View source for Earth:Indian Ocean

{{Short description|Ocean bounded by Asia, Africa and Australia}}
{{Infobox body of water
| name               = Indian Ocean
| other_name         = 
<!--    Images     -->
| image              = Indian Ocean-CIA WFB Map.png
| alt                = Extent of the Indian Ocean according to the International Hydrographic Organization
| caption            = Extent of the Indian Ocean according to [[Organization:International Hydrographic Organization|International Hydrographic Organization]]
| image_bathymetry   = Indian Ocean bathymetry srtm.png
| caption_bathymetry = Topographic/bathymetric map of the Indian Ocean region
<!--    Stats      -->
| location           = 
| coordinates        = {{Coord|20|S|80|E|type:waterbody_scale:100000000|display=title,inline}}
| type               = [[Earth:Ocean|Ocean]]
| etymology          = 
| part_of            = 
| inflow             = Zambezi, Ganges-Brahmaputra, Indus, Jubba, and Murray (largest 5)
| oceans             = 
| catchment          = {{Convert|21100000|km2|abbr=on}}
| basin_countries    = [[Place:South Asia|South]] and [[Place:Southeast Asia|Southeast Asia]], [[Place:Western Asia|Western Asia]], [[Place:Northeast Africa|Northeast]], [[Place:East Africa|East]] and [[Place:Southern Africa|Southern Africa]] and [[Earth:Australia (continent)|Australia]]
| length             = {{Convert|9600|km|abbr=on}}<br/>(Antarctica to Bay of Bengal)<ref name="Demo-etal-intro" />
| width              = {{Convert|7600|km|abbr=on}}<br/>(Africa to Australia)<ref name="Demo-etal-intro">{{Harvnb|Demopoulos|Smith|Tyler|2003|loc=Introduction, p. 219}}</ref>
| area               = {{Convert|70560000|km2|abbr=on}}
| depth              = {{Convert|3741|m|abbr=on}}
| max-depth          = {{Convert|7290|m|abbr=on}}<br />(Java Trench)
| volume             = <!-- {{convert|VALUE|UNITS}} must be used -->
| residence_time     = 
| salinity           = 
| shore              = {{Convert|66526|km|abbr=on}}<ref name="KeeIrv-2005">{{Harvnb|Keesing|Irvine|2005|loc=Introduction, p. 11–12; Table 1, p.12}}</ref>
| elevation          = <!-- {{convert|VALUE|UNITS}} must be used -->
| temperature_high   = <!-- {{convert|VALUE|UNITS}} must be used -->
| temperature_low    = <!-- {{convert|VALUE|UNITS}} must be used -->
| islands            = {{wipe|Madagascar}}, Sri Lanka, [[History:Maldives|Maldives]], Reunion, Seychelles, [[Earth:Mauritius|Mauritius]]
| islands_category   = Islands of the Indian Ocean
| sections           = 
| trenches           = 
| benches            = 
| cities             = Cities, ports and harbours list 
<!--      Map      -->
| pushpin_map             = Indian Ocean
<!--   Below       -->  
| reference          = <ref name="CIAWFB-2018">{{Harvnb|CIA World Fact Book 2018}}</ref>
}}

The '''Indian Ocean''' is the third-largest of the world's five [[Earth:Ocean|ocean]]ic divisions, covering {{Convert|70560000|km2|abbr=on}} or ~20% of the water on Earth's surface.<ref name="NOAA-volume">{{Harvnb|Eakins|Sharman|2010}}</ref> It is bounded by Asia to the north, Africa to the west and [[Earth:Australia (continent)|Australia]] to the east. To the south it is bounded by the [[Earth:Southern Ocean|Southern Ocean]], or [[Earth:Antarctica|Antarctica]], depending on the definition in use.<ref>{{cite web|url=http://www.merriam-webster.com/dictionary/indian%20ocean|title='Indian Ocean' — Merriam-Webster Dictionary Online|access-date=7 July 2012|quote=ocean E of Africa, S of Asia, W of Australia, & N of Antarctica area ab {{convert|73427795|km2}}|archive-date=16 October 2013|archive-url=https://web.archive.org/web/20131016082320/http://www.merriam-webster.com/dictionary/indian%20ocean|url-status=live}}</ref> Along its core, the Indian Ocean has large marginal, or regional seas, such as the Arabian Sea, Laccadive Sea, Bay of Bengal and Andaman Sea.

It is named after {{wipe|India}}, which projects into it, and been known by its current name since at least 1515. Previously, it was called the Eastern Ocean. It has an average depth of 3,741 m. All of the Indian Ocean is in the [[Earth:Eastern Hemisphere|Eastern Hemisphere]]. Unlike the Atlantic and Pacific, the Indian Ocean is bordered by landmasses and an archipelago on three sides, making it more like an embayed ocean centered on the Indian Peninsula. Its coasts and shelves differ from other oceans, with distinct features, such as a narrower [[Earth:Continental shelf|continental shelf]]. In terms of geology, the Indian Ocean is the youngest of the major oceans, with active spreading ridges and features like [[Earth:Seamount|seamount]]s and ridges formed by [[Earth:Hotspot (geology)|hotspot]]s.

The climate of the Indian Ocean is characterized by [[Earth:Monsoon|monsoon]]s. It is the warmest ocean, with a significant impact on global climate due to its interaction with the atmosphere. Its waters are affected by the Indian Ocean [[Earth:Walker circulation|Walker circulation]], resulting in unique oceanic currents and upwelling patterns. The Indian Ocean is ecologically diverse, with important marine life and ecosystems like coral reefs, mangroves, and sea grass beds. It hosts a significant portion of the world's tuna catch and is home to endangered marine species. It faces challenges like overfishing and pollution, including a significant [[Earth:Garbage patch|garbage patch]].

Historically, the Indian Ocean has been a hub of cultural and commercial exchange since ancient times. It played a key role in early human migrations and the spread of civilizations. In modern times, it remains crucial for global trade, especially in oil and hydrocarbons. Environmental and geopolitical concerns in the region include the effects of [[Earth:Climate change|climate change]], piracy, and strategic disputes over island territories.

==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, which projects into it. It was earlier known as the ''Eastern Ocean'', a term that was still in use during the mid-18th century, as opposed to the ''Western Ocean'' ([[Earth:Atlantic Ocean|Atlantic]]) before the [[Earth:Pacific Ocean|Pacific]] was surmised.<ref name=HarperIndianOcean>{{cite web |url=https://www.etymonline.com/word/Indian%20Ocean |title=Indian Ocean |last=Harper |first=Douglas |website=Online Etymology Dictionary |access-date=18 January 2011 |archive-date=14 January 2018 |archive-url=https://web.archive.org/web/20180114020412/https://www.etymonline.com/word/Indian%20Ocean |url-status=live |quote=first attested 1515 in Modern Latin (Oceanus Orientalis Indicus), named for India, which projects into it; earlier it was the Eastern Ocean, as opposed to the Western Ocean (Atlantic) before the Pacific was surmised.}}</ref>

The [[Social:Hindi|Hindi]] name for the Ocean is {{lang|hi|हिंद महासागर}} ({{translit|hi|ISO|Hind Mahāsāgar}}; {{trans|literal=yes|Ocean of India}}).Conversely, [[Earth:Ming treasure voyages|Chinese explorers]] (e.g., Zheng He during the Ming dynasty) who traveled to the Indian Ocean during the 15th century called it the Western Oceans.<ref>{{Harvnb|Hui|2010|loc=Abstract}}</ref> In Ancient Greek geography, the Indian Ocean region known to the Greeks was called the [[Earth:Erythraean Sea|Erythraean Sea]].<ref name="Periplus">{{Cite book
 | author = Anonymous | translator-last = Schoff | translator-first = Wilfred Harvey
 | title = Periplus of the Erythraean Sea
 | year = 1912| title-link = s:Periplus of the Erythraean Sea }}</ref>

==Geography==
{{multiple image
| align             = right
| direction         = vertical
| image1            = Indian Ocean surface.jpg
| caption1          = The ocean-floor of the Indian Ocean is divided by spreading ridges and crisscrossed by aseismic structures
| image2            = Blue Marble Eastern Hemisphere.jpg
| caption2          = A composite satellite image centred on the Indian Ocean
}}

===Extent and data===
The [[Earth:Borders of the oceans#Indian Ocean|borders of the Indian Ocean]], as delineated by the [[Organization:International Hydrographic Organization|International Hydrographic Organization]] in 1953 included the [[Earth:Southern Ocean|Southern Ocean]] but not the marginal seas along the northern rim but in 2002 the IHO delimited the Southern Ocean separately, which removed waters south of 60°s from the Indian Ocean but included the northern marginal seas.<ref>{{Harvnb|IHO 1953}}</ref><ref name="IHO-2002">{{Harvnb|IHO 2002}}</ref> Meridionally, the Indian Ocean is delimited from the Atlantic Ocean by the 20° east meridian, running south from Cape Agulhas, South Africa, and from the Pacific Ocean by the meridian of 146°49'E, running south from South East Cape on the island of Tasmania in Australia. The northernmost extent of the Indian Ocean (including marginal seas) is approximately 30° north in the Persian Gulf.<ref name="IHO-2002" /><!-- Fig. 1, p. 5-2 -->

The Indian Ocean covers {{Convert|70560000|km2|abbr=on}}, including the Red Sea and the Persian Gulf but excluding the Southern Ocean, or 19.5% of the world's oceans; its volume is {{Convert|264000000|km3|abbr=on}} or 19.8% of the world's oceans' volume; it has an average depth of {{Convert|3741|m|abbr=on}} and a maximum depth of {{Convert|7290|m|abbr=on}}.<ref name="NOAA-volume" />

