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107-551: Adare Seamounts , also known as Adare Mountains , are the seamounts in Balleny Basin named in association with Adare Peninsula and Cape Adare . Name approved by the Advisory Committee on Undersea Features , June 1988. [REDACTED]  This article incorporates public domain material from "Adare Seamounts" . Geographic Names Information System . United States Geological Survey . This article about

214-415: A commensal relationship , for example brittle stars , who climb the coral to get themselves off the seafloor, helping them to catch food particles, or small zooplankton, as they drift by. This is in sharp contrast with the typical deep-sea habitat, where deposit-feeding animals rely on food they get off the ground. In tropical zones extensive coral growth results in the formation of coral atolls late in

321-399: A certain pattern in terms of eruptive activity, first observed with Hawaiian seamounts but now shown to be the process followed by all seamounts of the ocean-ridge type. During the first stage the volcano erupts basalt of various types, caused by various degrees of mantle melting . In the second, most active stage of its life, ocean-ridge volcanoes erupt tholeiitic to mildly alkalic basalt as

428-692: A classic example being the Emperor Seamounts , an extension of the Hawaiian Islands . Formed millions of years ago by volcanism , they have since subsided far below sea level. This long chain of islands and seamounts extends thousands of kilometers northwest from the island of Hawaii . There are more seamounts in the Pacific Ocean than in the Atlantic, and their distribution can be described as comprising several elongate chains of seamounts superimposed on

535-437: A daunting task due to their sheer number. The most detailed seamount mappings are provided by multibeam echosounding ( sonar ), however after more than 5000 publicly held cruises, the amount of the sea floor that has been mapped remains minuscule. Satellite altimetry is a broader alternative, albeit not as detailed, with 13,000 catalogued seamounts; however this is still only a fraction of the total 100,000. The reason for this

642-462: 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

749-405: A global understanding of seamount ecosystems, and the roles they have in the biogeography , biodiversity , productivity and evolution of marine organisms. Possibly the best ecologically studied seamount in the world is Davidson Seamount , with six major expeditions recording over 60,000 species observations. The contrast between the seamount and the surrounding area was well-marked. One of

856-723: 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

963-626: A more or less random background distribution. Seamount chains occur in all three major ocean basins, with the Pacific having the most number and most extensive seamount chains. These include the Hawaiian (Emperor), Mariana, Gilbert, Tuomotu and Austral Seamounts (and island groups) in the north Pacific and the Louisville and Sala y Gomez ridges in the southern Pacific Ocean. In the North Atlantic Ocean,

1070-464: A number of seamounts are active undersea volcanoes; two examples are Kamaʻehuakanaloa (formerly Lo‘ihi) in the Hawaiian Islands and Vailulu'u in the Manu'a Group ( Samoa ). The most apparent lava flows at a seamount are the eruptive flows that cover their flanks, however igneous intrusions , in the forms of dikes and sills , are also an important part of seamount growth. The most common type of flow

1177-420: A particular pattern of growth, activity, subsidence and eventual extinction. The first stage of a seamount's evolution is its early activity, building its flanks and core up from the sea floor. This is followed by a period of intense volcanism, during which the new volcano erupts almost all (e.g. 98%) of its total magmatic volume. The seamount may even grow above sea level to become an oceanic island (for example,

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1284-463: 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

1391-787: 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")

1498-429: A result of a larger area melting in the mantle. This is finally capped by alkalic flows late in its eruptive history, as the link between the seamount and its source of volcanism is cut by crustal movement. Some seamounts also experience a brief "rejuvenated" period after a hiatus of 1.5 to 10 million years, the flows of which are highly alkalic and produce many xenoliths . In recent years, geologists have confirmed that

1605-504: 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

1712-414: A specific oceanic location or ocean current is a stub . You can help Misplaced Pages by expanding it . Seamount Earth's oceans contain more than 14,500 identified seamounts, of which 9,951 seamounts and 283 guyots, covering a total area of 8,796,150 km (3,396,210 sq mi), have been mapped but only a few have been studied in detail by scientists. Seamounts and guyots are most abundant in

