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, it climatic conditions are largely determined by the surrounding land. The status of " monsoon"The pressure contrast over land and sea causes strong winds - monsoons. In summer, when the land in the north of the ocean is very hot, a large area appears low pressure, causing heavy precipitation both over the continent and over 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. Region 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.
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 coincides with eastern border th 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 marginal seas 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 in the central Indian Ocean is shaped like an inverted V. Along the axis of this mid-ocean ridge runs a seismically active depression, or rift. 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. East of 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.V coastal areas 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 area (between 50 and 40° S) westerly winds from the cape occur 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 strong effect heating and cooling 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 for the most part 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.
General annual quantity 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 their 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 North Indian Ocean under strong influence monsoon and changing seasonally, are called 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. Maximum speed(20-30 miles/day) is observed near 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, the southward flow in the Southern Hemisphere is characterized by an inclination 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 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 area of 10° S. w. directed to the north, and the waters of the South Trade Wind Current cross the equator. Off the coast of Somalia, there is an intense rise in waters, 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.
Geographical position
Indian Ocean ranks third in area and volume of water. It occupies 1/5 of the area of the World Ocean and 1/7 of the surface of the planet (Fig. 1).
Rice. 1. Indian Ocean on the map.
Square Indian Ocean - 76.17 million km 2. Unlike the Pacific and Atlantic Oceans, it has a small number of seas, only 5. Temperature The surface layer of water is +17 °C, and the salinity is 36.5 ‰. The saltiest part of the Indian Ocean is the Red Sea, with a salinity of 41‰. Relief The Indian Ocean is unique: on the ocean floor there are 10 main basins, 11 underwater ridges and 1 trench more than 6 thousand meters deep.
Average depth The Indian Ocean is 3711 m, and the maximum is 7729 m. The coastline of the Indian Ocean is very slightly indented. Remember the location of the Indian Ocean objects: the Red Sea (Fig. 3), the Gulf of Aden, the Persian Gulf (Fig. 2), the Arabian Sea, the Bay of Bengal, the Greater Sunda Islands archipelago and the Mozambique Strait.
The most characteristic geographical feature of the Indian Ocean is that 84% of its area is located in the Southern Hemisphere, and there is no direct connection with the Northern Arctic Ocean.
Rice. 2. Persian Gulf
Rice. 3. Red Sea
According to modern data, the western border of the Indian Ocean is the meridian of 20° east. on the stretch between Antarctica and Cape Agulhas in southern Africa. In the northeast, its border runs along the shores of Asia to the Strait of Malacca along the islands of Sumatra, Java, Timor, and New Guinea. Further east through the Torres Strait along the west coast of Australia and the island of Tasmania. Further along 147° E. to Antarctica. The southern border of the ocean is the coast of Antarctica from 20° east. d. to 147° east. d. Northern border - the southern coast of Eurasia.
History of ocean exploration
The shores of the Indian Ocean are one of the areas of ancient civilizations. The exploration of the ocean began from the north by Indian, Egyptian and Phoenician sailors, who 3 thousand years BC. e. sailed in the Arabian and Red Seas and the Persian Gulf. The first descriptions of the routes of voyages in the Indian Ocean were made by the Arabs. For European geographical science, information about the ocean began to accumulate since the voyages Vasco da Gama(1497–1499) (Fig. 4), who, having rounded Africa, reached India.
In 1642–1643 Abel Tasman(Fig. 5) first passed from the Indian Ocean to the Pacific along the southern coast of Australia.
At the end of the 18th century, the first depth measurements were carried out here James Cook(Fig. 6).
Comprehensive and systematic study of the ocean began in late XIX century from the circumnavigation of the world by the English expedition on the Challenger ship (Fig. 7).
However, by the middle of the 20th century, the Indian Ocean was very poorly studied. In the 50s The Soviet expedition began work on the Ob ship (Fig. 8).
Today, the Indian Ocean is being studied by dozens of expeditions from different countries.
Lithospheric plates
At the bottom of the Indian Ocean there is a boundary of three lithospheric plates: African, Indo-Australian and Antarctic (Fig. 9). In the depression of the earth's crust, occupied by the waters of the Indian Ocean, all the large structural reliefs of the ocean floor are clearly expressed: shelf (accounting for more than 4% of the total ocean area), continental slope, ocean floor (ocean plains and basins, 56% of the total area ocean), mid-ocean ridges (17%), mountain ranges and underwater plateaus, deep-sea trench.
Rice. 9. Lithospheric plates on the map
Mid-ocean ridges divide the ocean floor into three large parts. The transition from the ocean floors to the continents is smooth, only in the northeastern part does the Sunda Islands arc form, under which the Indo-Australian lithospheric plate subducts. In this place, a deep-sea trench 4 thousand km long is formed. The deep Sunda Trench, like the underwater ridges, is a zone of active underwater volcanism and earthquakes.
Geological history of the ocean
Depression Indian Ocean is very young. It was formed about 150 million years ago as a result of the collapse of Gondwana and the moving apart of Africa, Australia, Antarctica and Hindustan. The Indian Ocean acquired its contours close to modern ones about 25 million years ago. Now the ocean is located within three lithospheric plates: African, Indo-Australian and Antarctic.
Climate
The Indian Ocean is located in the tropical and subequatorial zones of the Northern Hemisphere, as well as in all climatic zones Southern Hemisphere. Based on surface water temperatures, this is the warmest ocean. Temperature The Indian Ocean depends on latitude: the northern part of the ocean is warmer than the southern part. Monsoons also form in the northern Indian Ocean. The Indian Ocean washes the shores of big continent– Eurasia. Their interaction determines the features of surface currents and atmospheric circulation over the northern part of the ocean and the southern coast of Asia. In winter, an area of high atmospheric pressure forms over South Asia, and an area of low pressure forms over the ocean. Thus, a wind is formed - the northeast monsoon. In summer, on the contrary, the southwest monsoon forms.
Sailors have long known the changing nature of the winds and currents of the northern part of the Indian Ocean and skillfully used it while sailing on sailing ships. In Arabic, “monsoon” means “season”, and “breeze” in French means “light wind”. Small sailing ships in the northern part of the Indian Ocean are still used.
Tsunami
Underwater earthquake in the Indian Ocean that occurred December 26, 2004, caused a tsunami that was considered the deadliest natural disaster in modern history. The magnitude of the earthquake, according to various sources, ranged from 9.1 to 9.3. This is the second or third strongest earthquake on record. The epicenter of the earthquake was in the Indian Ocean north of the island of Simeulue, located off the northwestern coast of the island of Sumatra (Indonesia). The tsunami reached the shores of Indonesia, Sri Lanka, southern India, Thailand and other countries. The height of the waves exceeded 15 meters. The tsunami caused enormous destruction and a huge number of dead people even in Port Elizabeth, South Africa, 6 thousand 900 km from the epicenter (Fig. 10).
Rice. 10. After the earthquake, December 2004
According to various estimates, from 225 to 300 thousand people died. True number the deaths are unlikely to ever be known, as many people were swept out to sea.
Flora and fauna
Flora and fauna The Indian Ocean is quite rich. In the shallow waters of the tropical zone, corals grow, which create islands with red and green algae. Among coral islands best known Maldives(Fig. 11). These robust coral structures are home to many species of invertebrates such as crabs, sea urchins, sponges, and coral fish. There are huge areas of dense thickets of brown algae here. The open ocean is mostly inhabited by planktonic algae, while the Arabian Sea is characterized by blue-green algae, which constantly cause water blooms.
Rice. 11. Maldives
The fauna of the ocean is also rich. For example, among the animal waters of the Indian Ocean, the most common crustaceans are copepods, and siphonophores And jellyfish. The ocean is inhabited by squid, some species of flying fish, white shark, sailfish, poisonous sea snake, whales, turtles, and seals (Fig. 12). The most common birds are frigates and albatrosses.
Rice. 12. Undersea world Indian Ocean
The flora and fauna of the Indian Ocean is very diverse and interesting, as animals and plants live in a place favorable for development. This is a flower garden for nature lovers, environmentalists and tourists. Oil and natural gas are produced on the Indian Ocean shelf. The most famous place in the world for oil production is the Persian Gulf. The Indian Ocean is considered to be the most polluted by oil compared to other oceans. There are also many shipping routes in the Indian Ocean; there are large port cities and various places of recreation and tourism: Karachi, Dar es Salaam, Maputo, Mumbai, etc.