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

===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.<ref name="Prange-2008-p1382">{{Harvnb|Prange|2008|loc=Fluid Borders: Encompassing the Ocean, pp. 1382–1385}}</ref>

The active margins of the Indian Ocean have an average width (horizontal distance from land to shelf break<ref>{{Cite web|last=|first=|date=2011-03-04|title=Continental Shelf|url=https://education.nationalgeographic.org/resource/continental-shelf/|access-date=2021-10-05|website=National Geographic Society|language=en|archive-date=5 October 2021|archive-url=https://web.archive.org/web/20211005141557/https://www.nationalgeographic.org/encyclopedia/continental-shelf/|url-status=live}}</ref>) of {{Convert|19|+/-|0.61|km|abbr=on}} with a maximum width of {{Convert|175|km|abbr=on}}. The [[Earth:Passive margin|passive margin]]s have an average width of {{Convert|47.6|+/-|0.8|km|abbr=on}}.<ref>{{Harvnb|Harris|Macmillan-Lawler|Rupp|Baker|2014|loc=Table 2, p. 11}}</ref>
The average width of the slopes (horizontal distance from shelf break to foot of slope) of the continental shelves are {{Convert|50.4|-|52.4|km|abbr=on}} for active and passive margins respectively, with a maximum width of {{Convert|205.3|-|255.2|km|abbr=on}}.<ref>{{Harvnb|Harris|Macmillan-Lawler|Rupp|Baker|2014|loc=Table 3, p. 11}}</ref>

In correspondence of the Shelf break, also known as Hinge zone, the Bouguer gravity ranges from 0 to 30 [[Physics:Gal (unit)|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 from [[Earth:Antarctica#Geography|Antarctica]]."<ref name="1365-246X_208_3">{{cite journal|author=N. Damodara|author2=V. Vijaya Rao|author3=Kalachand Sain|author4=A.S.S.S.R.S. Prasad|author5=A.S.N. Murty|url=https://academic.oup.com/gji/article/208/3/1490/2929279?searchresult=1#58419117|title=Basement configuration of the West Bengal sedimentary basin, India as revealed by seismic refraction tomography: its tectonic implications|journal=Geophysical Journal International|volume=208|issue=3|date=January 3, 2017|pages=1490–1507|doi=10.1093/gji/ggw461|issn=1365-246X|publisher=Oxford University Press|oclc=6930280725|access-date=23 July 2021}}</ref>

Australia, Indonesia, and India are the three countries with the longest shorelines and [[Earth:Exclusive economic zone|exclusive economic zone]]s. 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).<ref name="KeeIrv-2005" />

====Rivers====
The Indian Ocean [[Earth:Drainage basin|drainage basin]] covers {{Convert|21100000|km2|abbr=on}}, 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 ({{Convert|740|km|abbr=on}}) than those of the other major oceans. The largest rivers are ([[Strahler number|order 5]]) the Zambezi, Ganges-Brahmaputra, Indus, Jubba, and Murray rivers and (order 4) the [[Place:Shatt al-Arab|Shatt al-Arab]], Wadi Ad Dawasir (a dried-out river system on the Arabian Peninsula) and Limpopo rivers.<ref>{{Harvnb|Vörösmarty|Fekete|Meybeck|Lammers|2000|loc=Drainage basin area of each ocean, pp. 609–616; Table 5, p 614; Reconciling Continental and Oceanic Perspectives, pp. 616–617}}</ref> After the breakup of East [[Earth:Gondwana|Gondwana]] and the formation of the Himalayas, the Ganges-Brahmaputra rivers flow into the world's largest delta known as the Bengal delta or Sunderbans.<ref name="1365-246X_208_3" />

===Marginal seas===
Marginal seas, gulfs, bays and straits of the Indian Ocean include:<ref name="IHO-2002" />

Along the east coast of Africa, the Mozambique Channel separates {{wipe|Madagascar}} from mainland Africa, while the Sea of Zanj is located north of Madagascar.

On the northern coast of the Arabian Sea, Gulf of Aden is connected to the Red Sea by the strait of Bab-el-Mandeb. In the Gulf of Aden, the Gulf of Tadjoura is located in Djibouti and the Guardafui Channel separates Socotra island from the Horn of Africa. The northern end of the Red Sea terminates in the Gulf of Aqaba and Gulf of Suez. The Indian Ocean is artificially connected to the [[Place:Mediterranean Sea|Mediterranean Sea]] without ship lock through the Suez Canal, which is accessible via the Red Sea. The Arabian Sea is connected to the Persian Gulf by the Gulf of Oman and the Strait of Hormuz. In the Persian Gulf, the Gulf of Bahrain separates Qatar from the Arabic Peninsula.

Along the west coast of India, the Gulf of Kutch and Gulf of Khambat are located in Gujarat in the northern end while the Laccadive Sea separates the Maldives from the southern tip of India. The Bay of Bengal is off the east coast of India. The Gulf of Mannar and the Palk Strait separate Sri Lanka from India, while Adam's Bridge separates the two. The Andaman Sea is located between the Bay of Bengal and the Andaman Islands.

In Indonesia, the so-called Indonesian Seaway is composed of the Malacca, Sunda and Torres Straits.
The Gulf of Carpentaria of located on the Australian north coast while the Great Australian Bight constitutes a large part of its southern coast.<ref>{{Cite web|url = https://www.livescience.com/29533-the-worlds-biggest-oceans-and-seas.html|title = The World's Biggest Oceans and Seas|website = Live Science|date = 4 June 2010|access-date = 9 September 2020|archive-date = 15 September 2020|archive-url = https://web.archive.org/web/20200915222930/https://www.livescience.com/29533-the-worlds-biggest-oceans-and-seas.html|url-status = live}}</ref><ref>{{cite web| url = https://www.worldatlas.com/| title = World Map / World Atlas / Atlas of the World Including Geography Facts and Flags - WorldAtlas.com| access-date = 28 April 2019| archive-date = 27 April 2019| archive-url = https://web.archive.org/web/20190427214956/https://www.worldatlas.com/| url-status = live}}</ref><ref>{{cite web| url = http://listofseas.com/| title = List of seas| access-date = 9 September 2020| archive-date = 8 November 2020| archive-url = https://web.archive.org/web/20201108163716/http://listofseas.com/| url-status = live}}</ref>

{{div col|colwidth=24em}}
# Arabian Sea - 3.862 million km<sup>2</sup>
# Bay of Bengal - 2.172 million km<sup>2</sup>
# Andaman Sea - 797,700 km<sup>2</sup>
# Laccadive Sea - 786,000 km<sup>2</sup>
# Mozambique Channel - 700,000 km<sup>2</sup>
# Timor Sea - 610,000 km<sup>2</sup>
# Red Sea - 438,000 km<sup>2</sup>
# Gulf of Aden - 410,000 km<sup>2</sup>
# Persian Gulf - 251,000 km<sup>2</sup>
# Flores Sea - 240,000 km<sup>2</sup>
# Molucca Sea - 200,000 km<sup>2</sup>
# Oman Sea - 181,000 km<sup>2</sup>
# Great Australian Bight - 45,926 km<sup>2</sup>
# Gulf of Aqaba - 239 km<sup>2</sup>
# Gulf of Khambhat
# Gulf of Kutch
# Gulf of Suez
{{div col end}}

==Climate==
[[File:Indian Ocean Monsoon.jpg|thumb|During summer, warm continental masses draw moist air from the Indian Ocean hence producing heavy rainfall. The process is reversed during winter, resulting in dry conditions.]]
Several features make the Indian Ocean unique. It constitutes the core of the large-scale [[Earth:Tropical Warm Pool|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 [[Earth:Thermocline|thermocline]]. That continent also drives the Indian Ocean [[Earth:Monsoon|monsoon]], the strongest on Earth, which causes large-scale seasonal variations in ocean currents, including the reversal of the [[Earth:Somali Current|Somali Current]] and [[Earth:Indian Monsoon Current|Indian Monsoon Current]]. Because of the Indian Ocean [[Earth:Walker circulation|Walker circulation]] there are no continuous equatorial easterlies. [[Earth:Upwelling|Upwelling]] occurs near the [[Place:Horn of Africa|Horn of Africa]] and the [[Place:Arabian Peninsula|Arabian Peninsula]] in the [[Earth:Northern Hemisphere|Northern Hemisphere]] and north of the trade winds in the Southern Hemisphere. The [[Earth:Indonesian Throughflow|Indonesian Throughflow]] is a unique Equatorial connection to the Pacific.<ref>{{Harvnb|Schott|Xie|McCreary|2009|loc=Introduction, pp. 1–2}}</ref>

The climate north of the [[Astronomy:Equator|equator]] is affected by a [[Earth:Monsoon|monsoon]] climate. Strong north-east winds blow from October until April; from May until October south and west winds prevail. In the Arabian Sea, the violent Monsoon brings rain to the Indian subcontinent. In the southern hemisphere, the winds are generally milder, but summer storms near Mauritius can be severe. When the monsoon winds change, cyclones sometimes strike the shores of the Arabian Sea and the Bay of Bengal.<ref name="oceanographer-2001">{{Cite web
 |title        = U.S. Navy Oceanographer
 |url          = http://oceanographer.navy.mil/indian.html
 |access-date  = 4 August 2001
 |archive-url  = https://web.archive.org/web/20010802084832/http://oceanographer.navy.mil/indian.html
 |archive-date = 2 August 2001
 |url-status=dead
 |df           = dmy-all
}}</ref> 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&nbsp;BP; a weak, dry phase 26,000–23,500&nbsp;BC; and a very weak phase 17,000–15,000&nbsp;BP,
corresponding to a series of dramatic global events: [[Earth:Bølling–Allerød warming|Bølling–Allerød warming]], [[Earth:Heinrich event|Heinrich]], and [[Earth:Younger Dryas|Younger Dryas]].<ref>{{Harvnb|Dutt|Gupta|Clemens|Cheng|2015|loc=Abstract; Introduction, pp. 5526–5527}}</ref>