1819-464: 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

1926-456: A summit collapse on the northern edge of Vlinder Seamount resulted in a pronounced headwall scarp and a field of debris up to 6 km (4 mi) away. A catastrophic collapse at Detroit Seamount flattened its whole structure extensively. Lastly, in 2004, scientists found marine fossils 61 m (200 ft) up the flank of Kohala mountain in Hawaii . Subsidation analysis found that at

2033-484: A wide variety of tectonic settings, resulting in a very diverse structural bank. Seamounts come in a wide variety of structural shapes, from conical to flat-topped to complexly shaped. Some are built very large and very low, such as Koko Guyot and Detroit Seamount ; others are built more steeply, such as Kamaʻehuakanaloa Seamount and Bowie Seamount . Some seamounts also have a carbonate or sediment cap . Many seamounts show signs of intrusive activity , which

2140-425: Is Bowie Seamount , which has also been declared a marine protected area by Canada for its ecological richness. The study of seamounts has been hindered for a long time by the lack of technology. Although seamounts have been sampled as far back as the 19th century, their depth and position meant that the technology to explore and sample seamounts in sufficient detail did not exist until the last few decades. Even with

2247-413: Is pillow lava , named so after its distinctive shape. Less common are sheet flows, which are glassy and marginal, and indicative of larger-scale flows. Volcaniclastic sedimentary rocks dominate shallow-water seamounts. They are the products of the explosive activity of seamounts that are near the water's surface, and can also form from mechanical wear of existing volcanic rock. Seamounts can form in

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2354-464: 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 ,

2461-619: 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

2568-785: 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

2675-435: Is done by bottom trawling , which scrapes whole ecosystems off seamounts. Because of their large numbers, many seamounts remain to be properly studied, and even mapped. Bathymetry and satellite altimetry are two technologies working to close the gap. There have been instances where naval vessels have collided with uncharted seamounts; for example, Muirfield Seamount is named after the ship that struck it in 1973. However,

2782-552: Is greatest as a proportion of seafloor area in the North Pacific Ocean, equal to 4.39% of that ocean region. The Arctic Ocean has only 16 seamounts and no guyots, and the Mediterranean and Black seas together have only 23 seamounts and 2 guyots. The 9,951 seamounts which have been mapped cover an area of 8,088,550 km (3,123,010 sq mi). Seamounts have an average area of 790 km (310 sq mi), with

2889-490: Is helped by geochemical exchange between the seamounts and the ocean water. Seamounts may thus be vital stopping points for some migratory animals , specifically whales . Some recent research indicates whales may use such features as navigational aids throughout their migration. For a long time it has been surmised that many pelagic animals visit seamounts as well, to gather food, but proof of this aggregating effect has been lacking. The first demonstration of this conjecture

2996-406: Is hurt by the simple lack of information available. Seamounts are very poorly studied, with only 350 of the estimated 100,000 seamounts in the world having received sampling, and fewer than 100 in depth. Much of this lack of information can be attributed to a lack of technology, and to the daunting task of reaching these underwater structures; the technology to fully explore them has only been around

3103-604: Is likely to lead to inflation , steepening of volcanic slopes, and ultimately, flank collapse. There are also several sub-classes of seamounts. The first are guyots , seamounts with a flat top. These tops must be 200 m (656 ft) or more below the surface of the sea; the diameters of these flat summits can be over 10 km (6.2 mi). Knolls are isolated elevation spikes measuring less than 1,000 meters (3,281 ft). Lastly, pinnacles are small pillar-like seamounts. Seamounts are exceptionally important to their biome ecologically, but their role in their environment

3210-452: Is poorly understood. Because they project out above the surrounding sea floor, they disturb standard water flow, causing eddies and associated hydrological phenomena that ultimately result in water movement in an otherwise still ocean bottom. Currents have been measured at up to 0.9 knots, or 48 centimeters per second. Because of this upwelling seamounts often carry above-average plankton populations, seamounts are thus centers where

3317-464: 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

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3424-468: Is responsible for as much as 95% of ecological damage to seamounts. Corals from seamounts are also vulnerable, as they are highly valued for making jewellery and decorative objects. Significant harvests have been produced from seamounts, often leaving coral beds depleted. Individual nations are beginning to note the effect of fishing on seamounts, and the European Commission has agreed to fund

