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120-503: It is the ocean region where the warm Indian Ocean and the cold Atlantic Ocean meet. This convergence leads to treacherous sailing conditions, accounting for numerous wrecked ships in the area over the years. However, the meeting of the oceans here also fuels the nutrient cycle for marine life, making it one of the best fishing grounds in South Africa . The Agulhas Bank stretches approximately 800 km (500 mi) along

240-695: A continuous fold belt that developed during the Gondwanide orogeny together with Sierra de la Ventana (Argentina), Pensacola Mountains (East Antarctica), and Ellsworth Mountains (West Antarctica). In the late Carboniferous and early Jurassic , the Karoo Supergroup was deposited in the Karoo Basin north of where the CFB is located today, and covering nearly two-thirds of present-day South Africa . Basaltic lavas were extruded 183 Mya to form

360-504: A deviation from the current's normal path known as Agulhas Current meanders (ACM). These bulges are occasionally (1-7 times per year) followed by a much larger offshore bulge, known as Natal pulses (NP). Natal pulses move along the coast at 20 km (12 mi) per day. An ACM can bulge up to 20 km (12 mi) and a NP up to 120 km (75 mi) from the current's mean position. The AC passes 34 km (21 mi) offshore and an ACM can reach 123 km (76 mi) offshore. When

480-729: A distinctively deeper sub-basin in the south, the South Outeniqua Basin. The sedimentary fill of these basins developed as the northern edge of the Falkland Plateau separated from the South African southern margin during the early Cretaceous . The Diaz Marginal Ridge (DMR) separates these basins from the AFFZ. The DMR is buried under 200–250 m (660–820 ft) of sediments and sedimentary rocks and 150–200 m (490–660 ft) of this sedimentary material

600-468: 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

720-519: A large glide plane scar. In the western part, the sediments are dammed by basement ridges, but, in the eastern part, they have spread into the Transkei Basin. A series of slump scarps along the western edge of the shelf are 18–2 Mya, but covered by younger sediments brought there by the Benguela upwelling . Anatomically modern humans evolved around 200  kya . The genetic diversity in

840-440: A large species that dominates the copepod community in terms of biomass, has a center of distribution on the central Agulhas Bank. Since 1997 the copepod biomass on the central Agulhas Bank has declined significantly while the biomass of pelagic fish has increased significantly. While it is likely that predation has played an important role in the copepod decline, global warming (sea surface temperature and chlorophyll A abundance)

960-747: 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

1080-472: A mean depth slightly over 100 m (330 ft). It is entirely within the exclusive economic zone of South Africa. The National Spatial Biodiversity Assessment 2004 recognised 34 biozones nested within 9 bioregions (of which four were offshore). The National Biodiversity Assessment 2011 replaced these ecozones and biozones with the terms ecoregions and ecozones. In 2011, the Agulhas Ecoregion

1200-470: 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

1320-790: 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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1440-504: 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

1560-464: 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

1680-473: 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 ,

1800-605: Is a relatively shallow area of rocky reef about 11 km offshore of Buffelsbaai, or 15.5 km, (about 8.3 nautical miles) bearing 218°T from Knysna Heads. Maximum depth in the immediate vicinity is about 80 m, and the shallowest part of the reef is about 29 m. The oldest rock found along the coastline of the Agulhas Bank are eugeosynclinal sediments of the up to 3 km (1.9 mi) thick Kaaimans Group deposited during continental rifting some 900 million years ago (Mya). The proto-South Atlantic closed during

1920-503: Is a thin coastal strip and a botanic hotspot which developed at the confluence of the Benguela Upwelling and Agulhas Current. According to what professor Curtis Marean calls the "Cape Floral Region – South Coast Model" for the origins of modern humans, the early hunter-gatherers survived on shellfish , as well as geophytes , fur seal , fish , seabirds , and wash-ups found on the exposed Agulhas Bank. The bank slopes into

2040-513: Is also common on the western bank, but the more stable atmospheric condition results in larger cold water plumes that sometimes merge to form a continuous upwelling regime along the South African south-west coast. This upwelling zone is the southernmost extension of the Benguela Current Large Maritime Ecosystem. The Agulhas Current regularly flows around the southern tip of the bank and brings warm water to