[[File:Aerosol pollution over Northern India, Bangladesh, and Bay of Bengal.jpg|thumb|upright=.9|Air pollution in South Asia spread over the Bay of Bengal and beyond.]]
The Indian Ocean is the warmest ocean in the world.<ref>{{Cite web | title = Which Ocean is the Warmest? | publisher = Worldatlas | date = 17 September 2018 | url = https://www.worldatlas.com/articles/which-ocean-is-the-warmest.html | access-date = 28 April 2019 | archive-date = 28 April 2019 | archive-url = https://web.archive.org/web/20190428092339/https://www.worldatlas.com/articles/which-ocean-is-the-warmest.html | url-status = live }}</ref> Long-term ocean temperature records show a rapid, continuous warming in the Indian Ocean, at about {{Convert|1.2|°C|abbr=on}} (compared to {{Convert|0.7|°C|abbr=on}} for the warm pool region) during 1901–2012.<ref name=":0">{{Harvnb|Roxy|Ritika|Terray|Masson|2014|loc=Abstract}}</ref> Research indicates that human induced greenhouse warming, and changes in the frequency and magnitude of [[Earth:El Niño|El Niño]] (or the [[Earth:Indian Ocean Dipole|Indian Ocean Dipole]]), events are a trigger to this strong warming in the Indian Ocean.<ref name=":0" />

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.<ref>{{Harvnb|Carton|Chepurin|Cao|2000|p=321}}</ref>

In 1999, the [[Earth:Indian Ocean Experiment|Indian Ocean Experiment]] showed that fossil fuel and biomass burning in South and Southeast Asia caused air pollution (also known as the [[Earth:Asian brown cloud|Asian brown cloud]]) that reach as far as the [[Earth:Intertropical Convergence Zone|Intertropical Convergence Zone]]. This pollution has implications on both a local and global scale.<ref>{{Harvnb|Lelieveld|Crutzen|Ramanathan|Andreae|2001|loc=Abstract}}</ref>

==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 [[Earth:Polar front|polar front]] (roughly 50° south latitude) is high in biologic productivity and dominated by non-stratified sediment composed mostly of siliceous [[Earth:Pelagic sediment#Oozes|oozes]]. Near the three major mid-ocean ridges the ocean floor is relatively young and therefore bare of sediment, except for the [[Earth:Southwest Indian Ridge|Southwest Indian Ridge]] due to its ultra-slow spreading rate.<ref>{{Harvnb|Ewing|Eittreim|Truchan|Ewing|1969|loc=Abstract}}</ref>

The ocean's [[Earth:Ocean current|currents]] are mainly controlled by the monsoon. Two large gyres, one in the northern hemisphere flowing clockwise and one south of the equator moving anticlockwise (including the Agulhas Current and [[Earth:Agulhas Return Current|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.<ref>{{Harvnb|Shankar|Vinayachandran|Unnikrishnan|2002|loc=Introduction, pp. 64–66}}</ref>

The Indian Ocean contains the largest submarine fans of the world, the [[Earth:Bengal Fan|Bengal Fan]] and Indus Fan, and the largest areas of slope terraces and [[Earth:Rift valley|rift valley]]s.
<ref>{{Harvnb|Harris|Macmillan-Lawler|Rupp|Baker|2014|loc=Geomorphic characteristics of ocean regions, pp. 17–18}}</ref>

The inflow of deep water into the Indian Ocean is 11&nbsp;[[Sverdrup|Sv]], most of which comes from the Circumpolar Deep Water (CDW). The CDW enters the Indian Ocean through the Crozet and {{wipe|Madagascar}} basins and crosses the [[Earth:Southwest Indian Ridge|Southwest Indian Ridge]] at 30°S. In the Mascarene Basin the CDW becomes a deep western boundary current 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 whilst most of it flows clockwise in the Mascarene Basin where an oscillating flow is produced by [[Rossby wave#Oceanic waves|Rossby waves]].<ref>{{Harvnb|Wilson|Piotrowski|Galy|McCave|2012|loc=Regional setting and hydrography, pp. 4–5; Fig. 1, p. 22}}</ref>

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. [[Earth:North Atlantic Deep Water|North Atlantic Deep Water]] reaches into the Indian Ocean south of Africa at a depth of {{Convert|2000|-|3000|m|abbr=on}} 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 (<{{Convert|4000|m|abbr=on}}) in the Southwest Indian Ridge, from where it continues into the Mozambique Channel and Prince Edward Fracture Zone.<ref name="Rogers-p5">{{Harvnb|Rogers|2012|loc=The Southern Indian Ocean and its Seamounts, pp. 5–6}}</ref>

North of 20° south latitude the minimum surface temperature is {{convert|22|C}}, exceeding {{convert|28|C}} to the east. Southward of 40° south latitude, temperatures drop quickly.<ref name="oceanographer-2001" />

The Bay of Bengal contributes more than half ({{convert|2950|km3|cumi|disp=or|abbr=on}}) of the [[Earth:Surface runoff|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 [[Earth:Indonesian Throughflow|Indonesian Throughflow]]. This mixed freshwater joins the [[Earth:South Equatorial Current|South Equatorial Current]] in the southern tropical Indian Ocean.<ref>{{Harvnb|Sengupta|Bharath Raj|Shenoi|2006|loc=Abstract; p. 4}}</ref>
[[Earth:Salinity#Seawater|Sea surface salinity]] is highest (more than 36&nbsp;[[Earth:Salinity#PSU|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&nbsp;PSU) in the Bay of Bengal because of river runoff and precipitation. The Indonesian Throughflow and precipitation results in lower salinity (34&nbsp;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.<ref>{{Harvnb|Felton|2014|loc=Results, pp. 47–48; Average for Table 3.1, p. 55}}</ref> 

An [[Earth:Indian Ocean garbage patch|Indian Ocean garbage patch]] was discovered in 2010 covering at least {{Convert|5|e6km2|abbr=off}}. Riding the southern [[Earth:Indian Ocean Gyre|Indian Ocean Gyre]], this vortex of plastic garbage constantly circulates the ocean from Australia to Africa, down the Mozambique Channel, and back to Australia in a period of six years, except for debris that gets indefinitely stuck in the centre of the gyre.<ref>{{Cite news | last = Parker | first = Laura | title = Plane Search Shows World's Oceans Are Full of Trash | publisher = National Geographic News | date = 4 April 2014 | url = https://news.nationalgeographic.com/news/2014/04/140404-garbage-patch-indian-ocean-debris-malaysian-plane/ | access-date = 30 December 2018 | archive-date = 8 April 2014 | archive-url = https://web.archive.org/web/20140408041528/http://news.nationalgeographic.com/news/2014/04/140404-garbage-patch-indian-ocean-debris-malaysian-plane/ | url-status = dead }}</ref>
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.<ref>{{Harvnb|Van Sebille|England|Froyland|2012}}</ref>

There are two [[Physics:Amphidromic point|amphidromes]] of opposite rotation in the Indian Ocean, probably caused by [[Rossby wave]] propagation.<ref>{{Harvnb|Chen|Quartly|2005|pp=5–6}}</ref>

[[Earth:Iceberg|Iceberg]]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&nbsp;Gt.<ref>{{Harvnb|Matsumoto|Bohnenstiehl|Tournadre|Dziak|2014|pp=3454–3455}}</ref>

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 [[Chemistry:Greenhouse gas|greenhouse gas]]es.<ref>{{Harvnb|Han|Meehl|Rajagopalan|Fasullo|2010|loc=Abstract}}</ref>

==Marine life==
{{Multiple image
| total_width       = 600
| image1            = CSIRO ScienceImage 3012 Dolphin.jpg
| image2            = Maldives Surgeonfish, Acanthurus leucosternon.jpg
| image3            = Vagues et manchots à l'assaut de la plage.jpg
| footer            = A dolphin off Western Australia and a swarm of [[Biology:Acanthurus leucosternon|surgeonfish]] near Maldives Islands represents the well-known, exotic fauna of the warmer parts of the Indian Ocean. King Penguins on a beach in the Crozet Archipelago near Antarctica attract fewer tourists.
}}

Among the tropical oceans, the western Indian Ocean hosts one of the largest concentrations of [[Earth:Phytoplankton|phytoplankton]] blooms in summer, due to the strong [[Earth:Monsoon|monsoon]] winds. The monsoonal wind forcing leads to a strong coastal and open ocean [[Earth:Upwelling|upwelling]], which introduces nutrients into the upper zones where sufficient light is available for [[Earth:Photosynthesis|photosynthesis]] and phytoplankton production. These phytoplankton blooms support the marine ecosystem, as the base of the marine food web, and eventually the larger fish species. The Indian Ocean accounts for the second-largest share of the most economically valuable [[Biology:Tuna|tuna]] catch.<ref>{{Harvnb|FAO 2016}}</ref> Its fish are of great and growing importance to the bordering countries for domestic consumption and export. Fishing fleets from Russia, Japan, {{wipe|South Korea}}, and Taiwan also exploit the Indian Ocean, mainly for shrimp and tuna.<ref name="CIAWFB-2018" />

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.<ref>{{Harvnb|Roxy|2016|loc=Discussion, pp. 831–832}}</ref>

Endangered and vulnerable marine mammals and turtles:<ref>{{Cite web | title = IUCN Red List | publisher = IUCN | url = https://www.iucnredlist.org/search?redListCategory=en | access-date = 8 July 2019 | archive-date = 8 July 2019 | archive-url = https://web.archive.org/web/20190708032948/https://www.iucnredlist.org/search?redListCategory=en | url-status = live }}.  Search parametres: Mammalia/Testudines, EN/VU, Indian Ocean Antarctic/Eastern/Western</ref>

