones where sufficient light is available for
photosynthesis Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemica ...
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 A tuna is a saltwater fish that belongs to the Tribe (biology), tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet ...
catch. Its fish are of great and growing importance to the bordering countries for domestic consumption and export. Fishing fleets from
Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
,
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
,
South Korea South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...
, and
Taiwan Taiwan, officially the Republic of China (ROC), is a Country, country in East Asia, at the junction of the East China Sea, East and South China Seas in the northwestern Pacific Ocean, with the China, People's Republic of China (PRC) to the n ...
also exploit the Indian Ocean, mainly for
shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the Decapoda, decapod order, although some Shrimp#Non-decapods , crustaceans out ...
and tuna. 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. Endangered and vulnerable marine mammals and turtles: 80% of the Indian Ocean is open ocean and includes nine
large marine ecosystem Large marine ecosystems (LMEs) are regions of the world's ocean The ocean (also the sea or the world ocean) is the body of Saline water, salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Water distribu ...
s: the
Agulhas Current The Agulhas Current () is the western boundary current of the southwest Indian Ocean. It flows south along the east coast of Africa from 27°S to 40°S. It is narrow, swift and strong. It is suggested that it is the largest western boundary curren ...
, Somali Coastal Current,
Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic language, Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''P ...
,
Arabian Sea The Arabian Sea ( ar, اَلْبَحرْ ٱلْعَرَبِيُّ, Al-Bahr al-ˁArabī) is a region of the northern Indian Ocean bounded on the north by Pakistan, Iran and the Gulf of Oman, on the west by the Gulf of Aden, Guardafui Channel a ...
,
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean, bounded on the west and northwest by India, on the north by Bangladesh, and on the east by Myanmar and the Andaman and Nicobar Islands of India. Its southern limit is a line between ...
,
Gulf of Thailand The Gulf of Thailand, also known as the Gulf of Siam, is a shallow inlet in the southwestern South China Sea, bounded between the southwestern shores of the Indochinese Peninsula and the northern half of the Malay Peninsula. It is around in le ...
, West Central Australian Shelf, Northwest Australian Shelf, and Southwest Australian Shelf. Coral reefs cover c. . The coasts of the Indian Ocean includes beaches and intertidal zones covering and 246 larger
estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...
.
Upwelling Upwelling is an physical oceanography, oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted ...
areas are small but important. The hypersaline
saltern A saltern is an area or installation for making salt. Salterns include modern salt-making works (saltworks), as well as hypersaline waters that usually contain high concentrations of Halophile, halophilic microorganisms, primarily haloarchaea but ...
s in India covers between and species adapted for this environment, such as '' Artemia salina'' and '' Dunaliella salina'', are important to bird life. Coral reefs, sea grass beds, and mangrove forests are the most productive ecosystems of the Indian Ocean — coastal areas produce 20 tones per square kilometre of fish. These areas, however, are also being urbanised with populations often exceeding several thousand people per square kilometre and fishing techniques become more effective and often destructive beyond sustainable levels while the increase in sea surface temperature spreads coral bleaching.
Mangrove A mangrove is a shrub or tree that grows in coastal saline water, saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves are taxonomically diverse, as a result of convergent evoluti ...
s covers in the Indian Ocean region, or almost half of the world's mangrove habitat, of which is located in Indonesia, or 50% of mangroves in the Indian Ocean. Mangroves originated in the Indian Ocean region and have adapted to a wide range of its habitats but it is also where it suffers its biggest loss of habitat. In 2016 six new animal species were identified at
hydrothermal vents A hydrothermal vent is a fissure vent, fissure on the seabed from which Geothermal gradient, geothermally heated water discharges. They are commonly found near volcano, volcanically active places, areas where tectonic plates are moving apart at m ...
in the Southwest Indian Ridge: a "Hoff" crab, a "giant peltospirid" snail, a whelk-like snail, a limpet, a scaleworm and a polychaete worm. The
West Indian Ocean coelacanth The West Indian Ocean coelacanth (''Latimeria chalumnae'') (sometimes known as gombessa, African coelacanth, or simply coelacanth) is a Sarcopterygii, crossopterygian, one of two extant species of coelacanth, a rare order of vertebrates more clo ...
was discovered in the Indian Ocean off South Africa in the 1930s and in the late 1990s another species, the
Indonesian coelacanth The Indonesian coelacanth (''Latimeria menadoensis'', Indonesian: ''raja laut'') is one of two living species of coelacanth, identifiable by its brown color. It is listed as Vulnerable species, vulnerable by the IUCN, while the other species, '' ...
, was discovered off Sulawesi Island, Indonesia. Most extant coelacanths have been found in the Comoros. Although both species represent an order of lobe-finned fishes known from the Early Devonian (410 ) and though extinct 66 mya, they are morphologically distinct from their Devonian ancestors. Over millions of years, coelacanths evolved to inhabit different environments — lungs adapted for shallow, brackish waters evolved into gills adapted for deep marine waters.


