Where is the deepest part of the Indian Ocean? Temperature, salinity and density of surface waters

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 more than a hundred active volcanoes, among which the famous one is 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. a special regime of water movement arises: 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 most interesting are the penguins that inhabit the coasts of South Africa, Antarctica and the islands of the temperate zone of the ocean.

Natural resources and economic development

The Indian Ocean has great biological wealth, but fishing is mainly limited to coastal 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 recent decades, the coasts of warm seas and the islands of the northern part of the ocean have become increasingly attractive for people to relax, and the tourism business is booming here. 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 message about the Indian Ocean will briefly tell you about the ocean, which is the third largest after the Pacific and Atlantic oceans. You can also use the report on the Indian Ocean to prepare for the lesson.

Message about the Indian Ocean

Indian Ocean: geographical location

The Indian Ocean is located in the Eastern Hemisphere. It is bounded by Eurasia in the northeast and north, Africa in the west, the Antarctic Convergence Zone in the southeast, the east coast of Africa in the south, and the west coast of Oceania and Australia in the east. This ocean is the third largest after the Atlantic and Pacific oceans. Its area is 76.2 million km 2, and the volume of water is 282.6 million km 3.

Features of the Indian Ocean

It was from the Indian Ocean that the study of water expanses began. Of course, the population of the most ancient civilizations did not swim far into open waters and considered the ocean to be a huge sea. The Indian Ocean is quite warm: the water temperature near the coast of Australia is +29 0 С, in the subtropics +20 0 С.

In this ocean, unlike other oceans, a small number of rivers flow. Mostly in the north. The rivers carry a large amount of sedimentary rocks into it, so the northern part of the ocean is quite polluted. The southern part of the Indian Ocean is much cleaner, as there are no freshwater arteries. Therefore, the water is crystal clear with a dark, blue tint. It is the lack of desalination and large evaporation that is the reason that the salinity of the Indian Ocean is much higher than in other oceans. The most salty part of the Indian Ocean is the Red Sea. Its salinity is 42% 0. Also, the salinity of the ocean is affected by icebergs, which swim far inland. Up to 40 0 ​​south latitude, the average salinity of the water is 32% 0.

Also in this ocean there is a huge speed of movement of the trade winds and monsoons. Therefore, large surface currents are formed here, changing every season. The largest of them is the Somali current, which flows from north to south in winter, and with the onset of summer it changes direction.

Relief of the bottom of the Indian Ocean

The bottom relief is varied and complex. A divergent system of mid-ocean ridges stands out in the southeast and northwest. They are characterized by the presence of rifts, transverse faults, seismicity and underwater volcanism. Between the ridges there are numerous deep-sea basins. The shelf at the bottom of the ocean is mostly small, but it is expanding off the coast of Asia.

Natural resources of the Indian Ocean

The Indian Ocean is full of minerals, emeralds, diamonds, pearls and other precious stones. The Persian Gulf is home to the largest oil field ever developed by man.

Climate of the Indian Ocean

Since the Indian Ocean borders on the continents, the climatic conditions are determined by some measure by the surrounding land. It has the unspoken status of "monsoon". The fact is that a sharp contrast over the sea and land is strong winds, monsoons.

In summer, in the north of the ocean, the land becomes very hot and a low pressure area arises, which causes heavy precipitation over the ocean and the mainland. This phenomenon was called the “southwest equatorial monsoon.” In winter, the weather is harsher: destructive hurricanes are observed in the ocean, floods on land. Asia is dominated by an area of ​​high pressure and trade winds.

Organic world of the Indian Ocean

The animal world is quite diverse and rich, especially in coastal areas and the tropical part. Coral reefs stretch along the entire Indian Ocean and continue into the Pacific. There are many thickets of mangroves in coastal waters. In the tropical region, there is a large amount of plankton, which, in turn, serves as food for larger fish (sharks, tuna). Sea turtles and snakes swim in the waters.

Anchovy, sardinella, mackerel, dolphin, flying fish, tuna, shark swim in the northern part. In the south there are white-blooded and notothenic fish, cetaceans and pinnipeds. In the thickets there is a large accumulation of shrimps, lobsters, krill.

It is interesting that against the background of such a vast diversity of the animal world, in the south of the Indian Ocean, an oceanic desert stands out, where life forms are minimal.