{| class="wikitable"
|-
 ! Name || Distribution || Trend
|-
 ! colspan="3" | Endangered
|-
 | [[Biology:Australian sea lion|Australian sea lion]]<br />(''Neophoca cinerea'') || Southwest Australia || Decreasing
|-
 | [[Biology:Blue whale|Blue whale]]<br />(''Balaenoptera musculus'') || Global || Increasing
|-
 | [[Biology:Sei whale|Sei whale]]<br />(''Balaenoptera borealis'') || Global || Increasing
|-
 | [[Biology:Irrawaddy dolphin|Irrawaddy dolphin]]<br />(''Orcaella brevirostris'') || Southeast Asia || Decreasing
|-
 | Indian Ocean humpback dolphin<br />(''Sousa plumbea'') || Western Indian Ocean || Decreasing
|-
 | [[Biology:Green sea turtle|Green sea turtle]]<br />(''Chelonia mydas'') || Global || Decreasing
|-
 ! colspan="3" | Vulnerable
|-
 | [[Biology:Dugong|Dugong]]<br />(''Dugong dugon'') || Equatorial Indian Ocean and Pacific || Decreasing
|-
 | [[Biology:Sperm whale|Sperm whale]]<br />(''Physeter macrocephalus'') || Global || Unknown
|-
 | [[Biology:Fin whale|Fin whale]]<br />(''Balaenoptera physalus'') || Global || Increasing
|-
 | [[Biology:Australian snubfin dolphin|Australian snubfin dolphin]]<br />(''Orcaella heinsohni'') || Northern Australia, New Guinea || Decreasing
|-
 | Indo-Pacific humpback dolphin<br />(''Sousa chinensis'') || Southeast Asia || Decreasing
|-
 | Indo-Pacific finless porpoise<br />(''Neophocaena phocaenoides'') || Northern Indian Ocean, Southeast Asia || Decreasing
|-
 | Australian humpback dolphin<br />(''Sousa sahulensis'') || Northern Australia, New Guinea || Decreasing
|-
 | Leatherback<br />(''Dermochelys coriacea'') || Global || Decreasing
|-
 | [[Biology:Olive ridley sea turtle|Olive ridley sea turtle]]<br />(''Lepidochelys olivacea'') || Global || Decreasing
|-
 | [[Biology:Loggerhead sea turtle|Loggerhead sea turtle]]<br />(''Caretta caretta'') || Global || Decreasing
|}

80% of the Indian Ocean is open ocean and includes nine [[Earth:Large marine ecosystem|large marine ecosystem]]s: the Agulhas Current, Somali Coastal Current, Red Sea, Arabian Sea, Bay of Bengal, Gulf of Thailand, West Central Australian Shelf, Northwest Australian Shelf and Southwest Australian Shelf. Coral reefs cover c. {{Convert|200000|km2|abbr=on}}. The coasts of the Indian Ocean includes beaches and intertidal zones covering {{Convert|3000|km2|abbr=on}} and 246 larger [[Earth:Estuary|estuaries]]. [[Earth:Upwelling|Upwelling]] areas are small but important. The hypersaline salterns in India covers between {{Convert|5000|-|10000|km2|abbr=on}} and species adapted for this environment, such as ''[[Biology:Artemia salina|Artemia salina]]'' and ''[[Biology:Dunaliella salina|Dunaliella salina]]'', are important to bird life.<ref>{{Harvnb|Wafar|Venkataraman|Ingole|Khan|2011|loc=Marine ecosystems of the IO}}</ref>

{{Multiple image | total_width = 400
 | image1 = Padadita Beach, Waingapu 18.jpg
 | image2 = Coelacanth1.JPG
 | footer = Left: Mangroves (here in East Nusa Tenggara, Indonesia) are the only tropical to subtropical forests adapted for a coastal environment.  From their origin on the coasts of the Indo-Malaysian region, they have reached a global distribution.<br />Right: The coelacanth (here a model from Oxford), thought extinct for millions of years, was rediscovered in the 20th century.  The Indian Ocean species is blue whereas the Indonesian species is brown.
}}
Coral reefs, sea grass beds, and mangrove forests are the most productive ecosystems of the Indian Ocean&nbsp;— coastal areas produce 20 tones of fish per square kilometre. 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 [[Physics:Sea surface temperature|sea surface temperature]] spreads coral bleaching.<ref>{{Harvnb|Souter|Lindén|2005|loc=Foreword, pp. 5–6}}</ref>

[[Earth:Mangrove|Mangrove]]s covers {{Convert|80984|km2|abbr=on}} in the Indian Ocean region, or almost half of the world's mangrove habitat, of which {{Convert|42500|km2|abbr=on}} 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.<ref>{{Harvnb|Kathiresan|Rajendran|2005|loc=Introduction; Mangrove habitat, pp. 104–105}}</ref>

In 2016, six new animal species were identified at hydrothermal vents in the Southwest Indian Ridge: a "Hoff" crab, a "giant peltospirid" snail, a whelk-like snail, a limpet, a scaleworm and a polychaete worm.<ref>{{cite news
 | title = New marine life found in deep sea vents
 | date = 15 December 2016
 | work = BBC News
 | url = https://www.bbc.co.uk/news/science-environment-38305989
 | access-date = 15 December 2016
 | archive-date = 15 December 2016
 | archive-url = https://web.archive.org/web/20161215042627/http://www.bbc.co.uk/news/science-environment-38305989
 | url-status = live
 }}</ref>

The [[Biology:West Indian Ocean coelacanth|West Indian Ocean coelacanth]] was discovered in the Indian Ocean off South Africa in the 1930s and in the late 1990s another species, the [[Biology:Indonesian coelacanth|Indonesian coelacanth]], was discovered off Sulawesi Island, Indonesia. Most extant coelacanths have been found in the Comoros. Although both species represent an order of [[Biology:Sarcopterygii|lobe-finned fishes]] known from the Early Devonian (410 {{Abbr|mya|million years ago}}) and though extinct 66 mya, they are morphologically distinct from their Devonian ancestors. Over millions of years, coelacanths evolved to inhabit different environments&nbsp;— lungs adapted for shallow, brackish waters evolved into gills adapted for deep marine waters.<ref>{{Harvnb|Cupello|Clément|Meunier|Herbin|2019|loc=Introduction, p. 29}}</ref>

