The Indian Ocean ranks third in terms of area. At the same time, compared to others, the greatest depth of the Indian Ocean is very modest - only 7.45 kilometers.
Location
It is not difficult to find it on the map - the Asian part of Eurasia is located in the north of the ocean, Antarctica lies on the southern shores, and Australia lies in the east on the path of the currents. Africa is located in its western part.
Most of the ocean area is located in the southern hemisphere. A very conventional line divides Indian and - from Africa, down the twentieth meridian to Antarctica itself. It is separated from the Pacific by the Indo-Chinese peninsula of Malacca, the border goes to the north then along the line that on the map connects the islands of Sumatra, Java, Sumba and New Guinea. The Indian Ocean does not have common borders with the fourth - the Arctic Ocean.
Square
The average depth of the Indian Ocean is 3897 meters. Moreover, it occupies an area of 74,917 thousand kilometers, which allows it to be in third place in size among its “brothers”. The shores of this huge body of water are very slightly indented - this is the reason why there are few seas in its composition.
Relatively few islands lie in this ocean. The most significant of them once broke away from the mainland, so they are located close to the coastline - Socotra, Madagascar, Sri Lanka. Far from the coast, in the open part, you can find islands born from volcanoes. These are Crozet, Mascarene and others. In the tropics, on volcanic cones, there are islands of coral origin, such as the Maldives, Cocos, Adamans and others.
The shores in the east and north-west are indigenous, while in the west and north-east they are mostly alluvial. The edge of the coast is very weakly indented, except for its northern part. This is where most of the large bays are concentrated.
Depth
Of course, over such a large area the depth of the Indian Ocean cannot be the same - the maximum is 7130 meters. This point is located in the Sunda Trench. Moreover, the average depth of the Indian Ocean is 3897 meters.
Sailors and explorers of the waters cannot rely on the average figure. Therefore, scientists have long compiled a map of the depths of the Indian Ocean. It accurately indicates the height of the bottom at various points, all the shallows, trenches, depressions, volcanoes and other relief features are visible.
Relief
Along the coast lies a narrow strip of continental shallows, about 100 kilometers wide. The shelf edge, located in the ocean, has a shallow depth - from 50 to 200 meters. Only in the north-west of Australia and along the Antarctic coast does it increase to 300-500 meters. The slope of the continent is quite steep, in some places divided by underwater valleys of large rivers such as the Ganges, Indus and others. In the northeast, the rather monotonous topography of the Indian Ocean floor is enlivened by the Sunda island arc. It is here that the most significant depth of the Indian Ocean is found. The maximum point of this trench is located 7130 meters below sea level.
Ridges, ramparts and mountains divided the bed into several basins. The most famous are the Arabian Basin, the African-Antarctic Basin and the Western Australian Basin. These depressions formed hilly ones located in the center of the ocean, and accumulative plains located not far from the continents, in those areas where sedimentary material arrives in sufficient quantities.
Among the large number of ridges, the East Indian is especially noticeable - its length is about 5 thousand kilometers. However, the bottom topography of the Indian Ocean also has other significant ridges - the Western Australian, meridional and others. The bed is also rich in various volcanoes, in some places forming chains and even quite large massifs.
Mid-ocean ridges are three branches of a mountain system that divide the ocean from the center to the north, southeast and southwest. The width of the ridges ranges from 400 to 800 kilometers, the height is 2-3 kilometers. The bottom topography of the Indian Ocean in this part is characterized by faults across the ridges. Along them, the bottom is most often displaced horizontally by 400 kilometers.
Unlike ridges, the Australian-Antarctic Rise is a shaft with gentle slopes, the height of which reaches a kilometer, and the width extends up to one and a half thousand kilometers.
The predominantly tectonic structures of the bottom of this particular ocean are quite stable. Active developing structures occupy a much smaller area and flow into similar structures in Indochina and East Africa. These main macrostructures are divided into smaller ones: plates, blocky and volcanic ridges, banks and coral islands, trenches, tectonic scarps, Indian Ocean depressions and others.
Among the various irregularities, the north of the Mascarene ridge occupies a special place. Presumably, this part previously belonged to the long-lost ancient continent of Gondwana.
Climate
The area and depth of the Indian Ocean make it possible to assume that the climate in its different parts will be completely different. And indeed it is. The northern part of this huge body of water has a monsoon climate. In summer, during a period of low pressure over mainland Asia, southwestern equatorial air flows dominate over the water. In winter, tropical air flows from the northwest dominate here.
A little south of 10 degrees south latitude, the climate over the ocean becomes much more constant. In tropical (and subtropical in summer) latitudes, southeastern trade winds dominate here. In temperate regions there are extratropical cyclones that move from west to east. Hurricanes are common in western tropical latitudes. Most often they sweep through in summer and autumn.
The air in the north of the ocean warms up to 27 degrees in summer. The African coast is blown with air with a temperature of about 23 degrees. In winter, the temperature drops depending on latitude: in the south it can be below zero, while in northern Africa the thermometer does not fall below 20 degrees.
Water temperature depends on currents. The coasts of Africa are washed by the Somali Current, which has fairly low temperatures. This leads to the fact that the water temperature in this region remains at around 22-23 degrees. In the north of the ocean, the upper layers of water can reach a temperature of 29 degrees, while in the southern regions, off the coast of Antarctica, it drops to -1. Of course, we are talking only about the upper layers, since the greater the depth of the Indian Ocean, the more difficult it is to draw conclusions about the water temperature.
Water
The depth of the Indian Ocean does not affect the number of seas at all. And there are fewer of them than in any other ocean. There are only two Mediterranean seas: the Red and the Persian Gulf. In addition, there is also the marginal Arabian Sea, and the Andaman Sea is only partially closed. In the east of the vast waters are Timor and
The largest rivers in Asia belong to the basin of this ocean: the Ganges, Salween, Brahmaputra, Irwadi, Indus, Euphrates and Tigris. Among African rivers, it is worth highlighting the Limpopo and Zambezi.
The average depth of the Indian Ocean is 3897 meters. And in this column of water a unique phenomenon occurs - a change in the direction of currents. The currents of all other oceans are constant from year to year, while in the Indian oceans the currents are subject to the winds: in winter they are monsoonal, in summer they are predominant.
