Wilkes Land is a large district of land in eastern Antarctica , formally claimed by Australia as part of the Australian Antarctic Territory , though the validity of this claim has been placed for the period of the operation of the Antarctic Treaty , to which Australia is a signatory.
107-505: Wilkes Land fronts on the southern Indian Ocean between Queen Mary Coast and Adelie Land , extending from Cape Hordern in 100°31' E to Pourquoi Pas Point , in 136°11' E. The region extends as a sector about 2600 km towards the South Pole , with an estimated land area of 2,600,000 km², mostly glaciated. It is further subdivided in the following coastal areas which can also be thought of as sectors extending to
214-614: A concentrated belt that stretches east–west except in East China where it is tilted east-northeast over Korea and Japan. The seasonal rain is known as Meiyu in China, Jangma in Korea, and Bai-u in Japan, with the latter two resembling frontal rain. The onset of the summer monsoon is marked by a period of premonsoonal rain over South China and Taiwan in early May. From May through August,
321-494: A distance of 2,400 km (1,500 miles ) of coast, thus providing substantial proof that Antarctica is a continent . This definition of extent excludes the area east of 142°02' E, George V Land , which was sighted by Wilkes but has been shown by later expeditions to be further south than the positions originally assigned by him. In 2006, a team of researchers led by Ralph von Frese and Laramie Potts used gravity measurements by NASA's GRACE satellites to discover
428-410: A dominant westerly component and a strong tendency to ascend and produce copious amounts of rain (because of the condensation of water vapor in the rising air). The intensity and duration, however, are not uniform from year to year. Winter monsoons, by contrast, have a dominant easterly component and a strong tendency to diverge, subside and cause drought. Similar rainfall is caused when moist ocean air
535-622: A few sub-systems, such as the Indian Subcontinental Monsoon which affects the Indian subcontinent and surrounding regions including Nepal, and the East Asian Monsoon which affects southern China, Taiwan , Korea and parts of Japan. The southwestern summer monsoons occur from June through September. The Thar Desert and adjoining areas of the northern and central Indian subcontinent heat up considerably during
642-468: 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 gases . Among the tropical oceans, the western Indian Ocean hosts one of the largest concentrations of phytoplankton blooms in summer, due to the strong monsoon winds. The monsoonal wind forcing leads to
749-547: A low pressure system known as a monsoon trough develops over South-East Asia and Australasia and winds are directed toward Australia. In the Philippines, northeast monsoon is called Amihan . The East Asian monsoon affects large parts of Indochina , the Philippines , China, Taiwan , Korea, Japan, and Siberia . It is characterised by a warm, rainy summer monsoon and a cold, dry winter monsoon. The rain occurs in
856-747: A maximum depth of 7,290 m (23,920 ft). All of the Indian Ocean is in the Eastern Hemisphere and the centre of the Eastern Hemisphere, the 90th meridian east , passes through the Ninety East Ridge . Within these waters are a number of islands. These include those controlled by surrounding countries, and independent island states and territories. Of the non-coastal islands, there are two broad clusters: one around Madagascar, and one south of India. A few other oceanic islands are scattered elsewhere. In contrast to
963-464: A more even temperature, while land temperatures are more variable. During warmer months sunlight heats the surfaces of both land and oceans, but land temperatures rise more quickly. As the land's surface becomes warmer, the air above it expands and an area of low pressure develops. Meanwhile, the ocean remains at a lower temperature than the land, and the air above it retains a higher pressure. This difference in pressure causes sea breezes to blow from
1070-470: 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
1177-790: A process of aridification began in the southwest Indian Ocean began around 4,000 years ago. 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 ( 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 black rhinoceros ( Diceros bicornis minor ), African wild dog ( Lycaon pictus ), cheetah ( Acynonix jubatus ), elephant ( Loxodonta africana ), and lion ( Panthera leo ). This biodiversity hotspot (and namesake ecoregion and "Endemic Bird Area")
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#17327721733671284-504: 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 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