==Biodiversity==
Of Earth's 36 [[Biology:Biodiversity hotspot|biodiversity hotspot]] nine (or 25%) are located on the margins of the Indian Ocean.
[[File:Vogeleiland.jpg|thumb|Madagascar's [[Biology:Elephant bird|Elephant bird]], Mauritius's Dodo bird and ostrich (from left to right)]]
* 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.<ref name="Mitter-2011-p12">{{Harvnb|Mittermeier|Turner|Larsen|Brooks|2011|loc=Table 1.2, pp. 12–13}}</ref>
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 [[Biology:Chameleon|chameleon]]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 [[Biology:Dung beetle|dung beetle]]s,<ref>{{Cite journal|title=Origin and Diversification of Dung Beetles in Madagascar|first1=Andreia|last1=Miraldo|first2=Helena|last2=Wirta|first3=Ilkka|last3=Hanski|date=20 April 2011|journal=Insects|volume=2|issue=2|pages=112–127|doi=10.3390/insects2020112|doi-access=free |pmid=26467617|pmc=4553453}}</ref><ref>{{Cite journal|url=https://www.sciencedirect.com/science/article/pii/S1055790308001073|title=An old adaptive radiation of forest dung beetles in Madagascar|first1=Helena|last1=Wirta|first2=Luisa|last2=Orsini|first3=Ilkka|last3=Hanski|date=1 June 2008|journal=Molecular Phylogenetics and Evolution|volume=47|issue=3|pages=1076–1089|via=ScienceDirect|doi=10.1016/j.ympev.2008.03.010|pmid=18424187 |s2cid=7509190 }}</ref> day geckos,<ref>[https://academic.oup.com/evolut/article/50/2/604/6870715 ADAPTIVE RADIATION OF DAY‐GECKOS (PHELSUMA) IN THE SEYCHELLES ARCHIPELAGO: A PHYLOGENETIC ANALYSIS]</ref><ref>{{Cite web|url=https://www.annualreviews.org/doi/10.1146/annurev-ecolsys-120213-091839#:~:text=For%20example%2C%20studies%20of%20the,2007|title=Gecko Adhesion as a Model System for Integrative Biology, Interdisciplinary Science, and Bioinspired Engineering &#124; Annual Review of Ecology, Evolution, and Systematics|doi=10.1146/annurev-ecolsys-120213-091839 }}</ref> and lemurs are all examples of adaptive radiation.<ref>{{Cite journal|title=Testing the adaptive radiation hypothesis for the lemurs of Madagascar|first=James P.|last=Herrera|date=31 January 2017|journal=Royal Society Open Science|volume=4|issue=1|pages=161014|doi=10.1098/rsos.161014|pmid=28280597|pmc=5319363|bibcode=2017RSOS....461014H }}</ref>
Many bones (250 bones per square metre) of recently extinct vertebrates have been found in the Mare aux Songes swamp in Mauritius, including bones of the [[Biology:Dodo|Dodo]] bird (''Raphus cucullatus'') and ''[[Biology:Cylindraspis|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.<ref>{{Harvnb|Rijsdijk|Hume|Bunnik|Florens|2009|loc=Abstract}}</ref>
* 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.<ref name="Mitter-2011-p12" />
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&nbsp;— the population of white rhinoceros (''Ceratotherium simum simum'') increased from less than 20 individuals in 1895 to more than 17,000 as of 2013. Other species still depend on fenced areas and management programs, including [[Biology:Black rhinoceros|black rhinoceros]] (''Diceros bicornis minor''), [[Biology:African wild dog|African wild dog]] (''Lycaon pictus''), cheetah (''Acynonix jubatus''), elephant (''Loxodonta africana''), and lion (''Panthera leo'').<ref>{{Harvnb|Di Minin|Hunter|Balme|Smith|2013|loc="The Maputaland-Pondoland-Albany biodiversity hotspot is internationally recognized...""}}</ref>
* 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.<ref name="Mitter-2011-p12" />
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 {{Convert|200|km|abbr=on}} from the coast and covering a total area of c. {{Convert|6200|km2|abbr=on}}. It also encompasses coastal islands, including Zanzibar and Pemba, and Mafia.<ref>{{Harvnb|WWF-EARPO|2006|loc=The unique coastal forests of eastern Africa, p. 3}}</ref>
* [[Place:Horn of Africa|Horn of Africa]]; 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.<ref name="Mitter-2011-p12" />[[File:Vaavu Atoll, Maldives - panoramio (20).jpg|thumb|[[Earth:Coral reef|Coral reef]]s of the Maldives]]
This area, one of the only two hotspots that are entirely arid, includes the [[Earth:Ethiopian Highlands|Ethiopian Highlands]], the East African Rift valley, the Socotra islands, as well as some small islands in the Red Sea and areas on the southern Arabic Peninsula. Endemic and threatened mammals include the [[Biology:Dibatag|dibatag]] (''Ammodorcas clarkei'') and [[Biology:Speke's gazelle|Speke's gazelle]] (''Gazella spekei''); the [[Biology:Somali wild ass|Somali wild ass]] (''Equus africanus somaliensis'') and hamadryas baboon (''Papio hamadryas''). It also contains many reptiles.<ref>{{Cite web
 | title = Horn of Africa | publisher = CEPF
 | url = https://www.cepf.net/our-work/biodiversity-hotspots/horn-africa | access-date = 18 August 2019}}</ref>
In Somalia, the centre of the {{Convert|1500000|km2|abbr=on}} hotspot, the landscape is dominated by [[Biology:Acacia|Acacia]]-[[Biology:Commiphora|Commiphora]] deciduous bushland, but also includes the Yeheb nut (''Cordeauxia edulus'') and species discovered more recently such as the Somali [[Biology:Cyclamen|cyclamen]] (''Cyclamen somalense''), the only cyclamen outside the Mediterranean. [[Biology:Warsangli linnet|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.<ref>{{Harvnb|Ullah|Gadain|2016|loc=Importance of biodiversity, pp. 17–19; Biodiversity of Somalia, pp.25–26}}</ref>
* The Western Ghats–Sri Lanka; 5,916 (3,049 endemic) species of plants; 457 (35) birds; 265 (176) reptiles; 191 (139) freshwater fishes; 204 (156) amphibians; and 143 (27) mammals.<ref name="Mitter-2011-p12" />
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.<ref>{{Harvnb|Bossuyt|Meegaskumbura|Beenaerts|Gower|2004}}</ref>
* 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.<ref name="Mitter-2011-p12" />[[File:О. Альдабра - поднятый атолл в архипелаге Сейшельских островов.jpg|thumb|[[Biology:Aldabra giant tortoise|Aldabra giant tortoise]] from the islands of the Aldabra Atoll in the Seychelles]]
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 [[Earth:Sea level rise|rising sea levels]] and glaciations have isolated ecosystems and thus promoted a high degree of endemism and [[Biology:Speciation|speciation]]. The region includes two centres of endemism: the Annamite Mountains and the northern highlands on the China-Vietnam border.<ref>{{Harvnb|CEPF 2012: ''Indo-Burma''|loc=Geography, Climate, and History, p. 30}}</ref>
Several distinct floristic regions, 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.<ref>{{Harvnb|CEPF 2012: ''Indo-Burma''|loc=Species Diversity and Endemism, p. 36}}</ref>
* [[Earth:Sundaland|Sundaland]]; 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.<ref name="Mitter-2011-p12" />
Sundaland encompasses 17,000 islands of which Borneo and Sumatra are the largest. Endangered mammals include the [[Biology:Bornean orangutan|Bornean]] and [[Biology:Sumatran orangutan|Sumatran orangutan]]s, the [[Biology:Proboscis monkey|proboscis monkey]], and the [[Biology:Javan rhinoceros|Javan]] and [[Biology:Sumatran rhinoceros|Sumatran rhinoceros]]es.<ref>{{Cite web | title = Sundaland: About this hotspot | publisher = CEPF | url = https://www.cepf.net/our-work/biodiversity-hotspots/sundaland | access-date = 1 September 2019 | archive-date = 6 October 2022 | archive-url = https://web.archive.org/web/20221006110745/https://www.cepf.net/our-work/biodiversity-hotspots/sundaland/ | url-status = live }}</ref>
* [[Biology:Wallacea|Wallacea]]; 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.<ref name="Mitter-2011-p12" />
* Southwest Australia; 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.<ref name="Mitter-2011-p12" />
Stretching from Shark Bay to Israelite Bay and isolated by the arid Nullarbor Plain, 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.<ref>{{Harvnb|Ryan|2009}}</ref>

==Geology==
{{Multiple image | width = 180
 | image1 = Opening of western Indian Ocean 150 Ma.png
 | image2 = Opening of eastern Indian Ocean 40 Ma.png
 | footer = Left: The oldest ocean floor of the Indian Ocean formed c. 150&nbsp;Ma when the Indian Subcontinent and Madagascar broke-up from Africa.  Right: The India–Asia collision c. 40&nbsp;Ma completed the closure of the [[Earth:Tethys Ocean|Tethys Ocean]] (grey areas north of India).  Geologically, the Indian Ocean is the ocean floor that opened up south of India.
}}
As the youngest of the major oceans,<ref>{{Harvnb|Stow|2006}}</ref> the Indian Ocean has active spreading ridges that are part of the worldwide system of [[Earth:Mid-ocean ridge|mid-ocean ridge]]s. In the Indian Ocean these spreading ridges meet at the Rodrigues Triple Point with the [[Earth:Central Indian Ridge|Central Indian Ridge]], including the [[Earth:Carlsberg Ridge|Carlsberg Ridge]], separating the [[Earth:African Plate|African Plate]] from the [[Earth:Indian Plate|Indian Plate]]; the [[Earth:Southwest Indian Ridge|Southwest Indian Ridge]] separating the African Plate from the [[Earth:Antarctic Plate|Antarctic Plate]]; and the [[Earth:Southeast Indian Ridge|Southeast Indian Ridge]] separating the [[Earth:Australian Plate|Australian Plate]] from the [[Earth:Antarctic Plate|Antarctic Plate]]. The Central Indian Ridge is intercepted by the Owen Fracture Zone.<ref name="Chatt-etal-2013">{{Harvnb|Chatterjee|Goswami|Scotese|2013|loc=Tectonic setting of the Indian Ocean, p. 246}}</ref>
Since the late 1990s, however, it has become clear that this traditional definition of the [[Earth:Indo-Australian Plate|Indo-Australian Plate]] cannot be correct; it consists of three plates&nbsp;— the [[Earth:Indian Plate|Indian Plate]], the [[Earth:Capricorn Plate|Capricorn Plate]], and [[Earth:Australian Plate|Australian Plate]]&nbsp;— separated by diffuse boundary zones.<ref>{{Harvnb|Royer|Gordon|1997|loc=Abstract}}</ref>
Since 20&nbsp;Ma the [[Earth:African Plate|African Plate]] is being divided by the East African Rift System into the Nubian and [[Earth:Somali Plate|Somalia]] plates.<ref>{{Harvnb|Bird|2003|loc=Somalia Plate (SO), pp. 39–40}}</ref>

There are only two trenches in the Indian Ocean: the {{Convert|6000|km|abbr=on}}-long Java Trench between Java and the Sunda Trench and the {{Convert|900|km|abbr=on}}-long Makran Trench south of Iran and Pakistan.<ref name="Chatt-etal-2013" />

A series of ridges and [[Earth:Seamount chain|seamount chain]]s produced by [[Earth:Hotspot (geology)|hotspots]] pass over the Indian Ocean. The Réunion hotspot (active 70–40 million years ago) connects Réunion and the Mascarene Plateau to the [[Earth:Chagos-Laccadive Ridge|Chagos-Laccadive Ridge]] and the [[Earth:Deccan Traps|Deccan Traps]] in north-western India; the Kerguelen hotspot (100–35 million years ago) connects the Kerguelen Islands and [[Earth:Kerguelen Plateau|Kerguelen Plateau]] to the [[Earth:Ninety East Ridge|Ninety East Ridge]] and the [[Earth:Rajmahal Traps|Rajmahal Traps]] in north-eastern India; the Marion hotspot (100–70 million years ago) possibly connects Prince Edward Islands to the [[Earth:Eighty Five East Ridge|Eighty Five East Ridge]].<ref>{{Harvnb|Müller|Royer|Lawver|1993|loc=Fig. 1, p. 275}}</ref> These hotspot tracks have been broken by the still active spreading ridges mentioned above.<ref name="Chatt-etal-2013" />

There are fewer seamounts in the Indian Ocean than in the Atlantic and Pacific. These are typically deeper than {{Convert|3000|m|abbr=on}} 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 [[Earth:Carlsberg Ridge|Carlsberg Ridge]], Madagascar Ridge, [[Earth:Central Indian Ridge|Central Indian Ridge]], [[Earth:Southwest Indian Ridge|Southwest Indian Ridge]], [[Earth:Chagos-Laccadive Ridge|Chagos-Laccadive Ridge]], [[Earth:Eighty Five East Ridge|85°E Ridge]], [[Earth:Ninety East Ridge|90°E Ridge]], [[Earth:Southeast Indian Ridge|Southeast Indian Ridge]], Broken Ridge, and East Indiaman Ridge. The Agulhas Plateau and Mascarene Plateau are the two major shallow areas.<ref name="Rogers-p5" />

