Which countries are washed by the Indian Ocean list. Indian Ocean description, interesting facts

The school course of the program in geography includes the study of the largest water areas - the oceans. This topic is quite interesting. Students are happy to prepare reports and abstracts on it. This article will provide information that contains a description of the geographical position of the Indian Ocean, its characteristics and features. So let's get started.

Brief description of the Indian Ocean

By scale and quantity of water reserves Indian Ocean comfortably located in third place, losing to the Pacific and Atlantic. A significant part of it is located on the territory of the Southern Hemisphere of our planet, and its natural aisles are:

• Southern part of Eurasia in the north.
• East coast of Africa in the west.
• northern and north western shores Australia in the east.
• Northern part of Antarctica in the south.

In order to specify the exact geographical position Indian Ocean, you need a map. It can also be used during a presentation. So, on the world map, the water area has the following coordinates: 14°05′33.68″ south latitude and 76°18′38.01″ east longitude.

According to one version, the ocean in question was first called Indian in the work of the Portuguese scientist S. Munster called "Cosmography", which was published in 1555.

Characteristic

The total, taking into account all the seas included in its composition, is 76.174 million square meters. km, the depth (average) is more than 3.7 thousand meters, and the maximum was recorded at over 7.7 thousand meters.

The geographical position of the Indian Ocean has its own characteristics. Due to its large size, it is found in several climatic zones. It is also worth paying attention to the size of the water area. For example, the maximum width is between Linde Bay and the Toros Strait. The length from west to east is almost 12 thousand km. And if we consider the ocean from north to south, then the largest indicator will be from Cape Ras Jaddi to Antarctica. This distance is 10.2 thousand km.

Features of the water area

Studying the features of the geographical position of the Indian Ocean, it is necessary to consider its boundaries. First, note that the entire water area is located in the Eastern Hemisphere. On the southwest side, it borders the Atlantic Ocean. In order to see this place on the map, you need to find 20 ° along the meridian in. e. The border with the Pacific Ocean is in the southeast. It runs along the 147° meridian east. e. With the North Arctic Ocean Indian not reported. Its border in the north is the largest continent - Eurasia.

The structure of the coastline has a weak dismemberment. There are several large bays and 8 seas. There are relatively few islands. The largest are Sri Lanka, Seychelles, Curia-Muria, Madagascar, etc.

Bottom relief

The characterization will not be complete if you do not consider the features of the relief.

The Central Indian Ridge is an underwater formation located in the central part of the water area. Its length is about 2.3 thousand km. The width of the relief formation is within 800 km. The height of the ridge is more than 1 thousand meters. Some peaks protrude from the water, forming volcanic islands.

The West Indian Ridge is located in the southwestern part of the ocean. There is a lot of seismic activity here. The length of the ridge is about 4 thousand km. But in width it is less than the previous one by about half.

The Arabian-Indian Range is an underwater relief formation. It is located in the northwestern part of the water area. Its length is slightly less than 4 thousand km, and its width is about 650 km. At the end point (Rodriguez Island) it passes into the Central Indian Range.

The bottom of the Indian Ocean consists of sediments from the Cretaceous period. In some places, their thickness reaches 3 km. has a length of about 4500 km in length, and its width varies from 10 to 50 km. It's called Javanese. The depth of the depression is 7729 m (the largest in the Indian Ocean).

Climatic features

One of the most important circumstances in the formation of climate is the geographical position of the Indian Ocean relative to the equator. It divides the water area into two parts (the largest is in the south). Naturally, this arrangement affects temperature fluctuations and rainfall. The highest temperatures were recorded in the waters of the Red Sea and the Persian Gulf. Here, the average is a mark of +35 ° С. And in the southern point, the temperature can drop to -16 ° C in winter and up to -4 degrees in summer.

The northern part of the ocean is located in a hot climate zone, due to which its waters are among the warmest in the oceans. Here it is mainly influenced by the Asian continent. Due to the current situation in the northern part, there are only two seasons - a hot rainy summer and a non-cold cloudless winter. As for the climate in this part of the water area, it practically does not change throughout the year.

Given the geographical position of the Indian Ocean, it is worth noting that its largest part is under the influence of air currents. From this we can conclude that the climate is mainly formed due to the monsoons. During the summer period, areas with low pressure are established over land, and areas with high pressure over the ocean. During this season, the wet monsoon runs from west to east. In winter, the situation changes, and then the dry monsoon begins to dominate, which comes from the east and moves to the west.

In the southern part of the water area, the climate is more severe, since it lies in the subarctic zone. Here, the ocean is influenced by proximity to Antarctica. Off the coast of this continent, the average temperature is fixed at around -1.5 ° C, and the buoyancy limit of ice reaches 60 ° parallel.

Summing up

The geographical position of the Indian Ocean is a very important issue that deserves special attention. Due to its large size, this area has many features. Along the coastline there are a huge number of cliffs, estuaries, atolls, coral reefs. It is also worth noting such islands as Madagascar, Socotra, Maldives. They represent sections A Andaman, Nicobar descended from volcanoes that rose to the surface.

Having studied the proposed material, each student will be able to present an informative and interesting presentation.

It has the fewest seas. It has a peculiar bottom topography, and in the northern part - a special system of winds and sea currents.

Mostly located in the Southern Hemisphere between, and. Its coastline is slightly indented, with the exception of the northern and northeastern parts, where almost all the seas and large bays are located.

Unlike other oceans, the mid-ocean ridges of the Indian Ocean consist of three branches radiating from its central part. The ridges are dissected by deep and narrow longitudinal depressions - grabens. One of these huge grabens is the Red Sea depression, which is a continuation of the faults in the axial part of the Arabian-Indian mid-ocean ridge.

Mid-ocean ridges divide the bed into 3 large sections that are part of three different ones. The transition from the ocean floor to the continents is gradual everywhere, only in the northeastern part of the ocean is the arc of the Sunda Islands, under which the Indo-Australian lithospheric plate plunges. Therefore, a deep-sea trench about 4000 km long stretches along these islands. There are over a hundred active volcanoes, among which the famous - Krakatau, earthquakes often occur.

At the surface of the Indian Ocean depends on the geographical latitude. The northern part of the Indian Ocean is much warmer than the southern part.

Monsoons form in the northern part of the Indian Ocean (to the north of 10 S). In summer, the southwest summer monsoon blows here, carrying moist equatorial air from the sea to land, in winter - the northeast winter monsoon, carrying dry tropical air from the continent.

The system of surface currents in the southern half of the Indian Ocean is similar to the system of currents in the corresponding latitudes of the Pacific and Atlantic oceans. However, north of 10°N. arises special treatment water movements: monsoonal seasonal currents appear, changing direction to the opposite twice a year.

The organic world of the Indian Ocean has much in common with the organic world of the Pacific and Atlantic Oceans in the corresponding latitudes. In the shallow waters of the hot zones, coral polyps are common, creating numerous reef structures, including islands. Among the fish, the most numerous are anchovies, tuna, flying fish, sailfish, and sharks. The tropical coasts of the mainland are often occupied by mangroves. They are characterized by peculiar plants with terrestrial respiratory roots and special animal communities (oysters, crabs, shrimps, mudskipper fish). The bulk of the ocean animals are invertebrate planktonic organisms. In tropical coastal areas, sea turtles, poisonous sea snakes, endangered mammals - dugongs are common. Whales, sperm whales, dolphins, and seals live in the cold waters of the southern part of the ocean. Among the birds, the penguins that inhabit the coast are the most interesting. South Africa, Antarctica and temperate ocean islands.

Natural resources and economic development

The Indian Ocean has great biological wealth, but fishing is mainly limited to coastal areas, where, in addition to fish, lobsters, shrimps, and mollusks are caught. In the open waters of hot zones, tuna is fished, and in cold waters - whales and krill.

The most important are oil and natural gas deposits. The Persian Gulf with the land adjacent to it stands out especially, where 1/3 of the oil of the foreign world is extracted.

In the last decades of the coast warm seas and the islands of the northern part of the ocean are becoming more and more attractive for people to relax, and the tourism business is booming here. Through the Indian Ocean, the volume of traffic is much less than through the Atlantic and Pacific Oceans. However, it plays an important role in the development of the countries of South and Southeast Asia.