Biodiversity

Of Earth's 36
biodiversity hotspot A biodiversity hotspot is a ecoregion, biogeographic region with significant levels of biodiversity that is threatened by human habitation. Norman Myers wrote about the concept in two articles in ''The Environmentalist'' in 1988 and 1990, after w ...
nine (or 25%) are located on the margins 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. The origin of this diversity is debated; the break-up of Gondwana can explain vicariance older than 100 mya, but the diversity on the younger, smaller islands must have required a Cenozoic dispersal from the rims of the Indian Ocean to the islands. A "reverse colonisation", from islands to continents, apparently occurred more recently; the
chameleon Chameleons or chamaeleons (Family (biology), family Chamaeleonidae) are a distinctive and highly specialized clade of Old World lizards with 202 species described as of June 2015. The members of this family are best known for their distinct ran ...
s, for example, first diversified on Madagascar and then colonised Africa. Several species on the islands of the Indian Ocean are textbook cases of evolutionary processes; the
dung beetle Dung beetles are beetle Beetles are insects that form the Taxonomic rank, order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, Elytron, elytra, distinguishing them from most other ...
s, day geckos, and
lemur Lemurs ( ) (from Latin ''lemures'' – ghosts or spirits) are Strepsirrhini, wet-nosed primates of the Superfamily (biology), superfamily Lemuroidea (), divided into 8 Family (biology), families and consisting of 15 genera and around 100 exist ...
s are all examples of
adaptive radiation In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic int ...
. Many bones (250 bones per square metre) of recently extinct vertebrates have been found in the
Mare aux Songes The Mare aux Songes () swamp is a lagerstätte located close to the sea in south eastern Mauritius. Many subfossils of recently extinct animals have accumulated in the swamp, which was once a lake, and some of the first subfossil remains of dodos w ...
swamp in Mauritius, including bones of the
Dodo The dodo (''Raphus cucullatus'') is an extinction, extinct flightless bird that was endemism, endemic to the island of Mauritius, which is east of Madagascar in the Indian Ocean. The dodo's closest genetic distance, genetic relative was the ...
bird (''Raphus cucullatus'') and '' Cylindraspis'' giant tortoise. An analysis of these remains suggests a process of aridification began in the southwest Indian Ocean began around 4,000 years ago. * Maputaland-Pondoland-Albany (MPA); 8,100 (1,900 endemic) species of plants; 541 (0) birds; 205 (36) reptiles; 73 (20) freshwater fishes; 73 (11) amphibians; and 197 (3) mammals. Mammalian megafauna once widespread in the MPA was driven to near extinction in the early 20th century. Some species have been successfully recovered since then — the population of
white rhinoceros The white rhinoceros, white rhino or square-lipped rhinoceros (''Ceratotherium simum'') is the largest extant species of rhinoceros. It has a wide mouth used for grazing (behaviour), grazing and is the most social of all rhino species. The white ...
(''Ceratotherium simum simum'') increased from less than 20 individuals in 1895 to more than 17,000 as of 2013. Other species are still dependent of fenced areas and management programs, including
black rhinoceros The black rhinoceros, black rhino or hook-lipped rhinoceros (''Diceros bicornis'') is a species of rhinoceros, native to eastern and southern Africa including Angola, Botswana, Kenya, Malawi, Mozambique, Namibia, South Africa, Eswatini, Tanzania ...
(''Diceros bicornis minor''),
African wild dog The African wild dog (''Lycaon pictus''), also called the painted dog or Cape hunting dog, is a wild Caninae, canine which is a native species to sub-Saharan Africa. It is the largest wild canine in Africa, and the only Neontology#Extant taxa vs ...
(''Lycaon pictus''),
cheetah The cheetah (''Acinonyx jubatus'') is a large Felidae, cat native to Africa and central Iran. It is the Fastest animals, fastest land animal, estimated to be capable of running at with the fastest reliably recorded speeds being , and as suc ...
(''Acynonix jubatus''),
elephant Elephants are the Largest and heaviest animals, largest existing land animals. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant. They are the only surviving members ...
(''Loxodonta africana''), and
lion The lion (''Panthera leo'') is a large Felidae, cat of the genus ''Panthera'' native to Africa and India. It has a muscular, broad-chested body; short, rounded head; round ears; and a hairy tuft at the end of its tail. It is sexually dimorphi ...
(''Panthera leo''). * Coastal forests of eastern Africa; 4,000 (1,750 endemic) species of plants; 636 (12) birds; 250 (54) reptiles; 219 (32) freshwater fishes; 95 (10) amphibians; and 236 (7) mammals. This biodiversity hotspot (and namesake ecoregion and "Endemic Bird Area") is a patchwork of small forested areas, often with a unique assemblage of species within each, located within from the coast and covering a total area of c. . It also encompasses coastal islands, including Zanzibar and Pemba, and Mafia. *
Horn of Africa The Horn of Africa (HoA), also known as the Somali Peninsula, is a large peninsula and Geopolitics, geopolitical region in East Africa.Robert Stock, ''Africa South of the Sahara, Second Edition: A Geographical Interpretation'', (The Guilford P ...
; 5,000 (2,750 endemic) species of plants; 704 (25) birds; 284 (93) reptiles; 100 (10) freshwater fishes; 30 (6) amphibians; and 189 (18) mammals. This area, one of the only two hotspots that are entirely arid, includes the
Ethiopian Highlands The Ethiopian Highlands is a rugged mass of mountains in Ethiopia in Northeast Africa. It forms the largest continuous area of its elevation in the continent, with little of its surface falling below , while the summits reach heights of up to . ...
, the East African Rift valley, the
Socotra Socotra or Soqotra (; ar, سُقُطْرَىٰ ; so, Suqadara) is an island of the Republic of Yemen in 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 Ea ...
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 The hamadryas baboon (''Papio hamadryas'' ) is a species of baboon within the Old World monkey family. It is the northernmost of all the baboons, being native to the Horn of Africa and the southwestern region of the Arabian Peninsula. These regi ...
(''Papio hamadryas''). It also contains many reptiles. In Somalia, the centre of the hotspot, the landscape is dominated by
Acacia ''Acacia'', commonly known as the wattles or acacias, is a large genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV class ...
-
Commiphora The genus of the myrrhs, ''Commiphora'', is the most species-rich genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV class ...
deciduous bushland, but also includes the Yeheb nut (''Cordeauxia edulus'') and species discovered more recently such as the Somali
cyclamen ''Cyclamen'' ( or ) is a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of ...
(''Cyclamen somalense''), the only cyclamen outside the Mediterranean. Warsangli linnet (''Carduelis johannis'') is an endemic bird found only in northern Somalia. An unstable political situation and mismanagement 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 Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
; 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. Encompassing the west coast of India and Sri Lanka, until c. 10,000 years ago a landbridge connected Sri Lanka to the Indian Subcontinent, hence this region shares a common community of species. * Indo-Burma; 13.500 (7,000 endemic) species of plants; 1,277 (73) birds; 518 (204) reptiles; 1,262 (553) freshwater fishes; 328 (193) amphibians; and 401 (100) mammals. Indo-Burma encompasses a series of mountain ranges, five of Asia's largest river systems, and a wide range of habitats. The region has a long and complex geological history, and long periods
rising sea levels Rising may refer to: * Rising, a stage in baking - see Proofing (baking technique) *Elevation * Short for Uprising, a rebellion Film and TV * Rising (Stargate Atlantis), "Rising" (''Stargate Atlantis''), the series premiere of the science fiction ...
and glaciations have isolated ecosystems and thus promoted a high degree of endemism and
speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...
. The region includes two centres of endemism: the Annamite Mountains and the northern highlands on the China-Vietnam border. Several distinct
floristic region A phytochorion, in phytogeography, is a geographic area with a relatively uniform composition of plant species. Adjacent phytochoria do not usually have a sharp boundary, but rather a soft one, a transitional area in which many species from both re ...
s, the Indian, Malesian, Sino-Himalayan, and Indochinese regions, meet in a unique way in Indo-Burma and the hotspot contains an estimated 15,000–25,000 species of vascular plants, many of them endemic. *
Sundaland Sundaland (also called Sundaica or the Sundaic region) is a Biogeography, biogeographical region of Southeast Asia, South-eastern Asia corresponding to a larger landmass that was exposed throughout the Pleistocene, last 2.6 million years duri ...
; 25,000 (15,000 endemic) species of plants; 771 (146) birds; 449 (244) reptiles; 950 (350) freshwater fishes; 258 (210) amphibians; and 397 (219) mammals. Sundaland encompasses 17,000 islands of which Borneo and Sumatra are the largest. Endangered mammals include the Bornean and
Sumatran orangutan The Sumatran orangutan (''Pongo abelii'') is one of the three species of orangutans. Critically Endangered, and found only in the north of the Indonesian island of Sumatra, it is rarer than the Bornean orangutan but more common than the recently ...
s, the
proboscis monkey The proboscis monkey (''Nasalis larvatus'') or long-nosed monkey is an arboreal Old World monkey with an unusually large nose, a reddish-brown skin color and a long tail. It is Endemism, endemic to the southeast Asian island of Borneo and is fou ...
, and the
Javan Javan () was the fourth son of Noah's son Japheth according to the "Generations of Noah" (Book of Genesis, chapter 10) in the Hebrew Bible. Josephus states the traditional belief that this individual was the ancestor of the Greeks. Also servin ...
and
Sumatran rhinoceros The Sumatran rhinoceros (''Dicerorhinus sumatrensis''), also known as the Sumatran rhino, hairy rhinoceros or Asian two-horned rhinoceros, is a rare member of the family Rhinocerotidae and one of five extant species of rhinoceros. It is the o ...
es. *
Wallacea Wallacea is a biogeography, biogeographical designation for a group of mainly Indonesian Archipelago, Indonesian islands separated by deep-water straits from the Asia, Asian and Australia (continent), Australian continental shelf, continental ...
; 10,000 (1,500 endemic) species of plants; 650 (265) birds; 222 (99) reptiles; 250 (50) freshwater fishes; 49 (33) amphibians; and 244 (144) mammals. *
Southwest Australia Southwest Australia is a biogeographic region in Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bou ...
; 5,571 (2,948 endemic) species of plants; 285 (10) birds; 177 (27) reptiles; 20 (10) freshwater fishes; 32 (22) amphibians; and 55 (13) mammals. Stretching from
Shark Bay Shark Bay (Malgana language, Malgana: ''Gathaagudu'', "two waters") is a World Heritage Site in the Gascoyne region of Western Australia. The http://www.environment.gov.au/heritage/places/world/shark-bay area is located approximately north ...
to Israelite Bay and isolated by the arid
Nullarbor Plain The Nullarbor Plain ( ; Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) ...
, the southwestern corner of Australia is a floristic region with a stable climate in which one of the world's largest floral biodiversity and an 80% endemism has evolved. From June to September it is an explosion of colours and the Wildflower Festival in Perth in September attracts more than half a million visitors.