2160-402: Is another source of edge upwelling west of Port Elisabeth. Plumes of warm surface water migrate onto the bank along its eastern edge, providing subtropical surface water from the Indian Ocean. In summer, easterly winds can intermittently drive coastal upwelling along the South African south coast. The Agulhas Bank is dominated by westerly winds and most of the upwelling on the bank is related to

2280-643: 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

2400-825: 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

2520-402: Is believed to have contributed to a smaller population. The shelf edge along the bank's southern tip is subject to sporadic upwelling. This slope and its surrounding seamounts are the spawning ground for sardine , anchovy , and horse mackerel . Eddies help transport water inshore and link the spawning habitat with important nursery areas. Eggs and larvae laid by the anchovy are transported via

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2640-597: Is composed of both terrestrial and marine sediments. Synclines along the coast of the southern Cape contains sediments from the Bokkveld Group. The Cape Fold Belt (CFB) rocks and the Karoo Basin were deposited 450 Mya; the Cape Supergroup 450-300 Mya during a series of transgression - regression cycles. Pan-African thrusts were reactivated 270-215 Mya to form the CFB which was then part of

2760-443: Is driven by the prevailing northward winds that produce an intense off-shore Ekman transport . Most of this upwelling is concentrated to a few upwelling cells in the southern region: Namaqua (30°S), Cape Columbine (32.5°S), and Cape Peninsula (34°S). The wind is most intense from October to February, and the contrast in sea surface temperature between the open sea and the shelf is most prominent during summer. Coastal upwelling

2880-531: Is located southeast of the shelf, separated from it by the Agulhas Passage (through which the Agulhas Current flows.) The Alphard Tertiary Igneous Province includes Palaeocene tuffs , trachybasalts , aegirine–augite trachytes and aegirine–augite phonolitic trachytes, which have been radiometrically dated at about 58 million years old. The intrusions appear to be tectonic effects. One of

3000-489: Is present on the eastern and central shelf. In summer, there is mixture of subtropical water separated by thermoclines from cool waters, but there is a considerable seasonal variation. On the shelf, bottom waters exhibit characteristics of the central Indian Ocean in the east and central Atlantic Ocean waters in the west. As the Agulhas Current flows south along the African east coast, it tends to bulge inshore frequently,

3120-469: 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

3240-497: 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

3360-495: Is undisturbed Cretaceous sediments younger than the oldest Cretaceous sedimentary rocks in the Southern Outeniqua Basin. The DMR must therefore have formed after the initial West Gondwana breakup 130-90 Mya. The DMR probably formed when new, hot oceanic crust slid past old, cold continental crust and the contrast in temperatures induced a thermal uplift. As West Gondwana drifted away from Africa roughly 125 Myr,

3480-748: 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,

3600-748: 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

3720-577: 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,

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3840-502: The Good Hope Jet to Africa's southwestern coast where they mature. Young anchovies then return to the Agulhas Bank to spawn. Young sardine and anchovy congregate along the west coast between March and September before they migrate to their spawning grounds on the Agulhas Bank. Sardines of intermediate age are present on the western Agulhas Bank between January and April before migrating to KwaZulu-Natal for winter. The spawning on

3960-758: The Karoo large igneous province ; a volcanism caused by the Bouvet hotspot which is linked to the Gondwana break-up. The Bouvet hotspot was located in or near present-day South Africa from the late Triassic 220 mya and until the Africa-Antarctica breakup 120 mya. The Bouvet hotspot track stretches south-east from the African continent, near the South Africa-Mozambique border, and east of the AFFZ down to Bouvet Island / Bouvet triple junction in

4080-525: The Last Glacial Maximum (LGM, 20 000 years ago), show that the Agulhas leakage (shedding of Agulhas rings) was significantly reduced. It has been hypothesised that the reason for this was that the Agulhas Current was stronger which resulted in a more eastward retroflection and therefore less leakage. However, analyses of such cores south of Africa show that the trajectory of the current

4200-629: 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

4320-818: 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,

4440-643: The Saldanian orogeny to form part of the supercontinent Gondwana (700-600 Mya). The Cape granites were emplaced and the Kaaimans Group rocks were folded and thermally metamorphosed during this period. The formation of the main basin in the Cape Province commenced 570 Mya and lasted for 200 My. The Table Mountain Group is 4 km (2.5 mi) thick and an erosional unconformity marking its base