The Indian Ocean ranks third in terms of area. At the same time, compared with others, the greatest depth of the Indian Ocean is very modest - only 7.45 kilometers.

Location

It is not difficult to find it on the map - the Asian part of Eurasia is located in the north of the ocean, Antarctica is located on the southern shores, and Australia lies in the east along the path of the currents. Africa is in the western part of it.

Most of the ocean area is located in the southern hemisphere. A very conditional line separates the Indian and - from Africa, down the twentieth meridian to Antarctica itself. It is separated from the Pacific by the Indochinese peninsulas of Malacca, the border goes to the north then along the line that on the map connects the islands of Sumatra, Java, Sumba and New Guinea. With the fourth - the Arctic - the Indian Ocean has no common borders.

Area

The average depth of the Indian Ocean is 3897 meters. At the same time, it occupies an area of ​​74,917 thousand kilometers, which allows it to be in third place in size among its "brothers". The shores of this huge reservoir are very weakly indented - this is the reason why there are few seas in its composition.

Relatively few islands lie in this ocean. The most significant of them once broke away from the mainland, so they are located close to the coastline - Socotra, Madagascar, Sri Lanka. Far from the coast, in the open part, you can find islands that originated from volcanoes. These are Crozet, Mascarensky and others. In the tropics, on the cones of volcanoes, there are islands of coral origin, such as the Maldives, Cocos, Adaman and others.

The shores in the east and northwest are indigenous, while in the west and northeast they are mostly alluvial. The edge of the coast is indented very weakly, except for its northern part. It is here that most of the large bays are concentrated.

Depth

Of course, on such a large area, the depth of the Indian Ocean cannot be the same - the maximum is 7130 meters. This point is located in the Sunda Trench. The average depth of the Indian Ocean is 3897 meters.

Sailors and water explorers cannot rely on the average figure. Therefore, scientists have long drawn up a map of the depths of the Indian Ocean. It accurately indicates the height of the bottom at various points, all the shoals, gutters, depressions, volcanoes and other features of the relief are visible.

Relief

Along the coast lies a narrow strip of continental shallows, about 100 kilometers wide. The edge of the shelf, located in the ocean, has a shallow depth - from 50 to 200 meters. Only in the northwest of Australia and along the Antarctic coast does it increase to 300-500 meters. The slope of the mainland is quite steep, in some places separated by underwater valleys of large rivers, such as the Ganges, Indus and others. In the northeast, the rather monotonous relief of the bottom of the Indian Ocean is enlivened by the Sunda Island Arc. It is here that the most significant depth of the Indian Ocean is found. The maximum point of this trough is located at 7130 meters below sea level.

Ridges, ramparts and mountains broke the bed into several basins. The most famous are the Arabian Basin, African-Antarctic and Western Australian. These depressions have formed hilly, located in the center of the ocean, and accumulative plains, located not far from the continents, in those areas where sedimentary material is supplied in sufficient quantities.

Among the large number of ridges, the East Indian is especially noticeable - its length is about 5 thousand kilometers. However, the relief of the bottom of the Indian Ocean has other significant ridges - the Western Australian, meridional and others. The bed is also rich in various volcanoes, in places forming chains and even rather large massifs.

Mid-ocean ridges - three branches of the mountain system, dividing the ocean from the center to the north, southeast and southwest. The width of the ranges ranges from 400 to 800 kilometers, the height is 2-3 kilometers. The relief of the bottom of the Indian Ocean in this part is characterized by faults across the ridges. Along them, the bottom is most often horizontally displaced by 400 kilometers.

Unlike the ridges, the Australo-Antarctic Rise is a rampart with gentle slopes, the height of which reaches a kilometer, while the width extends up to one and a half thousand kilometers.

The predominantly tectonic structures of the bottom of this particular ocean are quite stable. Active developing structures occupy a much smaller area and flow into similar structures in Indochina and East Africa. These main macrostructures are divided into smaller ones: plates, blocky and volcanic ridges, banks and coral islands, trenches, tectonic ledges, depressions of the Indian Ocean and others.

Among the various irregularities, a special place is occupied by the north of the Mascarene Range. Presumably, this part previously belonged to the long-lost ancient mainland Gondwana.

Climate

The area and depth of the Indian Ocean make it possible to assume that the climate in its different parts will be completely different. And indeed it is. The northern part of this huge body of water has a monsoonal climate. In the summer, during a period of low pressure over mainland Asia, southwestern flows of equatorial air predominate over the water. In winter, tropical air masses from the northwest dominate here.

A little south of 10 degrees south latitude, the climate over the ocean becomes much more constant. In tropical (and subtropical in summer) latitudes, southeast trade winds rule here. In temperate - extratropical cyclones that move from west to east. Hurricanes are often found in the west of tropical latitudes. Most often they sweep in the summer and autumn.

The air in the north of the ocean warms up to 27 degrees in summer. African coasts are blown with air with a temperature of about 23 degrees. In winter, the temperature drops depending on latitude: in the south it can be below zero, while in northern Africa the thermometer does not fall below 20 degrees.

The water temperature depends on the currents. The coast of Africa is washed by the Somali current, which has rather low temperatures. This leads to the fact that the water temperature in this region is kept at about 22-23 degrees. In the north of the ocean, the upper layers of water can reach a temperature of 29 degrees, while in the southern regions, off the coast of Antarctica, it drops to -1. Of course, we are talking only about the upper layers, since the greater the depth of the Indian Ocean, the more difficult it is to draw conclusions about the water temperature.

Water

The depth of the Indian Ocean does not affect the number of seas at all. And there are fewer of them than in any other ocean. mediterranean seas there are only two: Red and Persian Gulf. In addition, there is also the marginal Arabian Sea, the Andaman Sea, which is only partially enclosed. To the east of the vast waters are Timor and

The largest rivers in Asia belong to the basin of this ocean: the Ganges, Salween, Brahmaputra, Irwaddy, Indus, Euphrates and Tigris. Among the African rivers, it is worth highlighting the Limpopo and Zambezi.

The average depth of the Indian Ocean is 3897 meters. And in this column of water a unique phenomenon occurs - a change in the direction of currents. The currents of all other oceans are unchanged from year to year, while in the Indian currents are subject to winds: in winter they are monsoon, in summer they prevail.

Since the deep waters originate in the Red Sea and the Persian Gulf, almost all the water mass has a high salinity with a low percentage of oxygen.

coast

In the west and northeast, there are mainly alluvial shores, while in the northwest and east they are bedrock. As already mentioned, the coastline is almost flat, very weakly indented almost along the entire length of this water body. The exception is the northern part - it is here that most of the seas belonging to the Indian Ocean basin are concentrated.

inhabitants

The rather small average depth of the Indian Ocean boasts a wide variety of representatives of the animal and plant worlds. The Indian Ocean is located in the tropical and temperate zones. Shallow waters are full of corals and hydrocorals, among which lives great amount types of invertebrates. These are worms, and crabs, and sea ​​urchins, stars and other animals. An equal number of brightly colored tropical fish find shelter in these areas. The coasts are rich in mangroves, in which the mudskipper has settled - this fish can live for a very long time without water.

The flora and fauna of the beaches subject to low tide is very poor, as the hot sun rays destroy all living things here. in this sense, it is much more diverse: there is a rich selection of algae and invertebrates.

The open ocean is even richer in living beings - representatives of both the animal and plant worlds.

The main animals are copepods. More than a hundred species of them live in the waters of the Indian Ocean. Pteropods, siphonophores, jellyfish and other invertebrates are almost as numerous as species. Several species of flying fish, sharks, glowing anchovies, tuna, and sea snakes frolic in the waters of the ocean. Whales, pinnipeds, sea turtles, dugongs are no less common in these waters.

Feathered inhabitants are represented by albatrosses, frigates and several species of penguins.

Minerals

Oil deposits are being developed in the waters of the Indian Ocean. In addition, the ocean is also rich in phosphates, potash raw materials necessary for fertilizing agricultural land.

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.