Since deep waters originate in the Red Sea and the Persian Gulf, almost the entire body of water is highly salinized with a low percentage of oxygen.
Shores
In the west and north-east there are predominantly alluvial shores, while in the north-west and east there are primary shores. As already mentioned, the coastline is almost flat, very slightly indented along almost the entire length of this water body. The exception is the northern part - this is where most of the seas belonging to the Indian Ocean basin are concentrated.
Inhabitants
The rather shallow average depth of the Indian Ocean boasts a wide variety of animal and plant life. The Indian Ocean is located in tropical and temperate zones. The shallow waters are full of corals and hydrocorals, among which live a huge number of invertebrate species. These include worms, crabs, sea urchins, stars and other animals. No fewer brightly colored tropical fish find shelter in these areas. The coasts are rich in mangroves, in which the mudskipper has settled - this fish can live for a very long time without water.
The flora and fauna of beaches exposed to low tides is very poor, since the hot rays of the sun destroy all living things here. in this sense it is much more diverse: there is a rich selection of algae and invertebrates.
The open ocean is even richer in living creatures - representatives of both the animal and plant worlds.
The main animals are copepods. More than a hundred species live in the waters of the Indian Ocean. Pteropods, siphonophores, jellyfish and other invertebrates are almost as numerous in number of species. Several species of flying fish, sharks, glowing anchovies, tuna, and sea snakes frolic in the ocean waters. Whales, pinnipeds, sea turtles, and dugongs are no less common in these waters.
Feathered inhabitants are represented by albatrosses, frigate birds and several species of penguins.
Minerals
Oil deposits are being developed in the waters of the Indian Ocean. In addition, the ocean is rich in phosphates, potassium raw materials necessary for fertilizing agricultural land.
It has the least number of seas. It has a peculiar bottom topography, and in the northern part - a special system of winds and sea currents.
Mostly located in the Southern Hemisphere between, and. Its coastline is slightly indented, with the exception of the northern and northeastern parts, where almost all seas and large bays are located.
Unlike other oceans, the mid-ocean ridges of the Indian Ocean consist of three branches radiating from its central part. The ridges are dissected by deep and narrow longitudinal depressions - grabens. One of these huge grabens is the Red Sea depression, which is a continuation of the faults of the axial part of the Arabian-Indian mid-ocean ridge.
Mid-ocean ridges divide the bed into 3 large sections, which are part of three different ones. The transition from the ocean floor to the continents is gradual everywhere; only in the northeastern part of the ocean is the arc of the Sunda Islands located, under which the Indo-Australian lithospheric plate subducts. Therefore, a deep-sea trench about 4000 km long stretches along these islands. There are more than a hundred active volcanoes here, including the famous Krakatoa, and earthquakes often occur.
At the surface of the Indian Ocean depends on latitude. The northern part of the Indian Ocean is much warmer than the southern part.
Monsoons form in the northern part of the Indian Ocean (north of 10 S latitude). In summer, the southwestern summer monsoon blows here, carrying humid equatorial air from the sea to the land, and in winter - the northeastern winter monsoon, carrying dry tropical air from the continent.
The system of surface currents in the southern half of the Indian Ocean is similar to the system of currents in the corresponding latitudes of the Pacific and Atlantic oceans. However, north of 10°N. A special regime of water movement arises: monsoon seasonal currents appear, changing direction to the opposite twice a year.
The organic world of the Indian Ocean has much in common with the organic world of the Pacific and Atlantic oceans at the corresponding latitudes. In the shallow waters of hot zones, coral polyps are common, creating numerous reef structures, including islands. Among the fish, the most numerous are anchovies, tuna, flying fish, sailfish, and sharks. The tropical coasts of continents are often occupied by mangroves. They are characterized by peculiar plants with terrestrial respiratory roots and special communities of animals (oysters, crabs, shrimp, mudskipper fish). The bulk of ocean animals are invertebrate planktonic organisms. In tropical coastal areas, sea turtles, poisonous sea snakes, and endangered mammals - dugongs - are common. The cold waters of the southern part of the ocean are home to whales, sperm whales, dolphins, and seals. Among the birds, the most interesting are penguins that inhabit the coasts of South Africa, Antarctica and the islands of the temperate zone of the ocean.
Natural resources and economic development
The Indian Ocean has great biological wealth, but fishing is mainly limited to coastal zones, where, in addition to fish, lobsters, shrimp, and shellfish are caught. In the open waters of hot zones, tuna fishing is carried out, and in cold zones, whales and krill are fished.
The most important are oil and natural gas deposits. The Persian Gulf with its adjacent land stands out especially, where 1/3 of the world's oil is produced.
In recent decades, the coasts of warm seas and the islands of the northern part of the ocean have become increasingly attractive for people to relax, and the tourism business is booming here. The volume of traffic through the Indian Ocean is significantly less than through the Atlantic and Pacific oceans. However, it plays an important role in the development of South and Southeast Asian countries.
The Indian Ocean is the third largest ocean. Geologically it is largely a relatively young ocean, although it should be noted, as with other oceans, that many aspects of its earliest geological history and origins are not yet understood. Western border south of Africa: along the meridian of Cape Agulhas (20° E) to Antarctica (Donning Maud Land). Eastern border south of Australia: along the western border of Bass Strait from Cape Otway to King Island, then to Cape Grim (North-West Tasmania) and from the south-eastern tip of the island of Tasmania along 147° E. to Antarctica (Fisher Bay, George V Coast). There has been much debate regarding the eastern border north of Australia, due to the fact that some scientists attribute the Arafura Sea, and some even the Timor Sea
sea to the Pacific Ocean, although this is not entirely logical, since the Timor Sea, by the nature of its hydrological regime, is inextricably linked with the Indian Ocean, and the Sahul shelf, geologically, is clearly part of the North-West Australian Shield, connecting the area of the once existing Gondwana with the Indian ocean Most geologists draw this boundary along the narrowest (western) part of the Torres Strait; according to the definition of the International Hydrographic Bureau, the western border of the strait runs from Cape York (11° 05" S, 142° 03" E) to the mouth of the Bensbeck River (New Guinea) (141° 01" E), which also coincides with the eastern border of the Arafura Sea.