Geology

As the youngest of the major oceans, the Indian Ocean has active spreading ridges that are part of the worldwide system of
mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a Diverge ...
s. In the Indian Ocean these spreading ridges meet at the
Rodrigues Triple Point The Rodrigues Triple Junction (RTJ), also known as the Central Indian ceanTriple Junction (CITJ) is a geologic triple junction in the southern Indian Ocean where three tectonic plates meet: the African Plate, the Indo-Australian Plate, and the ...
with the Central Indian Ridge, including the Carlsberg Ridge, separating the
African Plate The African Plate is a List of tectonic plates#Major plates, major tectonic plate that includes much of the continent of Africa (except for its east Africa, easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by ...
from the
Indian Plate The Indian Plate (or India Plate) is a List of tectonic plates#Minor plates, minor tectonic plate straddling the equator in the Eastern Hemisphere. Originally a part of the ancient continent of Gondwana, the Indian Plate broke away from the ot ...
; the
Southwest Indian Ridge The Southwest Indian Ridge (SWIR) is a mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean. A divergent tectonic plate boundary separating the Somali Plate to the north from the Antarctic Plate t ...
separating the African Plate from the
Antarctic Plate The Antarctic Plate is a list of tectonic plates, tectonic plate containing the continent of Antarctica, the Kerguelen Plateau, and list of Antarctic and subantarctic islands, some remote islands in the Southern Ocean and other surrounding ocea ...
; and the
Southeast Indian Ridge The Southeast Indian Ridge (SEIR) is a mid-ocean ridge in the southern Indian Ocean. A divergent tectonic plate boundary stretching almost between the Rodrigues Triple Junction () in the Indian Ocean and the Macquarie Triple Junction () in the P ...
separating the
Australian Plate The Australian Plate is a major tectonic plate in the eastern hemisphere, eastern and, largely, southern hemisphere, southern hemispheres. Originally a part of the ancient continent of Gondwana, Australia remained connected to Indian plate, India ...
from the
Antarctic Plate The Antarctic Plate is a list of tectonic plates, tectonic plate containing the continent of Antarctica, the Kerguelen Plateau, and list of Antarctic and subantarctic islands, some remote islands in the Southern Ocean and other surrounding ocea ...
. The Central Indian Ridge is intercepted by the
Owen Fracture Zone The Owen Fracture Zone (OFZ), though misnamed a fracture zone, is a transform fault A transform fault or transform boundary, is a fault (geology), fault along a plate boundary where the motion (physics), motion is predominantly Horizontal pl ...
. Since the late 1990s, however, it has become clear that this traditional definition of the
Indo-Australian Plate The Indo-Australian Plate is a List of tectonic plates#Major plates, major tectonic plate that includes the Australia (continent), continent of Australia and the surrounding ocean and extends northwest to include the Indian subcontinent and the ad ...
cannot be correct; it consists of three plates — the
Indian Plate The Indian Plate (or India Plate) is a List of tectonic plates#Minor plates, minor tectonic plate straddling the equator in the Eastern Hemisphere. Originally a part of the ancient continent of Gondwana, the Indian Plate broke away from the ot ...
, the Capricorn Plate, and
Australian Plate The Australian Plate is a major tectonic plate in the eastern hemisphere, eastern and, largely, southern hemisphere, southern hemispheres. Originally a part of the ancient continent of Gondwana, Australia remained connected to Indian plate, India ...
 — separated by diffuse boundary zones. Since 20 Ma the
African Plate The African Plate is a List of tectonic plates#Major plates, major tectonic plate that includes much of the continent of Africa (except for its east Africa, easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by ...
is being divided by the
East African Rift The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. In the past it was considered to be part of a ...
System into the Nubian and
Somalia Somalia, , Osmanya script: 𐒈𐒝𐒑𐒛𐒐𐒘𐒕𐒖; ar, الصومال, aṣ-Ṣūmāl officially the Federal Republic of SomaliaThe ''Federal Republic of Somalia'' is the country's name per Article 1 of thProvisional Constitut ...
plates. There are only two trenches in the Indian Ocean: the -long Java Trench between Java and the Sunda Trench and the -long
Makran Trench The Makran Trench is the physiographic expression of a subduction zone along the northeastern margin of the Gulf of Oman adjacent to the southwestern coast of Balochistan Province, Balochistan of Pakistan and the southeastern coast of Iran. In ...
south of Iran and Pakistan. A series of ridges and seamount chains produced by
hotspots Hotspot, Hot Spot or Hot spot may refer to: Places * Hot Spot, Kentucky, a community in the United States Arts, entertainment, and media Fictional entities * Hot Spot (comics), a name for the DC Comics character Isaiah Crockett * Hot Spot (Tran ...
pass over the Indian Ocean. The
Réunion hotspot The Réunion hotspot is a volcanic A volcano is a rupture in the Crust (geology), crust of a Planet#Planetary-mass objects, planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and volcanic gas, gases to escape from a ma ...
(active 70–40 million years ago) connects
Réunion Réunion (; french: La Réunion, ; previously ''Île Bourbon''; rcf, label=Réunion Creole, Reunionese Creole, La Rényon) is an island in the Indian Ocean that is an overseas departments and regions of France, overseas department and region ...
and the
Mascarene Plateau The Mascarene Plateau is a oceanic plateau, submarine plateau in the Indian Ocean, north and east of Madagascar. The plateau extends approximately , from Seychelles in the north to Réunion in the south. The plateau covers an area of over of s ...
to the Chagos-Laccadive Ridge and the
Deccan Traps The Deccan Traps is a large igneous province of west-central India (17–24°N, 73–74°E). It is one of the largest volcanic features on Earth, taking the form of a large shield volcano. It consists of numerous layers of solidified flo ...
in north-western India; the
Kerguelen hotspot The Kerguelen hotspot is a volcanic A volcano is a rupture in the Crust (geology), crust of a Planet#Planetary-mass objects, planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and volcanic gas, gases to escape from a mag ...
(100–35 million years ago) connects the
Kerguelen Islands The Kerguelen Islands ( or ; in French commonly ' but officially ', ), also known as the Desolation Islands (' in French), are a archipelago, group of islands in the subantarctic, sub-Antarctic constituting one of the two exposed parts of the ...
and
Kerguelen Plateau The Kerguelen Plateau (, ), also known as the Kerguelen–Heard Plateau, is an oceanic plateau and a large igneous province (LIP) located on the Antarctic Plate, in the southern Indian Ocean. It is about to the southwest of Australia and is n ...
to 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 east, 90th meridian at the center of the Eastern Hemisphe ...
and the Rajmahal Traps in north-eastern India; the Marion hotspot (100–70 million years ago) possibly connects
Prince Edward Islands The Prince Edward Islands are two small uninhabited islands in the subantarctic, sub-Antarctic Indian Ocean that are part of South Africa. The islands are named Marion Island (named after Marc-Joseph Marion du Fresne, 1724–1772) and Prince ...
to the Eighty Five East Ridge. These hotspot tracks have been broken by the still active spreading ridges mentioned above. There are fewer seamounts in the Indian Ocean than in the Atlantic and Pacific. These are typically deeper than and located north of 55°S and west of 80°E. 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 The Southwest Indian Ridge (SWIR) is a mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean. A divergent tectonic plate boundary separating the Somali Plate to the north from the Antarctic Plate t ...
, Chagos-Laccadive Ridge, 85°E Ridge, 90°E Ridge,
Southeast Indian Ridge The Southeast Indian Ridge (SEIR) is a mid-ocean ridge in the southern Indian Ocean. A divergent tectonic plate boundary stretching almost between the Rodrigues Triple Junction () in the Indian Ocean and the Macquarie Triple Junction () in the P ...
,
Broken Ridge The Broken Ridge or Broken Plateau is an oceanic plateau An oceanic or submarine plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides. There are 184 oceanic pla ...
, and East Indiaman Ridge. The Agulhas Plateau and
Mascarene Plateau The Mascarene Plateau is a oceanic plateau, submarine plateau in the Indian Ocean, north and east of Madagascar. The plateau extends approximately , from Seychelles in the north to Réunion in the south. The plateau covers an area of over of s ...
are the two major shallow areas. The opening of the Indian Ocean began 156  when Africa separated from East
Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic, Jurassic period (about 180 million years ago). The fi ...
. The Indian Subcontinent began to separate from Australia-Antarctica 135–125 Ma and as the
Tethys Ocean The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean that covered most of the Earth Earth is the third planet from the Sun and the only astronomical object known to har ...
north of India began to close 118–84 Ma the Indian Ocean opened behind it.