1391-464: A strong coastal and open ocean upwelling , which introduces nutrients into the upper zones where sufficient light is available for photosynthesis and phytoplankton production. These phytoplankton blooms support the marine ecosystem, as the base of the marine food web, and eventually the larger fish species. The Indian Ocean accounts for the second-largest share of the most economically valuable tuna catch. Its fish are of great and growing importance to
1498-585: A weakening of the Leeuwin Current (LC). The weakening of the LC would have an effect on the sea surface temperature (SST) field in the Indian Ocean, as the Indonesian Throughflow generally warms the Indian Ocean. Thus these five intervals could probably be those of considerable lowering of SST in the Indian Ocean and would have influenced Indian monsoon intensity. During the weak LC, there
1605-473: Is a patchwork of small forested areas, often with a unique assemblage of species within each, located within 200 km (120 mi) from the coast and covering a total area of c. 6,200 km (2,400 sq mi). It also encompasses coastal islands, including Zanzibar and Pemba, and Mafia. This area, one of the only two hotspots that are entirely arid, includes the Ethiopian Highlands ,
1712-643: Is approximately 30° north in the Persian Gulf . The Indian Ocean covers 70,560,000 km (27,240,000 sq mi), including the Red Sea and the Persian Gulf but excluding the Southern Ocean, or 19.5% of the world's oceans; its volume is 264,000,000 km (63,000,000 cu mi) or 19.8% of the world's oceans' volume; it has an average depth of 3,741 m (12,274 ft) and
1819-825: Is artificially connected to the 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
1926-666: Is directly of "cyclonic" (i.e., monsoon-driven) origin (as opposed to " local convection "). The effects also extend westwards to the Mediterranean, where however the impact of the monsoon is to induce drought via the Rodwell-Hoskins mechanism . Around September, with the sun retreating south, the northern landmass of the Indian subcontinent begins to cool off rapidly, and air pressure begins to build over northern India. The Indian Ocean and its surrounding atmosphere still hold their heat, causing cold wind to sweep down from
2033-533: Is lifted upwards by mountains, surface heating, convergence at the surface, divergence aloft, or from storm-produced outflows at the surface. However the lifting occurs, the air cools due to expansion in lower pressure, and this produces condensation . The monsoon of western Sub-Saharan Africa is the result of the seasonal shifts of the Intertropical Convergence Zone and the great seasonal temperature and humidity differences between
2140-469: Is projected to push the tropical Indian Ocean into a basin-wide near-permanent heatwave state by the end of the 21st century, where marine heatwaves are projected to increase from 20 days per year (during 1970–2000) to 220–250 days per year. 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
2247-593: Is the possibility of reduced intensity of the Indian winter monsoon and strong summer monsoon, because of change in the Indian Ocean dipole due to reduction in net heat input to the Indian Ocean through the Indonesian Throughflow. Thus a better understanding of the possible links between El Niño , Western Pacific Warm Pool, Indonesian Throughflow, wind pattern off western Australia, and ice volume expansion and contraction can be obtained by studying
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#17327721733672354-497: Is the third-largest of the world's five oceanic divisions, covering 70,560,000 km (27,240,000 sq mi) or approximately 20% of the water area of Earth's surface . It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by the Southern Ocean , or Antarctica , depending on the definition in use. The Indian Ocean has large marginal, or regional seas, such as
2461-748: The Andaman Sea , the Arabian Sea , the Bay of Bengal , and the Laccadive Sea . Once called the Eastern Ocean, it is now named after India , which protrudes into it, and has been known by its current name since at least 1515. It is the only ocean named after a country. It has an average depth of 3,741 m. All of the Indian Ocean is in the Eastern Hemisphere . Unlike the Atlantic and Pacific,
2568-748: The Arabian Peninsula in the Northern Hemisphere and north of the trade winds in the Southern Hemisphere. The Indonesian Throughflow is a unique Equatorial connection to the Pacific. The climate north of the equator is affected by a monsoon climate. Strong north-east winds blow from October until April; from May until October south and west winds prevail. In the Arabian Sea, the violent Monsoon brings rain to
2675-577: 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 dibatag ( Ammodorcas clarkei ) and Speke's gazelle ( Gazella spekei ); the Somali wild ass ( Equus africanus somaliensis ) and hamadryas baboon ( Papio hamadryas ). It also contains many reptiles. In Somalia,