The northeastern border of the Indian Ocean runs (from island to island) through the Lesser Sunda Islands to the islands of Java, Sumatra and then to the islands of Singapore. About the marginal seas of the Indian Ocean, located along its northern border. The area south of the Cape Agulhas-Cape Louin line (Western Australia) is sometimes considered the southern sector of the Indian Ocean.
Indian Ocean area within the boundaries excluding the Arafura Sea 74,917 thousand km2, with the Arafura Sea 75,940 thousand km. Average depth 3897 m; maximum recorded depth 7437 m3. Volume of Indian Ocean waters 291,945 thousand km3.
Bottom relief
Bathymetrically, the Indian Ocean can be divided into five morphological units.Mainland margins
The Indian Ocean shelves are on average slightly narrower than the Atlantic Ocean shelves; their width ranges from a few hundred meters around some oceanic islands to 200 km or more in the Bombay area. The bend that forms the outer edge of the shelves of Africa, Asia and Australia has an average depth of 140 m. The boundary of the continental platform is formed by the continental slope, steep marginal scarps and the slopes of the trenches.
The continental slope is cut through by numerous underwater canyons. Particularly long underwater canyons lie along the continuation of the mouths of the Ganges and Indus rivers. The continental foot has slopes from 1:40 at the border with the continental slope to 1:1000 at the border with the abyssal plains. The relief of the continental foot is characterized by isolated seamounts, hills and canyons. Submarine canyons at the foot of the continental slope are usually narrow in diameter and difficult to detect, so few of them have been well surveyed. The areas around the mouths of the Ganges and Indus rivers have large accumulations of sediment known as archipelagic fans.
The Java Trench stretches along the Indonesian arc from Burma to Australia. On the Indian Ocean side it is bordered by a gently sloping outer ridge.
ocean bed
The most characteristic elements of the relief of the ocean floor are the abyssal plains. The slopes here range from 1: 1000 to 1: 7000. With the exception of isolated peaks of buried hills and mid-ocean canyons, the height of the relief of the ocean floor does not exceed 1-2 m. The abyssal plains of the northern and southern parts of the Indian Ocean are very clearly expressed, but near Australia they are less pronounced. The seaward margins of abyssal plains are usually characterized by abyssal hills; Some areas are characterized by low, linearly elongated ridges.
Microcontinents
The most characteristic feature of the bottom topography of the Indian Ocean are microcontinents elongated from north to south. In the northern part of the Indian Ocean, in the direction from west to east, the following aseismic microcontinents can be identified: Mozambique Ridge, Madagascar Ridge, Mascarene Plateau, Chagoss-Laccadive Plateau, Ninetiest Ridge. In the southern part of the Indian Ocean, the Kerguelen Plateau and the asymmetrical Broken Ridge, which extends from east to west, have a noticeable meridional linearity. Morphologically, microcontinents are easily distinguished from a mid-ocean ridge; they usually represent higher areas of massifs with more leveled relief.
A clearly defined microcontinent is the island of Madagascar. The presence of granites in the Seychelles also suggests that at least the northern part of the Mascarene Plateau is of continental origin. The Chagos Islands are coral islands rising above the surface of the Indian Ocean in the area of the vast, gently curved Chagos-Laccadive Plateau. The Nineteenth Ridge is perhaps the longest and most linear ridge discovered in the World Ocean during the International Indian Ocean Expedition. This ridge was traced from 10° N. w. up to 32° S
In addition to the microcontinents mentioned above, there is a distinct Diamantina fault zone in the Indian Ocean for 1,500 miles west of the southwestern tip of Australia. Broken Ridge, which forms the northern boundary of this fault zone, at 30° S. w. connects to the Ninetyist Ridge, which runs at right angles to the Diamantina fault zone in a north-south direction.
Mid-ocean ridge
The most pronounced feature of the Indian Ocean floor is the Central Indian Ridge, part of the global mid-ocean ridge, which is shaped like an inverted V in the central Indian Ocean. A seismically active depression, or rift, runs along the axis of this mid-ocean ridge. The entire ridge has a generally mountainous topography with trends parallel to the axis of the ridge.
Fracture zones
The Indian Ocean is dissected by several clearly defined fault zones that displace the axis of the mid-ocean ridge. To the east of the Arabian Peninsula and the Gulf of Aden is the Owen Fracture Zone, which shifts the axis of the mid-ocean ridge approximately 200 miles to the right. The recent formation of this displacement is indicated by the Whatli Trench, a well-defined depression with depths more than 1000 m greater than the depths of the Indian Abyssal Plain.
Several small right-lateral strike-slip faults displace the axis of the Carlsberg Ridge. In the Gulf of Aden, the axis of the mid-ocean ridge is displaced by several sinistral strike-slip faults running almost parallel to the Owen Fracture Zone. In the southwestern Indian Ocean, the axis of the mid-ocean ridge is offset by a series of left-lateral fault zones that have approximately the same orientation as the Owen Fracture Zone. The Malagasy Fracture Zone, which lies east of the Madagascar Ridge, is likely a southern extension of the fault zone Owen. In the area of the islands of Saint-Paul and Amsterdam, the axis of the mid-ocean ridge is displaced by the Amsterdam Fracture Zone. These zones run parallel to the Nintyist Ridge and have approximately the same meridional orientation as the fault zones in the western Indian Ocean. Although the Indian Ocean is most characterized by meridional strikes, the Diamantina and Rodriguez fault zones extend approximately from east to west.
The strongly dissected tectonic relief of the mid-ocean ridge in general presents a noticeable contrast with the very leveled relief of the continental foot and the almost completely smoothed relief of the abyssal plains. In the Indian Ocean, there are areas of smooth-wavy or wavy relief, apparently due to a thick cover of pelagic sediments. The slopes of the mid-ocean ridge south of the polar front are flatter than those north of the polar front. This may be a consequence of higher rates of pelagic sediment deposition due to increased organic productivity in the Southern Ocean.
The Crozet Plateau has an extremely smooth topography. In this region, the narrow zone of the mid-ocean ridge typically has a highly dissected topography, while the ocean floor in this area is extremely smooth.