Bibliography
1. Geography. Land and people. 7th grade: Textbook for general education. uch. / A.P. Kuznetsov, L.E. Savelyeva, V.P. Dronov, series “Spheres”. – M.: Education, 2011.
2. Geography. Land and people. 7th grade: atlas, “Spheres” series.
1. Internet portal "Complete Encyclopedia" ()
2. Internet portal "Geography" ()
3. Internet portal "All about sharks" ()
INDIAN OCEAN, the third largest ocean on Earth (after the Pacific and Atlantic), part of the World Ocean. Located between Africa in the northwest, Asia in the north, Australia in the east and Antarctica in the south.
Physiographical sketch
General information. The border of the Indian Ocean in the west (with the Atlantic Ocean south of Africa) is drawn along the meridian of Cape Agulhas (20° east longitude) to the coast of Antarctica (Donning Maud Land), in the east (with the Pacific Ocean south of Australia) - along the eastern border of Bass Strait to the island of Tasmania , and then along the meridian 146°55' east longitude to Antarctica, in the northeast (with the Pacific Ocean) - between the Andaman Sea and the Strait of Malacca, then along the southwestern shores of the island of Sumatra, the Sunda Strait, the southern coast of the island of Java, the southern the borders of the Bali and Savu seas, the northern border of the Arafura Sea, the southwestern shores of New Guinea and the western border of the Torres Strait. The southern high-latitude part of the Indian Ocean is sometimes referred to as the Southern Ocean, which combines the Antarctic sectors of the Atlantic, Indian and Pacific oceans. However, such geographical nomenclature is not generally accepted, and, as a rule, the Indian Ocean is considered within its usual boundaries. The Indian Ocean is the only ocean that is located mostly in the Southern Hemisphere and is bounded in the north by a powerful land mass. Unlike other oceans, its mid-ocean ridges form three branches radiating in different directions from the central part of the ocean.
The area of the Indian Ocean with seas, bays and straits is 76.17 million km2, the volume of water is 282.65 million km3, the average depth is 3711 m (2nd place after the Pacific Ocean); without them - 64.49 million km 2, 255.81 million km 3, 3967 m. The greatest depth in the deep-sea Sunda Trench is 7729 m at the point of 11°10' south latitude and 114°57' east longitude. The shelf zone of the ocean (conditionally depths up to 200 m) occupies 6.1% of its area, the continental slope (from 200 to 3000 m) 17.1%, the bed (over 3000 m) 76.8%. See the map.
Seas. There are almost three times fewer seas, bays and straits in the Indian Ocean than in the Atlantic or Pacific Oceans; they are mainly concentrated in its northern part. Seas of the tropical zone: Mediterranean - Red; marginal - Arabian, Laccadive, Andaman, Timor, Arafura; Antarctic zone: marginal - Davis, D'Urville, Cosmonauts, Riiser-Larsen, Commonwealth (see separate articles on the seas). The largest bays: Bengal, Persian, Aden, Oman, Great Australian, Carpentaria, Prydz. Straits: Mozambique, Babel-Mandeb, Bass, Hormuz, Malacca, Polk, Tenth Degree, Great Channel.
Islands. Unlike other oceans, the islands are few in number. The total area is about 2 million km 2. Most large islands mainland origin - Socotra, Sri Lanka, Madagascar, Tasmania, Sumatra, Java, Timor. Volcanic islands: Reunion, Mauritius, Prince Edward, Crozet, Kerguelen, etc.; coral - Laccadive, Maldives, Amirante, Chagos, Nicobar, most of Andaman, Seychelles; The coral Comoros, Mascarene, Cocos and other islands rise on volcanic cones.
Shores. The Indian Ocean is characterized by a relatively indented coastline, with the exception of the northern and northeastern parts, where most of the seas and main large bays; There are few convenient bays. The coasts of Africa in the western part of the ocean are alluvial, weakly dissected, and often surrounded by coral reefs; in the northwestern part - indigenous. In the north, low, weakly dissected shores with lagoons and sand bars, in places with mangroves, bordered on the landward side by coastal lowlands (Malabar Coast, Coromandel Coast) predominate; abrasion-accumulative (Konkan coast) and deltaic shores are also common. In the east, the shores are indigenous; in Antarctica, they are covered with glaciers descending to the sea, ending in ice cliffs several tens of meters high.
Bottom relief. In the bottom topography of the Indian Ocean, four main elements of geotexture are distinguished: the underwater continental margins (including the shelf and continental slope), transition zones, or island arc zones, the ocean floor and mid-ocean ridges. The area of the underwater continental margins in the Indian Ocean is 17,660 thousand km 2. The underwater margin of Africa is distinguished by a narrow shelf (from 2 to 40 km), its edge is located at a depth of 200-300 m. Only near the southern tip of the continent does the shelf expand significantly and in the area of the Agulhas Plateau extends up to 250 km from the coast. Significant areas of the shelf are occupied by coral structures. The transition from the shelf to the continental slope is expressed by a clear bend of the bottom surface and a rapid increase in its slope to 10-15°. The underwater margin of Asia off the coast of the Arabian Peninsula also has a narrow shelf, gradually expanding on the Malabar coast of Hindustan and off the coast of the Bay of Bengal, while the depth on its outer border increases from 100 to 500 m. The continental slope is clearly visible everywhere along the characteristic slopes of the bottom (height up to 4200 m, Sri Lanka island). The shelf and continental slope in some areas are cut by several narrow and deep canyons, the most pronounced canyons being underwater continuations of the channels of the Ganges rivers (together with the Brahmaputra River, it annually carries about 1,200 million tons of suspended and tractional sediment into the ocean, forming a sediment layer over 3,500 m thick ) and Ind. Australia's submarine margin is characterized by an extensive shelf, especially in the northern and northwestern parts; in the Gulf of Carpentaria and the Arafura Sea up to 900 km wide; greatest depth 500 m. The continental slope to the west of Australia is complicated by underwater ledges and individual underwater plateaus ( highest height 3600 m, Aru Islands). On the underwater outskirts of Antarctica, there are everywhere traces of the influence of the ice load of the huge glacier covering the continent. The shelf here belongs to a special glacial type. Its outer boundary almost coincides with the 500 m isobath. The shelf width is from 35 to 250 km. The continental slope is complicated by longitudinal and transverse ridges, individual ridges, valleys and deep trenches. At the foot of the continental slope, an accumulative plume composed of terrigenous material brought by glaciers is almost everywhere observed. The largest bottom slopes are observed in the upper part; with increasing depth, the slope gradually flattens out.
The transition zone on the floor of the Indian Ocean is distinguished only in the area adjacent to the arc of the Sunda Islands, and represents the south- eastern part Indonesian transition region. It includes: the Andaman Sea basin, the Sunda Islands island arc and deep-sea trenches. The most morphologically pronounced in this zone is the deep-sea Sunda Trench with a slope steepness of 30° or more. Relatively small deep-sea trenches are visible southeast of Timor Island and east of the Kay Islands, but due to their thick sedimentary layer maximum depths relatively small - 3310 m (Timor Trench) and 3680 m (Kai Trench). The transition zone is extremely seismically active.
The mid-ocean ridges of the Indian Ocean form three submarine mountain ranges radiating from the area at 22°S and 68°E to the northwest, southwest and southeast. Each of the three branches is divided according to morphological characteristics into two independent ridges: the northwestern - into the Middle Aden Ridge and the Arabian-Indian Ridge, the southwestern - into the West Indian Ridge and the African-Antarctic Ridge, the southeastern - into the Central Indian Ridge and Australian-Antarctic Rise. Thus, the median ridges divide the floor of the Indian Ocean into three large sectors. Sredinnye ridges They are vast uplifts, fragmented by transform faults into separate blocks, with a total length of over 16 thousand km, the foothills of which are located at depths of the order of 5000-3500 m. The relative height of the ridges is 4700-2000 m, the width is 500-800 km, the depth of the rift valleys is up to 2300 m.