2782-622: The Eemian interglacial, suggests that they had an average duration of around 64 years, with the minimum duration being around 50 years and the maximum approximately 80 years, similar to today. A study of marine plankton suggested that the South Asian Monsoon (SAM) strengthened around 5 million years ago. Then, during ice periods, the sea level fell and the Indonesian Seaway closed. When this happened, cold waters in
2889-685: The Hadley circulation during boreal winter. It is associated with the development of the Siberian High and the movement of the heating maxima from the Northern Hemisphere to the Southern Hemisphere. North-easterly winds flow down Southeast Asia, are turned north-westerly/westerly by Borneo topography towards Australia. This forms a cyclonic circulation vortex over Borneo, which together with descending cold surges of winter air from higher latitudes, cause significant weather phenomena in
2996-575: The Himalayas and Indo-Gangetic Plain towards the vast spans of the Indian Ocean south of the Deccan peninsula. This is known as the Northeast Monsoon or Retreating Monsoon. While travelling towards the Indian Ocean, the cold dry wind picks up some moisture from the Bay of Bengal and pours it over peninsular India and parts of Sri Lanka . Cities like Chennai , which get less rain from
3103-629: The Malacca , Sunda and Torres Straits . The Gulf of Carpentaria is located on the Australian north coast while the Great Australian Bight constitutes a large part of its southern coast. 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
3210-818: 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 waves . Water circulation in the Indian Ocean is dominated by the Subtropical Anticyclonic Gyre,
3317-785: The Sahara and the equatorial Atlantic Ocean. The ITCZ migrates northward from the equatorial Atlantic in February, reaches western Africa on or near June 22, then moves back to the south by October. The dry, northeasterly trade winds , and their more extreme form, the harmattan , are interrupted by the northern shift in the ITCZ and resultant southerly, rain-bearing winds during the summer. The semiarid Sahel and Sudan depend upon this pattern for most of their precipitation. The North American monsoon ( NAM ) occurs from late June or early July into September, originating over Mexico and spreading into
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3424-695: 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
3531-683: The South China Sea led to a timing of the monsoon beginning 15–20 million years ago and linked to early Tibetan uplift. Testing of this hypothesis awaits deep ocean sampling by the Integrated Ocean Drilling Program . The monsoon has varied significantly in strength since this time, largely linked to global climate change , especially the cycle of the Pleistocene ice ages. A study of Asian monsoonal climate cycles from 123,200 to 121,210 years BP, during
3638-562: The return of the westerlies ) is the result of a resurgence of westerly winds from the Atlantic, where they become loaded with wind and rain. These westerly winds are a common phenomenon during the European winter, but they ease as spring approaches in late March and through April and May. The winds pick up again in June, which is why this phenomenon is also referred to as "the return of the westerlies". The rain usually arrives in two waves, at
3745-508: 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
3852-423: The "Hinge zone may represent the relict of continental and proto-oceanic crustal boundary formed during the rifting of India from Antarctica ." 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
3959-768: The 15th century called it the Western Oceans. In Ancient Greek geography , the Indian Ocean region known to the Greeks was called the Erythraean Sea . The borders of the Indian Ocean , as delineated by the International Hydrographic Organization in 1953 included the Southern Ocean but not the marginal seas along the northern rim but in 2002 the IHO delimited the Southern Ocean separately, which removed waters south of 60°s from
4066-600: The 300-mile-wide Wilkes Land crater , which probably formed about 250 million years ago. Wilkes Land is featured prominently in the 1998 film The X-Files . Fox Mulder journeys to Antarctica to save his partner Dana Scully , who is being held there against her will. In the process, they discover a huge secret lab under the surface run by the Cigarette-Smoking Man . 69°00′S 120°00′E / 69.000°S 120.000°E / -69.000; 120.000 Indian Ocean The Indian Ocean
4173-727: The Arabian Peninsula) and Limpopo rivers. After the breakup of East 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 . Marginal seas , gulfs, bays and straits of the Indian Ocean include: Along the east coast of Africa, the Mozambique Channel separates Madagascar from mainland Africa, while