Indian Ocean climate
Air temperature. In January, the thermal equator for the Indian Ocean is slightly shifted south of the geographic one, in the area between 10 s. w. and 20 U. w. air temperature above 27° C. In the northern hemisphere, the 20° C isotherm, which separates the tropical zone from the temperate zone, runs from the south of the Arabian Peninsula and the Gulf of Suez through the Persian Gulf to the northern part of the Bay of Bengal almost parallel to the Tropic of Cancer. In the southern hemisphere, the 10°C isotherm, which separates the temperate zone from the subpolar zone, runs almost along the parallel of 45°S. In the mid-latitudes (southern hemisphere (between 10 and 30° S), isotherms of 27-21° C are directed from WSW to ENE, from South Africa through the Indian Ocean to Western Australia, indicating that the temperature of the western sector in some and at the same latitudes the temperature of the eastern sector is 1-3° C. Near the western coast of Australia, the isotherms of 27-21° C drop to the south due to the influence of the strongly heated continent.In May, the highest temperatures (above 30°C) are observed in the interior of the southern Arabian Peninsula, Northeast Africa, Burma and India. In India it reaches more than 35° C. The thermal equator for the Indian Ocean lies about 10° N. w. Isotherms from 20 to 10°C occur in the southern hemisphere between 30 and 45°S. w. from ESE to WNW, indicating that the western sector is warmer than the eastern one. In July, the zone of maximum temperatures on land moves north of the Tropic of Cancer.
Temperatures over the Arabian Sea and the Bay of Bengal have been decreasing slightly since May, and in addition, the air temperature in the Arabian Sea region is lower than over the Bay of Bengal. Near Somalia, the air temperature due to the rise of cold deep waters drops below 25 ° C. The lowest temperatures are observed in August. In the southern hemisphere, the area west of South Africa is slightly warmer than the central part at the same latitudes. Temperatures off the west coast of Australia are also much higher than inland.
In November, the thermal equator with a small zone of temperatures above 27.5° C almost coincides with the geographic equator. In addition, over the Indian Ocean region north of 20° S. w. the temperature is almost uniform (25-27 C) except for a small area over the central Indian Ocean.
Annual air temperature amplitudes for the central part, between 10° N. w. and 12° S. latitude, less than 2.5 C, and for the area between 4 ° N. w. and 7° S. w. - less than 1 C. In the coastal areas of the Bay of Bengal and the Arabian Sea, as well as in the area between 10 and 40 ° S. w. west of 100° W. d. annual amplitude exceeds 5° C.
Pressure field and surface winds. In January, the meteorological equator (minimum atmospheric pressure 1009-1012 mbar, calm and variable winds), like the thermal equator, is located about 10° south. w. it separates the northern and southern hemispheres, which differ in meteorological conditions.
The predominant wind north of the meteorological equator is the northeast trade wind, or more precisely the northeast monsoon, which changes direction to north at the equator and northwest (northwest monsoon) and the southern hemisphere. South of the meteorological equator, due to the heating of continents in the summer of the southern hemisphere, minimum pressure (less than 1009 mbar) is observed over Australia, Africa and the island of Madagascar. The high pressure area of southern subtropical latitudes is located along 35°S. the maximum pressure (above 1020 mbar) is observed over the central part of the Indian Ocean (near the islands of Saint-Paul and Amsterdam). The northern bulge of the 1014 mb isobar in the central Indian Ocean is caused by the effect of lower air and surface water temperatures, in contrast to the South Pacific, where a similar bulge is observed in the eastern sector of South America. South of the high pressure area there is a gradual decrease in pressure towards a subpolar depression near 64.5°S. sh., where the pressure is below 990 mbar. This pressure system creates two types of wind systems south of the meteorological equator. In the northern part, the southeast trade winds cover the entire Indian Ocean, with the exception of areas near Australia, where they change direction to the south or southwest. South of the trade wind region (between 50 and 40° S) westerly winds occur from the Cape of Good Hope to Cape Horn, in an area called the "roaring forties". The significant difference between westerly winds and trade winds is not only that the former have higher speeds, but also that the daily variations in direction and speed for the former are also much greater than for the latter. In July, for a wind field from the north of 10° S. w. The opposite picture to January is observed. An equatorial depression with pressure values below 1005 mbar is located over the eastern part of the Asian continent.
South of this depression the pressure gradually increases from the 20s. w. to 30° south sh., i.e. to the area of the southern borders of the “horse” latitudes. The southern trade winds cross the equator and become the southwest monsoons in the northern hemisphere, very intense, characterized by strong storms off the coast of Somalia in the Arabian Sea.
This area is a good example of a complete shift in winds with an annual cycle in the northern trade wind zone, which is a consequence of the strong heating and cooling effect of the Asian continent. In the middle and high latitudes of the southern hemisphere, the moderating effect of the Indian Ocean reduces the differences in pressure and wind fields in June and January.
However, at high latitudes, westerly winds increase significantly, and fluctuations in their direction and speed also increase. The frequency distribution of storm winds (more than 7 points) showed that in the winter of the Northern Hemisphere over most of the Indian Ocean north of 15° S. w. storm winds are virtually not observed (their frequency is less than 1%). In the area of 10° south. latitude, 85-95° east. (northwest of Australia) from November to April, tropical cyclones sometimes form, moving to the southeast and southwest. South of 40°S w. The frequency of storm winds is more than 10% even in the summer of the southern hemisphere. In the northern hemisphere summer, from June to August, the southwest monsoons in the western Arabian Sea (off the coast of Somalia) are always so strong that approximately 10-20% of the winds are force 7. During this season, calm zones (with a frequency of storm winds of less than 1%) shift to the area between 1° south. w. and 7° N. w. and west of 78° E. d. In the area of 35-40° S. w. The frequency of storm winds increases by 15-20% compared to the winter season.
Cloud cover and precipitation. In the northern hemisphere, cloud cover exhibits significant seasonal variations. During the northeast monsoon period (December-March), cloudiness over the Arabian Sea and Bay of Bengal is less than 2 points. However, in summer the southwest monsoons bring rainy weather to the region of the Malay Archipelago and Burma, with average cloudiness already 6-7 points. The area south of the equator, the southeastern monsoon zone, is characterized by high cloudiness throughout the year - 5-6 points in the summer of the northern hemisphere and 6-7 points in the winter. Even in the southeast monsoon zone there is a relatively large cloud cover and there are extremely rare areas of cloudless sky characteristic of the southeast Pacific monsoon zone. Cloudiness in areas west of Australia exceeds 6 points. However, near the coast of Western Australia it is quite cloudless.