3531-404: Is that often, in the late of stages of their life, extrusions begin to seep in the seamount. This activity leads to inflation, over-extension of the volcano's flanks, and ultimately flank collapse , leading to submarine landslides with the potential to start major tsunamis , which can be among the largest natural disasters in the world. In an illustration of the potent power of flank collapses,

3638-399: Is that the fishes that are targeted over seamounts are typically long-lived, slow-growing, and slow-maturing. The problem is confounded by the dangers of trawling , which damages seamount surface communities, and the fact that many seamounts are located in international waters, making proper monitoring difficult. Bottom trawling in particular is extremely devastating to seamount ecology, and

3745-463: Is that uncertainties in the technology limit recognition to features 1,500 m (4,921 ft) or larger. In the future, technological advances could allow for a larger and more detailed catalogue. Observations from CryoSat-2 combined with data from other satellites has shown thousands of previously uncharted seamounts, with more to come as data is interpreted. Seamounts are a possible future source of economically important metals. Even though

3852-490: 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

3959-498: The 2009 eruption of Hunga Tonga ). After a period of explosive activity near the ocean surface , the eruptions slowly die away. With eruptions becoming infrequent and the seamount losing its ability to maintain itself, the volcano starts to erode . After finally becoming extinct (possibly after a brief rejuvenated period), they are ground back down by the waves. Seamounts are built in a far more dynamic oceanic setting than their land counterparts, resulting in horizontal subsidence as

4066-663: 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,

4173-661: 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

4280-560: 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,

4387-608: 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

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4494-773: 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,

4601-678: The New England Seamounts extend from the eastern coast of the United States to the mid-ocean ridge. Craig and Sandwell noted that clusters of larger Atlantic seamounts tend to be associated with other evidence of hotspot activity, such as on the Walvis Ridge , Vitória-Trindade Ridge , Bermuda Islands and Cape Verde Islands . The mid-Atlantic ridge and spreading ridges in the Indian Ocean are also associated with abundant seamounts. Otherwise, seamounts tend not to form distinctive chains in

4708-671: 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

4815-562: 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

4922-423: 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

5029-732: 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

5136-694: 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

5243-473: 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

5350-541: 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

5457-569: 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

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5564-472: 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

5671-520: 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)

5778-405: 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

5885-505: 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

5992-445: 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

6099-494: 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

6206-476: 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

6313-723: 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

6420-432: 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

6527-461: 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

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6634-475: The Indian and Southern Oceans, but rather their distribution appears to be more or less random. Isolated seamounts and those without clear volcanic origins are less common; examples include Bollons Seamount , Eratosthenes Seamount , Axial Seamount and Gorringe Ridge . If all known seamounts were collected into one area, they would make a landform the size of Europe . Their overall abundance makes them one of

6741-401: 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

6848-522: 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

6955-450: The North Pacific Ocean, and follow a distinctive evolutionary pattern of eruption, build-up, subsidence and erosion. In recent years, several active seamounts have been observed, for example Kamaʻehuakanaloa (formerly Lōʻihi) in the Hawaiian Islands . Because of their abundance, seamounts are one of the most common marine ecosystems in the world. Interactions between seamounts and underwater currents, as well as their elevated position in

7062-513: The OASIS project, a detailed study of the effects of fishing on seamount communities in the North Atlantic . Another project working towards conservation is CenSeam , a Census of Marine Life project formed in 2005. CenSeam is intended to provide the framework needed to prioritise, integrate, expand and facilitate seamount research efforts in order to significantly reduce the unknown and build towards

7169-645: 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

7276-602: 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

7383-411: 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

7490-399: 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

7597-442: 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

7704-675: The average size of seamounts. Nearly 50% of guyot area and 42% of the number of guyots occur in the North Pacific Ocean, covering 342,070 km (132,070 sq mi). The largest three guyots are all in the North Pacific: the Kuko Guyot (estimated 24,600 km (9,500 sq mi)), Suiko Guyot (estimated 20,220 km (7,810 sq mi)) and the Pallada Guyot (estimated 13,680 km (5,280 sq mi)). Seamounts are often found in groupings or submerged archipelagos ,