4560-695: 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

4680-671: The great white shark , colonised the North Atlantic and Mediterranean by following their prey — bluefin tuna and swordfish . A vagrant Commerson's dolphin  — a species with two isolated populations, one along the southern coast of Argentina and the other around the Kerguelen Islands  — was sighted on the Agulhas Bank in 2004. It is not known from which population the sighted individual stems. The Kerguelen Islands are located 4,200 km (2,600 mi) and South America 6,300 km (3,900 mi) from

4800-582: 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

4920-423: 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

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5040-768: 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

5160-504: The AC meanders, its width broadens from 88 km (55 mi) to 125 km (78 mi) and its velocity weakens from 208 cm/s (82 in/s) to 136 cm/s (54 in/s). An ACM induces a strong inshore counter-current. Large-scale cyclonic meanders known as Natal pulses are formed as the Agulhas Current reaches the continental shelf on the South African east-coast (i.e. the eastern Agulhas Bank off Natal ). As these pulses move along

5280-403: The African coast, from off Cape Peninsula (18°E) to Port Alfred (26°E), and up to 250 km (160 mi) from it. The bank slopes down relatively steeply from the coast to about 50 m (160 ft) deep and reaches 200 m (660 ft) before dropping steeply to 1,000 m (3,300 ft) on its southern edge. The shelf spans an area of 116,000 km (45,000 sq mi) with

5400-478: The Agulhas Bank exposed, which greatly expanded the area of the SCP, but it also reconnected the SCP to the rest of Africa by the shallow water shelves, which broke the isolation of the SCP. Modern humans evolved on the SCP and the fluctuation in sea-levels would have resulted in a significant variation in selective pressure . No fossil records are known from the now submerged shelf, but a series of key fossil sites along

5520-477: The Agulhas Bank takes place 30–130 km (19–81 mi) offshore from September to February. The bank is the spawning area of deep reef fish species, including the threatened endemic red steenbras ( Petrus rupestris ). Other species have been overexploited, including daggerhead seabream or dageraad ( Chrysoblephus cristiceps ), black musselcracker ( Cymatoceps nasutus ), and silver kob ( Argyrosomus inodorus ). 57 species of sharks have been reported off

5640-399: The Agulhas Bank within 300 years, increasing the net inter-oceanic exchange with 4.1-4.5 Sv. The Alphard Banks are a small group of long extinct volcanic seamounts on the Agulhas Bank south of Cape Agulhas. They rise from the bottom at about 80 m to about 14 m on the top. They are the southernmost recreational diving sites on the African continental shelf, and are seldom dived due to

5760-553: The Agulhas Bank, but the west-ward direction of the Antarctic Circumpolar Current would force the dolphin to swim against the current from the Kerguelen Islands. Fossil beaked whales have been recovered by trawling from the seafloor off South Africa. Stranded pygmy sperm whales have been recorded on both the east and west coasts of South Africa. Indian Ocean The Indian Ocean

5880-412: The Agulhas Bank, seabird bycatch became a huge problem. Large numbers of albatrosses and petrels were killed — in average 0.6 birds per 1000 hooks, but up to 18 birds per 1000 hooks were reported. Since 2007, however, more restrictive permit conditions for foreign-flagged fleets and the use of birds scaring lines have decreased the number of killed birds by 85%. Cape fur seals are present along

6000-602: The Agulhas Leakage, the transport of warm water from the Indian Ocean to the Atlantic Ocean, which affects the global climate. The average diameter of the Agulhas rings is 320 km (200 mi), but they can reach 500 km. They extend down to the ocean floor; circulate at 0.3–1.5 m/s (0.98–4.92 ft/s); and move into the South Atlantic at 4–8 km (2.5–5.0 mi)/day. Only half of

6120-517: The Agulhas eddies that leave the Cape Basin manage to cross the Walvis Ridge and those that do tend to lose half their energy before reaching the ridge within six months. The Agulhas rings transport an estimated 1-5 Sv (millions m/s) of water from the Indian Ocean to the South Atlantic. The Agulhas rings are thought to be of global climatic importance. Their delivery of warm water from

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6240-413: 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

6360-423: 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

6480-482: 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

6600-462: 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

6720-418: The Cretaceous and because it separates oceanic crusts of different age, and not oceanic crust (~14 km thick) from continental crust (25 km thick). North of the AFFZ is the Outeniqua Basin which is a complex system of sub-basins separated from each other by faults and basement arches; there are several smaller fault-bounded sub-basins in the north (Bredasdorp, Infanta, Pletmos, Gamtoos, and Algoa) and