Physical-geographical 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 (Queen Maud Land), in the east (with the Pacific Ocean south of Australia) - along the eastern border of the Bass Strait to the island of Tasmania , and then along the meridian 146°55' E to Antarctica, in the northeast (with a basin Pacific Ocean) - between the Andaman Sea and the Strait of Malacca, further along the southwestern shores of the island of Sumatra, the Sunda Strait, the southern coast of the island of Java, the southern 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, this geographical nomenclature is not universally recognized, and, as a rule, the Indian Ocean is considered within its usual boundaries. The Indian Ocean is the only one of the oceans that is located mostly in the Southern Hemisphere and is limited in the north by a powerful landmass. Unlike other oceans, its mid-ocean ridges form three branches, diverging 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 km 2, the volume of water is 282.65 million km 3, 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-water Sunda Trench is 7729 m at 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 map.

Seas. Seas, bays and straits in the Indian Ocean are almost three times less than in the Atlantic or Pacific Ocean, 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 about 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, islands are few in number. The total area is about 2 million km2. Most major islands mainland origin - Socotra, Sri Lanka, Madagascar, Tasmania, Sumatra, Java, Timor. Volcanic islands: Reunion, Mauritius, Prince Edward, Crozet, Kerguelen and others; coral - Laccadive, Maldivian, Amirant, Chagos, Nicobar, most of the Andaman, Seychelles; coral Comoros, Mascarene, Cocos and other islands rise on volcanic cones.

coast. The Indian Ocean is distinguished by a relatively small indentation of the coastline, with the exception of the northern and northeastern parts, where most of the seas and the main large bays are located; there are few convenient bays. The coasts of Africa in the western part of the ocean are alluvial, poorly dissected, often surrounded by coral reefs; in the northwestern part - indigenous. In the north, low, slightly dissected coasts with lagoons and sand bars, places with mangroves, bordered by coastal lowlands (Malabar coast, Coromandel coast) prevail, abrasion-accumulative (Konkan coast) and deltaic coasts 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 topography of the bottom of the Indian Ocean, four main elements of geotecture are distinguished: the underwater margins of the continents (including the shelf and the continental slope), transitional zones, or zones of island arcs, the ocean floor, and mid-ocean ridges. The area of ​​the underwater margins of the continents in the Indian Ocean is 17660 thousand km2. 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 mainland, the shelf expands significantly and in the region 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 inflection of the bottom surface and a rapid increase in its slope up 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 at its outer border increases from 100 to 500 m. 4200 m, Sri Lanka). The shelf and the continental slope in some areas are cut by several narrow and deep canyons, the most pronounced canyons, which are underwater continuations of the channels of the Ganges rivers (together with the Brahmaputra River, it annually carries out into the ocean about 1200 million tons of suspended and entrained sediments, which formed a layer of sediments over 3500 m thick ) and Ind. The underwater margin of Australia is distinguished 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; the greatest depth is 500 m. The continental slope to the west of Australia is complicated by underwater ledges and separate underwater plateaus (the greatest height is 3600 m, the Aru Islands). On the underwater margin of Antarctica, everywhere there are traces of the influence of the ice load of a huge glacier covering the mainland. The shelf here belongs to a special glacial type. Its outer boundary almost coincides with the 500 m isobath. The width of the shelf is from 35 to 250 km. The continental slope is complicated by longitudinal and transverse ridges, separate ridges, valleys and deep trenches. At the foot of the continental slope, almost everywhere there is an accumulative plume composed of terrigenous material brought by glaciers. The largest slopes of the bottom are noted in the upper part; with increasing depth, the slope gradually flattens out.

The transition zone at the bottom of the Indian Ocean is distinguished only in the area adjacent to the arc of the Sunda Islands, and represents the southeastern part of the Indonesian transition region. It includes: the basin of the Andaman Sea, the island arc of the Sunda Islands and deep-sea trenches. The most morphologically expressed in this zone is the deep-water Sunda Trench with slopes of 30° or more. Relatively small deep-sea trenches stand out southeast of Timor Island and east of the Kai 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 underwater mountain ranges, diverging from the area with coordinates 22 ° south latitude and 68 ° east longitude to the northwest, southwest and southeast. Each of the three branches is divided according to morphological features into two independent ridges: the northwestern one - into the Middle Aden Ridge and the Arabian-Indian Ridge, the southwestern one - into the West Indian Ridge and the African-Antarctic Ridge, the southeastern one - into the Central the Indian Ridge and the Australo-Antarctic Rise. Thus, the median ridges divide the bed of the Indian Ocean into three large sectors. The median ridges are vast uplifts fragmented by transform faults into separate blocks with a total length of over 16 thousand km, the foot of which are located at depths of about 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, the largest basins are: Somali (with depths of 3000-5800 m), -5300 m), Mozambique (4000-6000 m), Madagascar Basin (4500-6400 m), Agulhas (4000-5000 m); underwater ranges: Mascarene Ridge, Madagascar, Mozambique; Plateau: Agulhas, Mozambique Plateau; separate mountains: Equator, Africana, Vernadsky, Hall, Bardin, Kurchatov; Amirant Trench, Mauritius Trench; canyons: Zambezi, Tanganyika and Tagela. The following basins are distinguished in the northeastern sector: Arabian (4000-5000 m), Central (5000-6000 m), Cocos (5000-6000 m), North Australian (5000-5500 m), West Australian Basin (5000-6500 m), Naturalista (5000-6000 m) and the South Australian Basin (5000-5500 m); underwater ranges: Maldives Ridge, East Indian Ridge, West Australian; Cuvier mountain range; Exmouth Plateau; upland Mill; separate mountains: Moscow State University, Shcherbakov and Afanasy Nikitin; East Indian Trench; canyons: rivers Indus, Ganges, Seatown and Murray. In the Antarctic sector - basins: Crozet (4500-5000 m), African-Antarctic basin (4000-5000 m) and Australo-Antarctic basin (4000-5000 m); plateau: Kerguelen, Crozet and Amsterdam; separate mountains: Lena and Ob. The shapes and sizes of the basins are different: from round ones with a diameter of about 400 km (Komorskaya) to oblong giants 5500 km long (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 splitting and subsidence of continental masses, and as a result of the spreading of the bottom and the neoformation of the oceanic crust within the mid-ocean (spreading) ridges, the system of which was repeatedly rebuilt. The modern system of mid-ocean ridges consists of three branches, converging at the point of the triple junction of Rodriguez. In the northern branch, the Arabian-Indian Ridge continues to the northwest of the Owen transform fault zone with the Gulf of Aden and Red Sea rift systems and connects with the East African intracontinental rift systems. In the southeastern branch, the Central Indian Ridge and the Australo-Antarctic Rise are separated by the Amsterdam Fault Zone, with which the plateau of the same name is connected with the volcanic islands of Amsterdam and St. Paul. The Arabian-Indian and Central Indian ridges are slow-spreading (the spreading rate is 2-2.5 cm/year), have a well-defined rift valley, and are crossed by numerous transform faults. The wide Australo-Antarctic Rise does not have a pronounced rift valley; spreading rate on it is higher than in other ridges (3.7-7.6 cm/year). South of Australia, the uplift is broken by the Australo-Antarctic fault zone, where the number of transform faults increases and the spreading axis shifts along the faults to the south. The ridges of the southwestern branch are narrow, with a deep rift valley, and are 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 faults, which shift the axis of the ridge 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 intrudes into the structures of the Central Indian Ridge as a narrow wedge, is considered the youngest.

The spreading ridges divide the ocean floor into three sectors - the African in the west, the Asian-Australian in the northeast and the Antarctic in the south. Within the sectors there are various types of intra-oceanic uplift, represented by "aseismic" ridges, plateaus and islands. Tectonic (blocky) uplifts have a block structure with different thicknesses of the crust; often include continental remnants. Volcanic uplifts are mainly associated with fault zones. Uplifts are the natural boundaries of deep-sea basins. The African sector is characterized by the predominance of fragments of continental structures (including microcontinents), within which the thickness of the earth's crust reaches 17-40 km Seychelles and a can of Saya de Malla). Volcanic uplifts and structures include the Comoros underwater ridge, crowned with archipelagos of coral and volcanic islands, the Amirantsky ridge, the Reunion Islands, Mauritius, Tromelin, and the Farquhar massif. In the western part of the African sector of the Indian Ocean (the western part of the Somali Basin, the northern part of the Mozambique Basin), adjacent to the eastern submarine 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 crossing them have been identified in the Somali and Mascarene basins.