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

7918-686: 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

8025-496: 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

8132-541: 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

8239-750: The crust to the surface. Volcanoes formed near or above subducting zones are created because the subducting tectonic plate adds volatiles to the overriding plate that lowers its melting point . Which of these two process involved in the formation of a seamount has a profound effect on its eruptive materials. Lava flows from mid-ocean ridge and plate boundary seamounts are mostly basaltic (both tholeiitic and alkalic ), whereas flows from subducting ridge volcanoes are mostly calc-alkaline lavas. Compared to mid-ocean ridge seamounts, subduction zone seamounts generally have more sodium , alkali , and volatile abundances, and less magnesium , resulting in more explosive, viscous eruptions. All volcanic seamounts follow

8346-667: 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

8453-425: The effect of seamounts on endemicity. They have , however, been confidently shown to provide a habitat to species that have difficulty surviving elsewhere. The volcanic rocks on the slopes of seamounts are heavily populated by suspension feeders , particularly corals , which capitalize on the strong currents around the seamount to supply them with food. These coral are therefore host to numerous other organisms in

8560-465: The first two have any potential of being targeted by mining in the next few decades. Some seamounts have not been mapped and thus pose a navigational danger. For instance, Muirfield Seamount is named after the ship that hit it in 1973. More recently, the submarine USS San Francisco ran into an uncharted seamount in 2005 at a speed of 35 knots (40.3 mph; 64.8 km/h), sustaining serious damage and killing one seaman. One major seamount risk

8667-417: The fish that feed on them aggregate, in turn falling prey to further predation, making seamounts important biological hotspots. Seamounts provide habitats and spawning grounds for these larger animals, including numerous fish. Some species, including black oreo (Allocyttus niger) and blackstripe cardinalfish (Apogon nigrofasciatus) , have been shown to occur more often on seamounts than anywhere else on

8774-445: The greatest danger from seamounts are flank collapses; as they get older, extrusions seeping in the seamounts put pressure on their sides, causing landslides that have the potential to generate massive tsunamis . Seamounts can be found in every ocean basin in the world, distributed extremely widely both in space and in age. A seamount is technically defined as an isolated rise in elevation of 1,000 m (3,281 ft) or more from

8881-580: 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

8988-497: The last few decades. Before consistent conservation efforts can begin, the seamounts of the world must first be mapped , a task that is still in progress. Overfishing is a serious threat to seamount ecological welfare. There are several well-documented cases of fishery exploitation, for example the orange roughy ( Hoplostethus atlanticus ) off the coasts of Australia and New Zealand and the pelagic armorhead ( Pseudopentaceros richardsoni ) near Japan and Russia. The reason for this

9095-481: 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

9202-614: 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

9309-400: 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

9416-602: 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

9523-516: The most common, and least understood, marine structures and biomes on Earth, a sort of exploratory frontier. Most seamounts are built by one of two volcanic processes, although some, such as the Christmas Island Seamount Province near Australia, are more enigmatic. Volcanoes near plate boundaries and mid-ocean ridges are built by decompression melting of rock in the upper mantle . The lower density magma rises through

9630-535: 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

9737-571: 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

9844-470: The ocean floor. Marine mammals , sharks , tuna , and cephalopods all congregate over seamounts to feed, as well as some species of seabirds when the features are particularly shallow. Seamounts often project upwards into shallower zones more hospitable to sea life, providing habitats for marine species that are not found on or around the surrounding deeper ocean bottom. Because seamounts are isolated from each other they form "undersea islands" creating

9951-470: The ocean makes up 70% of Earth's surface area, technological challenges have severely limited the extent of deep sea mining . But with the constantly decreasing supply on land, some mining specialists see oceanic mining as the destined future, and seamounts stand out as candidates. Seamounts are abundant, and all have metal resource potential because of various enrichment processes during the seamount's life. An example for epithermal gold mineralization on

10058-536: The primary ecological havens on the seamount is its deep sea coral garden, and many of the specimens noted were over a century old. Following the expansion of knowledge on the seamount there was extensive support to make it a marine sanctuary , a motion that was granted in 2008 as part of the Monterey Bay National Marine Sanctuary . Much of what is known about seamounts ecologically is based on observations from Davidson. Another such seamount

10165-519: 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

10272-399: The right technology available, only a scant 1% of the total number have been explored, and sampling and information remains biased towards the top 500 m (1,640 ft). New species are observed or collected and valuable information is obtained on almost every submersible dive at seamounts. Before seamounts and their oceanographic impact can be fully understood, they must be mapped,