History

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 Eurocentrism (also Eurocentricity or Western-centrism) is a World view, worldview that is centered on Western culture, Western civilization or a biased view that favors it over non-Western civilizations. The exact scope of Eurocentrism varies f ...
and largely dependent on 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 periods are often subdivided into Portuguese, Dutch, and British periods. A concept of an "Indian Ocean World" (IOW), similar to that of the "
Atlantic World The Atlantic World comprises the interactions among the peoples and empires bordering the Atlantic Ocean rim from the beginning of the Age of Discovery to the early 19th century. Atlantic history is split between three different contexts: trans-A ...
", exists but emerged much more recently and is not well established. The IOW is, nevertheless, 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 from them until European 19th-century colonial dominance. The diverse history of the Indian Ocean is a unique mix of cultures, ethnic 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.


First settlements

Pleistocene fossils of ''
Homo erectus ''Homo erectus'' (; meaning ":wikt:erectus, upright man") is an extinct species of archaic human from the Pleistocene, with its earliest occurrence about 2 million years ago. Several human species, such as ''H. heidelbergensis'' and ''H. ...
'' and other pre–''H. sapiens'' hominid fossils, similar to '' H. heidelbergensis'' in Europe, have been found in India. According to the
Toba catastrophe theory The Youngest Toba eruption was a supervolcano eruption Several types of volcanic eruptions—during which lava, tephra (Volcanic ash, ash, lapilli, volcanic bombs and volcanic blocks), and Volcanic gas, assorted gases are expelled from a ...
, a supereruption c. 74,000 years ago at
Lake Toba Lake Toba ( id, Danau Toba) (Toba Batak language, Toba Batak: ᯖᯀᯬ ᯖᯬᯅ; romanized: ''Tao Toba'') is a large natural lake in North Sumatra, Indonesia, occupying the caldera of a supervolcano. The lake is located in the middle of the no ...
, Sumatra, covered India with volcanic ashes and wiped out one or more lineages of such archaic humans in India and Southeast Asia. The ''Out of Africa'' theory states that ''Homo sapiens'' spread from Africa into mainland Eurasia. The more recent ''
Southern Dispersal In the context of the recent African origin of modern humans, the Southern Dispersal scenario (also the coastal migration or great coastal migration hypothesis) refers to the early migration along the southern coast of Asia, from the Arabian Pe ...
'' or ''Coastal hypothesis'' instead advocates that modern humans spread along the coasts of the Arabic Peninsula and southern Asia. This hypothesis is supported by
mtDNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondrion, mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mit ...
research which reveals a rapid dispersal event during the
Late Pleistocene The Late Pleistocene is an unofficial Age (geology), age in the international geologic timescale in chronostratigraphy, also known as Upper Pleistocene from a Stratigraphy, stratigraphic perspective. It is intended to be the fourth division of ...
(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 Sunda over
Wallacea Wallacea is a biogeography, biogeographical designation for a group of mainly Indonesian Archipelago, Indonesian islands separated by deep-water straits from the Asia, Asian and Australia (continent), Australian continental shelf, continental ...
to 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 ''Sorghum'' () is a genus of about 25 species of flowering plants in the grass family (Poaceae). Some of these species are grown as cereals for human consumption and some in pastures for animals. One species is grown for grain, while many other ...
,
pearl millet Pearl millet (''Cenchrus americanus'', commonly known as the synonym ''Pennisetum glaucum''; also known as 'Bajra' in Hindi language, Hindi, 'Sajje' in Kannada, 'Kambu' in Tamil language, Tamil, 'Bajeer' in Kumaoni language, Kumaoni and 'Maiwa' ...
,
finger millet ''Eleusine coracana'', or finger millet, also known as ragi in India, kodo in Nepal, is an Annual plant, annual herbaceous plant widely grown as a cereal crop in the arid and Semi-arid climate, semiarid areas in Africa and Asia. It is a tetraploi ...
,
cowpea The cowpea (''Vigna unguiculata'') is an Annual plant, annual Herbaceous plant, herbaceous legume from the genus ''Vigna''. Its tolerance for sandy soil and low rainfall have made it an important crop in the Semi-arid climate, semiarid regions a ...
, and
hyacinth bean ''Lablab purpureus'' is a species of bean in the family Fabaceae The Fabaceae or Leguminosae,Gujarat Gujarat (, ) is a States of India, state along the Western India, western coast of India. Its coastline of about is the longest in the country, most of which lies on the Kathiawar peninsula. Gujarat is the List of states and union territories ...
in India during the
Late Harappan The Indus Valley Civilisation (IVC), also known as the Indus Civilisation was a Bronze Age civilisation in the northwestern regions of South Asia, lasting from 3300 Common Era, BCE to 1300 BCE, and in its mature form 2600 B ...
(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.
Broomcorn millet ''Panicum miliaceum'' is a grain crop with many common names, including proso millet, broomcorn millet, common millet, hog millet, Kashfi millet, red millet, and white millet. Archaeobotany, Archaeobotanical evidence suggests millet was first dom ...
found its way from Central Asia to Africa, together with chicken and
zebu The zebu (; ''Bos indicus'' or ''Bos taurus indicus''), sometimes known in the plural as indicine cattle or humped cattle, is a species or subspecies of domestic cattle originating in the Indian sub-continent. Zebu are characterised by a fatty h ...
cattle, although the exact timing is disputed. Around 2000 BCE
black pepper Black pepper (''Piper nigrum'') is a flowering plant, flowering vine in the family Piperaceae, cultivated for its fruit, known as a peppercorn, which is usually dried and used as a spice and seasoning. The fruit is a drupe (stonefruit) which is ...
and
sesame Sesame ( or ; ''Sesamum indicum'') is a flowering plant in the genus ''Sesamum'', also called benne. Numerous wild relatives occur in Africa and a smaller number in India. It is widely naturalization (biology), naturalized in tropical regions a ...
, both native to Asia, appear in Egypt, albeit in small quantities. Around the same time the
black rat The black rat (''Rattus rattus''), also known as the roof rat, ship rat, or house rat, is a common long-tailed rodent of the stereotypical rat genus ''Rattus'', in the subfamily Murinae. It likely originated in the Indian subcontinent, but is n ...
and the
house mouse The house mouse (''Mus musculus'') is a small mammal of the order Rodentia, characteristically having a pointed snout, large rounded ears, and a long and almost hairless tail. It is one of the most abundant species of the genus ''Mus (genus), Mus ...
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
Gulf of Carpentaria The Gulf of Carpentaria (, ) is a large, shallow sea enclosed on three sides by northern Australia and bounded on the north by the eastern Arafura Sea (the body of water that lies between Australia and New Guinea). The northern boundary is ...
in northern Australia in 536 CE. Evidences for these impacts, the team argue, are micro-ejecta and
Chevron Chevron (often relating to V-shaped patterns) may refer to: Science and technology * Chevron (aerospace), sawtooth patterns on some jet engines * Chevron (anatomy), a bone * ''Eulithis testata'', a moth * Chevron (geology), a fold in rock lay ...
dune A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, fl ...
s in southern Madagascar and in the Australian gulf. Geological evidences suggest the tsunamis caused by these impacts reached above sea level and inland. The impact events must have disrupted human settlements and perhaps even contributed to major climate changes.