The northwestern (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 with archipelagos of coral islands - Laccadive, Maldives and Chagos; the so-called 79° ridge, Lanka ridge with Mount Athanasius Nikitin, East Indian (the so-called 90° ridge), Investigator, etc. Thick (8-10 km) sediments of the Indus, Ganges and Brahmaputra rivers in the northern Indian Ocean partially overlap the in this direction, the ridges, as well as the structures of the transition zone of the Indian Ocean - the southeastern outskirts of Asia. The Murri Range in the northern part of the Arabian Basin, which limits the Oman Basin from the south, is a continuation of the folded land structures; enters the Owen Fault Zone. To the south of the equator, a sublatitudinal zone of intraplate deformations up to 1000 km wide was revealed, which is characterized by high seismicity. It stretches in the Central and Coconut basins from the Maldives Range to the Sunda Trench. The Arabian Basin is underlain by the crust of the Paleocene-Eocene age, the Central Basin - by the crust of the Late Cretaceous - Eocene age; the bark is the youngest in the southern part of the basins. In the Coconut Basin, the age of the crust varies from Late Cretaceous in the south to Eocene in the north; an ancient spreading axis was established in its northwestern part, separating the Indian and Australian lithospheric plates until the middle Eocene. The Coconut Rise, a latitudinal uplift with numerous seamounts and islands (including the Cocos Islands) rising above it, and the Ru Rise adjacent to the Sunda Trench separate the southeastern (Australian) part of the Asian-Australian sector. The West Australian basin (Wharton) in the central part of the Asian-Australian sector of the Indian Ocean is underlain in the northwest by the Late Cretaceous crust, in the east by the Late Jurassic. Submerged continental blocks (marginal plateaus of Exmouth, Cuvier, Zenith, Naturalist) divide the eastern part of the basin into separate depressions - Cuvier (north of the Cuvier plateau), Perth (north of the Naturalist plateau). The crust of the North Australian Basin (Argo) is the most ancient in the south (Late Jurassic); becomes younger in a northerly direction (to the early Cretaceous). The age of the crust of the South Australian Basin is Late Cretaceous - Eocene. The Broken Plateau is an intra-oceanic uplift with an 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 uplifts with an increased thickness of the earth's crust: the Kerguelen Plateau, Crozet (Del Cano) and Conrad. Within the limits of the largest plateau Kerguelen, presumably laid down on an ancient transform fault, the thickness of the earth's crust (according to some data, the Early Cretaceous age) reaches 23 km. Towering above the plateau, the Kerguelen Islands are a multiphase volcanoplutonic structure (composed of alkaline basalts and syenites of the Neogene age). On Heard Island - Neogene-Quaternary alkaline volcanic rocks. In the western part of the sector, there are the Konrad plateau with the Ob and Lena volcanic mountains, 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, Australo-Antarctic basins and the Crozet basin is Late Cretaceous - Eocene.

The Indian Ocean is characterized by the predominance of passive margins (the continental margins of Africa, the Arabian and Hindustan peninsulas, Australia, and Antarctica). The active margin is observed in the northeastern part of the ocean (the Sunda zone of the Indian Ocean-Southeast Asia transition), where subduction (underthrust) of the ocean's lithosphere occurs under the Sunda island arc. A subduction zone limited in length - Makranskaya - was 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 middle of the Mesozoic during the breakup of the Gondwana part (see Gondwana) of the Patea supercontinent, which was preceded by continental rifting during the Late Triassic - Early Cretaceous. The formation of the first sections of the 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 bottom expansion and the new formation of the oceanic crust experienced the northern part of the Mozambique Basin (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 oceanic 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 to the north and west of Australia, off the coast of Antarctica and in the Mozambique Channel, died off. 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 Australo-Antarctic Rise. At the turn of the Cretaceous and Paleogene, Hindustan separated from the Mascarene-Seychelles block; the Arabian-Indian spreading ridge arose; spreading axes died off 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 a close to modern appearance at the beginning - middle of the Miocene. In the middle of the Miocene (about 15 million years ago), during the breakup of the Arabian and African plates, a new formation of oceanic crust began in the Gulf of Aden and the Red Sea.

Recent tectonic movements in the Indian Ocean have been 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 due to the presence of a seismofocal zone plunging in a northeasterly direction. During earthquakes on the northeastern margin of the Indian Ocean, the formation of a tsunami is possible.

Bottom sediments. The rate of sedimentation in the Indian Ocean is generally lower than in the Atlantic and Pacific oceans. The thickness of modern bottom sediments varies from a discontinuous distribution on mid-ocean ridges to several hundred meters in deep-water basins and 5000-8000 m at the foot of continental slopes. The most widespread are calcareous (mainly foraminiferal-coccolithic) muds covering over 50% of the ocean floor area (on continental slopes, ridges and the bottom of basins at depths up to 4700 m) in warm oceanic regions from 20° north latitude to 40° south latitude from high biological productivity of waters. Polygenic sediments - red deep-sea oceanic clays - occupy 25% of the bottom area at depths of more than 4700 m in the eastern and southeastern parts of the ocean from 10 ° north latitude to 40 ° south latitude and in bottom areas remote from islands and continents; in the tropics, red clays alternate with siliceous radiolarian silts that cover the bottom of deep-water basins of the equatorial belt. In deep-sea sediments, ferromanganese nodules are present as inclusions. Siliceous, mainly diatomaceous, oozes occupy about 20% of the bottom of the Indian Ocean; 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 the continents and within their underwater margins in the areas of river and iceberg runoff, significant wind removal of material. Sediments covering the African shelf are mainly of shell and coral origin; phosphorite concretions are widely developed in the southern part. Along the northwestern periphery of the Indian Ocean, as well as in the Andaman Basin and in the Sunda Trench, bottom sediments are mainly represented by deposits of turbidity (turbid) flows - turbidites with the participation of products of volcanic activity, underwater landslides, landslides, etc. Sediments of coral reefs are widespread in the 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 found in the Red Sea. In the metal-bearing sediments formed from these brines, the content of non-ferrous and rare metals is high. On continental slopes, seamounts, mid-ocean ridges, outcrops of bedrocks (basalts, serpentinites, peridotites) are noted. Bottom sediments around Antarctica stand out as a special type of iceberg deposits. They are characterized by the predominance of various detrital material, ranging from large boulders to silts and fine silts.

Climate. Unlike the Atlantic and Pacific Oceans, which have a meridional strike from the coast of Antarctica to the Arctic Circle and communicate 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 the land and ocean leads to a seasonal change in extensive minima and maxima of atmospheric pressure and to seasonal displacements of the tropical atmospheric front, which retreats southward to almost 10 ° south latitude in the winter of the Northern Hemisphere, and is located in the foothill regions of southern Asia in summer. As a result, a monsoonal climate dominates over the northern part of the Indian Ocean, which is primarily characterized by a change in wind direction during the year. The winter monsoon with relatively weak (3-4 m/s) and stable northeasterly winds operates from November to March. During this period, north of 10 ° south latitude, calms are not uncommon. The summer monsoon with southwesterly winds is observed 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 strength. In April and October, the baric field is usually restructured, and in these months the wind situation is unstable. Against the background of the prevailing monsoon atmospheric circulation over the northern part of the Indian Ocean, individual manifestations of cyclonic activity are possible. During the winter monsoon, there are cases of cyclones developing over the Arabian Sea, during the summer monsoon - over the waters of the Arabian Sea and the Bay of Bengal. Strong cyclones in these areas are sometimes formed during the periods of monsoon change.

At about 30° south latitude in the central part of the Indian Ocean, there is a stable area of ​​high pressure, the so-called South Indian High. This stationary anticyclone - an integral part of the southern subtropical high pressure area - remains all year round. The pressure at its center varies from 1024 hPa in July to 1020 hPa in January. Under the influence of this anticyclone, in the latitudinal band between 10 and 30 ° south latitude, stable southeast trade winds blow throughout the year.