Indian Ocean interesting facts

• The surface of the Indian Ocean is covered with luminous circles from time to time. They disappear, then reappear. Scientists have not yet reached a consensus on the nature of these circles, but suggest that they appear due to the huge concentration of plankton floating on the surface of the water.
• In the ocean is the most salty on the planet (after the Dead) - this is the Red Sea. Not a single river flows into it, so it is not only salty, but also transparent.
• The most dangerous poisoner lives in the Indian Ocean - the blue-ringed octopus. Its dimensions are no larger than a golf ball. However, after being hit by it, a person begins to experience suffocation after 5 minutes and dies after 2 hours.
• This is the warmest ocean on the planet.
• Near the island of Mauritius, you can observe an interesting natural phenomenon - an underwater waterfall. From the outside it looks real. Such an illusion arises due to the runoff of sand in the water and the deposition of silt.

We hope that the message about the Indian Ocean helped you prepare for the lesson. And you can add a story about the Indian Ocean through the comment form below.

One of most popular resorts, which many tourists from all over the world aspire to, is Goa. But some vacationers have a question: what is the sea or ocean in Goa?

This is a very important question, since sometimes the opportunity to swim in a reservoir depends on this geographical condition, since, for example, the ocean coast can be dangerous (a large number of sharks, poisonous jellyfish), and the sea coast is created for active water recreation.

Indian pools

If you wondered what awaits you on the coast (sea or ocean), get ready to get multiple answers that contradict each other.

Read on how to get to Goa by plane, and how long the flight takes.

Is there ocean or sea in India?

From the west, India is washed by the waters of the Arabian Sea, from the east by the Bay of Bengal, a small southern part by the Laccadive Sea, and the union territory of the Andaman and Nicobar Islands is washed by the waters. All these reservoirs, in turn, are part of the Indian Ocean.

Which body of water borders North and South Goa?

For many inexperienced tourists who decide to go on their vacation to Goa, the question of whether what waters wash the resort: marine or oceanic.

The answer here lies on the surface: Goa is located in the west of India, respectively, washed by the Arabian Sea.

Given that the Arabian Sea is an open part of the Indian Ocean, we can say that there is both the sea and the ocean. In the oceanic part of the water expanses of Goa, sharks are rarely found; large concentrations of them are found off the coast and Oceania.

Also, sharks are very fond of reef zones, so divers need to be careful when diving. found in the Indian Ocean tiger, gray and great white sharks, and the most dangerous resorts of these waters are Cosi Bay in South Africa, Seychelles, resorts in Australia.

Holidays in Goa

It should be noted that a beach holiday is not the strongest side state of Goa.

Coast

The sea coast of North Goa and South Goa is not much different. The only visible difference is that sand. In the southern part of the resort, the sand is whiter. Due to this, it visually seems that the beaches here are cleaner, and the sea is more transparent. In the northern half of the resort from Sinkerim-Candolim to Anjuna, the sand is more yellow with a grayish tinge, coarse.

In general, we can say that lovers of clean "paradise" beaches will have a hard time here, since the Indian mentality is rather indifferent to garbage, so you can talk about cleanliness and order here. forget.

Sea waters here seem cloudy, because it constantly worries and mixes with sand and clay from the coast, so lovers of diving off the coast with a mask will have to abandon the idea. Many tourists speak unfavorably about the coast of the northern part of the resort, since the bottom of the coastal waters here is strewn with sharp stones, which you can easily get hurt on.

Find out at what time of the year is best for a holiday in Goa.

In addition to uneven bottoms, dirty seas and unattractive beaches, here you may encounter, for example, cows roaming freely along the coast. So for those who love an unusual vacation, there will be something to remember after the trip.

Beaches

For those who cannot decide on a beach, here are some of the most popular beaches in both North and South Goa:

Entertainment

In addition to a beach holiday, Goa has a number of attractions, among which you can find something that is right for you so that your vacation will be remembered for a long time.

Read in what natural and man-made attractions are worth seeing in North and South Goa.

From water activities, which can be combined with beach passive recreation, are presented:

In addition to water activities, there are land excursions. For example, a popular excursion remains elephant riding. There are not many elephants here, but it is not difficult to find those who provide the opportunity to ride this animal. Sometimes even bathing with elephants is offered if the excursion route passes near a waterfall or spice plantations.

For those who like to experience another culture, there are Indian dance courses, cooking courses, as well as yoga.

Extreme lovers can purchase tickets for bullfighting- spectacles that are held spontaneously, without special arenas or preparations.