4280-697: The Asian monsoon has been linked to the uplift of the Tibetan Plateau after the collision of the Indian subcontinent and Asia around 50 million years ago. Because of studies of records from the Arabian Sea and that of the wind-blown dust in the Loess Plateau of China, many geologists believe the monsoon first became strong around 8 million years ago. More recently, studies of plant fossils in China and new long-duration sediment records from
4387-541: The Atlantic and 2.7 billion for the Pacific (some countries border more than one ocean). The Indian Ocean drainage basin covers 21,100,000 km (8,100,000 sq mi), virtually identical to that of the Pacific Ocean and half that of the Atlantic basin, or 30% of its ocean surface (compared to 15% for the Pacific). The Indian Ocean drainage basin is divided into roughly 800 individual basins, half that of
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4494-482: 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 margins of
4601-462: The Comoros. Although both species represent an order of lobe-finned fishes known from the Early Devonian (410 mya ) 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. Of Earth's 36 biodiversity hotspots nine (or 25%) are located on
4708-486: The EASM grew in strength, but it has been suggested to have decreased in strength during Heinrich events . The EASM expanded its influence deeper into the interior of Asia as sea levels rose following the LGM; it also underwent a period of intensification during the Middle Holocene, around 6,000 years ago, due to orbital forcing made more intense by the fact that the Sahara at the time was much more vegetated and emitted less dust. This Middle Holocene interval of maximum EASM
4815-406: The East Asian Winter Monsoon (EAWM) became stronger as the subarctic front shifted southwards. An abrupt intensification of the EAWM occurred 5.5 million years ago. The EAWM was still significantly weaker relative to today between 4.3 and 3.8 million years ago but abruptly became more intense around 3.8 million years ago as crustal stretching widened the Tsushima Strait and enabled greater inflow of
4922-403: The East India Coastal Current to the Arabian Sea from January to April. An Indian Ocean garbage patch was discovered in 2010 covering at least 5 million square kilometres (1.9 million square miles). Riding the southern Indian Ocean Gyre , this vortex of plastic garbage constantly circulates the ocean from Australia to Africa, down the Mozambique Channel , and back to Australia in
5029-405: The GDP and employs 70% of the population) is heavily dependent on the rains, for growing crops especially like cotton , rice , oilseeds and coarse grains. A delay of a few days in the arrival of the monsoon can badly affect the economy, as evidenced in the numerous droughts in India in the 1990s. The monsoon is widely welcomed and appreciated by city-dwellers as well, for it provides relief from
5136-411: The Indian Ocean but included the northern marginal seas. 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)
5243-405: The Indian Ocean have an average width (horizontal distance from land to shelf break ) of 19 ± 0.61 km (11.81 ± 0.38 mi) with a maximum width of 175 km (109 mi). The passive margins have an average width of 47.6 ± 0.8 km (29.58 ± 0.50 mi). The average width of the slopes (horizontal distance from shelf break to foot of slope) of
5350-457: The Indian Ocean includes beaches and intertidal zones covering 3,000 km (1,200 sq mi) and 246 larger estuaries . Upwelling areas are small but important. The hypersaline salterns in India covers between 5,000–10,000 km (1,900–3,900 sq mi) 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
5457-445: 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 continental shelf . In terms of geology, the Indian Ocean is the youngest of the major oceans, with active spreading ridges and features like seamounts and ridges formed by hotspots . The climate of
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#17327721733675564-432: The Indian Ocean is characterized by monsoons . 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 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
5671-424: The Indian Ocean region, or almost half of the world's mangrove habitat, of which 42,500 km (16,400 sq mi) 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 in
5778-666: 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 ecosystems : 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. 200,000 km (77,000 sq mi). The coasts of
5885-432: The Indian Ocean, probably caused by Rossby wave propagation. Icebergs drift as far north as 55° south latitude , similar to the Pacific but less than in the Atlantic where icebergs reach up to 45°S. The volume of iceberg loss in the Indian Ocean between 2004 and 2012 was 24 Gt . Since the 1960s, anthropogenic warming of the global ocean combined with contributions of freshwater from retreating land ice causes