Antiquity

The history of the Indian Ocean is marked by maritime trade; cultural and commercial exchange probably date back at least seven thousand years. Human culture spread early on the shores of the Indian Ocean and was always linked to the cultures of the Mediterranean and the 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. During this period, independent, short-distance oversea communications along its
littoral The littoral zone or nearshore is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely inundated), to coastal areas ...
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 the Arabian Sea. Sherds of Ubaid (2500–500 BCE) pottery have been found in the western Gulf at
Dilmun Dilmun, or Telmun, (Sumerian language, Sumerian: , later 𒉌𒌇(𒆠), ni.tukki = DILMUNki; ar, دلمون) was an ancient East Semitic-speaking civilization in Eastern Arabia mentioned from the 3rd millennium BC onwards. Based on contextual ...
, present-day
Bahrain Bahrain ( ; ; ar, البحرين, al-Bahrayn, locally ), officially the Kingdom of Bahrain, ' is an island country in Western Asia. It is situated on the Arab states of the Persian Gulf, Persian Gulf, and comprises a small archipelago made u ...
; traces of exchange between this trading centre and
Mesopotamia Mesopotamia ''Mesopotamíā''; ar, بِلَاد ٱلرَّافِدَيْن or ; syc, ܐܪܡ ܢܗܪ̈ܝܢ, or , ) is a historical region of Western Asia situated within the Tigris–Euphrates river system, in the northern part of the F ...
. The
Sumer Sumer () is the earliest known civilization in the historical region of southern Mesopotamia (south-central Iraq), emerging during the Chalcolithic and Early Bronze Age, early Bronze Ages between the sixth and fifth millennium BC. It is one of ...
ians traded grain, pottery, and
bitumen Asphalt, also known as bitumen (, ), is a sticky, black, highly viscosity, viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a Pitch (resin), pitch. Before the ...
(used for reed boats) for copper, stone, timber, tin, dates, onions, and pearls. Coast-bound vessels transported goods between the
Indus Valley civilisation The Indus Valley Civilisation (IVC), also known as the Indus Civilisation was a Bronze Age civilisation in the northwestern regions of South Asia, lasting from 3300 Common Era, BCE to 1300 BCE, and in its mature form 2600 B ...
(2600–1900 
BCE Common Era (CE) and Before the Common Era (BCE) are year notations for the Gregorian calendar The Gregorian calendar is the calendar used in most parts of the world. It was introduced in October 1582 by Pope Gregory XIII as a modificatio ...
) in the Indian subcontinent (modern-day Pakistan and Northwest India) and the Persian Gulf and Egypt. The Red Sea, one of the main trade routes in Antiquity, was explored by
Egyptians Egyptians ( arz, المَصرِيُون, translit=al-Maṣriyyūn, ; arz, المَصرِيِين, translit=al-Maṣriyyīn, ; cop, ⲣⲉⲙⲛ̀ⲭⲏⲙⲓ, remenkhēmi) are an ethnic group native to the Nile Valley in Egypt. Egyptian ident ...
and
Phoenicia Phoenicia () was an ancient Semitic-speaking peoples, ancient thalassocracy, thalassocratic civilization originating in the Levant region of the eastern Mediterranean, primarily located in modern Lebanon. The territory of the Phoenician city-st ...
ns during the last two millennia BCE. In the 6th century, BCE Greek explorer
Scylax of Caryanda Scylax of Caryanda ( el, Σκύλαξ ὁ Καρυανδεύς) was a Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-Euro ...
made a journey to India, working for the Persian king 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 Alexander III of Macedon ( grc, wikt:Ἀλέξανδρος, Ἀλέξανδρος, Alexandros; 20/21 July 356 BC – 10/11 June 323 BC), commonly known as Alexander the Great, was a king of the Ancient Greece, ancient Greek kingdom of Maced ...
, who ordered a circumnavigation of the Arabian Peninsula in 323 BCE. During the two centuries that followed the reports of the explorers of 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 elephant A war elephant was an elephant that was Animal training, trained and guided by humans for combat. The war elephant's main use was to charge (warfare), charge the enemy, break their ranks and instill terror and fear. Elephantry is a term for spe ...
s. 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 A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in Atmosphere of Earth, atmospheric circulation and precipitation associated with annu ...
(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 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. ''
Periplus of the Erythraean Sea The ''Periplus of the Erythraean Sea'' ( grc, Περίπλους τῆς Ἐρυθρᾶς Θαλάσσης, ', modern Greek '), also known by its Latin name as the , is a Greco-Roman world, Greco-Roman periplus written in Koine Greek that describ ...
'', an
Alexandria Alexandria ( or ; ar, ٱلْإِسْكَنْدَرِيَّةُ ; grc-gre, Αλεξάνδρεια, Alexándria) is the second largest city in Egypt, and the largest city on the Mediterranean coast. Founded in by Alexander the Great, Alexandria ...
n 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 A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in Atmosphere of Earth, atmospheric circulation and precipitation associated with annu ...
winds. The contemporaneous settlement of
Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Afric ...
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. 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 Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Afric ...
around 1 CE. In the 2nd or 1st century BCE,
Eudoxus of Cyzicus Eudoxus of Cyzicus (; el, Εὔδοξος ὁ Κυζικηνός, ''Eúdoxos ho Kyzikēnós''; fl. c. 130 BC) was a ethnic Greek, Greek navigator who explored the Arabian Sea for Ptolemy VIII Physcon, Ptolemy VIII, king of the Hellenistic civili ...
was the first
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
to cross the Indian Ocean. The probably fictitious sailor Hippalus is said to have learnt the direct route from
Arabia The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plate. ...
to India around this time. During the 1st and 2nd centuries AD intensive trade relations developed between
Roman Egypt , conventional_long_name = Roman Egypt , common_name = Egypt , subdivision = Roman province, Province , nation = the Roman Empire , era = Late antiquity , capital = Alexandria , title_leader = Praefectus Augustalis , image_ ...
and the Tamil kingdoms of the Cheras,
Cholas The Chola dynasty was a Tamils, Tamil thalassocratic Tamil Dynasties, empire of southern India and one of the longest-ruling dynasties in the history of the world. The earliest datable references to the Chola are from inscriptions dated ...
and Pandyas in
Southern India South India, also known as Dakshina Bharata or Peninsular India, consists of the peninsular southern part of India. It encompasses the States and union territories of India, Indian states of Andhra Pradesh, Karnataka, Kerala, Tamil Nadu, and T ...
. 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 The ''Periplus of the Erythraean Sea'' ( grc, Περίπλους τῆς Ἐρυθρᾶς Θαλάσσης, ', modern Greek '), also known by its Latin name as the , is a Greco-Roman world, Greco-Roman periplus written in Koine Greek that describ ...
'' 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.