A little about seasonality

In addition to the place of rest, you need to choose the time of rest. High or low season, large or small number of tourists, high or low prices - all this is very important when organizing a holiday.

High season starts in Goa around December and ends in February. It is in December that the most motley audience strives to get a unique golden tan, as well as swim in the sea.

Water temperature in the high season it is not much different from other times in Goa, it ranges from +26 to +29 degrees. You can swim in Goa all year round, so it is not necessary to choose a tourist peak for this. The air temperature is around 29°C to 31°C all year round.

Silence covers Goa in May, this month the parties subside, the hotels are empty, restaurants and cafes are closed. May days bring suffocating heat, stuffiness and the rainy season to the Indian state.

Water in the sea it warms up to +30 degrees, with constant unrest and such a temperature, it is impossible to swim. The only plus of a holiday in the low season, perhaps, will be the prices.

The coast of the Arabian Sea in Goa is next video:

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' east longitude to Antarctica, in the northeast (with the Pacific basin) - 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, 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, the islands are few in number. The total area is about 2 million km2. The largest islands of mainland origin are 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 the thick sedimentary layer, their maximum depths are 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 ridges: 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. In the northeastern sector, basins are distinguished: 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 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 Mozambique plateaus, the Madagascar ridge with the island of Madagascar, individual blocks of the Mascarene plateau with the bank of the Seychelles and the bank of Saya de -Malya). 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, 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, supposedly 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. The 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 neoformation 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. Outcrops of metal-bearing brines with temperatures up to 70°C and salinity up to 300‰ have been found in the rift valley of 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 region, persists 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 off the eastern coast of the island of Madagascar (over 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. The eastern coast of Africa and the island of Madagascar, the coasts 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 the northern regions of the Arabian Sea and the Bay of Bengal, the water temperature is 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 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°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 salinization during the formation of sea ice and the 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 maximum development of the ice cover reaches 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 off the east coast of the island of Madagascar turns south along it (the 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 coast 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. The 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 pteropods, 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 - the living lobe-finned fish Latimeria chalumnae, which was considered extinct tens of millions of years ago. The "fossil" coelacanth lives at a depth of more than 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 the Egyptian pharaoh Necho II, circled Africa by sea. 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. Oceanographic studies of the Indian Ocean began with systematic measurements of water temperature during the round-the-world voyages of the 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, the monograph "Geography of the Indian and Pacific Oceans" by P. G. Schott 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. During the MIOE, major geographical discoveries were made: the underwater West Indian and East Indian ridges were discovered; etc., deep-sea trenches - the Ob, Chagos, Vima, Vityaz, etc. In the history of the study of the Indian Ocean, the results of studies carried out in 1959-77 by the Vityaz research vessel (10 voyages) and dozens of other Soviet expeditions on ships of the Hydrometeorological Service stand out and the State Committee for Fisheries. 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). Since its successful completion in the late 1990s, the amount 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. Over 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 maritime transportation 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 of the 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. The main export item to the USA, Japan and the countries of Western Europe is 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 boats, glass products, rolled steel, etc. Industrial goods, cars, electronic equipment, etc. predominate in oncoming flows. ocean is occupied by the carriage of passengers.

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 the open areas of the 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 practically 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 mined 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 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) , in the Maldives, 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-Tannura (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).

Geographic location and size. The Indian Ocean is the third largest basin of the World Ocean, located mainly in the Southern Hemisphere between the coasts of Africa, Asia, Australia and Antarctica, which are its natural boundaries. Only in the southwest and southeast, where the Indian Ocean is connected by wide passages with the Atlantic and Pacific oceans, the borders are conditionally drawn from the extreme point of Africa - Cape Agulhas and Cape South on the island of Tasmania and further to the coast of Antarctica, that is, 20 ° in . d. in the west and 147 ° in. d.

In the northeast, the Indian Ocean is connected to the Australo-Asian seas through the Malacca, Sunda and Torres Straits. Tugh its border runs from the extreme northern point of Australia - Cape York to the mouth of the Benebek River on the island of New Guinea. Further, it turns west and northwest along the Lesser Sunda Islands and the islands of Java, Sumatra and the Malay Peninsula.