5992-411: The Indian Ocean. While the Indian Ocean warmed at a rate of 1.2°C per century during 1950–2020, climate models predict accelerated warming, at a rate of 1.7 °C–3.8 °C per century during 2020–2100. Though the warming is basin-wide, maximum warming is in the northwestern Indian Ocean including the Arabian Sea, and reduced warming off the Sumatra and Java coasts in the southeast Indian Ocean. Global warming
6099-401: 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 . 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
6206-445: The Late Holocene, significant glacial accumulation in the Himalayas still occurred due to cold temperatures brought by westerlies from the west. During the Middle Miocene , the July ITCZ, the zone of rainfall maximum, migrated northwards, increasing precipitation over southern China during the East Asian Summer Monsoon (EASM) while making Indochina drier. During the Late Miocene Global Cooling (LMCG), from 7.9 to 5.8 million years ago,
6313-408: 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 warming , Heinrich , and Younger Dryas . The Indian Ocean is the warmest ocean in
6420-402: The Pacific were impeded from flowing into the Indian Ocean. It is believed that the resulting increase in sea surface temperatures in the Indian Ocean increased the intensity of monsoons. In 2018, a study of the SAM's variability over the past million years found that precipitation resulting from the monsoon was significantly reduced during glacial periods compared to interglacial periods like
6527-399: 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 (740 km (460 mi)) than those of the other major oceans. The largest rivers are ( order 5 ) the Zambezi , Ganges - Brahmaputra , Indus , Jubba , and Murray rivers and (order 4) the Shatt al-Arab , Wadi Ad Dawasir (a dried-out river system on
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#17327721733676634-417: The South Pole: In a wider sense, Wilkes Land extends further East to Point Alden in 142°02' E, thereby including Adélie Land , which is claimed by France. Wilkes Land is named after Lieutenant Charles Wilkes (later a rear admiral ), the American explorer who commanded the 1838–42 United States Exploring Expedition . The naming is in recognition of Wilkes' discovery of the continental margin over
6741-441: 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
6848-411: The Southwest Indian Ridge, from where it continues into the Mozambique Channel and Prince Edward Fracture Zone . North of 20° south latitude the minimum surface temperature is 22 °C (72 °F), exceeding 28 °C (82 °F) to the east. Southward of 40° south latitude , temperatures drop quickly. The Bay of Bengal contributes more than half (2,950 km or 710 cu mi) of
6955-399: 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 was discovered in the Indian Ocean off South Africa in the 1930s and in the late 1990s another species, the Indonesian coelacanth , was discovered off Sulawesi Island , Indonesia. Most extant coelacanths have been found in
7062-422: The Southwest Monsoon first hits the Western Ghats of the coastal state of Kerala , India, thus making this area the first state in India to receive rain from the Southwest Monsoon. This branch of the monsoon moves northwards along the Western Ghats ( Konkan and Goa ) with precipitation on coastal areas, west of the Western Ghats. The eastern areas of the Western Ghats do not receive much rain from this monsoon as
7169-535: The Southwest Monsoon, receive rain from this Monsoon. About 50% to 60% of the rain received by the state of Tamil Nadu is from the Northeast Monsoon. In Southern Asia, the northeastern monsoons take place from October to December when the surface high-pressure system is strongest. The jet stream in this region splits into the southern subtropical jet and the polar jet. The subtropical flow directs northeasterly winds to blow across southern Asia, creating dry air streams which produce clear skies over India. Meanwhile,
7276-458: The air temperature remains relatively stable for two reasons: water has a relatively high heat capacity (3.9 to 4.2 J g K ), and because both conduction and convection will equilibrate a hot or cold surface with deeper water (up to 50 metres). In contrast, dirt, sand, and rocks have lower heat capacities (0.19 to 0.35 J g K ), and they can only transmit heat into the earth by conduction and not by convection. Therefore, bodies of water stay at
7383-445: The arrival at the Eastern Himalayas, the winds turns towards the west, travelling over the Indo-Gangetic Plain at a rate of roughly 1–2 weeks per state, pouring rain all along its way. June 1 is regarded as the date of onset of the monsoon in India, as indicated by the arrival of the monsoon in the southernmost state of Kerala. The monsoon accounts for nearly 80% of the rainfall in India. Indian agriculture (which accounts for 25% of