6840-404: The DWBC breaks into anticyclonic eddies during periods of strong meridional overturning circulation . One such NADW eddy was observed in 2003 and the researchers speculated that a deeply penetrating Agulhas ring pinched it off the NADW slope current. Spinning at 20 cm/s (7.9 in/s), these deep-water eddies move around the southern tip of the Agulhas Bank and into the Indian Ocean. Most of

6960-429: The Early Cretaceous as West Gondwana (South America) broke up from Africa. The AFFZ is characterized by a pronounced topographic anomaly, the Agulhas Ridge (41°S,16°E-43°S,9°E) which rises more than 2 km above the surrounding sea floor. The only equivalent in size are the neighbouring Diaz Ridge and the Falkland Escarpment. The Agulhas Ridge is unique because it was not formed during the continental breakup during

7080-403: 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

7200-411: 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)

7320-405: 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

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7440-457: 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

7560-445: 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

7680-432: 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

7800-424: 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

7920-666: 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

8040-432: 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

8160-411: 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

8280-401: 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

8400-412: The Indian to the Atlantic Ocean can control the rate of thermohaline overturning of the entire Atlantic. Other factors contribute, to various degrees, to the inter-ocean exchanges in the region, including filaments from the Agulhas Current and intrusions of water from Antarctica. Cold, cyclonic eddies have been observed in the southwestern Atlantic. Based on model simulations, researchers have found that

8520-408: 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

8640-703: The NADW flow (more than 7 Sv ) meanders east around the Agulhas Plateau together with the surface Agulhas Return Current, but a smaller portion (3 Sv) continues north along the African east-coast as the Agulhas Undercurrent. Of 89.5 Sv released from the North Atlantic, 3.6 Sv leaves the South Atlantic south of the Agulhas Bank. However, 0.9 Sv recirculate in the basin north of the Walvis Ridge for centuries, of which 50-90% end up flowing south of

8760-668: 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

8880-504: The South African coast. Fur seals are protected in South Africa since 1893 although a small number are occasionally culled to protect sea birds. Many seals are caught in fishery nets and boat propellers, but the seals are also regularly accused of stealing fish from the fisheries. Sharks are known to prey on them, but in 2012 a cape fur seal was observed preying on and consuming a mid-sized blue shark. 51 species, or more than 50%, of

9000-464: The South Atlantic seafloor formed between them and magnetic anomalies north of the AFFZ reflects phase of the seafloor spreading. South of the AFFZ traces can be found of how the Falkland Plateau and the Agulhas Bank moved relative to each other. On a modern map, the Falkland Plateau can still be rotated and fitted into the Natal Valley in the Indian Ocean east of South Africa. The Agulhas Plateau

9120-457: The South Atlantic. 100 Mya, the region where the triple junction was located passed over the hotspot, resulting in a continuous eruption that lasted to about 94 Mya and the seafloor spreading that still separates Antarctica, Africa, and South America. The Agulhas-Falkland Fracture Zone (AFFZ) stretches 1,200 kilometres (750 mi) across the South Atlantic. It is one of the largest and most spectacular fracture zones on Earth. It developed during

9240-619: 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

9360-554: 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

9480-532: 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

9600-464: The anchovy and sardine: from February to September on the Western Cape but from January to July on St Croix Island off Eastern Cape. After breeding, the birds forage further offshore: 10–15 km (6.2–9.3 mi) off the western coast and up to 40 km (25 mi) from their colonies off Eastern Cape. In 2005, when Korean and Philippine vessels started longline fishing along the edges of

9720-473: The apparent endemism.) The degree of endemism varies considerably among taxa: Bryozoa 64%, Mollusca 56%, Echinodermata 3.6%, Porifera 8.8%, Amphipoda 33%, Isopoda 85%, or Cumacea 71%. Fisheries are one of the major threats to the biodiversity of the Agulhas Bank. Copepods comprise 90% of the zooplankton carbon on the Agulhas Bank, and are thus an important source of food for pelagic fish and juvenile squids. The population of Calanus agulhensis ,

9840-756: 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

9960-422: The bank. It then retroflects back into the Indian Ocean south-west of the bank. This retroflection results in intense eddy activities such as meanders, eddies, and filaments. In upper layer water, the Agulhas rings and eddies move warm and salty water into the large South Atlantic gyre , which exports it to the tropics. In the lower ocean layers water is transported in the opposite direction. Cyclonic eddies