The name "Indian" was given to the ocean by the Portuguese scientist S. Munster in his work "Cosmography" (1555 p.). The area of ​​​​the ocean with the seas is 76.17 million km 2, the average depth is 3,711 m, the maximum is 7,209 m, the volume of water is 282.7 million km 3. At its widest point, the ocean extends from west to east from Linde Bay to the Torres Strait at 10 ° S. sh. at 11900 km, and from north to south along 60 ° E. from Cape Ras Jadd to the coast of Antarctica at 10200 km.

The Indian Ocean is a kind of basin with its own unique features. First, due to the location of most of it in the Southern Hemisphere, it is characterized by a meridional asymmetry of water circulations. Secondly, the classical monsoon circulation of the atmosphere takes place here. Thirdly, civilization was born on its shores, the first states on Earth arose. Modern racial and ethnic complexes that have developed on the shores of the ocean belong to several "worlds" that, although they interact with each other, are still very different in their historical features and economic and cultural types. Therefore, the ocean has attracted and continues to attract the attention of many researchers.

Islands. There are few islands in the Indian Ocean. They are concentrated mainly in the western part and are divided into three genetic types: continental, volcanic and coral. The largest ones belong to the mainland - Madagascar, Sri Lanka, Greater Sunda, as well as Socotra, Curia-wall, Masirah and a chain of small islands along the coasts of Arabia, Indochina and Western Australia. Most of the mainland islands are limestone plateaus on old Precambrian granites. But, besides them, they are mountainous, composed of Precambrian rocks. The Seychelles have a special structure. These are the only structures within the ocean floor, composed of granites.

Seas. Due to the weak dissection of the coast in the Indian Ocean, there are few seas and bays. In the north there are only two seas - the Red and Arabian, as well as four large bays - Aden, Oman, Persian and Bengal. In the east, the marginal seas are located - Andaman, Timor, Arafura and the Gulf of Carpentaria. The southern shores of Australia are washed by the waters of the Great Gulf.

Along the coast of Antarctica, the seas are conditionally defined: Riiser-Larsen, Cosmonauts, Commonwealth, Davis, Mawson, D "Urville.

According to the nature of the structure, the Indian Ocean basin is divided into four parts: the underwater margins of the continents, transitional zones, mid-ocean ridges and the bed.

According to modern ideas about the origin of continents and oceans, based on the theory of lithospheric plates, the Indian Ocean began to form at the beginning of the Mesozoic era after the Paleozoic continent Gondwana split into separate parts. The foundation of the modern continents of the Southern Hemisphere - Africa, Antarctica, South America, as well as the Hindustan Peninsula - these are parts of the ancient continent of Gondwana. At first, the continents diverged very slowly. Moreover, Australia and Antarctica were still one array. Tens of millions of years passed, and the width of the Indian Ocean was no more than the modern Red Sea. And only at the end of the Mesozoic era did a real ocean already exist, which washed the western shores of the then single Australo-Antarctic continent. This continent existed for another tens of millions of years, until it split into two parts. And after that, Antarctica relatively quickly retreated to the south.

The bottom of the Indian Ocean is a typical oceanic-type crust, consisting of three layers: on top - sediments and weakly compacted sedimentary rocks; below - sedimentary and volcanic rocks; even lower - the basalt layer.

The top layer consists of loose sediments. Their thickness varies from several tens of meters to 200 mm, and near the continents - up to 1.5-2.5 km.

The middle layer is significantly compacted, consists mainly of sedimentary rocks and has a thickness of 1 to 3 km.

The lower (basalt) layer consists of oceanic basalt and has a thickness of 4-6 km.

An interesting feature of the earth's crust of the Indian Ocean is that it contains sections of the continental crust, that is, crust with a granite layer. They come to the surface of the ocean in the form of the Seychelles, Mascarene, Kerguelen and, possibly, the Maldives. Within these, as marine geologists say, microcontinents, the thickness of the earth's crust increases to 30-35 km.

At the bottom of the Indian Ocean, the Mid-Indian Ridge is divided into three parts: Arabian-Indian, West Indian and Central Indian. The latter passes into the Australo-Antarctic Rise. All ridges have well-defined rift valleys, there are active volcanic and seismic phenomena. The East Indian Ridge, which extends almost meridional from the Bay of Bengal to the Australo-Antarctic Rise, has no rift valley, composed of horst blocks of igneous rocks topped with Cenozoic sedimentary rocks. The formation and development of this ridge has not been fully studied.

From the bottom of the rift valleys, scientists have raised silicon-rich basalts, gabbro, dunites, serpentinites, peridotites and chromites, which are considered to be the material of the mantle.