Age of Discovery

Unlike the Pacific Ocean where the civilization of the
Polynesians Polynesians form an ethnolinguistic group of closely related people who are Indigenous peoples of Oceania , native to Polynesia (islands in the Polynesian Triangle), an expansive region of Oceania in the Pacific Ocean. They trace their early pre ...
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 Maldives (, ; dv, ދިވެހިރާއްޖެ, translit=Dhivehi Raajje, ), officially the Republic of Maldives ( dv, ދިވެހިރާއްޖޭގެ ޖުމްހޫރިއްޔާ, translit=Dhivehi Raajjeyge Jumhooriyyaa, label=none, ), is an archipelag ...
were the only island group in the Central Indian Ocean region where an ancient civilization flourished.
Maldivians Maldivians (; ދިވެހިން, ''dhivehin'') are an Indo-Aryan peoples, Indo-Aryan ethnic group and nation native to the historic region of the Maldive Islands comprising what is now the Maldives, Republic of Maldives and the island of Minico ...
, on their annual trade trip, took their oceangoing trade ships to
Sri Lanka Sri Lanka (, ; si, ශ්‍රී ලංකා, Śrī Laṅkā, translit-std=ISO (); ta, இலங்கை, Ilaṅkai, translit-std=ISO ()), formerly known as Ceylon and officially the Democratic Socialist Republic of Sri Lanka, is an ...
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 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 has been found in Shanga, Kenya. Trade across the Indian Ocean gradually introduced Arabic script and rice as a 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. From 1405 to 1433 admiral
Zheng He Zheng He (; 1371–1433 or 1435) was a Chinese history of the Chinese navy, mariner, Chinese exploration, explorer, Foreign relations of imperial China, diplomat, fleet admiral, and court eunuch during China's History of the Ming dynasty, earl ...
said to have led large fleets of the
Ming Dynasty The Ming dynasty (), officially the Great Ming, was an Dynasties in Chinese history, imperial dynasty of China, ruling from 1368 to 1644 following the collapse of the Mongol Empire, Mongol-led Yuan dynasty. The Ming dynasty was the last ort ...
on several
treasure voyages The Ming treasure voyages were the seven maritime expeditions undertaken by Ming dynasty, Ming China's Chinese treasure ship, treasure fleet between 1405 and 1433. The Yongle Emperor ordered the construction of the treasure fleet in 1403. The ...
through the Indian Ocean, ultimately reaching the coastal countries of
East Africa East Africa, Eastern Africa, or East of Africa, is the eastern subregion A subregion is a part of a larger region or continent and is usually based on location. Cardinal directions, such as south are commonly used to define a subregion. ...
. The Portuguese navigator
Vasco da Gama Vasco da Gama, 1st Count of Vidigueira (; ; c. 1460s – 24 December 1524), was a Portugal in the Age of Discovery, Portuguese explorer and the first European to reach India by sea. His initial voyage to India by way of Cape of Good Hope (14 ...
rounded the
Cape of Good Hope The Cape of Good Hope ( af, Kaap die Goeie Hoop ) ;''Kaap'' in isolation: pt, Cabo da Boa Esperança is a rocky headland on the Atlantic Ocean, Atlantic coast of the Cape Peninsula in South Africa. A common misconception is that the Cape o ...
during his first voyage in 1497 and became the first European to sail to India. The
Swahili people The Swahili people ( sw, WaSwahili) comprise mainly Bantu peoples, Bantu, Afro-Arabs, Afro-Arab and Comoros, Comorian ethnic groups inhabiting the Swahili coast, an area encompassing the Zanzibar archipelago and mainland Tanzania, Tanzania's seab ...
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 Malindi is a town on Malindi Bay at the mouth of the Sabaki River, lying on the Indian Ocean coast of Kenya. It is 120 kilometres northeast of Mombasa. The population of Malindi was 119,859 as of the 2019 census. It is the largest urban centre ...
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 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 pt, União Ibérica , conventional_long_name =Iberian Union , common_name = , year_start = 1580 , date_start = 25 August , life_span = 1580–1640 , event_start = War of the Portuguese Succession , event_end = Portuguese Restoration War ...
(1580–1640). The
Ottoman Empire The Ottoman Empire, * ; is an archaic version. The definite article forms and were synonymous * and el, Оθωμανική Αυτοκρατορία, Othōmanikē Avtokratoria, label=none * info page on book at Martin Luther University) ...
began its expansion into the Indian Ocean in 1517 with the conquest of Egypt under Sultan
Selim I Selim I ( ota, سليم الأول; tr, I. Selim; 10 October 1470 – 22 September 1520), known as Selim the Grim or Selim the Resolute ( tr, links=no, Yavuz Sultan Selim), was the List of sultans of the Ottoman Empire, Sultan of the Ottoman ...
. 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 Abu Abdullah Muhammad ibn Battutah (, ; 24 February 13041368/1369),; fully: ; Arabic: commonly known as Ibn Battuta, was a Berbers, Berber Maghrebi people, Maghrebi scholar and explorer who travelled extensively in the lands of Afro-Eurasia, ...
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, nevertheless, began their own parallel era of discovery which rivalled the European expansion. The establishment of the
Dutch East India Company The United East India Company ( nl, Verenigde Oostindische Compagnie, the VOC) was a chartered company established on the 20th March 1602 by the States General of the Netherlands amalgamating existing companies into the first joint-stock ...
in the early 17th century lead to a quick increase in the volume of the slave trade in the region; there were perhaps up to slaves in various Dutch colonies during the 17th and 18th centuries in the Indian Ocean. For example, some 4000 African slaves were used to build the Colombo fortress in
Dutch Ceylon Dutch Ceylon (Sinhala language, Sinhala: Tamil language, Tamil: ) was a governorate established in present-day Sri Lanka by the Dutch East India Company. Although the Dutch managed to capture most of the coastal areas in Sri Lanka, they were ...
. Bali and neighbouring islands supplied regional networks with slaves 1620–1830. Indian and Chinese slave traders supplied Dutch Indonesia with perhaps slaves during the 17th and 18th centuries. The
East India Company The East India Company (EIC) was an English, and later British, joint-stock company founded in 1600 and dissolved in 1874. It was formed to Indian Ocean trade, trade in the Indian Ocean region, initially with the East Indies (the Indian subco ...
(EIC) was established during the same period and in 1622 one of its ships carried slaves from the
Coromandel Coast The Coromandel Coast is the southeastern coastal region of the Indian subcontinent, bounded by the Utkal Plains to the north, the Bay of Bengal to the east, the Kaveri delta to the south, and the Eastern Ghats to the west, extending over an ...
to
Dutch East Indies The Dutch East Indies, also known as the Netherlands East Indies ( nl, Nederlands(ch)-Indië; ), was a Dutch colony consisting of what is now Indonesia. It was formed from the nationalised trading posts of the Dutch East India Company, whic ...
. The EIC mostly traded in African slaves but also some Asian slaves purchased from Indian, Indonesian and Chinese slave traders. The French established colonies on the islands of
Réunion Réunion (; french: La Réunion, ; previously ''Île Bourbon''; rcf, label=Réunion Creole, Reunionese Creole, La Rényon) is an island in the Indian Ocean that is an overseas departments and regions of France, overseas department and region ...
and
Mauritius Mauritius ( ; french: Maurice, link=no ; mfe, label=Mauritian Creole, Moris ), officially the Republic of Mauritius, is an island nation in the Indian Ocean about off the southeast coast of the African continent, east of Madagascar. It incl ...
in 1721; by 1735 some 7,200 slaves populated the
Mascarene Islands The Mascarene Islands (, ) or Mascarenes or Mascarenhas Archipelago is a group of 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 a ...
, a number which had reached in 1807. The British captured the islands in 1810, however, and because the British had prohibited the slave trade in 1807 a system of clandestine slave trade developed to bring slaves to French planters on the islands; in all – slaves were exported to the Mascarene Islands from 1670 until 1848. In all, European traders exported – slaves within the Indian Ocean between 1500 and 1850 and almost that same amount were exported from the Indian Ocean to the Americas during the same period. Slave trade in the Indian Ocean was, nevertheless, very limited compared to slaves exported across the Atlantic.