In each of the three sectors of the ocean floor of the Indian Ocean, characteristic relief forms are distinguished: basins, individual ridges, plateaus, mountains, trenches, canyons, etc. In the western sector there are the largest basins: Somalia (with depths of 3000-5800 m), Mascarene (4500 -5300 m), Mozambique (4000-6000 m), Madagascar Basin (4500-6400 m), Agulhas (4000-5000 m); underwater ridges: Mascarene Ridge, Madagascar, Mozambique; plateau: Agulhas, Mozambican plateau; individual mountains: Equator, Africana, Vernadsky, Hall, Bardin, Kurchatov; Amirante Trench, Mauritius Trench; Canyons: Zambezi, Tanganyika and Tagela. In the northeastern sector there are basins: Arabian (4000-5000 m), Central (5000-6000 m), Coconut (5000-6000 m), North Australian (5000-5500 m), Western Australian Basin (5000-6500 m). m), Naturalista (5000-6000 m) and South Australian Basin (5000-5500 m); underwater ridges: Maldives Ridge, East Indian Ridge, Western Australian; Cuvier mountain range; Exmouth plateau; Mill Hill; individual mountains: Moscow State University, Shcherbakova and Afanasy Nikitin; East Indian Trench; Canyons: Indus, Ganges, Seatown and Murray rivers. In the Antarctic sector there are basins: Crozet (4500-5000 m), African-Antarctic Basin (4000-5000 m) and Australian-Antarctic Basin (4000-5000 m); plateaus: Kerguelen, Crozet and Amsterdam; separate mountains: Lena and Ob. The shapes and sizes of the basins are different: from round with a diameter of about 400 km (Comoros) to oblong giants with a length of 5500 km (Central), the degree of their isolation and the bottom topography are different: from flat or gently undulating to hilly and even mountainous.
Geological structure. The peculiarity of the Indian Ocean is that its formation occurred both as a result of the split and subsidence of continental masses, and as a result of the spreading of the bottom and new formation oceanic crust within the mid-ocean (spreading) ridges, the system of which was repeatedly rebuilt. The modern mid-ocean ridge system consists of three branches that converge at the Rodriguez Triple Junction. In the northern branch, the Arabian-Indian Ridge continues northwest of the Owen transform fault zone with the Gulf of Aden and Red Sea rift systems and connects with the intracontinental rift systems of East Africa. In the southeastern branch, the Central Indian Ridge and the Australian-Antarctic Rise are separated by the Amsterdam fault zone, which is connected to the plateau of the same name with the volcanic islands of Amsterdam and Saint-Paul. The Arabian-Indian and Central Indian ridges are slow-spreading (spreading speed is 2-2.5 cm/year), have a well-defined rift valley, and are crossed by numerous transform faults. The wide Australasian-Antarctic Rise does not have a pronounced rift valley; the spreading rate on it is higher than in other ridges (3.7-7.6 cm/year). To the south of Australia, the uplift is broken up by the Australian-Antarctic fault zone, where the number of transform faults increases and the spreading axis shifts along the faults in a southerly direction. The ridges of the southwestern branch are narrow, with a deep rift valley, densely crossed by transform faults oriented at an angle to the strike of the ridge. They are characterized by a very low spreading rate (about 1.5 cm/year). The West Indian Ridge is separated from the African-Antarctic Ridge by the Prince Edward, Du Toit, Andrew-Bain and Marion fault systems, which shift the ridge axis almost 1000 km to the south. The age of the oceanic crust within the spreading ridges is predominantly Oligocene-Quaternary. The West Indian Ridge, which penetrates like a narrow wedge into the structures of the Central Indian Ridge, is considered the youngest.
Spreading ridges divide the ocean floor into three sectors - African in the west, Asian-Australian in the northeast and Antarctic in the south. Within the sectors there are various types of intra-oceanic uplift, represented by “aseismic” ridges, plateaus and islands. Tectonic (block) uplifts have a block structure with varying crustal thickness; often include continental remains. Volcanic uplifts are mainly associated with fault zones. The uplifts are the natural boundaries of deep-sea basins. The African sector is distinguished by the predominance of fragments of continental structures (including microcontinents), within which the thickness of the earth's crust reaches 17-40 km (the Agulhas and Mozambican plateaus, the Madagascar ridge with the island of Madagascar, individual blocks of the Mascarene plateau with the Bank of the Seychelles Islands and the Saya de Bank -Malya). Volcanic uplifts and structures include the Comoros underwater ridge, crowned by archipelagos of coral and volcanic islands, the Amirante Range, the Reunion Islands, Mauritius, Tromelin, and the Farquhar Massif. In the western part of the African sector of the Indian Ocean (western part of the Somali Basin, northern part of the Mozambique Basin), adjacent to the eastern underwater margin of Africa, the age of the earth's crust is predominantly Late Jurassic-Early Cretaceous; in the central part of the sector (Mascarene and Madagascar basins) - Late Cretaceous; in the northeastern part of the sector (eastern part of the Somali Basin) - Paleocene-Eocene. Ancient spreading axes and transform faults intersecting them have been identified in the Somali and Mascarene basins.
The northwestern (near-Asian) part of the Asian-Australian sector is characterized by meridional “aseismic” ridges of a block structure with an increased thickness of the oceanic crust, the formation of which is associated with a system of ancient transform faults. These include the Maldives Ridge, crowned by archipelagos of coral islands - Laccadive, Maldives and Chagos; the so-called 79° ridge, the Lanka ridge with Mount Afanasia Nikitin, the East Indian (the so-called 90° ridge), Investigator, etc. Thick (8-10 km) sediments of the Indus, Ganges and Brahmaputra rivers in the northern part of the Indian Ocean partially overlap the extending in this direction there are ridges, as well as structures of the transition zone between the Indian Ocean and the southeastern edge of Asia. The Murray Ridge in the northern part of the Arabian Basin, bounding the Oman Basin from the south, is a continuation of folded land structures; falls within the Owen fault zone. South of the equator, a sublatitudinal zone of intraplate deformations up to 1000 km wide has been identified, which is characterized by high seismicity. It stretches in the Central and Cocos Basins from the Maldives Ridge to the Sunda Trench. The Arabian Basin is underlain by crust of Paleocene-Eocene age, the Central Basin by crust of Late Cretaceous - Eocene age; the crust is youngest in the southern part of the basins. In the Cocos Basin, the crust ranges in age from Late Cretaceous in the south to Eocene in the north; in its northwestern part, an ancient spreading axis was established, which separated the Indian and Australian lithospheric plates until the mid-Eocene. The Coconut Rise, a latitudinal uplift with numerous seamounts and islands (including the Cocos Islands) towering above it, and the Rhu Rise, adjacent to the Sunda Trench, separate the southeastern (Australian) part of the Asian-Australian sector. The Western Australian Basin (Wharton) in the central part of the Asian-Australian sector of the Indian Ocean is underlain by Late Cretaceous crust in the northwest and Late Jurassic in the east. Submerged continental blocks (marginal plateaus of Exmouth, Cuvier, Zenith, Naturalista) divide the eastern part of the basin into separate depressions - Cuvier (north of the Cuvier plateau), Perth (north of the Naturalista plateau). The crust of the North Australian Basin (Argo) is the oldest in the south (Late Jurassic); becomes younger in a northern direction (until the Early Cretaceous). The age of the crust of the South Australian Basin is Late Cretaceous - Eocene. The Brocken Plateau is an intra-oceanic rise with increased (from 12 to 20 km, according to various sources) crustal thickness.
In the Antarctic sector of the Indian Ocean there are mainly volcanic intra-oceanic rises with increased thickness of the earth's crust: the Kerguelen, Crozet (Del Caño) and Conrad plateaus. Within largest plateau Kerguelen, presumably founded on an ancient transform fault, the thickness of the earth's crust (according to some data, Early Cretaceous age) reaches 23 km. Rising above the plateau, the Kerguelen Islands are a multiphase volcanoplutonic structure (composed of alkali basalts and syenites of Neogene age). On Heard Island there are Neogene-Quaternary alkaline volcanics. In the western part of the sector there are the Conrad plateau with the volcanic mountains Ob and Lena, as well as the Crozet plateau with a group of volcanic islands Marion, Prince Edward, Crozet, composed of Quaternary basalts and intrusive massifs of syenites and monzonites. The age of the earth's crust within the African-Antarctic, Australian-Antarctic basins and the Late Cretaceous Crozet Basin is Eocene.