In summer, sea fog (20-40%) and very poor visibility are often observed off the coast of Somalia and the southern part of the Arabian Peninsula. The water temperature here is 1-2°C lower than the air temperature, which causes condensation, enhanced by dust brought from deserts on the continents. The area south of 40° S. w. also characterized by frequent sea fog throughout the year.
Total annual precipitation for the Indian Ocean is high - more than 3000 mm at the equator and more than 1000 mm in the western zone of the southern hemisphere. Between 35 and 20° S. w. in the trade wind zone, precipitation is relatively rare; The area off the western coast of Australia is especially dry, with precipitation less than 500 mm. The northern boundary of this dry zone is parallels 12-15° S, that is, it does not reach the equator, as in the South Pacific Ocean. The northwest monsoon zone is generally the boundary region between the northern and southern wind systems. To the north of this area (between the equator and 10° S) is the equatorial rainy zone, which stretches from the Java Sea to the Seychelles. In addition, very high rainfall is observed in the eastern part of the Bay of Bengal, especially in the Malay Archipelago region. The western Arabian Sea is very dry, and the rainfall in the Gulf of Aden and the Red Sea is less than 100 mm. Maximum precipitation in rainy zones is in December-February between 10 and 25° S. w. and in March-April between 5 s. w. and 10th south. w. in the western part of the Indian Ocean. Maximum values in the summer of the northern hemisphere are observed in the Bay of Bengal. The heaviest rains almost throughout the year are observed west of the island of Sumatra.
Temperature, salinity and density of surface waters
In February, the northern Indian Ocean experiences typical winter conditions. In the interior regions of the Persian Gulf and the Red Sea, the surface water temperature is 15 and 17.5 ° C, respectively, while in the Gulf of Aden it reaches 25 ° C. Isotherms of 23-25 ° C go from southwest to northeast, and therefore , the surface waters of the western part of the Indian Ocean are warmer than the surface waters of the eastern part for the same latitudes (the same for air temperature).This difference is caused by water circulation. It is observed in all seasons of the year. In the southern hemisphere, where it is summer at this time, the zone of high surface temperatures (above 28 ° C) runs in the direction ENE from the eastern coast of Africa to the area west of the island of Sumatra and then south of Java and north of Australia, where the water temperature sometimes exceeds 29° C. Isotherms 25-27° C between 15 and 30 degrees south. w. directed from WSW to ENE, from the coast of Africa to approximately 90-100° E. etc., then they turn to the southwest, just like in the western part of the Bay of Bengal, in contrast to the South Pacific, where these isotherms are directed off the coast of South America to the ENE. Between 40 and 50° S. w. there is a transition zone between water masses of mid-latitudes and polar waters, which is characterized by thickening of isotherms; temperature difference is about 12° C.
In May, the surface waters of the northern Indian Ocean heat up to a maximum and have temperatures generally above 29 ° C. At this time, the northeast monsoons give way to the southwest, although rains and sea level rise are not yet observed at this time. In August, only in the Red Sea and the Persian Gulf the water temperature reaches a maximum (above 30 ° C), however, the surface waters of most of the northern sector of the Indian Ocean including the Gulf of Aden, the Arabian Sea and most of the Bay of Bengal, with the exception of its western regions, have lower temperatures than in May. The zone of low temperatures of the surface layer (below 25°C) stretches from the coast of Somalia to the southeastern coast of the Arabian Peninsula. The decrease in temperature is caused by the intense rise of cold deep waters due to the southwest monsoons. In addition, in August there are three characteristic features of temperature distribution south of 30°S. latitude: isotherms of 20-25° C in the eastern and central parts of the Indian Ocean are directed from WSW to ENE, and thickening of isotherms is noted between 40 and 48° S. sh., and isotherms west of Australia are directed south. In November, surface water temperatures are generally close to the annual average. The low temperature zone (below 25°C) between the Arabian Peninsula and Somalia and the high temperature zone in the western Bay of Bengal are almost disappearing. In a huge area of water north of 10° south. w. surface layer temperatures range between 27 and 27.7° C.
The salinity of surface waters of the southern Indian Ocean has the same distribution features that are characteristic of the South Pacific Ocean. To the west of Australia, the maximum salinity value is observed (above 36.0 ppm). The equatorial zone of low salinity, corresponding to the transition zone between the southeast trade winds and the monsoons, extends to 10° S. sh., but clearly expressed only in the eastern part of the Indian Ocean.
The minimum salinity values in this zone are observed south of the islands of Sumatra and Java. The salinity of surface waters in the northern Indian Ocean varies not only regionally but also seasonally. In the summer of the northern hemisphere, the salinity of surface waters has the following characteristic features: it is extremely low in the Bay of Bengal, quite high in the Arabian Sea and very high (above 40 ppm) in the Persian Gulf and the Red Sea.
The density of surface waters in the southern Indian Ocean in the summer of the southern hemisphere decreases uniformly northward from approximately 27.0 in the region of 53-54° S. w. to 23.0 at 17° S. sh.; in this case, the isopycnals run almost parallel to the isotherms. Between 20° S. w. and 0° there is a huge zone of low-density waters (below 23.0); near the islands of Sumatra and Java there is a zone with a density below 21.5, corresponding to the zone of minimum salinity in this area. In the northern Indian Ocean, density changes are influenced by salinity. In summer, the density decreases from 22.0 in the southern part of the Bay of Bengal to 19.0 in its northwestern part, while for most of the Arabian Sea it is above 24.0, and near the Suez Canal and in the Persian Gulf it reaches 28.0 and respectively. 25.0. In addition, seasonal changes in surface water density are mainly caused by changes in temperature. For example, the northern part of the Indian Ocean is characterized by an increase in density by 1.0–2.0 from summer to winter.