South of 40° South latitude, atmospheric pressure in all seasons decreases uniformly 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 transport of air is maintained. The highest average wind speed (up to 15 m/s) is observed in the middle of winter in the Southern Hemisphere. For the higher southern latitudes of the Indian Ocean, storm conditions are typical throughout almost the entire year, under which winds with speeds of more than 15 m/s, causing waves with a height of more than 5 m, have a frequency of 30%. East winds and two or three cyclones per year are usually observed south of 60 ° south latitude along the coast of Antarctica, most often in July - August.

In July, the highest air temperatures in the near 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 water area of ​​the Indian Ocean, the air temperature changes almost everywhere in accordance with the geographical 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 the equatorial zone, near the northern coasts of the Arabian Sea and the Bay of Bengal - about 20°C. In the southern part of the ocean, the temperature drops evenly from 26°C in the Southern Tropic to 0°C and somewhat lower at the latitude of the Antarctic Circle. The amplitude of annual fluctuations in air temperature 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 eastern shores islands of Madagascar (more than 3500 mm). In the northern coastal part of the Arabian Sea, the least amount of precipitation falls (100-200 mm per year).

The northeastern regions of the Indian Ocean are located in seismically active areas. East coast of Africa and the island of Madagascar, the coast of the Arabian Peninsula and the Hindustan Peninsula, almost all island archipelagos of volcanic origin, the western coasts of Australia, especially the arc of the Sunda Islands, in the past were repeatedly exposed to tsunami waves of various strengths, up to catastrophic ones. In 1883, after the explosion of the Krakatau volcano in the Jakarta region, a tsunami with a wave height of over 30 m was recorded, in 2004 a tsunami caused by an earthquake in the region 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 time of the southwest monsoon (May - September), the winter - the northeast monsoon (November - March). A feature of the seasonal variability of the hydrological regime is that the restructuring of the hydrological fields is somewhat late 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 northern regions The Arabian Sea and the Bay of Bengal have a water temperature of about 25°C. In the southern part of the Indian Ocean, a zonal temperature distribution is characteristic everywhere, which gradually decreases from 27-28 ° C at 20 ° south latitude to negative values ​​\u200b\u200bat the edge of drifting ice, located approximately at 65-67 ° south latitude. In the summer season, the highest water temperatures in the surface layer are observed in the Persian Gulf (up to 34°С), in the northwest of the Arabian Sea (up to 30°С), in the eastern part of the equatorial zone (up to 29°С). In the coastal regions of the Somali and Arabian peninsulas, abnormally low values ​​\u200b\u200bare observed at this time of the year (sometimes less than 20 ° C), 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 retains a zonal character, with the difference that its negative values ​​\u200b\u200bin the winter of the Southern Hemisphere occur much further north, already at about 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 region of the Somali coast and in the Gulf of Oman of the Arabian Sea exceeds 7°C. The water temperature rapidly decreases vertically: at a depth of 250 m, it drops below 15°C almost everywhere, and below 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 central regions- about 2.5°С, in the southern part decreases from 2°С at 50° south latitude to 0°С off the coast of Antarctica. Temperatures in the deepest (over 5000 m) basins range from 1.25°С to 0°С.

The salinity of the surface waters of the Indian Ocean is determined by the balance between the amount of evaporation and the total amount of precipitation and river runoff for each area. The absolute maximum of salinity (over 40‰) is observed in the Red Sea and the Persian Gulf, in the Arabian Sea everywhere, except for 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 arc of the Sunda Islands, where fresh river flow is large and the greatest amount of precipitation falls. In the northern part of the Bay of Bengal in February, salinity is 30-31‰, in August - 20‰. An extensive tongue of waters with a salinity of 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 salinity during the formation sea ​​ice and corresponding desalination during the period of ice melting. Seasonal changes in salinity are noticeable only in the upper 250-meter layer. With increasing depth, not only seasonal fluctuations, but also the spatial variability of salinity fade, deeper than 1000 m it fluctuates between 35-34.5‰.

Density. The highest water density in the Indian Ocean is noted in the Suez and Persian Gulfs (up to 1030 kg / m 3) and in cold Antarctic waters (1027 kg / m 3), the average - in the warmest and most saline waters in the northwest (1024-1024, 5 kg / m 3), the smallest - in the most fresh waters in the northeastern part of the ocean and in the Bay of Bengal (1018-1022 kg / m 3). With depth, mainly due to a decrease in water temperature, its density increases, sharply increasing in the so-called jump layer, which is most pronounced in the equatorial zone of the ocean.

Ice regime. The severity of the climate in the southern part of the Indian Ocean is such that the process of formation of sea ice (at air temperatures below -7 ° C) can occur almost all year round. The ice cover reaches its maximum development in September-October, when the width of the drifting ice belt reaches 550 km, the smallest - in January-February. The ice cover is characterized by high seasonal variability and its formation is very fast. The ice edge moves to the north at a speed of 5-7 km/day, just as quickly (up to 9 km/day) retreats 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 near the coasts of the mainland moves under the influence of katabatic winds in the general direction to the west and northwest. Near the northern edge, the ice drifts eastward. A characteristic feature of the Antarctic ice cover is a large number of icebergs breaking off from the outlet and ice shelves of Antarctica. Table-shaped icebergs are especially large, which can reach a gigantic length of several tens of meters, towering 40-50 meters above the water. Their number rapidly decreases with distance from the coast of the mainland. The duration of the existence of large icebergs is on average 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 changes significantly from summer to winter. 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 with speeds of 50-80 cm/s; with a rod passing approximately along 18 ° south latitude, the South Equatorial Current propagates in the same direction, having an average speed on the surface of about 30 cm / s. Connecting off the coast of Africa, the waters of these two streams give rise to the Inter-trade countercurrent, which carries its waters to the east with velocities in the core of about 25 cm/s. Along the North African coast with a general direction to the south, the waters of the Somali current move, partially passing into the Intertrade countercurrent, and to the south, the Mozambique and Cape of Agulhas currents, going south at speeds of about 50 cm / s. Part of the South Equatorial Current east coast Islands Madagascar turns along it to the south (Madagascar current). South of 40 ° south latitude, the entire water area of ​​the ocean is crossed from west to east by the flow of the longest and most powerful West Wind Current in the World Ocean (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 West Australian Current. In August, the Somali current follows in a general direction to the northeast and, at a speed of up to 150 cm / s, draws water into the northern part of the Arabian Sea, from where the Monsoon current, skirting the western and southern coasts 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. Thus, an extensive clockwise circulation is created in the northern part of the Indian Ocean, consisting of the Monsoon, South Equatorial and Somali currents. In the southern part of the ocean, from February to August, the pattern of currents changes little. Off the coast of Antarctica, in a narrow coastal strip, a current is observed all year round, caused by katabatic winds and directed from east to west.

water masses. In the vertical structure of the water masses of the Indian Ocean, according to hydrological characteristics and depth of occurrence, 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 stand out 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. So, in intermediate waters, the lower limit of which reaches 2000 m in temperate and low latitudes and up to 1000 m in high latitudes, Persian and Red Sea in the Arabian Sea, Bengal in the Bay of Bengal, Subantarctic and Antarctic intermediate water masses stand out. 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 water everywhere, except for the Bay of Bengal, is represented by one Antarctic bottom water mass, which fills all deep-water basins. The upper limit of bottom water is located on average at a horizon of 2500 m off the coast of Antarctica, where it forms, up to 4000 m in the central regions of the ocean and rises to almost 3000 m north of the equator.

Tides and excitement. Semidiurnal and irregular semidiurnal tides are most widespread on the shores of the Indian Ocean. Semi-diurnal tides are observed on the African coast south of the equator, in the Red Sea, off the northwestern shores of the Persian Gulf, in the Bay of Bengal, 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 shores of the Sunda island arc. Diurnal and irregular daily tides are observed 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 Channel (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. Excitement reaches its greatest strength in temperate latitudes in the zone of action of westerly winds, where the frequency of waves with a height of over 6 m is 17% per year. Near Kerguelen Island, waves 15 m high and 250 m long were recorded, off the coast of Australia, 11 m and 400 m, respectively.