The sounding trench with a depth of more than 7700 m is similar both in origin and characteristics to the Pacific Ocean trenches.

Relief. Continental margins are quite clearly expressed almost everywhere. The shores of the continents enveloping a narrow strip of the shelf. Only in the Persian Gulf, off the coast of Pakistan, Western India, as well as in the Bay of Bengal, in the Andaman, Timor and Arafura seas, the shelf expands to 300-350 km, and in the Gulf of Carpentaria - up to 700 km. The monotony of the relief of these areas is broken by coral structures and flooded river valleys.

At a depth of 100-200 m, a steep continental slope is formed, dissected by narrow deep canyons, starting mainly at the mouths of the rivers. There are especially many of them on the African slope along Kenya and Somalia. Often, canyons branch into several branches, along which river silt is carried out. Settling at the foot of the slope, the silt forms huge underwater deltas, which merge into an inclined accumulative plain. Particularly large cones formed in the pre-estuary private Ganges and Indus.

The Australian slope, unlike the African one, is larger and complicated by several plateaus - Exmouth, Naturalista, Cuviet, etc.

The transition zone is expressed only in the northeast. Here is the basin of the Andaman Sea, the inner island arc of the Sunda Archipelago, a steep underwater ridge parallel to the arc, including the Andaman and Nicobar Islands, and the deep Sunda Trench, extending for 4000 km along the islands of Java and Sumatra from the small Sunda Islands to the coast of Myanmar (Burma). In this trench, the maximum depth of the Indian Ocean is 7,729 m. The transition zone is characterized by eruptions and volcanism. In the Gulf of Sunda there is an island and the volcano Krakatoa, which became world famous as a result of its catastrophic explosion in August 1883.

The median ridge is one of the bottom relief forms. The total length of the mid-ocean ridges is about 20,000 km, the width is from 150 to 1000 km, and the height is from 2.5 to 4.0 km.

An important feature of the rift zones of the Middle Indian spine is their continuation on the continents. In the western part of the Gulf of Aden, the fault zone forks into two parts. One branch goes north in the form of a Red Sea rift, the second turns west, forming a system of East African faults.

The median ridge divides the bed of the Indian Ocean into three segments: African, Asian-Australian and Antarctic. In each of these segments, a number of other ridges have been identified. So, in the center of the Asian-Australian segment, the high East Indian Ridge rises above the ocean floor, stretching straight in the meridional direction for more than 5000 km. It is a system of narrow handfuls with flat tops. The latitudinal Western Australian Range adjoins it in the south. It is also a horst, but asymmetrical, with gentle northern and steep southern slopes. The depth of water above its very point is only 563 m. In the northern part of the segment is the Maldives Range, consisting of a series of plateau-like shallow banks with coral reefs.

In the Antarctic segment, the Kerguelen spine with underwater volcanoes is distinguished. One of the massifs of this ridge forms the basalt island of Kerguelen.

In the African segment, the high Madagascar and Mascarene ranges. In addition, the Agulhas Plateau, Cheyne Ranges, Amirantskiyta Metical are distinguished here.

The ocean bed is divided into large basins by a system of underwater ridges. The most important of them are Central, Western Australian, South Australian, Australo-Antarctic, Madagascar, Mascarene, Mozambique, Somali, Arabian. There are a number of smaller ones, and in total there are 24 basins in the ocean.

The relief of the bottom of the basins is different. It consists mainly of abyssal-hilly plains, among which groups of seamounts stand out. In some basins, the plains are undulating-hummocky, for example, the Agulhas Plain. The Arabian and Central Basins filled with sediments from the Indta Ganges can be considered as flat abyssal plains.

In many basins, separate seamounts rise above the bottom: Afanasia Nikitin, Bardin, Kurchatov, etc.

Climate. In the northern part of the ocean, a huge landmass that surrounds the ocean from the north plays a decisive role in shaping the circulation of the atmosphere and climatic features. Uneven heating of water and land contributes to the formation of seasonal baric systems, which give rise to monsoonal circulation. The leading role in the formation of seasonal winds is played by South and Southeast Asia. Cyclones do not enter here, the air temperature rarely changes here, which is typical of tropical latitudes.