Indian Ocean Currents
Currents in the northern Indian Ocean, which are strongly influenced by the monsoon and vary seasonally, are called the southwest and northeast monsoon drifts for summer and winter respectively. The Southern Trade Wind Current and the Western Wind Current pass through the southern part of the Indian Ocean. In addition to these currents, closely related to wind systems, there are currents of a local nature, caused mainly by the density structure of the Indian Ocean, such as the Mozambique Current, Cape Agulhas Current, Inter-trade (equatorial) countercurrent, Somali Current and West Australian Current.The southern Indian Ocean experiences a large anticyclonic circulation similar to that in the southern Pacific and Atlantic Oceans, but is subject to greater annual variations. Its extreme southern part is the Western Winds Current (between 38 and 50° S), 200-240 miles wide, increasing in an easterly direction. This current borders the subtropical and Antarctic convergence zones. The speed of the current depends on the strength of the wind and varies seasonally and regionally. The maximum speed (20-30 miles/day) is observed near the Kerguelen Island. In the summer of the southern hemisphere, this current, when approaching Australia, turns north and connects with the current coming from the Pacific Ocean south of Australia.
In winter, the wind drift joins the southward current along the western coasts of Australia and continues into the Pacific Ocean along the southern coasts of Australia. The eastern part of the aiticyclonic circulation in the southern hemisphere is the Western Australian Current, which has a steady northerly direction only in the summer of the southern hemisphere and reaches 10-15 miles/day north of 30° S. w. This current becomes weak in winter and changes direction to the south.
The northern part of the anticyclonic gyre is the Southern Trade Wind Current, which originates in the area where the Western Australian Current exits the Tropic of Capricorn under the influence of southeastern trade winds. The maximum speed of the current (more than 1 knot) is observed in its eastern part in the winter of the southern hemisphere, when the westerly flow from the Pacific Ocean increases north of Australia. In the summer of the southern hemisphere, when this flow becomes easterly, the northern boundary of the South Trade Wind Current is between 100 and 80° E. located about 9° south. latitude, shifting slightly to the southeast from 80° east. d.; Its southern border at this time passes about 22° south. w. in the eastern sector. In the winter of the southern hemisphere, the northern boundary of this current shifts northward by 5-6°, following the northern shift of the southeast trade wind. Before the island of Madagascar, the current divides into several branches.
One of them goes north around the island of Madagascar at a speed of up to 50-60 miles/day and then turns west. It splits again into two branches at Cape Delgado. One branch turns north (East African Coastal Current), the other turns south, following through the Mozambique Channel (Mozambique Current). The speed of this current varies from almost zero to 3-4 knots during the northeast monsoon.
The Cape Agulhas Current is formed from the continuation of the Mozambique Current and the southern branch of the South Trade Wind Current south of the island of Mauritius. This current, narrow and clearly defined, extends from the coast for less than 100 km. As is known, a southward flow in the Southern Hemisphere is characterized by a tilt of the water surface to the left. At a distance of 110 km from Port Elizabeth, the slope of the level towards the ocean increases by approximately 29 cm. Between Durban and 25° E. The speed of this current at the edge of the Agulhas Bank reaches 3-4.5 knots. South of Africa, the main part of the current turns sharply to the south and then to the east and thus unites with the current of the Western Winds. However, a small one continues to move into the Atlantic Ocean. Due to the change in directions and razor-sharp currents, numerous eddies and gyres develop along the coast of South Africa, the position of which changes throughout the year.
North of 10° S. w. There is strong variability in Indian Ocean surface currents from winter to summer. During the northeast monsoon, from November to March, the Northern Trade Wind Current (drift of the northeast monsoon) develops. The southern boundary of this current varies from 3-4° N. w. in November up to 2-3° S. w. in February. In March, the current turns north again and disappears with the advent of the southwest monsoon drift. With the onset of the northeastern monsoon (from November), the Intertrade Countercurrent begins to develop. It is formed under the combined influence of the current running southwest of the coast of Somalia and the East African Coastal Current running north from the cape. Delgado. The countercurrent is narrow and reaches almost to the island of Sumatra. Its northern boundary in November passes north of the equator, and in February it shifts to 2-3° S. Later, the current rises again to the north and then disappears. The southern boundary of the current lies between 7 and 8° S. w. Current speed between 60 and 70° E. d. reaches 40 miles/day, but further east it decreases.
During the period of the southwest monsoon, from April to October, the Northern Trade Wind Current (the drift of the northeast Monsoon disappears and is replaced by the drift of the southwest monsoon, going east south of India. South of the island of Sri Lanka its speed is 1-2 knots, and sometimes reaches 3 knots. The branches of this current create a clockwise circulation in the Arabian Sea, following the contours of the coastline. The speed of the southeasterly flow off the western coast of India reaches 10-42 miles / day. During this season, the Somali Current along the coast of Somalia in the region of 10 ° S latitude is directed north, and the waters of the South Trade Wind Current cross the equator.An intense rise of water occurs off the coast of Somalia, causing cooling of surface waters over a large area.
Subsurface currents in the Indian Ocean north of 10°S. w. were measured at horizons of 15, 50, 100, 200, 300, 500 and 700 m during the 31st voyage of the Vityaz (January-April 1960), at approximately 140 deep-sea stations.
As established, at a depth of 15 m, the distribution of currents turned out to be almost similar to the surface one in the winter of the northern hemisphere, with the exception that, according to observational data, the Intertrade Countercurrent originates at 60° E. and covers the area between 0 and 3° S. those. its width is much smaller than on the surface. On the horizon 200 m of current south of 5° N. w. have the opposite direction to the currents at a horizon of 15 m: they are directed to the east under the Northern and Southern Trade Wind Currents and to the west under the Inter-Trade Wind Countercurrent east of 70° E. d. At a depth of 500 m, the current is between 5° N. w. and 10° S. w. in general they have an eastern direction and form a small cyclonic gyre centered at 5°S. latitude, 60° east. d. In addition, direct current measurements and dynamic calculation data for the period November-December 1960, obtained during the 33rd voyage of the Vityaz, indicate that the observed current system does not yet correspond to the current system characteristic of the winter monsoon , despite the fact that northwest winds are already beginning to prevail here. At a depth of 1500 m south of 18° S. w. An easterly current was detected at a speed of 2.5-45 cm/s. About 80° E. This current combines with the southern flow, which has a speed of 4.5-5.5 cm/s and its speed is rapidly increasing. About 95°E. This current sharply turns north and then west, forming an anticyclonic gyre, the northern and southern parts of which have speeds of 15-18 and 54 cm/s, respectively.