7490-442: 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 ) that reach as far as the Intertropical Convergence Zone . This pollution has implications on both a local and global scale. Forty percent of the sediment of the Indian Ocean is found in the Indus and Ganges fans. The oceanic basins adjacent to
7597-507: The beginning of June, and again in mid- to late June. The European monsoon is not a monsoon in the traditional sense in that it doesn't meet all the requirements to be classified as such. Instead, the return of the westerlies is more regarded as a conveyor belt that delivers a series of low-pressure centres to Western Europe where they create unsettled weather. These storms generally feature significantly lower-than-average temperatures, fierce rain or hail, thunder, and strong winds. The return of
7704-414: The behaviour of the LC during Quaternary at close stratigraphic intervals. The South American summer monsoon (SASM) is known to have become weakened during Dansgaard–Oeschger events. The SASM has been suggested to have been enhanced during Heinrich events. Monsoons were once considered as a large-scale sea breeze caused by higher temperature over land than in the ocean. This is no longer considered as
7811-400: The bordering countries for domestic consumption and export. Fishing fleets from Russia, Japan, South Korea , and Taiwan also exploit the Indian Ocean, mainly for shrimp and tuna. 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
7918-670: The cause and the monsoon is now considered a planetary-scale phenomenon involving the annual migration of the Intertropical Convergence Zone between its northern and southern limits. The limits of the ITCZ vary according to the land–sea heating contrast and it is thought that the northern extent of the monsoon in South Asia is influenced by the high Tibetan Plateau. These temperature imbalances happen because oceans and land absorb heat in different ways. Over oceans,
8025-638: The centre of the 1,500,000 km (580,000 sq mi) hotspot, the landscape is dominated by Acacia - Commiphora deciduous bushland, but also includes the Yeheb nut ( Cordeauxia edulus ) and species discovered more recently such as the Somali cyclamen ( Cyclamen somalense ), the only cyclamen outside the Mediterranean. Warsangli linnet ( Carduelis johannis ) is an endemic bird found only in northern Somalia. An unstable political situation and mismanagement has resulted in overgrazing which has produced one of
8132-714: The climax of summer heat in June. However, the roads take a battering every year. Often houses and streets are waterlogged and slums are flooded despite drainage systems. A lack of city infrastructure coupled with changing climate patterns causes severe economic loss including damage to property and loss of lives, as evidenced in the 2005 flooding in Mumbai that brought the city to a standstill. Bangladesh and certain regions of India like Assam and West Bengal , also frequently experience heavy floods during this season. Recently, areas in India that used to receive scanty rainfall throughout
8239-399: The colder months, the cycle is reversed. Then the land cools faster than the oceans and the air over the land has higher pressure than air over the ocean. This causes the air over the land to flow to the ocean. When humid air rises over the ocean, it cools, and this causes precipitation over the oceans. (The cool air then flows towards the land to complete the cycle.) Most summer monsoons have
8346-505: The continental shelves are 50.4–52.4 km (31.3–32.6 mi) for active and passive margins respectively, with a maximum width of 205.3–255.2 km (127.6–158.6 mi). In correspondence of the Shelf break , 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
8453-551: 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 due to its ultra-slow spreading rate. The ocean's currents are mainly controlled by
8560-687: 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 reaches into the Indian Ocean south of Africa at a depth of 2,000–3,000 m (6,600–9,800 ft) and flows north along the eastern continental slope of Africa. Deeper than NADW, Antarctic Bottom Water flows from Enderby Basin to Agulhas Basin across deep channels (<4,000 m (13,000 ft)) in
8667-459: The hot summers. This causes a low pressure area over the northern and central Indian subcontinent. To fill this void, the moisture-laden winds from the Indian Ocean rush into the subcontinent. These winds, rich in moisture, are drawn towards the Himalayas . The Himalayas act like a high wall, blocking the winds from passing into Central Asia, and forcing them to rise. As the clouds rise, their temperature drops, and precipitation occurs . Some areas of