In January, the zone of high air temperature is located south of the equator. The Eurasian continent at this time is strongly cooled, and an area of ​​high pressure is formed above it. The pressure is low over the ocean. Temperature and pressure contrasts are the reason for the formation of the northeast monsoon. The winter monsoon is much weaker than the summer monsoon. Its average speed is 2-4 m/s. This is due to the fact that the mountain ranges of the Himalayas and the Iranian Highlands trap cold air from the north and limit the development of the northeast wind.

In spring, the land heats up quickly and already in May - June the air temperature reaches + 40 ° C. A low pressure zone is established here, due to which the air moves from the sea in summer. The southeast trade wind, crossing the equator and falling into the zone of this area, turns to the right, gradually intensifies and turns into a southwest monsoon. This relatively stable and strong wind, which speed is 8-10 m / s, sometimes becomes stormy in the Arabian Sea. The Himalayas also contribute to the strengthening of the summer monsoon, which causes moist air to rise. In this case, a lot of latent heat from vaporization is released, which is spent on maintaining the monsoon circulation.

The summer monsoon begins in June-July, bringing great cloudiness, thunderstorms, and storm winds to India. Its delay or weakening causes droughts in India, and excessive rainfall leads to catastrophic floods.

The influence of the African continent on the development of monsoons is felt at a distance of 800 km. Due to the combined action of Asia and Africa, the monsoons cover the waters of the Arabian Sea and part of the near-equator zone of the ocean.

So, in the northern part of the ocean, there are two main seasons: a warm and quiet winter with clear skies and a weak northeast monsoon and a wet, cloudy, rainy summer with severe storms. This is a classic area of ​​tropical monsoons.

A completely different circulation of the atmosphere over the rest of the ocean. North of 10°S sh. the southeast trade wind prevails, blowing from the subtropical area of ​​high pressure to the equatorial depression. Further south of Indian High between 40 and 55°S. sh. strong westerly winds blow in temperate latitudes. Their average speed is 8-14 m / s, but quite often they turn into storms.

One of the important features of atmospheric circulation is the constant westerly winds in the equatorial zone of the eastern part of the ocean. According to scientists, these winds arise under the influence of the baric minimum that prevails over the islands of Indonesia.

The Indian Ocean is characterized by tropical cyclones. They originate most often in the Arabian Sea during the off-season, when the quiet surface of the water warms up to + 30 ° C.

Moving north to the shores of India, Pakistan and Bangladesh, they cause great destruction and loss of life. The hurricane in November 1970 had catastrophic consequences, from which 300 thousand people died. Such hurricanes, but half as often, originate in the Bay of Bengal near the Mascarene Islands in and on the northern coast of Australia.

The air heats up intensively in the equatorial-tropical zone, where average monthly temperatures reach 27.32 ° C, and in the north of the Arabian Sea and in the Bay of Bengal - plus 40 ° C. The air here is always 0.5 1.0 ° C colder from water and only in places of upwelling it is warmer.

In high latitudes, the air temperature drops, in particular in the coastal zone of Antarctica, to -50 ° C.

The absolute humidity of the air corresponds to the temperature distribution. The largest average monthly values ​​(32-34 mb) are typical for the northern part of the Arabian Sea and the Bay of Bengal, the smallest - for the Antarctic zone.

Relative humidity never falls below 60% and never exceeds 85%, except in areas of Antarctica, where it is always above 90%. Areas with supersaturated air are also areas of frequent fogs.

Cloudiness and precipitation over the ocean depend on the development of convection and frontal zones. Clearly develops in the intratropical convection zone. Together with cumulonimbus clouds, reaching a height of 16 km, stratocumulus and altocumulus clouds develop here. The latter often line up in separate strands for hundreds of kilometers. Precipitation occurs in the form of short-term showers and averages 2000-3000 mm per year.

In the zone of trade winds and northeast monsoons, the development of cloudiness at a height of 1–2 km is limited by the inversion layer. Here are typical underdeveloped fair weather cumulus clouds. There are few rainfalls. Off the coast of Arabia in the Red Sea and the Persian Gulf, they do not exceed 100 mm per year. A completely different cloudiness is formed over the cold West Australian Current, where instead of cumulus clouds, thick stratocumulus clouds hang over the water surface without precipitation. Evaporation in these zones exceeds precipitation by 500-1000 mm.