10080-476: The bank. Squid and small pelagic fishes are also caught. Before the introduction of the EEZ, foreign fisheries used roch-hopper gear trawling on the bank. Most of the catches are short-lived shelf-zone pelagic species and more long-lived deep-water species. The large populations of sardine and anchovy also present on the shelf follow an annual cycle. Anchovy spawn on the western Agulhas Bank in early summer while

10200-400: 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

10320-701: 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

10440-473: The coast on the Agulhas Bank, they tend to pinch off Agulhas rings from the Agulhas Current. Such a ring shedding can be triggered by a Natal pulse alone, but sometimes meanders on the Agulhas Return Current merge to contribute to the shedding of an Agulhas ring. Agulhas rings are large anticyclonic eddies or warm core rings of ocean water that are pinched off the Agulhas Current along

10560-444: The coastal margin of the present SCP provide earliest traces of anatomically modern humans and the use of marine resources. South Africa began oil exploration on the Agulhas Bank in the 1980s. Of more than 200 offshore wells in South Africa, most are found on Bredasdorp Basin on the Agulhas Bank. The Agulhas Bank is also significant for fisheries who use demersal trawling , demersal longline fishing , and midwater trawl fishing on

10680-505: 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

10800-551: 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

10920-656: The distance offshore. The Alpard banks are in the Alphard Banks Controlled-Pelagic Linefish Zone of the Agulhas Bank Complex Marine Protected Area . The habitats are depth and profile related, with the shallower, flatter, areas of the pinnacle tops dominated by spiny kelp ( Ecklonia radiata ), and encrusting invertebrates, and the deeper, steeper, areas below 30 m having little kelp and a more upright invertebrate community. Dalgleish Bank

11040-755: The east coast has fewer commercial fisheries, the large human population along there has resulted in overexploitation of coastal fish and invertebrate stocks by recreational and subsistence fishers. A small aquaculture industry produces mussels and oysters offshore. Several pelagic species are heavily harvested by the commercial fleet: purse-seine fishery is used to catch sardines, anchovies, and round herring; mid-water trawl fishery to catch horse mackerel and chub mackerel; pelagic longline and pole fishery to catch tunas and swordfish; while hook and line are used inshore to catch squid and teleost species, including snoek and geelbek . All these species are relatively common and are considered having an important role in

11160-464: The eastern edge of the Agulhas Bank from where they move into the South Atlantic . As the Agulhas Current reaches the east coast of South Africa, large solitary meanders known as Natal pulses form at irregular intervals. 165 days after the appearance of a Natal pulse, an Agulhas ring is formed off Durban. The Agulhas rings are among the largest eddies in the world and play an important role in

11280-612: 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

11400-400: The ecosystem. There are at least 12,914 marine species in South Africa, but small bodied species are poorly documented and the abyssal zone is almost completely unexplored. Almost a quarter of South Africa's coast line is protected, excluding deeper water. A third of the marine species are endemic to South Africa (though poor levels of taxonomic research in adjoining countries probably affects

11520-608: The human lineage is relatively low, which indicate one or several population bottlenecks late in our lineage. It has been estimated that the population was limited to perhaps 600 individuals during the MIS 6 glacial stage (195-125 kya), one of the longest cold periods in the Quaternary of Africa. A technological and behavioural revolution that occurred globally about 50 kya led to a cultural complexity which happened in South Africa around 120-70 kya. The Cape Floral Region

11640-413: The interaction of the Agulhas Current and the eastern edge of the bank can result in the Agulhas rings. The provenance of ocean sediments can be determined by analysing terrigenous strontium isotope ratios in deep ocean cores. Sediments underlying the Agulhas Current and Return Current have significantly higher ratios than surrounding sediments. Analyses of cores in the South Atlantic deposited during

11760-409: The interaction of the Agulhas Current on the eastern edge, but easterly winds do occur, especially in summer and fall, and can generate local upwelling cells. As the current is diverged away from the coast, dynamic processes draws an onshore Ekman layer of cold water from below the warm shelf-edge flow. In spring and summer, at a depth of 100 m (330 ft), a semi-permanent ridge of cold water

11880-593: 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

12000-485: The largest known slumps occurred on the south-eastern edge of the Agulhas Bank in the Pliocene or more recently. Stretching from a depth of 190–700 m (620–2,300 ft), the so-called Agulhas slump is 750 km (470 mi) long, 106 km (66 mi) wide, and has a volume of 20,000 km (4,800 cu mi). It is a composite slump with proximal and distal allochthonous sediment masses separated by