8774-593: The islands of the Indian Ocean are textbook cases of evolutionary processes; the dung beetles , day geckos , and lemurs are all examples of adaptive radiation . 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 Dodo bird ( Raphus cucullatus ) and Cylindraspis giant tortoise. An analysis of these remains suggests
8881-481: The margins of the Indian Ocean. 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 chameleons , for example, first diversified on Madagascar and then colonised Africa. Several species on
8988-634: The mid-18th century, as opposed to the Western Ocean ( Atlantic ) before the Pacific was surmised. In modern times, the name Afro-Asian Ocean has occasionally been used. The Hindi name for the Ocean is हिंद महासागर ( Hind Mahāsāgar ; lit. transl. Ocean of India ). Conversely, Chinese explorers (e.g., Zheng He during the Ming dynasty ) who traveled to the Indian Ocean during
9095-513: The monsoon is not a simple response to heating but a more complex interaction of topography, wind and sea, as demonstrated by its abrupt rather than gradual withdrawal from the region. The Australian monsoon (the "Wet") occurs in the southern summer when the monsoon trough develops over Northern Australia . Over three-quarters of annual rainfall in Northern Australia falls during this time. The European Monsoon (more commonly known as
9202-464: The monsoon. Two large gyres , one in the northern hemisphere flowing clockwise and one south of the equator moving anticlockwise (including the Agulhas Current and Agulhas Return Current ), constitute the dominant flow pattern. During the winter monsoon (November–February), however, circulation is reversed north of 30°S and winds are weakened during winter and the transitional periods between
9309-622: 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 valleys . 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 basins and crosses the Southwest Indian Ridge at 30°S. In
9416-458: The most degraded hotspots where only c. 5 % of the original habitat remains. Monsoon A monsoon ( / m ɒ n ˈ s uː n / ) is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscillation of the Intertropical Convergence Zone (ITCZ) between its limits to
9523-543: The most productive ecosystems of the Indian Ocean ;— 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 sea surface temperature spreads coral bleaching. Mangroves covers 80,984 km (31,268 sq mi) in
9630-541: The north and south of the equator. Usually, the term monsoon is used to refer to the rainy phase of a seasonally changing pattern, although technically there is also a dry phase. The term is also sometimes used to describe locally heavy but short-term rains. The major monsoon systems of the world consist of the West African , Asian– Australian , the North American , and South American monsoons. The term
9737-576: The north between approximately 8,000 and 4,000 BP, and most recently retreated southward once more between 4,000 and 0 BP. The January ITCZ migrated further south to its present location during the Middle Miocene, strengthening the summer monsoon of Australia that had previously been weaker. Five episodes during the Quaternary at 2.22 Ma ( PL-1), 1.83 Ma (PL-2), 0.68 Ma (PL-3), 0.45 Ma (PL-4) and 0.04 Ma (PL-5) were identified which showed
9844-638: 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
9951-413: The ocean to the land, bringing moist air inland. This moist air rises to a higher altitude over land and then it flows back toward the ocean (thus completing the cycle). However, when the air rises, and while it is still over the land, the air cools . This decreases the air's ability to hold water , and this causes precipitation over the land. This is why summer monsoons cause so much rain over land. In
10058-609: The present day. The Indian Summer Monsoon (ISM) underwent several intensifications during the warming following the Last Glacial Maximum, specifically during the time intervals corresponding to 16,100–14,600 BP, 13,600–13,000 BP, and 12,400–10,400 BP as indicated by vegetation changes in the Tibetan Plateau displaying increases in humidity brought by an intensifying ISM. Though the ISM was relatively weak for much of
10165-530: The region include the effects of climate change , piracy, and strategic disputes over island territories. The Indian Ocean has been known by its present name since at least 1515, when the Latin form Oceanus Orientalis Indicus ( lit. ' 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
10272-510: The region. Examples are the formation of a rare low-latitude tropical storm in 2001, Tropical Storm Vamei , and the devastating flood of Jakarta in 2007. The onset of the monsoon over Australia tends to follow the heating maxima down Vietnam and the Malay Peninsula (September), to Sumatra , Borneo and the Philippines (October), to Java , Sulawesi (November), Irian Jaya and northern Australia (December, January). However,