The Indian Ocean is characterized by the predominance of passive margins (continental margins of Africa, the Arabian and Hindu peninsulas, Australia, Antarctica). An active margin is observed in the northeastern part of the ocean (the Sunda transition zone between the Indian Ocean and Southeast Asia), where subduction of the ocean lithosphere occurs under the Sunda island arc. A subduction zone of limited extent, the Makran subduction zone, has been identified in the northwestern part of the Indian Ocean. Along the Agulhas Plateau, the Indian Ocean borders the African continent along a transform fault.
The formation of the Indian Ocean began in the mid-Mesozoic during the breakup of the Gondwanan part (see Gondwana) of the supercontinent Patea, which was preceded by continental rifting during the Late Triassic - Early Cretaceous. The formation of the first sections of oceanic crust as a result of the separation of continental plates began in the Late Jurassic in the Somali (about 155 million years ago) and North Australian (151 million years ago) basins. In the Late Cretaceous, the northern part of the Mozambique Basin experienced the spreading of the bottom and the new formation of oceanic crust (140-127 million years ago). The separation of Australia from Hindustan and Antarctica, accompanied by the opening of basins with oceanic crust, began in the Early Cretaceous (about 134 million years ago and about 125 million years ago, respectively). Thus, in the Early Cretaceous (about 120 million years ago), narrow ocean basins arose, cutting into the supercontinent and dividing it into separate blocks. In the middle of the Cretaceous period (about 100 million years ago), the ocean floor began to grow intensively between Hindustan and Antarctica, which led to the drift of Hindustan in a northerly direction. In the time interval of 120-85 million years ago, the spreading axes that existed north and west of Australia, off the coast of Antarctica and in the Mozambique Channel, died out. In the Late Cretaceous (90-85 million years ago), a split began between Hindustan with the Mascarene-Seychelles block and Madagascar, which was accompanied by bottom spreading in the Mascarene, Madagascar and Crozet basins, as well as the formation of the Australian-Antarctic Rise. At the Cretaceous-Paleogene boundary, Hindustan separated from the Mascarene-Seychelles block; the Arabian-Indian spreading ridge arose; the extinction of spreading axes occurred in the Mascarene and Madagascar basins. In the middle of the Eocene, the Indian lithospheric plate merged with the Australian one; the still developing system of mid-ocean ridges was formed. The Indian Ocean acquired its appearance close to its modern one in the early - middle Miocene. In the mid-Miocene (about 15 million years ago), during the split of the Arabian and African plates, new formation of oceanic crust began in the Gulf of Aden and the Red Sea.
Modern tectonic movements in the Indian Ocean are noted in mid-ocean ridges (associated with shallow-focus earthquakes), as well as in individual transform faults. The area of intense seismicity is the Sunda island arc, where deep-focus earthquakes are caused by the presence of a seismofocal zone plunging in the northeast direction. During earthquakes on the northeastern edge of the Indian Ocean, a tsunami may form.
Bottom sediments. Sedimentation rates in the Indian Ocean are generally lower than those in the Atlantic and Pacific oceans. Power thickness of modern bottom sediments varies from a discontinuous distribution at mid-ocean ridges to several hundred meters in deep-sea basins and 5000-8000 m at the foot of continental slopes. The most widespread are calcareous (mainly foraminiferal-coccolithic) silts, covering over 50% of the ocean floor area (on continental slopes, ridges and the bottom of basins at depths of up to 4700 m) in warm oceanic areas from 20° northern latitude up to 40° south latitude with high biological productivity of waters. Polygenic sediments - red deep-sea oceanic clays - occupy 25% of the bottom area at depths of over 4700 m in the eastern and southeastern parts of the ocean from 10° north latitude to 40° south latitude and in areas of the bottom remote from islands and continents; in the tropical region, red clays alternate with siliceous radiolarian silts covering the bottom of deep-sea basins of the equatorial belt. Ferromanganese nodules are present in deep-sea sediments in the form of inclusions. Siliceous, predominantly diatomaceous, silts occupy about 20% of the Indian Ocean floor; distributed at great depths south of 50° south latitude. The accumulation of terrigenous sediments (pebbles, gravel, sands, silts, clays) occurs mainly along the coasts of continents and within their underwater margins in areas of river and iceberg runoff and significant wind removal of material. The sediments covering the African shelf are mainly of shell and coral origin; phosphorite nodules are widely developed in the southern part. Along the northwestern periphery of the Indian Ocean, as well as in the Andaman Basin and the Sunda Trench, bottom sediments are represented mainly by deposits of turbidity (turbidity) flows - turbidites with the participation of products of volcanic activity, underwater landslides, landslides, etc. Sediments of coral reefs are widespread in western parts of the Indian Ocean from 20° south latitude to 15° north latitude, and in the Red Sea - up to 30° north latitude. IN rift valley Outcrops of metal-bearing brines with temperatures up to 70°C and salinity up to 300‰ have been discovered in the Red Sea. Metalliferous sediments formed from these brines contain a high content of non-ferrous and rare metals. On continental slopes, seamounts, and mid-ocean ridges, there are outcrops of bedrock (basalts, serpentinites, peridotites). Bottom sediments around Antarctica are classified as a special type of iceberg sediment. They are characterized by a predominance of a variety of clastic material, ranging from large boulders to silts and fine silts.
Climate. Unlike the Atlantic and Pacific oceans, which have a meridional extension from the shores of Antarctica to the North Arctic Circle and communicating with the Arctic Ocean, the Indian Ocean in the northern tropical region is bordered by a land mass, which largely determines the characteristics of its climate. The uneven heating of land and ocean leads to seasonal changes in extensive minimums and maximums of atmospheric pressure and to seasonal shifts of the tropical atmospheric front, which in the winter of the Northern Hemisphere retreats south to almost 10° south latitude, and in the summer is located in the foothills of southern Asia. As a result, the northern part of the Indian Ocean is dominated by a monsoon climate, which is primarily characterized by changes in wind direction throughout the year. The winter monsoon with relatively weak (3-4 m/s) and stable northeast winds operates from November to March. During this period, calms are common north of 10° south latitude. The summer monsoon with southwest winds occurs from May to September. In the northern tropical region and in the equatorial zone of the ocean, the average wind speed reaches 8-9 m/s, often reaching storm force. In April and October, a restructuring of the pressure field usually occurs, and during these months the wind situation is unstable. Against the background of the prevailing monsoon atmospheric circulation over the northern part of the Indian Ocean, isolated manifestations of cyclonic activity are possible. During the winter monsoon, there are known cases of cyclones developing over the Arabian Sea, and during the summer monsoon - over the waters of the Arabian Sea and the Bay of Bengal. Strong cyclones in these areas sometimes form during periods of monsoon change.
At approximately 30° south latitude in the central Indian Ocean there is a stable area of high pressure, the so-called South Indian High. This stationary anticyclone - part of the southern subtropical high pressure area - persists throughout the year. The pressure at its center varies from 1024 hPa in July to 1020 hPa in January. Under the influence of this anticyclone, stable southeastern trade winds blow throughout the latitudinal band between 10 and 30° south latitude throughout the year.
South of 40° south latitude, atmospheric pressure uniformly decreases in all seasons from 1018-1016 hPa at the southern periphery of the South Indian High to 988 hPa at 60° south latitude. Under the influence of the meridional pressure gradient in the lower layer of the atmosphere, a stable westerly air transport is maintained. The highest average wind speed (up to 15 m/s) is observed in the middle of winter in the Southern Hemisphere. The higher southern latitudes of the Indian Ocean are characterized by storm conditions throughout most of the year, in which winds with speeds of more than 15 m/s, causing waves above 5 m in height, have a frequency of 30%. South of 60° south latitude along the coast of Antarctica, easterly winds and two or three cyclones per year are usually observed, most often in July - August.