About 20-25° S. latitude, 70-80° east. The southern branch of this current has a speed of less than 3.5 cm/s. At a horizon of 2000 m between 15 and 23° S. w. the same current has an eastern direction and a speed of less than 4 cm/s. About 68°E. d. a branch departs from it, going north at a speed of 5 cm/s. Anticyclonic gyre between 80 and 100° E. at a horizon of 1500 m covers a large area between 70 and 100° east. e. A current coming south from the Bay of Bengal meets another current coming from the east at the equator and turns north and then northwest to the Red Sea.
On the horizon 3000 m between 20 and 23° S. w. the current is directed to the east with speeds in some places up to 9 cm/s. Cyclonic gyre at 25-35° S. latitude, 58-75° E. d. becomes clearly expressed here at speeds of up to 5 cm/s. Anticyclic cycle between 80 and 100 centuries. observed at a horizon of 1500 m, here it breaks up into a number of small vortices.
Water masses
The Indian Ocean, in addition to the subantarctic water mass, is characterized by three main water masses: the central water mass of the Indian Ocean (subtropical subsurface), the equatorial water mass of the Indian Ocean, extending to medium depths, and the deep water of the Indian Ocean, below the horizon of 1000 m. There are also intermediate water masses. These are Antarctic intermediate waters, the waters of the Red Sea and others at medium depths.
AND . Here, the boundaries between the oceans are conventionally drawn from the southern tip of Africa - the Cape of Good Hope along 20° east. and from the southern tip along 147° E. d. The most complex border of the Indian Ocean is in the northeast, where it runs along the northern part of the Strait of Malacca, the southwestern and southern shores of the Greater and Lesser Sunda Islands, the southwestern shore of Novaya and the Torres Strait.
There are relatively few seas in the Indian Ocean - the Red, Andaman, Timor, Arafura, etc. There are also few islands. They are concentrated mainly in the western part of the ocean. The largest - Tasmania, Socotra - are of continental origin. The remaining islands are small in size and are either surface peaks of volcanoes or coral atolls - Chagos, Laccadive, Amirante, etc. There are also volcanic islands bordered by coral reefs - Mascarene, Comoros, Andaman, Nicobar. They occupy a special place: within the ocean floor, this is the only formation composed of granites, i.e., belonging to the continental type.
Unlike the Pacific and Atlantic, the Indian Ocean does not go far to the north and does not connect with.
The Indian Ocean is one of the areas of ancient civilizations. It began to be developed by the peoples who inhabited its shores as early as four millennia BC. And yet, until recently, it remained one of the least studied oceans. Only in the last 25-30 years has the situation changed dramatically. In the conditions of modern life, the role of the Indian Ocean in the international arena has noticeably increased, which is largely explained by its rich natural and human resources (more than 2 billion people). It has shipping routes in different directions connecting the world's largest ports. The Indian Ocean accounts for 17-18% of the port cargo turnover of capitalist countries. The largest ports are Madras, Colombo, Port Elizabeth, Aden, Basra, Daman.
Geological structure of the bottom and the most important features of the relief. Within the Indian Ocean, there are the underwater continental margins, the ocean floor, mid-ocean ridges and a very insignificant transition zone.
Underwater. Despite the small width of the shelf (7-80 km), the underwater margin of the continents within the Indian Ocean occupies a significant area, which is associated with the spread of marginal plateaus.
The Persian Gulf is completely shelf with depths of 100 m and a bottom leveled by accumulative processes. Alluvial material also plays a large role in the structure of the narrow shelf. In the northern part of the Bay of Bengal, a layer of terrigenous material accumulates and is carried into the Ganges and Brahmaputra Seas, so the shelf here is also not wide. The shelf is wide. From depths of 100-200 m, a narrow continental slope begins, in some places dissected by underwater canyons, of which the most impressive are the canyons and the Ganges. At a depth of 1000-1500 m, the continental slope gives way to the continental foot, where there are extensive (up to several hundred kilometers wide) cones of turbidity currents, forming an inclined plain.
The underwater margin of the African continent also has a narrow shelf. A narrow and steep continental slope characterizes the coast and the Mozambique Channel. Numerous submarine canyons off the coast of Africa serve as paths for turbidity currents, which form a relatively clearly defined wide continental foot. The bottom of the Mozambique Channel is composed of continental-type crust, which indicates a relatively recent separation from Africa due to the subsidence of the platform.
The shelf section of the Australian Platform is distinguished by the widespread development of coral structures. In the Bass Strait area, the shelf relief has a structural-denudation character. The continental slope is very gentle, furrowed with canyons. The transition of the slope to the continental foot is not clearly defined.
Transition zone. The Indian Ocean Transition Zone occupies just over 2% of the total ocean area and is represented by only part of the Indonesian Transition Region. A pronounced element of this area is the Sunda (Javan) deep-sea trench (7729 m). It can be traced to the northern part of the Bay of Bengal and reaches a length of 4000 km. To the north and northeast of it is the outer island arc of the Sunda Islands, which begins in the north with the Andaman Islands and continues with the Nicobar Islands. South of the island of Sumatra, the outer arc becomes entirely underwater, and then the islands again rise above the surface of the ocean in the form of the islands of Sumba and Timor. Along the island of Timor, a small trench with a depth of up to 3300 m appears again. Behind the outer arc, parallel to it, the Bali depression stretches with a depth of up to 4850 m, separating from the outer inner island arc, which consists of the large islands of Sumatra, Java, Bali. The role of an island arc in Sumatra and Java is played by their volcanic ridges external to the Indian Ocean. And part of these same islands, facing the South China and Java Seas, are accumulative lowlands with a continental type of crust. Active are characterized by 95 volcanoes, of which 26 are active. The most famous is Krakatoa.
Mid-ocean ridges. The Indian Ocean contains a system of mid-ocean ridges that form the basis of the Indian Ocean floor framework.