Flora and fauna. The main part of the Indian Ocean is located within the tropical and southern temperate zones. The absence of the 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 hinders deep-sea convection, which negatively affects the renewal of deep waters in 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 depletion of the species composition and reduces the total zooplankton biomass in the intermediate layers. When oxygen-poor waters in the Arabian Sea reach the shelf, local kills occur (death of hundreds of thousands of tons of fish). At the same time, the second factor (monsoons) creates favorable conditions for high biological productivity in coastal areas. Under the influence of the summer monsoon, water is driven along the Somali and Arabian coasts, which causes a powerful upwelling that brings waters rich in nutrient salts to the surface. The winter monsoon, although to a lesser extent, leads to seasonal upwelling with similar effects off the western coast of the Hindustan Peninsula.

The coastal zone of the ocean is characterized by the greatest species diversity. The shallow waters of the tropical zone are characterized by numerous 6- and 8-ray stony corals, hydrocorals, which, together with red algae, can create underwater reefs and atolls. The richest fauna of various invertebrates (sponges, worms, crabs, mollusks, sea urchins, brittle stars and starfish), small but brightly colored fish of coral reefs live among the powerful coral structures. Most of the coasts are occupied by mangroves. At the same time, the fauna and flora of the beaches and rocks that dry out at low tide are quantitatively depleted due to the depressing effect of the sun's rays. In the temperate zone, life on such stretches of coasts is much richer; dense thickets of red and brown algae (kelp, fucus, macrocystis) develop here, various invertebrates are abundant. According to L. A. Zenkevich (1965), over 99% of all species of bottom and bottom animals living in the ocean live in the littoral and sublittoral zones.

The open spaces of the Indian Ocean, especially the surface layer, are also characterized by rich flora. The food chain in the ocean begins with microscopic unicellular plant organisms - phytoplankton, which inhabits mainly the uppermost (about 100-meter) layer of ocean waters. Among them, several species of peridinium and diatom algae predominate, and in the Arabian Sea - cyanobacteria (blue-green algae), often causing the so-called water bloom during mass development. There are three areas of the highest phytoplankton production in the northern Indian Ocean: the Arabian Sea, the Bay of Bengal and the 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 there are up to 300,000 cells/l during the spring flowering period. 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 number rapidly decreases with increasing depth and decreases by 2-3 orders of magnitude towards the bottom layers. Most of the zooplankton, especially those living in the upper layers, are fed by phytoplankton, so the patterns of spatial distribution of phytoplankton and zooplankton are largely similar. The highest rates 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 is copepods (more than 100 species), somewhat less winged molluscs, jellyfish, siphonophores and other invertebrates. Of the unicellular, radiolarians are typical. In the Antarctic region of the Indian Ocean, a huge number of euphausian crustaceans of several species, united under the name "krill", is characteristic. Euphausiids form the main food base 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. Of the cephalopods in the Indian Ocean, cuttlefish, numerous squids and octopuses are common. Of the fish, the most abundant are several species of flying fish, luminous anchovies (dollfish), sardinella, sardine, mackerel pike, notothenia, sea bass, several types of tuna, blue marlin, grenadier, sharks, rays. Sea turtles and poisonous sea snakes live in warm waters. The fauna of aquatic mammals is represented by various cetaceans. Of the baleen whales, the following are common: blue, sei whale, fin whale, humpback whale, Australian (Cape) Chinese. Toothed whales are represented by sperm whales, several species of dolphins (including killer whales). In the coastal waters of the southern part of the ocean, pinnipeds are widespread: Weddell seal, crabeater seal, seals - Australian, Tasmanian, Kerguelen and South African, Australian sea lion, sea leopard, etc. Among the birds, the most characteristic are the wandering albatross, petrels, large frigate, 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. The "fossil" coelacanth lives at a depth of over 200 m in two places - near the Comoros and in the waters of the Indonesian archipelago.

Research History

The northern coastal regions, especially the Red Sea and deeply incised bays, began to be used by man for navigation and fishing already in the era of ancient civilizations, several thousand years before our era. For 600 years BC, the Phoenician navigators who were in the service of Egyptian pharaoh Necho II, sailed around Africa. In 325-324 BC, an ally of Alexander the Great, Nearchus, commanding a fleet, sailed from India to Mesopotamia and compiled the first descriptions of the coast 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 navigational guides for this area. In the first half of the 15th century, Chinese navigators led by 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 a sea route for Europeans to India and the countries of Southeast Asia. A few years later, the Portuguese discovered the island of Madagascar, the 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. Start oceanographic research Indian Ocean is based on systematic measurements of water temperature during circumnavigations Russian ships "Rurik" (1815-18) and "Enterprise" (1823-26). In 1831-36, an English expedition took place on the Beagle ship, on which Charles Darwin carried out geological and biological work. Comprehensive oceanographic measurements in the Indian Ocean were carried out during the British expedition on board the Challenger 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 first half of the 20th century, oceanographic observations began to be carried out regularly, and by the 1950s they were carried out at almost 1500 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, the Scientific Committee on Oceanography of UNESCO conducted the International Indian Ocean Expedition (IIOE), the largest of those previously operating in the Indian Ocean. Scientists from more than 20 countries of the world (USSR, Australia, Great Britain, India, Indonesia, Pakistan, Portugal, USA, France, Germany, Japan, etc.) took part in the MIOE program. In the course of MIOE, major geographical discoveries: discovered underwater West Indian and East Indian ridges, tectonic fault zones - Owen, Mozambique, Tasmanskaya, Diamantina, etc., seamounts - Ob, Lena, Afanasia Nikitina, Bardina, Zenith, Equator, etc., deep-sea trenches - Ob , Chagos, Vima, Vityaz, etc. In the history of the study of the Indian Ocean, the results of research carried out in 1959-77 by the Vityaz research vessel (10 voyages) and dozens of other Soviet expeditions on ships of the Hydrometeorological Service and the State Fisheries Committee stand out. Since the early 1980s, ocean research has been carried out within the framework of 20 international projects. The research of the Indian Ocean became especially active during the International World Ocean Circulation Experiment (WOCE). After its successful completion in the late 1990s, the volume of modern oceanographic information for the Indian Ocean has doubled.

Economic use

The coastal zone of the Indian Ocean is characterized by an exceptionally high population density. More than 35 states are located on the coasts and islands of the ocean, in which about 2.5 billion people (over 30% of the world's population) live. 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 of the region, the problems of finding living space, creating jobs, providing food, clothing and housing, and medical care are acute.

The use of the Indian Ocean, as well as other seas and oceans, is carried out in several main areas: transport, fishing, mining, and recreation.

Transport. The role of the Indian Ocean in shipping increased significantly with the creation of the Suez Canal (1869), which opened a short sea route of communication with the states washed by the waters. Atlantic Ocean. The Indian Ocean is a region of 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 Straits of Malacca and Sunda) there are routes for ships going to the Pacific Ocean and back. Main export to USA, Japan and countries Western Europe- crude oil from the Persian Gulf region. In addition, agricultural products are exported - 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, chemicals and pharmaceuticals, textiles, cut gems and jewellery. The Indian Ocean accounts for about 10% of the world's shipping traffic; at the end of the 20th century, about 0.5 billion tons of cargo per year was transported through its waters (according to IOC). According to these indicators, it ranks third after the Atlantic and Pacific Oceans, yielding to them in terms of the intensity of shipping and total volumes of cargo transportation, but surpassing all other sea transport communications in terms of oil transportation. The main transport routes across the Indian Ocean are directed to the Suez Canal, the Strait of Malacca, the southern tip of Africa and Australia, and along the northern coast. Shipping is most intensive in the northern regions, although it is limited by storm conditions during the summer monsoon, less intensive in the central and southern regions. The growth of oil production in the countries of the Persian Gulf, in Australia, Indonesia and other places contributed to the construction and modernization of oil ports and the emergence of giant tankers in the Indian Ocean.