The opening of the Indian Ocean began {{Circa}} 156&nbsp;{{Abbr|Ma|million year ago}} when Africa separated from East [[Earth:Gondwana|Gondwana]]. The Indian Subcontinent began to separate from Australia-Antarctica 135–125 Ma and as the [[Earth:Tethys Ocean|Tethys Ocean]] north of India began to close 118–84&nbsp;Ma the Indian Ocean opened behind it.<ref name="Chatt-etal-2013" />

==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 ''[[Earth:Terra incognita|mare incognitum]]''. The written history of the Indian Ocean, however, has been [[Social:Eurocentrism|Eurocentric]] and largely dependent on the availability of written sources from the European colonial era. This history is often divided into an ancient period followed by an Islamic period; the subsequent periods are often subdivided into [[Place:Portuguese Empire|Portuguese]], [[Place:Dutch Empire|Dutch]], and [[Place:British Empire|British]] periods.<ref>{{Harvnb|Parthasarathi|Riello|2014|loc=Time and the Indian Ocean, pp. 2–3}}</ref>

A concept of an "Indian Ocean World" (IOW), similar to that of the "[[History:Atlantic World|Atlantic World]]", 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 [[Place:Mesopotamia|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.<ref>{{Harvnb|Campbell|2017|loc=The Concept of the Indian Ocean World (IOW), pp. 25–26}}</ref>

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.<ref>{{Harvnb|Bouchard|Crumplin|2010|loc=Abstract}}</ref>

===First settlements===
[[File:Peopling of eurasia.jpg|thumb|According to the ''Coastal hypothesis'', modern humans spread from Africa along the northern rim of the Indian Ocean.]]
Pleistocene fossils of ''[[Biology:Homo erectus|Homo erectus]]'' and other pre–''H. sapiens'' hominid fossils, similar to ''[[Biology:Homo heidelbergensis|H. heidelbergensis]]'' in Europe, have been found in India. According to the [[Earth:Toba catastrophe theory|Toba catastrophe theory]], a supereruption c. 74,000 years ago at [[Earth:Lake Toba|Lake Toba]], Sumatra, covered India with volcanic ashes and wiped out one or more lineages of such archaic humans in India and Southeast Asia.<ref>{{Harvnb|Patnaik|Chauhan|2009|loc=Abstract}}</ref>

The [[Biology:Recent African origin of modern humans|''Out of Africa'']] theory states that ''Homo sapiens'' spread from Africa into mainland Eurasia. The more recent ''[[Earth:Southern Dispersal|Southern Dispersal]]'' or ''Coastal hypothesis'' instead advocates that modern humans spread along the coasts of the Arabic Peninsula and southern Asia. This hypothesis is supported by [[Biology:Mitochondrial DNA|mtDNA]] research which reveals a rapid dispersal event during the [[Earth:Late Pleistocene|Late Pleistocene]] (11,000&nbsp;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 {{Convert|0.7|-|4.0|km|abbr=on}} per year. It eventually resulted in modern humans migrating from [[Earth:Sundaland|Sunda]] over [[Biology:Wallacea|Wallacea]] to [[Earth:Australia (continent)|Sahul]] (Southeast Asia to Australia).<ref>{{Harvnb|Bulbeck|2007|p=315}}</ref> 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.<ref>{{Harvnb|McPherson|1984|loc=History and Patterns, pp. 5–6}}</ref>

Food globalisation began on the Indian Ocean littoral c. 4.000&nbsp;years ago. Five African crops&nbsp;— [[Biology:Sorghum bicolor|sorghum]], [[Biology:Pennisetum glaucum|pearl millet]], [[Biology:Eleusine coracana|finger millet]], [[Biology:Vigna unguiculata|cowpea]] and [[Biology:Lablab purpureus|hyacinth bean]]&nbsp;— somehow found their way to Gujarat in India during the Late Harappan (2000–1700 BCE). Gujarati merchants evolved into the first explorers of the Indian Ocean as they traded African goods such as ivory, tortoise shells, and slaves. [[Biology:Panicum miliaceum|Broomcorn millet]] found its way from Central Asia to Africa, together with chicken and [[Biology:Zebu|zebu]] cattle, although the exact timing is disputed. Around 2000&nbsp;BCE [[Biology:Piper nigrum|black pepper]] and [[Biology:Sesamum indicum|sesame]], both native to Asia, appear in Egypt, albeit in small quantities. Around the same time the black rat and the house mouse emigrate from Asia to Egypt. Banana reached Africa around 3000&nbsp;years ago.<ref>{{Harvnb|Boivin|Crowther|Prendergast|Fuller|2014|loc=The Earliest Evidence, pp. 4–7}}</ref>

[[File:A young Onge mother with her baby.jpg|thumb|upright|The Andaman Negritos are thought to be the first inhabitants of the Andaman Islands, having emigrated from the mainland tens of thousands of 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.<ref>{{Harvnb|Rubin|Horton|Sieh|Pilarczyk|2017|loc=Abstract}}</ref>

A group of scientists have argued that two large-scale impact events have occurred in the Indian Ocean: the [[Earth:Burckle Crater|Burckle Crater]] in the southern Indian Ocean in 2800 BCE and the Kanmare and Tabban craters in the Gulf of Carpentaria in northern Australia in 536 CE. Evidences for these impacts, the team argue, are micro-ejecta and [[Earth:Chevron (land form)|Chevron]] [[Earth:Dune|dune]]s in southern Madagascar and in the Australian gulf. Geological evidences suggest the tsunamis caused by these impacts reached {{Convert|205|m|abbr=on}} above sea level and {{Convert|45|km|abbr=on}} inland. The impact events must have disrupted human settlements and perhaps even contributed to [[Earth:Extreme weather events of 535–536|major climate changes]].<ref>{{Harvnb|Gusiakov|Abbott|Bryant|Masse|2009|loc=Abstract}}</ref>

===Antiquity===
The history of the Indian Ocean is marked by maritime trade; cultural and commercial exchange probably date back at least seven thousand years.<ref name="Alpers-pp1-2">{{Harvnb|Alpers|2013|loc=Chapter 1. Imagining the Indian Ocean, pp. 1–2}}</ref> 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 {{circa|2000&nbsp;BCE}}, however, cultures on its shores were only loosely tied to each other; bronze, for example, was developed in Mesopotamia {{circa|3000&nbsp;BCE}} but remained uncommon in Egypt before 1800&nbsp;BCE.<ref>{{Harvnb|Beaujard|Fee|2005|p=417}}</ref>
During this period, independent, short-distance oversea communications along its littoral margins evolved into an all-embracing network. The début of this network was not the achievement of a centralised or advanced civilisation but of local and regional exchange in the Persian Gulf, the Red Sea, and the Arabian Sea. Sherds of [[History:Ubaid period|Ubaid]] (2500–500&nbsp;BCE) pottery have been found in the western Gulf at Dilmun, present-day Bahrain; traces of exchange between this trading centre and [[Place:Mesopotamia|Mesopotamia]]. The Sumerians traded grain, pottery, and [[Chemistry:Bitumen|bitumen]] (used for [[Engineering:Reed boat|reed boat]]s) for copper, stone, timber, tin, dates, onions, and pearls.<ref name="Alpers-pp19-22">{{Harvnb|Alpers|2013|loc=Chapter 2. The Ancient Indian Ocean, pp. 19–22}}</ref>
Coast-bound vessels transported goods between the Indus Valley civilisation (2600–1900&nbsp;BCE) in the Indian subcontinent (modern-day Pakistan and Northwest India) and the Persian Gulf and Egypt.<ref name="Alpers-pp1-2" />
[[File:Austronesian maritime trade network in the Indian Ocean.png|thumb|The Austronesian maritime trade network was the first trade routes in the Indian Ocean.]]
The Red Sea, one of the main trade routes in Antiquity, was explored by Egyptians and [[History:Phoenicia|Phoenicia]]ns during the last two millennia BCE. In the 6th century, BCE Greek explorer Scylax of Caryanda made a journey to India, working for the Persian king Darius, and his now-lost account put the Indian Ocean on the maps of Greek geographers. The Greeks began to explore the Indian Ocean following the conquests of Alexander the Great, who ordered a circumnavigation of the Arabian Peninsula in 323&nbsp;BCE. During the two centuries that followed the reports of the explorers of [[History:Ptolemaic Kingdom|Ptolemaic Egypt]] resulted in the best maps of the region until the Portuguese era many centuries later. The main interest in the region for the Ptolemies was not commercial but military; they explored Africa to hunt for war elephants.<ref>{{Harvnb|Burstein|1996|pp=799–801}}</ref>

The [[Earth:Rub' al Khali|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 [[Earth:Monsoon|monsoon]] (from ''mawsim'', the Arabic word for season), however, was used by sailors long before being "discovered" by Hippalus in the 1st century. Indian wood have been found in Sumerian cities, there is evidence of Akkad coastal trade in the region, and contacts between India and the Red Sea dates back to 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.<ref>{{Harvnb|Forbes|1981|loc=Southern Arabia and the Central Indian Ocean: Pre- Islamic Contacts, pp. 62–66}}</ref>
[[File:Indo-Roman trade.jpg|thumb|Greco-Roman trade with ancient India according to the ''Periplus of the Erythraean Sea'' 1st century CE]]
''Periplus of the Erythraean Sea'', an [[Place:Alexandria|Alexandria]]n guide to the world beyond the Red Sea&nbsp;— including Africa and India&nbsp;— 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 [[Earth:Monsoon|monsoon]] winds.<ref name="Alpers-pp1-2" /> The contemporaneous settlement of {{wipe|Madagascar}} by Austronesian sailors shows that the littoral margins of the Indian Ocean were being both well-populated and regularly traversed at least by this time. Albeit the monsoon must have been common knowledge in the Indian Ocean for centuries.<ref name="Alpers-pp1-2" />