10379-439: The same biogeographical interest. As they are formed from volcanic rock , the substrate is much harder than the surrounding sedimentary deep sea floor. This causes a different type of fauna to exist than on the seafloor, and leads to a theoretically higher degree of endemism . However, recent research especially centered at Davidson Seamount suggests that seamounts may not be especially endemic, and discussions are ongoing on

10486-720: The seafloor is Conical Seamount, located about 8 km south of Lihir Island in Papua New Guinea. Conical Seamount has a basal diameter of about 2.8 km and rises about 600 m above the seafloor to a water depth of 1050 m. Grab samples from its summit contain the highest gold concentrations yet reported from the modern seafloor (max. 230 g/t Au, avg. 26 g/t, n=40). Iron - manganese , hydrothermal iron oxide , sulfide , sulfate , sulfur , hydrothermal manganese oxide , and phosphorite (the latter especially in parts of Micronesia) are all mineral resources that are deposited upon or within seamounts. However, only

10593-475: The seamount moves with the tectonic plate towards a subduction zone . Here it is subducted under the plate margin and ultimately destroyed, but it may leave evidence of its passage by carving an indentation into the opposing wall of the subduction trench. The majority of seamounts have already completed their eruptive cycle, so access to early flows by researchers is limited by late volcanic activity. Ocean-ridge volcanoes in particular have been observed to follow

10700-529: The seamount's life. In addition soft sediments tend to accumulate on seamounts, which are typically populated by polychaetes ( annelid marine worms ) oligochaetes ( microdrile worms), and gastropod mollusks ( sea slugs ). Xenophyophores have also been found. They tend to gather small particulates and thus form beds, which alters sediment deposition and creates a habitat for smaller animals. Many seamounts also have hydrothermal vent communities, for example Suiyo and Kamaʻehuakanaloa seamounts. This

10807-566: The smallest seamounts found in the Arctic Ocean and the Mediterranean and Black Seas; whilst the largest mean seamount size, 890 km (340 sq mi), occurs in the Indian Ocean . The largest seamount has an area of 15,500 km (6,000 sq mi) and it occurs in the North Pacific. Guyots cover a total area of 707,600 km (273,200 sq mi) and have an average area of 2,500 km (970 sq mi), more than twice

10914-442: The surrounding seafloor, and with a limited summit area, of conical form. There are more than 14,500 seamounts. In addition to seamounts, there are more than 80,000 small knolls , ridges and hills less than 1,000 m in height in the world's oceans. Most seamounts are volcanic in origin, and thus tend to be found on oceanic crust near mid-ocean ridges , mantle plumes , and island arcs . Overall, seamount and guyot coverage

11021-452: The time of their deposition, this would have been 500 m (1,640 ft) up the flank of the volcano, far too high for a normal wave to reach. The date corresponded with a massive flank collapse at the nearby Mauna Loa , and it was theorized that it was a massive tsunami, generated by the landslide, that deposited the fossils. Geology Ecology Geography and geology Ecology Indian Ocean The Indian Ocean

11128-517: 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

11235-422: The water, attract plankton , corals , fish, and marine mammals alike. Their aggregational effect has been noted by the commercial fishing industry , and many seamounts support extensive fisheries. There are ongoing concerns on the negative impact of fishing on seamount ecosystems, and well-documented cases of stock decline, for example with the orange roughy ( Hoplostethus atlanticus ). 95% of ecological damage

11342-478: 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

11449-822: Was published in 2008. The effect that seamounts have on fish populations has not gone unnoticed by the commercial fishing industry . Seamounts were first extensively fished in the second half of the 20th century, due to poor management practices and increased fishing pressure seriously depleting stock numbers on the typical fishing ground, the continental shelf . Seamounts have been the site of targeted fishing since that time. Nearly 80 species of fish and shellfish are commercially harvested from seamounts, including spiny lobster (Palinuridae), mackerel (Scombridae and others), red king crab ( Paralithodes camtschaticus ), red snapper ( Lutjanus campechanus ), tuna (Scombridae), Orange roughy ( Hoplostethus atlanticus ), and perch (Percidae). The ecological conservation of seamounts

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