Modern era

Scientifically, the Indian Ocean remained poorly explored before the International Indian Ocean Expedition in the early 1960s. However, 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. The
Suez Canal The Suez Canal ( arz, قَنَاةُ ٱلسُّوَيْسِ, ') is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea to the Red Sea through the Isthmus of Suez and dividing Africa and Asia. The long canal is a popular ...
opened in 1869 when the
Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going fr ...
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. 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
scyphozoa The Scyphozoa are an exclusively marine class of the phylum Cnidaria, referred to as the true jellyfish (or "true jellies"). The class name Scyphozoa comes from the Greek language, Greek word ''skyphos'' (), denoting a kind of drinking cup and ...
n 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 the economy in the region but also cause ecological damage in a much wider area. Throughout the colonial era, islands such as
Mauritius Mauritius ( ; french: Maurice, link=no ; mfe, label=Mauritian Creole, Moris ), officially the Republic of Mauritius, is an island nation in the Indian Ocean about off the southeast coast of the African continent, east of Madagascar. It incl ...
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 World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
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 Port Louis (french: Port-Louis; mfe, label=Mauritian Creole, Polwi or , ) is the capital city of Mauritius. It is mainly located in the Port Louis District, with a small western part in the Black River District. Port Louis is the country's eco ...
and threaten the U.S. base on
Diego Garcia Diego Garcia is an island of the British Indian Ocean Territory, a disputed overseas territory of the United Kingdom. It is a militarised atoll just south of the equator in the central Indian Ocean, and the largest of the 60 small islands of ...
. 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 The Cellular Jail, also known as Kālā Pānī (), was a British colonial prison in the Andaman and Nicobar Islands. The prison was used by the British Raj, colonial government of India for the purpose of Penal transportation, exiling crimina ...
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
tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a tsunamis in lakes, large lake. Earthquakes, volcanic eruptions and othe ...
s caused by the
2004 Indian Ocean earthquake An earthquake and a tsunami, known as the Boxing Day Tsunami and, by the scientific community, the Sumatra–Andaman earthquake, occurred at 07:58:53 local time (UTC+07:00, UTC+7) on 26 December 2004, with an epicentre off the west coast of no ...
. 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
pirate Piracy is an act of robbery or criminal violence by ship or boat-borne attackers upon another ship or a coastal area, typically with the goal of stealing cargo and other valuable goods. Those who conduct acts of piracy are called pirates, v ...
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 The Indian Navy is the navy, maritime branch of the Indian Armed Forces. The President of India is the Supreme Commander of the Indian Navy. The Chief of the Naval Staff (India), Chief of Naval Staff, a four-star rank, four-star Admiral (India ...
.
Malaysian Airlines Flight 370 Malaysia Airlines Flight 370 (MH370/MAS370) was an international passenger flight operated by Malaysia Airlines that disappeared on 8 March 2014 while flying from Kuala Lumpur International Airport in Malaysia to its planned destination ...
, a
Boeing 777 The Boeing 777, commonly referred to as the Triple Seven, is an American long-range Wide-body aircraft, wide-body airliner developed and manufactured by Boeing Commercial Airplanes. It is the world's largest twinjet. The 777 was designed to ...
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 Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...
. Despite an extensive search, the whereabouts of the remains of the aircraft is unknown. The
Sentinelese The Sentinelese, also known as the Sentineli and the North Sentinel Islanders, are an indigenous people who inhabit North Sentinel Island in the Bay of Bengal in the northeastern Indian Ocean. Designated a particularly vulnerable tribal group ...
people of
North Sentinel Island North Sentinel Island is one of the Andaman Islands, an Indian archipelago in the Bay of Bengal which also includes South Sentinel Island. It is home to the Sentinelese, an uncontacted peoples, indigenous people in voluntary isolation who have d ...
, which lies near
South Andaman Island South Andaman Island is the southernmost island of the Great Andaman and is home to the majority of the population of the Andaman Islands. It belongs to the South Andaman district, South Andaman administrative Districts of India, district, part o ...
in the Bay of Bengal, have been called by experts the most isolated people in the world. The sovereignty of the
Chagos Archipelago The Chagos Archipelago () or Chagos Islands (formerly the Bassas de Chagas, and later the Oil Islands) is a group of seven atolls comprising more than 60 islands in the Indian Ocean about 500 kilometres (310 mi) south of the Maldives archi ...
in the Indian Ocean is disputed between the United Kingdom and
Mauritius Mauritius ( ; french: Maurice, link=no ; mfe, label=Mauritian Creole, Moris ), officially the Republic of Mauritius, is an island nation in the Indian Ocean about off the southeast coast of the African continent, east of Madagascar. It incl ...
. In February 2019, the
International Court of Justice The International Court of Justice (ICJ; french: Cour internationale de justice, links=no; ), sometimes known as the World Court, is one of the United Nations System#Six principal organs, six principal organs of the United Nations (UN). It s ...
in
The Hague The Hague ( ; nl, Den Haag or ) is a list of cities in the Netherlands by province, city and municipalities of the Netherlands, municipality of the Netherlands, situated on the west coast facing the North Sea. The Hague is the country's ad ...
issued an advisory opinion stating that the UK must transfer the Chagos Archipelago to Mauritius. On 26 February 2022, an AB Aviation Flight 1103
Cessna 208 The Cessna 208 Caravan is a utility aircraft produced by Cessna. The project was commenced on November 20, 1981, and the prototype first flew on December 9, 1982. The production model was certified by the FAA in October 1984 and its Cargo ...
crashed into Indian Ocean, killing all 14 on board.