In July, the highest air temperatures in the surface layer of the atmosphere are observed at the top of the Persian Gulf (up to 34°C), the lowest - off the coast of Antarctica (-20°C), over the Arabian Sea and the Bay of Bengal on average 26-28°C. Over the Indian Ocean, air temperature almost everywhere varies in accordance with geographic latitude.
In the southern part of the Indian Ocean, it gradually decreases from north to south by about 1°C for every 150 km. In January, the highest air temperatures (26-28°C) are observed in equatorial belt, off the northern coasts of the Arabian Sea and Bay of Bengal - about 20°C. In the southern part of the ocean, the temperature gradually decreases from 26 ° C in the Southern Tropics to 0 ° C and slightly lower at the latitude of the Antarctic Circle. The amplitude of annual air temperature fluctuations over most of the Indian Ocean is on average less than 10°C and only off the coast of Antarctica increases to 16°C.
The greatest amount of precipitation per year falls in the Bay of Bengal (over 5500 mm) and off the eastern coast of the island of Madagascar (over 3500 mm). The northern coastal part of the Arabian Sea receives the least amount of precipitation (100-200 mm per year).
The northeastern Indian Ocean is located in seismically active areas. The eastern coast of Africa and the island of Madagascar, the shores of the Arabian Peninsula and the Hindustan Peninsula, almost all island archipelagos of volcanic origin, the western shores of Australia, especially the arc of the Sunda Islands, have been repeatedly exposed to tsunami waves in the past different strengths, even catastrophic. In 1883, after the explosion of the Krakatau volcano in the Jakarta area, a tsunami with a wave height of over 30 m was recorded; in 2004, a tsunami caused by an earthquake in the area of the island of Sumatra had catastrophic consequences.
Hydrological regime. Seasonality in changes in hydrological characteristics (primarily temperature and currents) is most clearly manifested in the northern part of the ocean. The summer hydrological season here corresponds to the duration of the southwest monsoon (May - September), the winter - to the northeast monsoon (November - March). A feature of the seasonal variability of the hydrological regime is that the restructuring of hydrological fields is somewhat delayed relative to the meteorological fields.
Water temperature. In the winter of the Northern Hemisphere, the highest water temperatures in the surface layer are observed in the equatorial zone - from 27°C off the coast of Africa to 29°C or more east of the Maldives. In the northern regions of the Arabian Sea and Bay of Bengal, the water temperature is about 25°C. The southern part of the Indian Ocean is characterized by a zonal temperature distribution, which gradually decreases from 27-28°C at 20°S latitude to negative values at the edge of the drifting ice, located at approximately 65-67°S latitude. In the summer season, the highest water temperatures in the surface layer are observed in the Persian Gulf (up to 34°C), in the north-west of the Arabian Sea (up to 30°C), and in the eastern part of the equatorial zone (up to 29°C). In the coastal areas of the Somali and Arabian peninsulas, abnormally low values (sometimes less than 20°C) are observed at this time of year, which is the result of the rise to the surface of cooled deep waters in the Somali Current system. In the southern part of the Indian Ocean, the distribution of water temperature throughout the year remains zonal, with the difference that its negative values in the winter of the Southern Hemisphere are found much further north, already around 58-60° south latitude. The amplitude of annual fluctuations in water temperature in the surface layer is small and averages 2-5°C; only in the area of the Somali coast and in the Gulf of Oman in the Arabian Sea does it exceed 7°C. The water temperature quickly decreases vertically: at a depth of 250 m it almost everywhere drops below 15°C, deeper than 1000 m - below 5°C. At a depth of 2000 m, temperatures above 3°C are observed only in the northern part of the Arabian Sea, in the central regions - about 2.5°C, in the southern part it decreases from 2°C at 50° south latitude to 0°C off the coast of Antarctica. Temperatures in the deepest (over 5000 m) basins range from 1.25°C to 0°C.
The salinity of surface waters of the Indian Ocean is determined by the balance between the amount of evaporation and the total amount of precipitation and river flow for each region. The absolute maximum salinity (over 40‰) is observed in the Red Sea and the Persian Gulf, in the Arabian Sea everywhere, with the exception of a small area in the southeastern part, salinity is above 35.5‰, in the band of 20-40° south latitude - more than 35‰ . The area of low salinity is located in the Bay of Bengal and in the area adjacent to the Sunda Islands arc, where fresh river flow is high and precipitation is greatest. In the northern part of the Bay of Bengal in February, salinity is 30-31‰, in August - 20‰. A vast tongue of water with salinity up to 34.5‰ at 10° south latitude extends from the island of Java to 75° east longitude. In Antarctic waters, salinity is everywhere below the average oceanic value: from 33.5‰ in February to 34.0‰ in August, its changes are determined by slight salinization during the formation of sea ice and corresponding freshening during the melting of ice. Seasonal changes salinity is noticeable only in the upper, 250-meter layer. With increasing depth, not only do they attenuate seasonal variations, but also spatial variability of salinity; deeper than 1000 m it ranges from 35-34.5‰.
Density. Highest density water in the Indian Ocean is observed in the Suez and Persian Gulfs (up to 1030 kg/m 3) and in the cold Antarctic waters (1027 kg/m 3), average - in the warmest and saltiest waters in the northwest (1024-1024.5 kg /m3), the smallest - in the most desalinated waters in the northeastern part of the ocean and in the Bay of Bengal (1018-1022 kg/m3). With depth, mainly due to a decrease in water temperature, its density increases, sharply increasing in the so-called jump layer, which is most noticeably expressed in the equatorial zone of the ocean.
Ice mode. The severity of the climate in the southern Indian Ocean is such that the formation of sea ice (at air temperatures below -7°C) can occur almost all year round. The ice cover reaches its greatest development in September - October, when the width of the drifting ice belt reaches 550 km, the smallest - in January - February. Ice cover is characterized by great seasonal variability and its formation occurs very quickly. The ice edge moves north at a speed of 5-7 km/day, and retreats just as quickly (up to 9 km/day) to the south during the melting period. Fast ice is established annually, reaches an average width of 25-40 km and almost completely melts by February. Drifting ice off the coast of the continent moves under the influence of katabatic winds in a general direction to the west and northwest. Near the northern edge, the ice drifts eastward. A characteristic feature of the Antarctic ice sheet is the large number of icebergs breaking off from the outlet and shelf glaciers of Antarctica. Table-shaped icebergs are especially large, which can reach a gigantic length of several tens of meters, rising 40-50 m above the water. Their number quickly decreases as they move away from the shores of the mainland. The average lifespan of large icebergs is 6 years.
Currents. The circulation of surface waters in the northern part of the Indian Ocean is formed under the influence of monsoon winds and therefore varies significantly from the summer to the winter season. In February, from 8° north latitude near the Nicobar Islands to 2° north latitude off the coast of Africa, the surface winter Monsoon current passes at speeds of 50-80 cm/s; with a core passing approximately 18° south latitude, the Southern Trade Wind Current, which has average speed on the surface about 30 cm/s. Connecting off the coast of Africa, the waters of these two streams give rise to the Intertrade Countercurrent, which carries its waters to the east with velocities in the core of about 25 cm/s. Along the North African coast from general direction to the south the waters of the Somali Current move, partially turning into the Intertrade Countercurrent, and to the south - the Mozambique and Cape Agulhas currents, moving south at speeds of about 50 cm/s. Part of the South Trade Wind Current off the eastern coast of the island of Madagascar turns south along it (Madagascar Current). South of 40° south latitude, the entire ocean area is crossed from west to east by the flow of the longest and most powerful current in the World Ocean, the Western Winds (Antarctic Circumpolar Current). The velocities in its rods reach 50 cm/s, and the flow rate is about 150 million m 3 /s. At 100-110° east longitude, a stream branches off from it, heading north and giving rise to the Western Australian Current. In August, the Somali Current follows a general direction to the northeast and, at a speed of up to 150 cm/s, pushes water into the northern part of the Arabian Sea, from where the Monsoon Current, skirting the western and southern shores of the Hindustan Peninsula and the island of Sri Lanka, carries water to the shores of the island Sumatra turns south and merges with the waters of the South Trade Wind Current. Thus, an extensive clockwise gyre is created in the northern part of the Indian Ocean, consisting of the Monsoon, South Trade Wind and Somali Currents. In the southern part of the ocean, the pattern of currents changes little from February to August. Off the coast of Antarctica, in a narrow coastal strip, a current caused by katabatic winds and directed from east to west is observed all year round.