10379-559: The southwest United States by mid-July. It affects Mexico along the Sierra Madre Occidental as well as Arizona , New Mexico , Nevada , Utah , Colorado , West Texas and California . It pushes as far west as the Peninsular Ranges and Transverse Ranges of Southern California, but rarely reaches the coastal strip (a wall of desert thunderstorms only a half-hour's drive away is a common summer sight from
10486-562: The subcontinent receive up to 10,000 mm (390 in) of rain annually. The southwest monsoon is generally expected to begin around the beginning of June and fade away by the end of September. The moisture-laden winds on reaching the southernmost point of the Indian Peninsula , due to its topography, become divided into two parts: the Arabian Sea Branch and the Bay of Bengal Branch . The Arabian Sea Branch of
10593-546: The summer monsoon shifts through a series of dry and rainy phases as the rain belt moves northward, beginning over Indochina and the South China Sea (May), to the Yangtze River Basin and Japan (June) and finally to northern China and Korea (July). When the monsoon ends in August, the rain belt moves back to southern China. The rainy season occurs from September to February and it is a major source of energy for
10700-690: The sunny skies along the coast during the monsoon). The North American monsoon is known to many as the Summer , Southwest , Mexican or Arizona monsoon. It is also sometimes called the Desert monsoon as a large part of the affected area are the Mojave and Sonoran deserts . However, it is controversial whether the North and South American weather patterns with incomplete wind reversal should be counted as true monsoons. The Asian monsoons may be classified into
10807-599: The ventilation of the Indian Ocean thermocline . That continent also drives the Indian Ocean monsoon , the strongest on Earth, which causes large-scale seasonal variations in ocean currents, including the reversal of the Somali Current and Indian Monsoon Current . Because of the Indian Ocean Walker circulation there are no continuous equatorial easterlies. Upwelling occurs near the Horn of Africa and
10914-764: The warm Tsushima Current into the Sea of Japan. Circa 3.0 million years ago, the EAWM became more stable, having previously been more variable and inconsistent, in addition to being enhanced further amidst a period of global cooling and sea level fall. The EASM was weaker during cold intervals of glacial periods such as the Last Glacial Maximum (LGM) and stronger during interglacials and warm intervals of glacial periods. Another EAWM intensification event occurred 2.6 million years ago, followed by yet another one around 1.0 million years ago. During Dansgaard–Oeschger events ,
11021-670: The wind does not cross the Western Ghats. The Bay of Bengal Branch of Southwest Monsoon flows over the Bay of Bengal heading towards north-east India and Bengal , picking up more moisture from the Bay of Bengal. The winds arrive at the Eastern Himalayas with large amounts of rain. Mawsynram , situated on the southern slopes of the Khasi Hills in Meghalaya , India, is one of the wettest places on Earth. After
11128-487: The world. Long-term ocean temperature records show a rapid, continuous warming in the Indian Ocean, at about 1.2 °C (34.2 °F) (compared to 0.7 °C (33.3 °F) for the warm pool region) during 1901–2012. Research indicates that human induced greenhouse warming , and changes in the frequency and magnitude of El Niño (or the Indian Ocean Dipole ), events are a trigger to this strong warming in
11235-604: The year, like the Thar Desert , have surprisingly ended up receiving floods due to the prolonged monsoon season. The influence of the Southwest Monsoon is felt as far north as in China's Xinjiang . It is estimated that about 70% of all precipitation in the central part of the Tian Shan Mountains falls during the three summer months, when the region is under the monsoon influence; about 70% of that
11342-637: Was associated with an expansion of temperate deciduous forest steppe and temperate mixed forest steppe in northern China. By around 5,000 to 4,500 BP, the East Asian monsoon's strength began to wane, weakening from that point until the present day. A particularly notable weakening took place ~3,000 BP. The location of the EASM shifted multiple times over the course of the Holocene: first, it moved southward between 12,000 and 8,000 BP, followed by an expansion to
11449-575: Was first used in English in British India and neighboring countries to refer to the big seasonal winds blowing from the Bay of Bengal and Arabian Sea in the southwest bringing heavy rainfall to the area. The etymology of the word monsoon is not wholly certain. The English monsoon came from Portuguese monção ultimately from Arabic موسم ( mawsim , "season"), "perhaps partly via early modern Dutch monson ". Strengthening of
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