In the southwest of the ocean begins the West Indian Ridge, which has a northeastern strike and is characterized by all the signs of rifting (high, submarine volcanism, rift structure of the ridge). On the eastern slope of the ridge there are two large volcanic massifs protruding above the water. Their peaks form Prince Edward and Crozet Islands. In the area of Rodriguez Island, at a latitude of about 20° S. sh., the West Indian Ridge connects with the Arabian-Indian.
The Arabian-Indian ridge has been studied quite fully. The rift structure of the ridge zone is clearly expressed in it, seismicity is high, and ultrabasic rocks emerge on the bottom surface. In the north, the Arabian-Indian Ridge takes on an almost latitudinal strike and is replaced by rift-block structures of the bottom of the Gulf of Aden. In the western part of the Gulf of Aden, the rift system bifurcates and forms two branches. The southern branch invades the African continent in the form of the East African rifts, and the northern branch is formed by the rifts of the Gulf of Aqaba and the Dead Sea. In the central regions of the Red Sea, powerful outlets of hot (up to + 70° C) and extremely salty (up to 300% o) waters were discovered at great depths.
The next link in the system of mid-ocean ridges is the Central Indian Ridge. It stretches from Rodrigues Island, i.e., from the junction of the West Indian and Arabian-Indian ridges, to the southeast to the islands of Amsterdam and Saint-Paul, where the Amsterdam Fault separates it from another link in the mid-ocean system in the Indian Ocean - Australian-Antarctic Rise.
The Australian-Antarctic Rise, in its morphological features, is closest to the mid-ocean rises of the Pacific Ocean. This is a wide swell-like elevation of the ocean floor with a predominance of low-mountain and hilly terrain. There are no rift zones on most of the uplift.
In the east and southeast of the ocean, the system of mid-ocean ridges is represented by the Mascarene, Mozambique, and Madagascar ridges.
Another large ridge in the Indian Ocean is the East Indian Ridge. It extends from approximately 32° S. w. almost in a meridional direction to the Bay of Bengal and has a length of 5000 km. This is a narrow mountain rise, broken by longitudinal faults. Opposite its middle part in an eastern direction is the rise of the Cocos Islands, represented by several volcanic cones. The tops of the Cocos Islands are covered with coral atolls. Christmas Island is also located here, which is a raised ancient atoll with an absolute height of 357 m.
From the southern edge of the East Indian Ridge, the Western Australian Ridge, consisting of plateau-like uplifts and sharply defined ridges, extends almost in a latitudinal direction to the east. According to many American scientists, it is composed of continental-type crust up to 20 km thick. On the slopes of the ridge, fragments of dolerites similar to those of the island of Tasmania were discovered.
ocean bed. A system of numerous ridges and uplifts divides the floor of the Indian Ocean into 24 basins, of which the largest are the Somali, Mascarene, Madagascar, Mozambique, Central, Cocos, Western, South Australian, African-Antarctic, etc. The deepest of them are the Amsterdam (7102 m), African-Antarctic (6972 m), Western Australian (6500 m), Madagascar (6400 m). The relief of the bottoms of the basins is represented by small-hilly and small-block dissection, as well as plains with large-hilly and large-block dissection.
As in the Pacific Ocean, faults with submeridional and meridional strikes play an important role on the floor of the Indian Ocean. Faults of sublatitudinal and latitudinal strike are less common.
The floor of the Indian Ocean is characterized by hundreds of individual underwater mountain peaks. The most significant among them are: a mountain in the Central Basin, Mount Shcherbakova in the Western Australian Basin. In the Arabian Sea in 1967, a seamount called Mount MSU was discovered, with a characteristic flat top that gives it a resemblance to the guyots of the Atlantic and Pacific oceans.
Bottom sediments. Bottom sediments at low latitudes are dominated by carbonate foraminiferal silt. It occupies over half the area of the ocean floor. At the greatest depths there are red clay and radiolarian silt, and at shallow depths there are coral deposits. Along Antarctica, diatomaceous oozes can be traced in a wide strip, and near the continent itself - iceberg deposits.
The Indian Ocean ranks third in area after the Pacific and Atlantic. The average depth is about 4 km, and the maximum is recorded in the Java Trench and is 7,729 m.
The Indian Ocean washes the shores of the most ancient centers of civilization and it is believed that it was the very first to be explored. The routes of the first voyages did not go far into open waters, so the ancients who lived on the ocean considered it simply a huge sea.
The Indian Ocean appears to be the most populous of animals. Fish stocks have always been famous for their abundance. Northern waters served as almost the only source of food for people. Pearls, diamonds, emeralds and other precious stones - they are all found in the Indian Ocean.
The ocean is also rich in minerals. The Persian Gulf contains one of the largest oil fields developed by man.
A small number of rivers flow into the Indian Ocean, mainly in the north. These rivers carry a lot of sediment into the ocean, so this part of the ocean cannot boast of cleanliness. Things are different in the south, where the ocean has no freshwater arteries. The water appears crystal clear to the observer, with a dark blue tint.
The lack of sufficient desalination, as well as high evaporation, explains why the salinity of its waters is slightly higher compared to other oceans. The saltiest part of the Indian Ocean is the Red Sea (42%).
Climate
Since the Indian Ocean has extensive borders with continents, the climatic conditions are largely determined by the surrounding land. The ocean is assigned the status of " monsoon"The pressure contrast over land and sea causes strong winds - monsoons. In summer, when the land in the northern ocean is very hot, a large area of low pressure occurs, causing heavy precipitation over both the continent and the ocean. This is the so-called southwest equatorial monsoon".
In contrast, winter is characterized by harsher weather in the form of destructive hurricanes and flooding on land. An area of high pressure over Asia causes trade winds.
The speed of the monsoons and trade winds is so fast that they form large surface currents that change every season. The largest such current is Somali, which flows from north to south in winter and changes its direction in summer.
The Indian Ocean is quite warm. The water surface temperature in Australia reaches 29 degrees, but in the subtropics it is colder, around 20. Icebergs, which can float quite high, up to 40 degrees south latitude, have a minor but quite noticeable effect on the water temperature, as well as on its salinity. . Before this area, salinity averages 32% and increases closer to the north.