The most developed transport routes for the transportation of oil, gas and oil products: the Persian Gulf - the Red Sea - the Suez Canal - the Atlantic Ocean; Persian Gulf - Strait of Malacca - Pacific Ocean; the Persian Gulf - the southern tip of Africa - the Atlantic Ocean (especially before the reconstruction of the Suez Canal, 1981); The Persian Gulf - the coast of Australia (the port of Fremantle). Mineral and agricultural raw materials, textiles, precious stones, jewelry, equipment, computer equipment are transported from India, Indonesia, and Thailand. Australia transports coal, gold, aluminium, alumina, iron ore, diamonds, uranium ores and concentrates, manganese, lead, zinc; wool, wheat, meat products, as well as internal combustion engines, cars, electrical products, river vessels, glass products, rolled steel, etc. Industrial goods, automobiles, electronic equipment, etc. predominate in oncoming flows. 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; fish and other seafood accounts for 5-7% of the total world catch. The catch of fish and non-fish objects is concentrated mainly in the northern part of the ocean, and in the west it is twice as large as the catch in the eastern part. The largest production volumes of bioproducts are observed in the Arabian Sea off the western coast of India and off the coast of Pakistan. Shrimps are harvested in the Persian and Bengal bays, and lobsters are harvested off the east coast of Africa and on tropical islands. IN open areas Ocean in the tropical zone, tuna fishing is widely developed, which is carried out by countries with a well-developed fishing fleet. In the Antarctic region, nototheniids, ice fish and krill are mined.

Mineral resources. Deposits of oil and natural combustible gas or oil and gas shows have been discovered almost throughout the shelf area of ​​the Indian Ocean. Actively developed oil and gas fields are of the greatest industrial importance in the bays: Persian (Persian Gulf oil and gas basin), Suez (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 (gas-bearing Carnarvon basin), in the Bass Strait (gas-bearing Gippsland basin). Gas deposits have been explored in the Andaman Sea, oil and gas bearing areas - in the Red Sea, the Gulf of Aden, along the coast of Africa. Coastal-marine 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 southwest coast Australia (mining of ilmenite, rutile, monazite and zircon); in the coastal regions 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 have been identified as potential sources for the extraction of iron, manganese, copper, zinc, nickel, etc.; there are deposits of rock salt. In the coastal zone of the Indian Ocean, sand is mined for construction and glass production, gravel, limestone.

Recreational resources. Since the 2nd half of the 20th century, the use of ocean recreational resources has been of great importance for the economies of coastal countries. Old resorts are being developed and new ones are being built on the coast of the continents and on numerous tropical islands in the ocean. The most visited resorts are in Thailand (the island of Phuket, 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) , on the Maldives, in Sri Lanka, Seychelles, Mauritius, Madagascar, South Africa, etc.

Sharm El Sheikh. Hotel "Concord".

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), El Kuwait (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 VF Relief of the bottom of the Indian Ocean. M., 1979; Indian Ocean. L., 1982; Udintsev GB 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. Nepronov. K., 1990; Neiman V. G., Burkov V. A., Shcherbinin A. D. Dynamics of the waters of the Indian Ocean. M., 1997; Pushcharovsky Yu. M. Tectonics of the Earth. Fav. works. M., 2005. Vol. 2: Tectonics of the oceans.

M. G. Deev; N. N. Turko (geological structure).

The Indian Ocean has the fewest seas compared to other oceans. In the northern part are located the most large seas: Mediterranean - the Red Sea and the Persian Gulf, the semi-enclosed Andaman Sea and the marginal Arabian Sea; in the eastern part - the Arafura and Timor seas.

There are relatively few islands. The largest of them are of continental origin and are located near the coast: Madagascar, Sri Lanka, Socotra. In the open part of the ocean, there are volcanic islands - Mascarene, Crozet, Prince Edward, etc. In tropical latitudes, coral islands rise on volcanic cones - Maldives, Laccadive, Chagos, Cocos, most of the Andaman, etc.

Shores in the N.-W. and the East are indigenous, in the S.-V. and the West are dominated by alluvial. The coastline is slightly indented, with the exception of the northern part of the Indian Ocean. Almost all the seas and large bays (Aden, Oman, Bengal) are located here. In the southern part there are the Gulf of Carpentaria, the Great Australian Gulf and the gulfs of Spencer, St. Vincent, etc.

A narrow (up to 100 km) continental shelf (shelf) stretches along the coast, the outer edge of which has a depth of 50-200 m (only near Antarctica and northwestern Australia up to 300-500 m). The continental slope is a steep (up to 10-30°) ledge, locally dissected by the underwater valleys of the Indus, Ganges, and other rivers. m). The bed of the Indian Ocean is divided by ridges, mountains and ramparts into a number of basins, the most significant of which are the Arabian Basin, the West Australian Basin, and the African-Antarctic Basin. The bottom of these basins is formed by accumulative and hilly plains; the first are located near the continents in areas with an abundant supply of sedimentary material, the second - in the central part of the ocean. Among the numerous ridges of the bed, the straightness and length (about 5,000 km) distinguish the meridional East Indian Ridge, which connects in the south with the latitudinal West Australian Ridge; large meridional ridges stretch to the south from the Hindustan peninsula and about. Madagascar. Volcanoes are widely represented on the ocean floor (Mt. Bardina, Mt. Shcherbakov, Mt. Lena, and others), which in places form large massifs (to the north of Madagascar) and chains (to the east of the Cocos Islands). Mid-ocean ridges - mountain system, consisting of three branches diverging from the central part of the ocean to the north (Arabian-Indian ridge), southwest. (West Indian and African-Antarctic ridges) and Yu.-V. (Central Indian Ridge and Australo-Antarctic Rise). This system has a width of 400–800 km, a height of 2–3 km, and is most dissected by an axial (rift) zone with deep valleys and rift mountains bordering them; transverse faults are characteristic, along which horizontal displacements of the bottom up to 400 km are noted. The Australo-Antarctic Rise, in contrast to the median ridges, is a gentler swell 1 km high and up to 1500 km wide.

The bottom sediments of the Indian Ocean are thickest (up to 3-4 km) at the foot of the continental slopes; in the middle of the ocean - small (about 100 m) thickness and in places where the dissected relief is distributed - discontinuous distribution. The most widely represented are foraminiferal (on the continental slopes, ridges and at the bottom of most basins at a depth of up to 4700 m), diatoms (south of 50 ° S), radiolarian (near the equator) and coral sediments. Polygenic sediments - red deep-sea clays - are distributed south of the equator at a depth of 4.5-6 km or more. Terrigenous sediments - off the coast of the continents. Chemogenic sediments are mainly represented by ferromanganese nodules, while riftogenic sediments are represented by destruction products of deep rocks. Outcrops of bedrocks are most often found on continental slopes (sedimentary and metamorphic rocks), mountains (basalts) and mid-ocean ridges, where, in addition to basalts, serpentinites and peridotites have been found, representing little-altered matter of the Earth's upper mantle.

The Indian Ocean is characterized by the predominance of stable tectonic structures both on the bed (thalassocratons) and along the periphery (continental platforms); active developing structures - modern geosynclines (Sonda arc) and georiftogenals (mid-ocean ridge) - occupy smaller areas and continue in the corresponding structures of Indochina and rifts of East Africa. These main macrostructures, which differ sharply in morphology, the structure of the earth's crust, seismic activity, and volcanism, are subdivided into smaller structures: plates, usually corresponding to the bottom of oceanic basins, blocky ridges, volcanic ridges, sometimes topped with coral islands and banks (Chagos, Maldives, etc.). .), trench-faults (Chagos, Ob, etc.), often confined to the foot of blocky ridges (East Indian, West Australian, Maldives, etc.), fault zones, tectonic ledges. Among the structures of the Indian Ocean bed, a special place (according to the presence of continental rocks - granites of the Seychelles and the continental type of the earth's crust) is occupied by the northern part of the Mascarene Range - a structure that is apparently part of the ancient Gondwana mainland.

Minerals: on the shelves - oil and gas (especially the Persian Gulf), monazite sands (the coastal region of Southwestern India), etc.; in rift zones - ores of chromium, iron, manganese, copper, etc.; on the bed - huge accumulations of iron-manganese nodules.