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 {{wipe|Madagascar}} around 1&nbsp;CE.<ref>{{Harvnb|Fitzpatrick|Callaghan|2009|loc=The colonisation of Madagascar, pp. 47–48}}</ref>

In the 2nd or 1st century BCE, Eudoxus of Cyzicus was the first Greek to cross the Indian Ocean. The probably fictitious sailor Hippalus is said to have learnt the direct route from Arabia to India around this time.<ref>{{Harvnb|El-Abbadi|2000}}</ref> During the 1st and 2nd centuries AD intensive trade relations developed between Roman Egypt and the Tamil kingdoms of the Cheras, Cholas and Pandyas in Southern India. Like the Indonesian people above, the western sailors used the monsoon to cross the ocean. The unknown author of the ''Periplus of the Erythraean Sea'' describes this route, as well as the commodities that were traded along various commercial ports on the coasts of the Horn of Africa and India circa 1&nbsp;CE. Among these trading settlements were Mosylon and Opone on the Red Sea littoral.<ref name="Periplus" />

===Age of Discovery===
[[File:Silk route.jpg|thumb|upright=1.35|The economically important Silk Road was blocked from Europe by the Ottoman Empire in {{circa}} 1453 with the fall of the Byzantine Empire. This spurred exploration, and a new sea route around Africa was found, triggering the [[Age of Discovery|Age of Discovery]].]]
{{Multiple image | width = 180
 | image1 = Color etopo1 ice low indian ocean westward routes.jpg
 | image2 = Color etopo1 ice low indian ocean eastward routes.jpg
 | footer = Preferred sailing routes across the Indian Ocean
}}
Unlike the Pacific Ocean where the civilization of the Polynesians reached most of the far-flung islands and atolls and populated them, almost all the islands, archipelagos and atolls of the Indian Ocean were uninhabited until colonial times. Although there were numerous ancient civilizations in the coastal states of Asia and parts of Africa, the [[History:Maldives|Maldives]] were the only island group in the Central Indian Ocean region where an ancient civilization flourished.<ref>{{Harvnb|Cabrero|2004|p=32}}</ref> Maldivians, on their annual trade trip, took their oceangoing trade ships to Sri Lanka rather than mainland India, which is much closer, because their ships were dependent of the [[Earth:Indian Monsoon Current|Indian Monsoon Current]].<ref>{{Harvnb|Romero-Frias|2016|loc=Abstract; p. 3}}</ref>

Arabic missionaries and merchants began to [[Social:Spread of Islam#East Africa|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.<ref>{{Harvnb|LaViolette|2008|loc=Conversion to Islam and Islamic Practice, pp. 39–40}}</ref>
Muslim merchants traded an estimated 1000 African slaves annually between 800 and 1700, a number that grew to {{circa|4000}} 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.<ref name="Allen-2017-overview">{{Harvnb|Allen|2017|loc=Slave Trading in the Indian Ocean: An Overview, pp. 295–299}}</ref>

From 1405 to 1433 admiral Zheng He said to have led large fleets of the Ming dynasty on several treasure voyages through the Indian Ocean, ultimately reaching the coastal countries of East Africa.<ref>{{Harvnb|Dreyer|2007|p=1}}</ref>
[[File:Descobrimentos e explorações portuguesesV2.png|thumb|upright=1.3|For most of the 16th century, the Portuguese dominated the [[Earth:Indian Ocean trade|Indian Ocean trade]].]]
The Portuguese navigator Vasco da Gama rounded the Cape of Good Hope during his first voyage in 1497 and became the first European to sail to India. The Swahili people he encountered along the African east coast lived in a series of cities and had established trade routes to India and to China. Among them, the Portuguese kidnapped most of their pilots in coastal raids and on board ships. A few of the pilots, however, were gifts by local Swahili rulers, including the sailor from Gujarat, a gift by a Malindi ruler in Kenya, who helped the Portuguese to reach India. In expeditions after 1500, the Portuguese attacked and colonised cities along the African coast.<ref>{{Harvnb|Felber Seligman|2006|loc=The East African Coast, pp. 90–95}}</ref>
European slave trade in the Indian Ocean began when Portugal established [[History:Portuguese India|Estado da Índia]] in the early 16th century. From then until the 1830s, {{circa|200}} slaves were exported from Mozambique annually and similar figures has been estimated for slaves brought from Asia to the Philippines during the Iberian Union (1580–1640).<ref name="Allen-2017-overview" />

The [[Place:Ottoman Empire|Ottoman Empire]] began its expansion into the Indian Ocean in 1517 with the conquest of Egypt under Sultan Selim I. Although the Ottomans shared the same religion as the trading communities in the Indian Ocean the region was unexplored by them. Maps that included the Indian Ocean had been produced by Muslim geographers centuries before the Ottoman conquests; Muslim scholars, such as Ibn Battuta in the 14th century, had visited most parts of the known world; contemporarily with Vasco da Gama, Arab navigator Ahmad ibn Mājid had compiled a guide to navigation in the Indian Ocean; the Ottomans, nevertheless, began their own parallel era of discovery which rivalled the European expansion.<ref>{{Harvnb|Casale|2003}}</ref>
[[File:Upton Castle at Ile de France 1810.jpg|thumb|British invasion of Mauritius during the Napoleonic Wars on 29 November 1810]]
The establishment of the Dutch East India Company 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 {{formatnum:500000}} slaves in various [[Place:Dutch Empire|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. Bali and neighbouring islands supplied regional networks with {{circa|{{formatnum:100000}}–{{formatnum:150000}}}} slaves 1620–1830. Indian and Chinese slave traders supplied Dutch Indonesia with perhaps {{formatnum:250000}} slaves during the 17th and 18th centuries.<ref name="Allen-2017-overview" />

The East India Company (EIC) was established during the same period and in 1622 one of its ships carried slaves from the Coromandel Coast to Dutch East Indies. 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 and [[Earth:Mauritius|Mauritius]] in 1721; by 1735 some 7,200 slaves populated the Mascarene Islands, a number which had reached {{formatnum:133000}} in 1807. The [[History:United Kingdom of Great Britain and Ireland|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 {{formatnum:336000}}–{{formatnum:388000}} slaves were exported to the Mascarene Islands from 1670 until 1848.<ref name="Allen-2017-overview" />

In all, European traders exported {{formatnum:567900}}–{{formatnum:733200}} 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 {{circa|{{formatnum:12000000}}}} slaves exported across the Atlantic.<ref name="Allen-2017-overview" /> The island of Zanzibar was the center of the Indian Ocean slave trade in the 19th century. In the mid-19th century, as many as 50,000 slaves passed annually through the port.<ref>[http://ngm.nationalgeographic.com/ngm/data/2001/10/01/html/ft_20011001.6.html "Swahili Coast: East Africa's Ancient Crossroads"]{{Webarchive|url= https://web.archive.org/web/20180119091452/http://ngm.nationalgeographic.com/ngm/data/2001/10/01/html/ft_20011001.6.html |date=19 January 2018 }}, ''Did You Know?'' sidebar by Christy Ullrich, ''National Geographic''.</ref>

===Late modern era===
[[File:Malé (8685996006).jpg|thumb|Malé's population has increased from 20,000 people in 1987 to more than 220,000 people in 2020.]]
Scientifically, the Indian Ocean remained poorly explored before the [[Earth:International Indian Ocean Expedition|International Indian Ocean Expedition]] in the early 1960s. However, the [[Challenger expedition|''Challenger'' expedition]] 1872–1876 only reported from south of the polar front. The [[Valdivia Expedition|''Valdivia'' expedition]] 1898–1899 made deep samples in the Indian Ocean. In the 1930s, the John Murray Expedition mainly studied shallow-water habitats. The [[Earth:Albatross expedition|Swedish Deep Sea Expedition]] 1947–1948 also sampled the Indian Ocean on its global tour and the Danish [[Earth:Galathea expeditions|''Galathea'']] sampled deep-water fauna from Sri Lanka to South Africa on its second expedition 1950–1952. The Soviet research vessel [[Engineering:RV Vityaz (1939)|''Vityaz'']] also did research in the Indian Ocean.<ref name="Demo-etal-intro" />

The Suez Canal opened in 1869 when the [[History:Industrial Revolution|Industrial Revolution]] dramatically changed global shipping – the sailing ship declined in importance as did the importance of European trade in favour of trade in East Asia and Australia.<ref>{{Harvnb|Fletcher|1958|loc=Abstract}}</ref>
The construction of the canal introduced many non-indigenous species into the Mediterranean. For example, the goldband goatfish (''[[Biology:Upeneus moluccensis|Upeneus moluccensis]]'') has replaced the red mullet (''[[Biology:Mullus barbatus|Mullus barbatus]]''); since the 1980s huge swarms of [[Biology:Scyphozoa|scyphozoa]]n jellyfish (''[[Biology:Rhopilema nomadica|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.<ref>{{Harvnb|Galil|Boero|Campbell|Carlton|2015|pp=973–974}}</ref>