Trade

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 Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
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
mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
s, and offshore placer deposits are actively exploited by bordering countries, particularly India, Pakistan, South Africa, Indonesia, Sri Lanka, and Thailand. In particular, the maritime part of the
Silk Road The Silk Road () was a network of Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern Hemisphere, Northern and Eastern Hemispheres, it spans from the British Isles a ...
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 Hanoi or Ha Noi ( or ; vi, Hà Nội ) is the capital and second-largest city of Vietnam. It covers an area of . It consists of 12 urban districts, one district-leveled town and 17 rural districts. Located within the Red River Delta, Hanoi i ...
to
Jakarta Jakarta (; , bew, Jakarte), officially the Special Capital Region of Jakarta ( id, Daerah Khusus Ibukota Jakarta) is the capital city, capital and list of Indonesian cities by population, largest city of Indonesia. Lying on the northwest coa ...
,
Singapore Singapore (), officially the Republic of Singapore, is a sovereign island country, island country and city-state in maritime Southeast Asia. It lies about one degree of latitude () north of the equator, off the southern tip of the Malay Pen ...
and
Kuala Lumpur , anthem = ''Maju dan Sejahtera'' , image_map = , map_caption = , pushpin_map = Malaysia#Southeast Asia#Asia , pushpin_map_caption = , coordinates = , sub ...
through the
Strait of Malacca The Strait of Malacca is a narrow stretch of water, 500 mi (800 km) long and from 40 to 155 mi (65–250 km) wide, between the Malay Peninsula (Peninsular Malaysia) to the northeast and the Indonesian island of Sumatra to the southwest, connec ...
via the Sri Lankan
Colombo Colombo ( ; si, කොළඹ, translit=Koḷam̆ba, ; ta, கொழும்பு, translit=Koḻumpu, ) is the executive and judicial Capital city, capital and largest city of Sri Lanka by population. According to the Brookings Institutio ...
opposite the southern tip of India via Malé, the capital of the Maldives, to the East African
Mombasa Mombasa ( ; ) is a coastal city in southeastern Kenya along the Indian Ocean. It was the first capital of the British East Africa, before Nairobi was elevated to capital city status. It now serves as the capital of Mombasa County. The town is ...
, from there to
Djibouti Djibouti, ar, جيبوتي ', french: link=no, Djibouti, so, Jabuuti officially the Republic of Djibouti, is a country in the Horn of Africa, bordered by Somalia to the south, Ethiopia to the southwest, Eritrea in the north, and the Red S ...
, then through the Red Sea over the
Suez Canal The Suez Canal ( arz, قَنَاةُ ٱلسُّوَيْسِ, ') is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea to the Red Sea through the Isthmus of Suez and dividing Africa and Asia. The long canal is a popular ...
into the Mediterranean, there via
Haifa Haifa ( he, חֵיפָה ' ; ar, حَيْفَا ') is the List of cities in Israel, third-largest city in Israel—after Jerusalem and Tel Aviv—with a population of in . The city of Haifa forms part of the Haifa metropolitan area, the thir ...
,
Istanbul Istanbul ( , ; tr, İstanbul ), formerly known as Constantinople ( grc-gre, Κωνσταντινούπολις; la, Constantinopolis), is the List of largest cities and towns in Turkey, largest city in Turkey, serving as the country's economic, ...
and
Athens Athens ( ; el, Αθήνα, Athína ; grc, Ἀθῆναι, Athênai (pl.) ) is a coastal city in the Mediterranean and is both the capital and largest city of Greece. With a population close to four million, it is also the seventh largest c ...
to the Upper Adriatic to the northern Italian junction of
Trieste Trieste ( , ; sl, Trst ; german: Triest ) is a city and seaport in northeastern Italy. It is the capital city, and largest city, of the Regions of Italy#Autonomous regions with special statute, autonomous region of Friuli Venezia Giulia, one of ...
with its international free port and its rail connections to Central and
Eastern Europe Eastern Europe is a subregion of the Europe, European continent. As a largely ambiguous term, it has a wide range of geopolitical, geographical, ethnic, cultural, and socio-economic connotations. The vast majority of the region is covered by Russ ...
. The Silk Road has become internationally important again on the one hand through European integration, the end of the Cold War and free world trade and on the other hand through Chinese initiatives. Chinese companies have made investments in several Indian Ocean ports, including
Gwadar Gwadar ( Balochi/ ur, ) is a port city with located on the southwestern coast of Balochistan, Pakistan Pakistan ( ur, ), officially the Islamic Republic of Pakistan ( ur, , label=none), is a country in South Asia. It is the world's ...
,
Hambantota Hambantota ( si, හම්බන්තොට, ta, அம்பாந்தோட்டை) is the main town in Hambantota District, Southern Province, Sri Lanka, Southern Province, Sri LankaThe prominent Sri Lankan Malays, Malays (මැලේ) ...
,
Colombo Colombo ( ; si, කොළඹ, translit=Koḷam̆ba, ; ta, கொழும்பு, translit=Koḻumpu, ) is the executive and judicial Capital city, capital and largest city of Sri Lanka by population. According to the Brookings Institutio ...
and
Sonadia Sonadia Island is a small island of about , offshore of the Cox's Bazar Cox's Bazar (; bn, কক্সবাজার, Kôksbajar; ) is a city, fishing port, tourism centre, and Cox's Bazar District, district headquarters in Southeastern ...
. This has sparked a debate about the strategic implications of these investments. There are also Chinese investments and related efforts to intensify trade in
East Africa East Africa, Eastern Africa, or East of Africa, is the eastern subregion A subregion is a part of a larger region or continent and is usually based on location. Cardinal directions, such as south are commonly used to define a subregion. ...
and in European ports such as
Piraeus Piraeus ( ; el, Πειραιάς ; grc, Πειραιεύς ) is a Port#Ancient Greece, port city within the Athens urban area ("Greater Athens"), in the Attica (region), Attica region of Greece. It is located southwest of Athens' city centr ...
and
Trieste Trieste ( , ; sl, Trst ; german: Triest ) is a city and seaport in northeastern Italy. It is the capital city, and largest city, of the Regions of Italy#Autonomous regions with special statute, autonomous region of Friuli Venezia Giulia, one of ...
.Guido Santevecchi: Di Maio e la Via della Seta: «Faremo i conti nel 2020», siglato accordo su Trieste in Corriere della Sera, 5 November 2019.


See also

*
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
*
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. Original ...
*
Indo-Pacific The Indo-Pacific is a vast biogeography, biogeographic region of Earth. In a narrow sense, sometimes known as the Indo-West Pacific or Indo-Pacific Asia, it comprises the tropical waters of the Indian Ocean, the western and central Pacific O ...
* Indian Ocean in World War II * Indian Ocean literature * Indian Ocean Naval Symposium * Indian Ocean Research Group *
Indian Ocean slave trade The Indian Ocean slave trade, sometimes known as the East African slave trade or Arab slave trade, was multi-directional slave trade and has changed over time. Africans were sent as slaves to the Middle East, to Indian Ocean islands (including Ma ...
*
List of islands in the Indian Ocean The islands of the Indian Ocean are part of either the eastern, western, or southern areas. Some prominently large islands include Madagascar, Sri Lanka, and the Indonesia, Indonesian islands of Sumatra and Java. Eastern Indian Ocean *Andaman Isl ...
* List of ports and harbours of the Indian Ocean * List of sovereign states and dependent territories in the Indian Ocean *
Indian Ocean Rim Association The Indian Ocean Rim Association (IORA), formerly known as the Indian Ocean Rim Initiative and the Indian Ocean Rim Association for Regional Cooperation (IOR-ARC), is an international organisation consisting of 23 states bordering the Indian Ocea ...
*
Maritime Silk Road The Maritime Silk Road or Maritime Silk Route is the Maritime history, maritime section of the historic Silk Road that connected Southeast Asia, China, the Indian subcontinent, the Arabian peninsula, Somalia, Egypt and Europe. It began by the 2n ...
*
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 60th parallel south, 60° S latitude and encircling Antarctica. With a size of , it is regarded ...
*
Territorial claims in Antarctica Seven sovereign states – Argentina, Australia, Chile, France, New Zealand, Norway, and the United Kingdom – have made eight land claim, territorial claims in Antarctica. These countries have tended to place their Antarctic scientific observa ...


References


Notes


Sources

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Further reading

* Bahl, Christopher D. "Transoceanic Arabic historiography: sharing the past of the sixteenth-century western Indian Ocean." ''Journal of Global History'' 15.2 (2020): 203–223. * Palat, Ravi. ''The Making of an Indian Ocean World-Economy, 1250–1650: Princes, Paddy fields, and Bazaars'' (2015) * Pearson, Michael (2015). ''Trade, Circulation, and Flow in the Indian Ocean World'' (Palgrave Series in Indian Ocean World Studies), . * Schnepel, Burkhard and Edward A. Alpers, eds. ''Connectivity in Motion: Island Hubs in the Indian Ocean World'' (2017). * Schottenhammer, Angela, ed. ''Early Global Interconnectivity across the Indian Ocean World, Volume I: Commercial Structures and Exchanges'' (2019) * Schottenhammer, Angela, ed. ''Early Global Interconnectivity across the Indian Ocean World, Volume II: Exchange of Ideas, Religions, and Technologies'' (2019) * Serels, Steven, ed. ''The Impoverishment of the African Red Sea Littoral, 1640–1945'' (2018)


External links

* * * {{Authority control Oceans East Africa South Asia Western Asia Oceans surrounding Antarctica