12120-481: 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

12240-634: 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

12360-464: 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

12480-622: 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

12600-430: The most degraded hotspots where only c. 5 % of the original habitat remains. Natal Province The Province of Natal ( Afrikaans : Natalprovinsie ), commonly called Natal , was a province of South Africa from May 1910 until May 1994. Its capital was Pietermaritzburg . During this period rural areas inhabited by the black African population of Natal were organised into the bantustan of KwaZulu , which

12720-543: 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

12840-589: 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

12960-609: The recognized species of cetaceans are present in the southern African subregion (between the equator and the Antarctic ice edge), of which 36 have been sighted in South African and Namibian waters. A vulnerable population of fish-eating killer whales are present offshore on the Agulhas Bank. Observations peak in January while few are sighted in April and May. The killer whales move in pods of 1-4 individuals and are mostly sited over

13080-470: The reefs are within protected areas, but only a few of those protected areas include protection from fishing. The Agulhas Bank is a natural boundary between ocean currents from the Atlantic Ocean , Indian Ocean , and Southern Ocean , resulting in one of the most turbulent waters of the world oceans. The Agulhas Current flows south along the African east-coast and along the south-eastern edge of

13200-530: 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

13320-463: The sardines span over a broader season and area — eggs are transported by currents to the nursery area in the St Helena Bay on the South African west coast from where juvenile then migrate back to the Agulhas Bank to spawn. South Africa has a relatively large fishing industry mostly catching pelagic pilchard and anchovy and demersal hake on the south and western coasts. Though

13440-542: The sea and a reconstruction of how the coastline has changed over 440 kya shows that the coast during the Pleistocene was located as far as 90 km (56 mi) from the present coast. The present South African southern coastal plain (SCP) is still separated from the rest of Africa by the Cape Fold Belt . During glacial maxima the sea-level dropped 120 metres (390 ft). This not only left large parts of

13560-457: The shelf edge off the south-east coast. An analysis of killer whale mtDNA has shown that there was a peak inter-oceanic migration events during the Eemian interglacial period , 131-114 kya. This peak coincides with a period of maximal Agulhas leakage which promoted a rapid and episodic interchange of killer whale lineages. During this period killer whales and other marine top predators, such as

13680-599: 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

13800-615: The western bank along the bank's western edge. Regularly, the mesoscale eddies from the east interact with the Benguela upwelling system on the African west coast. Flowing south along the South American continental slope, the Deep Western Boundary Current (DWBC) carries North Atlantic Deep Water (NADW) into the South Atlantic. At about 8°S and at a depth of 2,200–3,500 m (7,200–11,500 ft),

13920-404: The western coast of South Africa, of which 21 are squaloid sharks . The main food source for African penguins ( Spheniscus demersus ) is anchovy and sardine which they forage between Cape Columbine and the central Agulhas Bank. The birds have colonies on Dassen Island , on the South African west coast, and Bird Island , on the south coast. African penguins breed opportunistically, following

14040-487: 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

14160-582: Was divided into four distinct ecozones: Agulhas inshore, Agulhas inner shelf, Agulhas outer shelf, and Agulhas shelf edge. 33 different benthic habitats types were identified on the Agulhas Bank. There are dozens of warm temperate reefs along the coast of the Agulhas Ecoregion spanning from 5–30 m (16–98 ft) below sea level. Many rocky sub-tidal reefs are of aeolianite or sandstone origin, but granite , quartzite and siltstone reefs are also present. The Agulhas reefs are very heterogeneous and include several possible different sub-types. Some of

14280-409: Was progressively separated from the province, becoming partially autonomous in 1981. Of the white population, the majority were English -speaking people of British descent, causing Natal to become the only province to vote "No" to the creation of a republic in the referendum of 1960 , due to very strong monarchist , pro- British Commonwealth , and anti- secessionist sentiment. In the latter part of

14400-537: Was the same during the LGM and that the reduced leakage must be explained by a weaker current. Consequently, it can be predicted that a stronger Agulhas Current will result in its retroflection occurring more eastward and an increased Agulhas leakage. Compared to the Agulhas Current, the Benguela Current on the west and south-west coast of Africa is more intense and steadier. Its dynamic southern upwelling system

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