Water masses. In the vertical structure of the water masses of the Indian Ocean, according to hydrological characteristics and depth, surface, intermediate, deep and bottom waters are distinguished. Surface waters are distributed in a relatively thin surface layer and, on average, occupy the upper 200-300 m. From north to south, water masses are distinguished in this layer: Persian and Arabian in the Arabian Sea, Bengal and South Bengal in the Bay of Bengal; further, south of the equator - Equatorial, Tropical, Subtropical, Subantarctic and Antarctic. As the depth increases, the differences between neighboring water masses decrease and their number decreases accordingly. Thus, in intermediate waters, the lower limit of which reaches 2000 m in temperate and low latitudes and up to 1000 m in high latitudes, the Persian and Red Sea in the Arabian Sea, the Bengal in the Bay of Bengal, the Subantarctic and Antarctic intermediate water masses are distinguished. Deep waters are represented by the North Indian, Atlantic (in the western part of the ocean), Central Indian (in the eastern part) and Circumpolar Antarctic water masses. Bottom waters everywhere, except the Bay of Bengal, are represented by one Antarctic bottom water mass, filling all deep-sea basins. Upper limit bottom water is located on average at a horizon of 2500 m off the coast of Antarctica, where it is formed, up to 4000 m in the central regions of the ocean and rises to almost 3000 m north of the equator.
Tides and swells. Semidiurnal and irregular semidiurnal tides are most common on the shores of the Indian Ocean. Semidiurnal tides are observed on the African coast south of the equator, in the Red Sea, off the northwestern coast of the Persian Gulf, in the Bay of Bengal, and off the northwestern coast of Australia. Irregular semidiurnal tides - off the Somali Peninsula, in the Gulf of Aden, off the coast of the Arabian Sea, in the Persian Gulf, off the southwestern coast of the Sunda island arc. Diurnal and irregular tides occur off the western and southern coasts of Australia. The highest tides are off the northwestern coast of Australia (up to 11.4 m), in the mouth zone of the Indus (8.4 m), in the mouth zone of the Ganges (5.9 m), off the coast of the Mozambique Strait (5.2 m) ; in the open ocean, tides vary from 0.4 m near the Maldives to 2.0 m in the southeastern Indian Ocean. The excitement reaches greatest strength in temperate latitudes in the zone of action of westerly winds, where the frequency of waves over 6 m in height is 17% per year. Waves with a height of 15 m and a length of 250 m were recorded near the Kerguelen Island, and 11 m and 400 m, respectively, off the coast of Australia.
Flora and fauna. The main part of the Indian Ocean is located within the tropical and southern temperate zones. The absence of a northern high-latitude region in the Indian Ocean and the action of monsoons lead to two differently directed processes that determine the characteristics of the local flora and fauna. The first factor complicates deep-sea convection, which negatively affects the renewal of deep waters of the northern part of the ocean and the increase in oxygen deficiency in them, which is especially pronounced in the Red Sea intermediate water mass, which leads to a depletion of species composition and reduces the total biomass of zooplankton in the intermediate layers. When oxygen-poor waters in the Arabian Sea reach the shelf, local death occurs (death of hundreds of thousands of tons of fish). At the same time, the second factor (monsoons) forms in coastal areas favorable conditions for high biological productivity. Under the influence of the summer monsoon, water is driven along the Somali and Arabian coasts, which causes powerful upwelling, bringing water rich in nutritious salts to the surface. The winter monsoon, although to a lesser extent, leads to seasonal upwelling with similar consequences off the western coast of the Indian subcontinent.
The coastal zone of the ocean has the greatest species diversity. The shallow waters of the tropical zone are characterized by numerous 6- and 8-rayed madrepore corals and hydrocorals that, together with red algae, can create underwater reefs and atolls. Among the powerful coral structures lives a rich fauna of various invertebrates (sponges, worms, crabs, mollusks, sea urchins, brittle stars and starfish), small but brightly colored coral reef fish. Most of the coasts are occupied by mangroves. At the same time, the fauna and flora of beaches and rocks that dry out at low tide are quantitatively depleted due to the depressing effect of sunlight. In the temperate zone, life on such sections of the coast is much richer; Dense thickets of red and brown algae (kelp, fucus, macrocystis) develop here, and a variety of invertebrates are abundant. According to L.A. Zenkevich (1965), over 99% of all species of bottom and benthic animals living in the ocean live in the littoral and sublittoral zones.
For open spaces The Indian Ocean, especially the surface layer, is also characterized by a rich flora. food chain in the ocean it begins with microscopic single-celled plant organisms - phytoplankton, which inhabit mainly the uppermost (about 100-meter) layer of ocean waters. Among them, several species of peridinian and diatom algae predominate, and in the Arabian Sea - cyanobacteria (blue-green algae), which often cause mass development so-called water bloom. In the northern Indian Ocean, there are three areas of highest phytoplankton production: the Arabian Sea, Bay of Bengal and Andaman Sea. The greatest production is observed off the coast of the Arabian Peninsula, where the number of phytoplankton sometimes exceeds 1 million cells/l (cells per liter). Its high concentrations are also observed in the subantarctic and Antarctic zones, where during the spring flowering period there are up to 300,000 cells/l. The lowest phytoplankton production (less than 100 cells/l) is observed in the central part of the ocean between parallels 18 and 38° south latitude.
Zooplankton inhabits almost the entire thickness of oceanic waters, but its quantity quickly decreases with increasing depth and decreases by 2-3 orders of magnitude towards the bottom layers. The food for most zooplankton, especially those living in the upper layers, is phytoplankton, so the patterns of spatial distribution of phyto- and zooplankton are largely similar. The highest levels of zooplankton biomass (from 100 to 200 mg/m3) are observed in the Arabian and Andaman seas, the Bengal, Aden and Persian Gulfs. The main biomass of ocean animals consists of copepod crustaceans (more than 100 species), with slightly less pteropods, jellyfish, siphonophores and other invertebrate animals. Radiolarians are typical of unicellular organisms. The Antarctic region of the Indian Ocean is characterized by a huge number of euphausian crustaceans of several species, collectively called “krill”. Euphausiids create the main food supply for the largest animals on Earth - baleen whales. In addition, fish, seals, cephalopods, penguins and other bird species feed on krill.
Organisms that move freely in the marine environment (nekton) are represented in the Indian Ocean mainly by fish, cephalopods, and cetaceans. Among the cephalopods common in the Indian Ocean are cuttlefish, numerous squids and octopuses. Of the fish, the most abundant are several species of flying fish, luminous anchovies (coryphaenas), sardinella, sardine, mackerel, nototheniids, groupers, several types of tuna, blue marlin, grenadier, sharks, and rays. Warm waters are home to sea turtles and poisonous sea snakes. The fauna of aquatic mammals is represented by various cetaceans. The most common baleen whales are: blue whale, sei whale, fin whale, humpback whale, Australian (Cape) and Chinese whales. Toothed whales are represented by sperm whales and several species of dolphins (including killer whales). In the coastal waters of the southern part of the ocean, pinnipeds are widespread: the Weddell seal, the crabeater seal, fur seals - Australian, Tasmanian, Kerguelen and South African, Australian sea lion, leopard seal, etc. Among the birds, the most typical are the wandering albatross, petrels, great frigatebird, phaetons , cormorants, gannets, skuas, terns, gulls. South of 35° south latitude, on the coasts of South Africa, Antarctica and the islands, there are numerous colonies of several species of penguins.
In 1938, a unique biological phenomenon was discovered in the Indian Ocean - a living lobe-finned fish, Latimeria chalumnae, which was considered extinct tens of millions of years ago. “Fossil” coelacanth lives at a depth of over 200 m in two places - near the Comoros Islands and in the waters of the Indonesian archipelago.