The climate of the northern part of the Indian Ocean is monsoonal; in summer, when an area of ​​low pressure develops over Asia, southwestern flows of equatorial air dominate here, in winter - northeastern flows of tropical air. South of 8-10 ° S sh. atmospheric circulation is much more constant; here, in tropical (summer and subtropical) latitudes, stable southeasterly trade winds dominate, and in temperate latitudes, extratropical cyclones moving from West to East. In tropical latitudes in the western part, hurricanes occur in summer and autumn. average temperature air in the northern part of the ocean in summer is 25-27 ° C, off the coast of Africa - up to 23 ° C. In the southern part, it decreases in summer to 20-25 ° C at 30 ° S. sh., up to 5-6 ° С at 50 ° S. sh. and below 0 ° С south of 60 ° S. sh. In winter, the air temperature varies from 27.5 °C near the equator to 20 °C in the northern part, to 15 °C at 30 ° S. sh., up to 0-5 ° С at 50 ° S. sh. and below 0 ° С south of 55-60 ° S. sh. At the same time, in the southern subtropical latitudes, the temperature in the West all year round under the influence of the warm Madagascar current is 3-6 °C higher than in the East, where the cold West Australian current exists. Cloudiness in the monsoon northern part of the Indian Ocean in winter is 10-30%, in summer up to 60-70%. In summer, there is also the greatest amount of precipitation. The average annual precipitation in the east of the Arabian Sea and the Bay of Bengal is more than 3000 mm, near the equator 2000-3000 mm, in the west of the Arabian Sea up to 100 mm. In the southern part of the ocean, the average annual cloudiness is 40-50%, south of 40 ° S. sh. - up to 80%. The average annual precipitation in the subtropics is 500 mm to the east and 1,000 mm to the west; in temperate latitudes, more than 1,000 mm; near Antarctica, it drops to 250 mm.

The circulation of surface waters in the northern part of the Indian Ocean has a monsoonal character: in summer - northeast and east currents, in winter - southwest and west currents. During the winter months between 3° and 8° S. sh. develops an inter-trade (equatorial) countercurrent. In the southern part of the Indian Ocean, water circulation forms an anticyclonic circulation, which is formed from warm currents - the South Trade Winds in the north, Madagascar and Needles in the West, and cold currents - the Western Winds in the South and the West Australian in the East South of 55 ° S. sh. several weak cyclonic water cycles develop, closing off the coast of Antarctica with an easterly current.

The heat balance is dominated by a positive component: between 10° and 20° N. sh. 3.7-6.5 GJ/(m2×year); between 0° and 10°S sh. 1.0-1.8 GJ/(m2×year); between 30° and 40°S sh. - 0.67-0.38 GJ/(m2×year) [from - 16 to 9 kcal/(cm2×year)]; between 40° and 50°S sh. 2.34-3.3 GJ/(m2×year); south of 50°S sh. -1.0 to -3.6 GJ/(m2×yr) [-24 to -86 kcal/(cm2×yr)]. In the expenditure part of the heat balance north of 50 ° S. sh. the main role belongs to the cost of heat for evaporation, and south of 50 ° S. sh. - heat exchange between the ocean and the atmosphere.

The surface water temperature reaches its maximum (over 29 °C) in May in the northern part of the ocean. In the summer of the Northern Hemisphere, it is 27-28 ° C here and only off the coast of Africa decreases to 22-23 ° C under the influence of cold waters coming to the surface from the depths. At the equator, the temperature is 26-28 ° C and decreases to 16-20 ° C at 30 ° S. sh., up to 3-5 ° С at 50 ° S. sh. and below -1 ° С south of 55 ° S. sh. In the winter of the Northern Hemisphere, the temperature in the north is 23–25°C, at the equator 28°C, and at 30°S. sh. 21-25 ° С, at 50 ° S sh. from 5 to 9 ° С, south of 60 ° S sh. temperatures are negative. In subtropical latitudes all year round in the West, the water temperature is 3-5 °C higher than in the East.

The salinity of water depends on the water balance, which is formed on average for the surface of the Indian Ocean from evaporation (-1380 mm/year), precipitation (1000 mm/year) and continental runoff (70 cm/year). Main stock fresh water give the rivers of South Asia (Ganges, Brahmaputra, etc.) and Africa (Zambezi, Limpopo). The highest salinity is observed in the Persian Gulf (37-39‰), in the Red Sea (41‰) and in the Arabian Sea (more than 36.5‰). In the Bay of Bengal and the Andaman Sea, it decreases to 32.0-33.0‰, in the southern tropics - to 34.0-34.5‰. In the southern subtropical latitudes, salinity exceeds 35.5‰ (maximum 36.5‰ in summer, 36.0‰ in winter), and south of 40°S. sh. drops to 33.0-34.3‰. The highest water density (1027) is observed in the Antarctic latitudes, the lowest (1018, 1022) - in the northeastern part of the ocean and in the Bay of Bengal. In the northwestern part of the Indian Ocean, the density of water is 1024-1024.5. The oxygen content in the surface water layer increases from 4.5 ml/l in the northern part of the Indian Ocean to 7-8 ml/l south of 50°S. sh. At depths of 200-400 m, the oxygen content is much lower in absolute value and varies from 0.21-0.76 in the north to 2-4 ml / l in the south, at greater depths it gradually increases again and in the bottom layer is 4.03 -4.68 ml/l. The color of the water is predominantly blue, in the Antarctic latitudes it is blue, in some places with greenish hues.

Tides in the Indian Ocean, as a rule, are small (near the coast of the open ocean and on the islands from 0.5 to 1.6 m), only at the tops of some bays they reach 5-7 m; in the Gulf of Cambay 11.9 m. The tides are predominantly semi-diurnal.

Ice forms at high latitudes and is carried by winds and currents along with icebergs in a northerly direction (up to 55°S in August and up to 65-68°S in February).

The deep circulation and vertical structure of the Indian Ocean is shaped by waters sinking into the subtropical (subsurface waters) and Antarctic (intermediate waters) convergence zones and along the continental slope of Antarctica (bottom waters), as well as from the Red Sea and the Atlantic Ocean (deep waters). Subsurface waters have a temperature of 10-18°C at a depth of 100-150 m to 400-500 m, salinity of 35.0-35.7‰, intermediate waters occupy a depth of 400-500 m to 1000-1500 m, have a temperature of 4 to 10°C, salinity 34.2-34.6‰; deep waters at a depth of 1000-1500 m to 3500 m have a temperature of 1.6 to 2.8 ° C, salinity 34.68-34.78‰; bottom waters below 3500 m in the south have a temperature of -0.07 to -0.24 ° C, salinity 34.67-34.69 ‰, in the north - about 0.5 ° C and 34.69-34.77 ‰ respectively.

Flora and fauna

The entire water area of ​​the Indian Ocean lies within the tropical and southern temperate zones. The shallow waters of the tropical zone are characterized by numerous 6- and 8-ray corals, hydrocorals, capable of creating islands and atolls together with calcareous red algae. The richest fauna of various invertebrates (sponges, worms, crabs, molluscs, sea urchins, brittle stars and starfish), small but brightly colored coral fish live among the powerful coral structures. Most of the coasts are occupied by mangroves, in which the mud jumper stands out - a fish that can exist in the air for a long time. The fauna and flora of the beaches and rocks that dry out at low tide are quantitatively depleted as a result of the depressing effect of the sun's rays. In the temperate zone, life on such stretches of coasts is much richer; dense thickets of red and brown algae (kelp, fucus, reaching the enormous size of macrocystis) develop here, various invertebrates are abundant. For the open spaces of the Indian Ocean, especially for the surface layer of the water column (up to 100 m), rich flora is also characteristic. Of the unicellular planktonic algae, several species of peredinium and diatom algae predominate, and in the Arabian Sea - blue-green algae, which often cause the so-called water bloom during mass development.

Copepods (more than 100 species) make up the bulk of the ocean's animals, followed by pteropods, jellyfish, siphonophores, and other invertebrates. Of the unicellular, radiolarians are characteristic; numerous squids. Of the fish, the most abundant are several species of flying fish, luminous anchovies - myctophids, dolphins, large and small tunas, sailfish and various sharks, poisonous sea snakes. Sea turtles and large marine mammals (dugongs, toothed and toothless whales, pinnipeds) are common. Among the birds, the most characteristic are albatrosses and frigates, as well as several species of penguins that inhabit the coasts of South Africa, Antarctica and islands lying in the temperate zone of the ocean.