[[File:Diego garcian.jpg|thumb|upright=.9|A Chagossian on Diego Garcia in 1971, before the British expelled the islanders. He spoke a French-based creole language and his ancestors were likely brought as slaves in the 19th century.]]
Throughout the colonial era, islands such as [[Earth:Mauritius|Mauritius]] were important shipping nodes for the Dutch, French, and British. Mauritius, an inhabited island, became populated by slaves from Africa and indenture labour from India. The end of World War II marked the end of the colonial era. The British left Mauritius in 1974 and with 70% of the population of Indian descent, Mauritius became a close ally of India. In the 1980s, during the Cold War, the South African regime acted to destabilise several island nations in the Indian Ocean, including the Seychelles, Comoros, and Madagascar. India intervened in Mauritius to prevent a coup d'état, backed up by the United States who feared the Soviet Union could gain access to [[Place:Port Louis|Port Louis]] and threaten the U.S. base on Diego Garcia.<ref>{{Harvnb|Brewster|2014b|loc=Excerpt}}</ref>
Iranrud was 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&nbsp;— there were Indian slaves and settlers as well as black indentured labourers. There were also a string of prison camps across the Indian Ocean, such as Cellular Jail in the Andamans, in which prisoners, exiles, POWs, forced labourers, merchants and people of different faiths were forcefully united. On the islands of the Indian Ocean, therefore, a trend of creolisation emerged.<ref>{{Harvnb|Hofmeyr|2012|loc=Crosscutting Diasporas, pp. 587–588}}</ref>

On 26 December 2004, fourteen countries around the Indian Ocean were hit by a wave of [[Tsunami|tsunami]]s caused by the 2004 Indian Ocean earthquake. The waves radiated across the ocean at speeds exceeding {{Convert|500|km/h|abbr=on}}, reached up to {{Convert|20|m|abbr=on}} in height, and resulted in an estimated 236,000 deaths.<ref>{{Harvnb|Telford|Cosgrave|2006|loc=Immediate effects of the disaster, pp. 33–35}}</ref>

In the late 2000s, the ocean evolved into a hub of pirate activity. By 2013, attacks off the Horn region's coast had steadily declined due to active private security and international navy patrols, especially by the Indian Navy.<ref>{{Harvnb|Arnsdorf|2013}}</ref>

Malaysia Airlines Flight 370, a [[Engineering:Boeing 777|Boeing 777]] airliner with 239 persons on board, disappeared on 8 March 2014 and is alleged to have crashed into the southern Indian Ocean about {{Convert|2500|km|abbr=on}} from the coast of southwest Western Australia. Despite an extensive search, the whereabouts of the remains of the aircraft is unknown.<ref>{{Harvnb|MacLeod|Winter|Gray|2014}}</ref>

The Sentinelese people of North Sentinel Island, which lies near South Andaman Island in the Bay of Bengal, have been called by experts the most isolated people in the world.<ref>{{Cite web|url=http://www.bbc.com/future/story/20140804-sad-truth-of-uncontacted-tribes|title=Anthropology: The sad truth about uncontacted tribes|last=Nuwer|first=Rachel|work=BBC|date=4 August 2014|access-date=15 May 2021|archive-date=30 August 2019|archive-url=https://web.archive.org/web/20190830173844/http://www.bbc.com/future/story/20140804-sad-truth-of-uncontacted-tribes|url-status=live}}</ref>

The sovereignty of the Chagos Archipelago in the Indian Ocean is disputed between the United Kingdom and [[Earth:Mauritius|Mauritius]].<ref>{{cite news |title=Chagos Islands dispute: UK 'threatened' Mauritius |url=https://www.bbc.com/news/world-africa-45300739 |work=BBC News |date=27 August 2018 |access-date=15 May 2021 |archive-date=23 March 2021 |archive-url=https://web.archive.org/web/20210323145031/https://www.bbc.com/news/world-africa-45300739 |url-status=live }}</ref> In February 2019, the International Court of Justice in [[Place:The Hague|The Hague]] issued an advisory opinion stating that the UK must transfer the Chagos Archipelago to Mauritius.<ref>{{cite news |title=Foreign Office quietly rejects International Court ruling to hand back Chagos Islands |url=https://inews.co.uk/news/politics/foreign-office-quietly-rejects-international-court-ruling-to-hand-back-chagos-islands-450078 |work=inews.co.uk |date=18 June 2020 |access-date=15 May 2021 |archive-date=30 January 2021 |archive-url=https://web.archive.org/web/20210130042318/https://inews.co.uk/news/politics/foreign-office-quietly-rejects-international-court-ruling-to-hand-back-chagos-islands-450078 |url-status=live }}</ref>

==Trade==
{{Main|Earth:Indian Ocean trade}}
[[File:Shipping routes.png|thumb|Major [[Engineering:Maritime transport|ocean trade routes]] in the world include the northern Indian Ocean.]]
The sea lanes in the Indian Ocean are considered among the most strategically important in the world with more than 80 percent of the world's seaborne trade in oil transits through 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.<ref>{{Cite news|url=https://thediplomat.com/2011/03/why-the-indian-ocean-matters/|title=Why the Indian Ocean Matters|last=DeSilva-Ranasinghe|first=Sergei|work=The Diplomat|date=2 March 2011}}</ref>
<!-- [[File:Lamu dhow 5.JPG|thumb|A [[Engineering:Dhow|dhow]] off the coast of Kenya]] -->

The Indian Ocean provides major sea routes connecting the Middle East, Africa, and East Asia with Europe and the Americas. It carries a particularly heavy traffic of petroleum and petroleum products from the oil fields of the Persian Gulf and Indonesia. Large reserves of hydrocarbons are being tapped in the offshore areas of Saudi Arabia, Iran, India, and Western Australia. An estimated 40% of the world's offshore oil production comes from the Indian Ocean.<ref name="CIAWFB-2018" /> Beach sands rich in heavy minerals, and offshore placer deposits are actively exploited by bordering countries, particularly India, Pakistan, South Africa, Indonesia, Sri Lanka, and Thailand.
[[File:A general view of Mombasa Port on Kenya's Indian Ocean coast.jpg|thumb|Mombasa Port on Kenya's Indian Ocean coast]]
In particular, the maritime part of the Silk Road leads through the Indian Ocean on which a large part of the global container trade is carried out. The Silk Road runs with its connections from the Chinese coast and its large container ports to the south via [[Place:Hanoi|Hanoi]] to [[Place:Jakarta|Jakarta]], Singapore and [[Place:Kuala Lumpur|Kuala Lumpur]] through the Strait of Malacca via the Sri Lankan [[Place:Colombo|Colombo]] opposite the southern tip of India via [[Place:Malé|Malé]], the capital of the Maldives, to the East African [[Place:Mombasa|Mombasa]], from there to Djibouti, then through the Red Sea over the Suez Canal into the Mediterranean, there via Haifa, Istanbul and [[Place:Athens|Athens]] to the Upper Adriatic to the northern Italian junction of Trieste with its international free port and its rail connections to [[Place:Central Europe|Central]] and Eastern Europe.<ref>Bernhard Simon: Can The New Silk Road Compete With The Maritime Silk Road? in The Maritime Executive, 1 January 2020.</ref><ref>Marcus Hernig: Die Renaissance der Seidenstraße (2018), pp 112.</ref><ref>Wolf D. Hartmann, Wolfgang Maennig, Run Wang: Chinas neue Seidenstraße. (2017), pp 59.</ref><ref>Matteo Bressan: Opportunities and challenges for BRI in Europe in Global Time, 2 April 2019.</ref>

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, Hambantota, [[Place:Colombo|Colombo]] and Sonadia. This has sparked a debate about the strategic implications of these investments.<ref>{{Harvnb|Brewster|2014a}}</ref> There are also Chinese investments and related efforts to intensify trade in East Africa and in European ports such as Piraeus and Trieste.<ref>Harry G. Broadman "Afrika's Silk Road" (2007), pp 59.</ref><ref>Andreas Eckert: Mit Mao nach Daressalam, In: Die Zeit 28. March 2019, p 17.</ref><ref>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.</ref>

==See also==
* [[Earth:Indo-Pacific|Indo-Pacific]]
* [[Physics:Indian Ocean Geoid Low|Indian Ocean Geoid Low]]
* Indian Ocean in World War II
* [[Earth:Indian Ocean literature|Indian Ocean literature]]
* [[Earth:Indian Ocean Naval Symposium|Indian Ocean Naval Symposium]]
* [[Earth:Indian Ocean Research Group|Indian Ocean Research Group]]
* [[Earth:List of islands in the Indian Ocean|List of islands in the Indian Ocean]]
* List of sovereign states and dependent territories in the Indian Ocean
* [[Organization:Indian Ocean Rim Association|Indian Ocean Rim Association]]
* Maritime Silk Road
* Territorial claims in Antarctica

==References==
===Citations===
{{reflist|21em}}

===Sources===
{{Refbegin|30em}}
* {{Cite journal |last=Allen |first=R. B. |title=Ending the history of silence: reconstructing European slave trading in the Indian Ocean |year=2017 |journal=Tempo |volume=23 |issue=2 |pages=294–313 |url=http://www.scielo.br/pdf/tem/v23n2/1980-542X-tem-23-02-00294.pdf |access-date=30 June 2019 |doi=10.1590/tem-1980-542x2017v230206 |doi-access=free}}<!-- {{Harvnb|Allen|2017}} -->
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{{Refend}}

==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), {{ISBN|978-1137564887}}.
* 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==
{{commons+cat|Indian Ocean|Indian_Ocean}}
* {{Cite web
 | title = The Indian Ocean in World History | publisher = Sultan Qaboos Cultural Center | format = Flash
 | url = http://www.indianoceanhistory.org/ | access-date = 25 July 2015}}
* {{Cite web
 | title = The Indian Ocean Trade: A Classroom Simulation
 | publisher = African Studies Center, Boston University
 | url = http://www.bu.edu/africa/files/2011/11/Indian-Ocean-Trade.pdf | access-date = 25 July 2015}}
{{Ocean}}
{{Regions of the world}}


[[Category:Indian Ocean| ]]
[[Category:Oceans]]

{{Sourceattribution|Indian Ocean}}