History of the study
The northern coastal areas, especially the Red Sea and the deeply incised bays, began to be used by humans for navigation and fishing already in the era of ancient civilizations, several thousand years BC. 600 years BC, Phoenician sailors, in the service of the Egyptian pharaoh Necho II, circumnavigated Africa. In 325-324 BC, Alexander the Great's comrade Nearchus, commanding a fleet, sailed from India to Mesopotamia and compiled the first descriptions of the coastline from the mouth of the Indus River to the top of the Persian Gulf. In the 8th-9th centuries, the Arabian Sea was intensively explored by Arab navigators, who created the first sailing directions and navigation guides for this area. In the 1st half of the 15th century, Chinese sailors under the leadership of Admiral Zheng He made a series of voyages along the Asian coast to the west, reaching the coast of Africa. In 1497-99, the Portuguese Gama (Vasco da Gama) laid out for the Europeans sea route to India and countries South-East Asia. A few years later, the Portuguese discovered the island of Madagascar, Amirante, Comoros, Mascarene and Seychelles. Following the Portuguese, the Dutch, French, Spanish and British entered the Indian Ocean. The name "Indian Ocean" first appeared on European maps in 1555. In 1772-75, J. Cook penetrated the Indian Ocean to 71° south latitude and made the first deep-sea measurements. Oceanographic research in the Indian Ocean began with systematic measurements of water temperature during the circumnavigation of the Russian ships "Rurik" (1815-18) and "Enterprise" (1823-26). In 1831-36, an English expedition took place on the ship Beagle, on which Charles Darwin carried out geological and biological work. Complex oceanographic measurements in the Indian Ocean were carried out during the British expedition on the Challenger ship in 1873-74. Oceanographic work in the northern part of the Indian Ocean was carried out in 1886 by S. O. Makarov on the ship “Vityaz”. In the 1st half of the 20th century, oceanographic observations began to be made regularly, and by the 1950s they were carried out at almost 1,500 deep-sea oceanographic stations. In 1935, P. G. Schott’s monograph “Geography of the Indian and Pacific Oceans” was published - the first major publication that summarized the results of all previous studies in this region. In 1959, the Russian oceanographer A. M. Muromtsev published a fundamental work - “The Main Features of the Hydrology of the Indian Ocean.” In 1960-65, UNESCO's Scientific Committee on Oceanography conducted the International Indian Ocean Expedition (IIOE), the largest of those previously operating in the Indian Ocean. Scientists from more than 20 countries (USSR, Australia, Great Britain, India, Indonesia, Pakistan, Portugal, USA, France, Germany, Japan, etc.) took part in the MIOE program. During the MIOE, major geographical discoveries were made: the underwater West Indian and East Indian ridges, zones tectonic faults- Owen, Mozambique, Tasmanian, Diamantina, etc., seamounts - Ob, Lena, Afanasia Nikitina, Bardina, Zenit, Equator, etc., deep-sea trenches - Ob, Chagos, Vima, Vityaz, etc. In the history of the study of the Indian Ocean, especially highlights the results of research carried out in 1959-77 by the research vessel “Vityaz” (10 voyages) and dozens of others Soviet expeditions on ships of the Hydrometeorological Service and the State Fisheries Committee. Since the early 1980s, ocean research has been carried out within 20 international projects. Research in the Indian Ocean was especially intensified during the World Ocean Circulation Experiment (WOCE). Since its successful completion in the late 1990s, the amount of current oceanographic information on the Indian Ocean has doubled.
Economic use
The coastal zone of the Indian Ocean has an exceptionally high population density. There are over 35 states on the coasts and islands of the ocean, home to about 2.5 billion people (over 30% of the Earth's population). The bulk of the coastal population is concentrated in South Asia (more than 10 cities with a population of over 1 million people). In most countries in the region there are acute problems of obtaining living space, creating jobs, providing food, clothing and housing, and medical care.
The Indian Ocean, like other seas and oceans, is used in several main areas: transport, fishing, mining, and recreation.
Transport. The role of the Indian Ocean in maritime transport increased significantly with the creation of the Suez Canal (1869), which opened a short sea route for communication with states washed by the waters of the Atlantic Ocean. The Indian Ocean is an area for transit and export of all kinds of raw materials, in which almost all major seaports are of international importance. In the northeastern part of the ocean (in the Malacca and Sunda Straits) there are routes for ships traveling to the Pacific Ocean and back. The main export item to the USA, Japan and Western European countries is crude oil from the Persian Gulf region. In addition, products are exported Agriculture- natural rubber, cotton, coffee, tea, tobacco, fruits, nuts, rice, wool; wood; mineral raw materials - coal, iron ore, nickel, manganese, antimony, bauxite, etc.; machinery, equipment, tools and hardware, chemical and pharmaceutical products, textiles, processed gemstones and jewelry. The Indian Ocean accounts for about 10% of global shipping traffic; at the end of the 20th century, about 0.5 billion tons of cargo were transported through its waters per year (according to IOC). According to these indicators, it ranks 3rd after the Atlantic and Pacific oceans, inferior to them in terms of shipping intensity and total volume of cargo transportation, but surpassing all other sea transport communications in terms of oil transportation volume. The main transport routes along the Indian Ocean are towards the Suez Canal, the Strait of Malacca, the southern tips of Africa and Australia and along the northern coast. Shipping is most intense in the northern regions, although it is limited by storm conditions during the summer monsoon, and less intense in the central and southern regions. The growth of oil production in the Persian Gulf countries, Australia, Indonesia and other places contributed to the construction and modernization of oil ports and the appearance of giant tankers in the Indian Ocean.
The most developed transport routes for the transportation of oil, gas and petroleum products: Persian Gulf - Red Sea - Suez Canal - Atlantic Ocean; Persian Gulf - Strait of Malacca - Pacific Ocean; Persian Gulf - southern tip of Africa - Atlantic Ocean (especially before the reconstruction of the Suez Canal, 1981); Persian Gulf - Australian coast (port of Fremantle). Mineral and agricultural raw materials, textiles, precious stones, jewelry, equipment, and computer equipment are transported from India, Indonesia, and Thailand. From Australia, coal, gold, aluminum, alumina, iron ore, diamonds, uranium ores and concentrates, manganese, lead, zinc are transported; wool, wheat, meat products, as well as engines internal combustion, passenger cars, electrical products, river vessels, glass products, rolled steel, etc. Oncoming flows are dominated by industrial goods, automobiles, electronic equipment, etc. Passenger transportation occupies an important place in the transport use of the Indian Ocean.
Fishing. Compared to other oceans, the Indian Ocean has a relatively low biological productivity, the production of fish and other seafood accounts for 5-7% of the total world catch. Fishing and non-fishery fishing is concentrated mainly in the northern part of the ocean, and in the west it is twice as much as in the eastern part. The largest volumes of bioproduct production are observed in the Arabian Sea off the western coast of India and off the coast of Pakistan. Shrimp are harvested in the Persian and Bengal Bays, and lobsters are harvested off the east coast of Africa and on tropical islands. In open ocean areas in the tropical zone, tuna fishing is widely developed, carried out by countries with well-developed fishing fleets. In the Antarctic region, nototheniids, icefish and krill are caught.
Mineral resources. Deposits of oil and natural combustible gas or oil and gas shows have been identified almost throughout the entire shelf area of the Indian Ocean. The most industrially important are the actively developed oil and gas fields in the Gulfs: Persian (Persian Gulf oil and gas basin), Suez (oil and gas basin of the Gulf of Suez), Cambay (Kambay oil and gas basin), Bengal (Bengal oil and gas basin); off the northern coast of the island of Sumatra (North Sumatra oil and gas basin), in the Timor Sea, off the northwestern coast of Australia (Carnarvon oil and gas basin), in Bass Strait (Gippsland oil and gas basin). Gas deposits have been explored in the Andaman Sea, oil and gas bearing areas in the Red Sea, Gulf of Aden, and along the coast of Africa. Coastal-sea placers of heavy sands are developed off the coast of the island of Mozambique, along the southwestern and northeastern coasts of India, off the northeastern coast of the island of Sri Lanka, along the southwestern coast of Australia (mining ilmenite, rutile, monazite and zircon); in the coastal areas of Indonesia, Malaysia, Thailand (cassiterite mining). Industrial accumulations of phosphorites have been discovered on the shelves of the Indian Ocean. Large fields of ferromanganese nodules, a promising source of Mn, Ni, Cu, and Co, have been established on the ocean floor. In the Red Sea, metal-bearing brines and sediments identified are potential sources for the production of iron, manganese, copper, zinc, nickel, etc.; There are deposits of rock salt. In the coastal zone of the Indian Ocean, sand, gravel, and limestone are mined for construction and glass production.
Recreational resources. From the 2nd half of the 20th century great importance for the economy of coastal countries has use recreational resources ocean. Old resorts are being developed and new ones are being built on the coasts of continents and on numerous tropical islands in the ocean. The most visited resorts are in Thailand (Phuket Island, etc.) - over 13 million people a year (together with the coast and islands of the Gulf of Thailand in the Pacific Ocean), in Egypt [Hurghada, Sharm el-Sheikh (Sharm el-Sheikh), etc. ] - over 7 million people, in Indonesia (the islands of Bali, Bintan, Kalimantan, Sumatra, Java, etc.) - over 5 million people, in India (Goa, etc.), in Jordan (Aqaba), in Israel (Eilat) , in the Maldives, in Sri Lanka, in the Seychelles, on the islands of Mauritius, Madagascar, South Africa, etc.
Sharm el-Sheikh. Hotel Concorde.
Port cities. On the shores of the Indian Ocean there are specialized oil loading ports: Ras Tanura ( Saudi Arabia), Kharq (Iran), Ash-Shuaiba (Kuwait). The largest ports of the Indian Ocean: Port Elizabeth, Durban (South Africa), Mombasa (Kenya), Dar es Salaam (Tanzania), Mogadishu (Somalia), Aden (Yemen), Kuwait City (Kuwait), Karachi (Pakistan), Mumbai, Chennai, Kolkata, Kandla (India), Chittagong (Bangladesh), Colombo (Sri Lanka), Yangon (Myanmar), Fremantle, Adelaide and Melbourne (Australia).
Lit.: Geological and geophysical atlas of the Indian Ocean. M., 1975; Kanaev V.F. Relief of the bottom of the Indian Ocean. M., 1979; Indian Ocean. L., 1982; Udintsev G. B. Regional geomorphology of the ocean floor. Indian Ocean. M., 1989; Lithosphere of the Indian Ocean: according to geophysical data / Ed. A. V. Chekunov, Yu. P. Neprochnov. K., 1990; Neiman V. G., Burkov V. A., Shcherbinin A. D. Dynamics of Indian Ocean waters. M., 1997; Pushcharovsky Yu. M. Tectonics of the Earth. Favorite works. M., 2005. T. 2: Tectonics of the oceans.
M. G. Deev; N. N. Turko (geological structure).
The Indian Ocean makes up 20% of the World Ocean by volume. It is bounded by Asia to the north, Africa to the west and Australia to the east.
In the zone 35° S. passes the conventional border with the Southern Ocean.
Description and characteristics
The waters of the Indian Ocean are famous for their transparency and azure color. The fact is that few freshwater rivers, these “troublemakers,” flow into this ocean. Therefore, by the way, the water here is much saltier than in others. It is in the Indian Ocean that the saltiest sea in the world, the Red Sea, is located.
The ocean is also rich in minerals. The area near Sri Lanka has been famous for its pearls, diamonds and emeralds since ancient times. And the Persian Gulf is rich in oil and gas.
Area: 76.170 thousand sq. km
Volume: 282.650 thousand cubic km
Average depth: 3711 m, greatest depth - Sunda Trench (7729 m).
Average temperature: 17°C, but in the north the waters warm up to 28°C.
Currents: two cycles are conventionally distinguished - northern and southern. Both move clockwise and are separated by the Equatorial Countercurrent.
Main currents of the Indian Ocean
Warm:
Northern Passatnoe- originates in Oceania, crosses the ocean from east to west. Beyond the peninsula, Hindustan is divided into two branches. Part flows to the north and gives rise to the Somali Current. And the second part of the flow heads south, where it merges with the equatorial countercurrent.
South Passatnoe- begins at the islands of Oceania and moves from east to west all the way to the island of Madagascar.
Madagascar- branches off from the South Passat and flows parallel to the Mozambique from north to south, but slightly east of the Madagascar coast. Average temperature: 26°C.
Mozambican- another branch of the South Trade Wind Current. It washes the coast of Africa and in the south merges with the Agulhas Current. Average temperature - 25°C, speed - 2.8 km/h.
Agulhas, or Cape Agulhas Current- narrow and fast current, running along the east coast of Africa from north to south.
Cold:
Somali- a current off the coast of the Somali Peninsula, which changes its direction depending on the monsoon season.
Current of the West Winds encircles the globe in southern latitudes. In the Indian Ocean from it is the South Indian Ocean, which, near the coast of Australia, turns into the Western Australian Ocean.
Western Australian- moves from south to north along the western coast of Australia. As you approach the equator, the water temperature rises from 15°C to 26°C. Speed: 0.9-0.7 km/h.
The underwater world of the Indian Ocean
Most of the ocean is located in the subtropical and tropical zones, and is therefore rich and diverse in species.
The tropical coastline is represented by vast thickets of mangroves, home to numerous colonies of crabs and amazing fish - mudskippers. Shallow waters provide excellent habitat for corals. And in temperate waters brown, calcareous and red algae grow (kelp, macrocysts, fucus).
Invertebrate animals: numerous mollusks, a huge number of species of crustaceans, jellyfish. There are many sea snakes, especially poisonous ones.
Sharks of the Indian Ocean are the special pride of the water area. The largest number of shark species live here: blue, gray, tiger, great white, mako, etc.
Of the mammals, the most common are dolphins and killer whales. A South part the ocean is natural environment habitat of many species of whales and pinnipeds: dugongs, fur seals, seals. The most common birds are penguins and albatrosses.
Despite the richness of the Indian Ocean, seafood fishing here is poorly developed. The catch is only 5% of the world's. Tuna, sardines, stingrays, lobsters, lobsters and shrimp are caught.
Indian Ocean exploration
The coastal countries of the Indian Ocean are centers of ancient civilizations. That is why the development of the water area began much earlier than, for example, the Atlantic or Pacific Ocean. Approximately 6 thousand years BC. The waters of the ocean were already plied by the shuttles and boats of ancient people. The inhabitants of Mesopotamia sailed to the shores of India and Arabia, the Egyptians conducted a lively maritime trade with the countries of East Africa and the Arabian Peninsula.
Key dates in the history of ocean exploration:
7th century AD - Arab sailors compiled detailed navigation maps of the coastal zones of the Indian Ocean, explored the waters near the eastern coast of Africa, India, the islands of Java, Ceylon, Timor, and the Maldives.
1405-1433 - seven sea travel Zheng He and the study of trade routes in the northern and eastern parts of the ocean.
1497 - Vasco de Gama's voyage and exploration of the eastern coast of Africa.
(Expedition of Vasco de Gama in 1497)
1642 - two raids by A. Tasman, exploration of the central part of the ocean and discovery of Australia.
1872-1876 - the first scientific expedition of the English corvette Challenger, studying the biology of the ocean, relief, and currents.
1886-1889 - expedition of Russian explorers led by S. Makarov.
1960-1965 - international Indian Ocean expedition established under the auspices of UNESCO. Study of hydrology, hydrochemistry, geology and ocean biology.
1990s - present day: studying the ocean using satellites, compiling a detailed bathymetric atlas.
2014 - after the crash of a Malaysian Boeing, detailed mapping of the southern part of the ocean was carried out, new underwater ridges and volcanoes were discovered.
The ancient name of the ocean is Eastern.
Many species of wildlife in the Indian Ocean have unusual property- they glow. In particular, this explains the appearance of luminous circles in the ocean.
In the Indian Ocean, ships are periodically found in good condition, however, where the entire crew disappears remains a mystery. Over the last century, this happened to three ships at once: the Cabin Cruiser, the tankers Houston Market and Tarbon.