In temperate and high latitudes, cloudiness sharply increases, both frontal and convection clouds develop, giving precipitation throughout the year. their number does not exceed 1000-2000 mm. Despite strong winds, evaporation in the temperate zone is negligible, because the air is sufficiently saturated with moisture. Precipitation is about 500-1000 mm higher than evaporation.

hydrological features. The movement of water on the surface of the Indian Ocean is due to the action of the wind, and at great depths - to an uneven distribution of density. Since surface waters are mainly mixed in the direction of wind systems, three large-scale circulations are clearly distinguished in the ocean: the monsoonal circulation, the southern subtropical anticyclonal current, and the Antarctic circumpolar current. The last two systems are similar to the corresponding systems of other oceans, but the south subtropical anticyclonal circulation differs from the Pacific and Atlantic ones in that it does not have a clearly defined eastern link along the coast of Australia. At the same time, its western link - the current of Cape Agulhas - is the strongest of such currents in the Southern Hemisphere. Its average speed is 1 m / s, and in some places it reaches 2 m / s.

A component of the subtropical anticyclonic circulation in the north is the South Tradewind current, which originates in the south of the island of Java and carries water from the Timor Sea and the Sunda Strait to the coast of Africa. On the approach to the island of Madagascar, it bifurcates. Most of the flow continues to move west, while a smaller part turns south along the eastern coast of Madagascar. Off the coast of South Africa, it merges with the Mozambique Current and gives rise to the Cape Agulhas Current. The latter is a narrow stream of blue water reaching the extreme southern point of Africa.

Having met with the green waters of the Antarctic Circumpolar Current, this current turns back, forming the Agulyaska Reverse Current. Thus, a small anticyclonal eddy about 300 km wide is formed in southern Africa. At the confluence of the Agulya Current with the northern jet of the Antarctic Circumpolar Current, a noticeably pronounced subantarctic front arises.

A separate independent whirlwind, structurally related to the subtropical circulation, is formed in the Great Australian Gulf.

Rather complex circulation in the northern part of the ocean, where monsoon winds prevail. During the southwest monsoon, the waters move clockwise. The monsoon cycle is formed by three main currents: the South Tradewind, Somali and Monsoon. During the southeast monsoon, oceanic circulation is less pronounced, and the movement of water is counterclockwise. To the north of the equator, the monsoon current develops for an event, off the coast of Somalia it turns south.

Between the equator and 8°S sh. an equatorial countercurrent forms across the ocean.

The general pattern of water circulation on the ocean surface persists down to a depth of 200 m with some minor changes associated with the drift of the currents.

In the subsurface layers of the equatorial latitudes, water is constantly moving eastward in view of the surface Equatorial countercurrent, discovered in 1959

At depths of 1000-2000 m, the water circulation changes from latitudinal to meridional. The nature of its movement depends on the bottom topography. In the African sector, waters move north along the western slopes of the basins, and in the opposite direction along the eastern ones. In the Asian-Australian sector, the positive forms of the bottom topography contribute to the development of cyclonic gyres and meanders. In negative forms, anticyclonic gyres develop.

In the water balance of the Indian Ocean, water exchange with the Atlantic and Pacific Oceans is of primary importance.

Almost 6 million km 3 of water per year enters the Indian Ocean from the Atlantic and a smaller amount flows through the Antarctic Current into the Pacific Ocean. Evaporation exceeds precipitation. These components of the water balance are 115,400 and 84,000 km 3 per year, respectively, so in many places the salinity of the waters is increased. River runoff from the continents - 6000 km 3 per year. Even less moisture (540 km 3) comes from continental ice.

Water masses form on the surface of the ocean or come from other places. In the process of direct exchange of energy and matter between the ocean and the atmosphere in a layer of water 200-300 m thick, in accordance with the development of planetary processes, surface waters are formed. their dynamics and physicochemical properties have latitudinal zonality.

Subsurface waters are formed in the polar latitudes due to the sinking of supercooled surface waters, and in tropical regions - in the process of sinking highly mineralized waters formed during high evaporation. The center of formation under surface water is also the Arabian Sea.

Intermediate waters are formed in the zone of the southern front from the surface waters of Antarctica. Lightly salted and cold waters, plunging under warm and salty ones, move northward to almost 10 ° N. sh., carrying with it a high concentration of oxygen, phosphates, nitrates, organic forms of phosphorus and nitrogen and other minerals. At a depth of 500-1000 m, these waters collide with the salty Red Sea-Arabian waters with a high concentration of phosphates and nitrates and a low oxygen content. Between 5 ° s. sh. and 10°S sh. there is an interaction and mixing of these waters with the intermediate waters of the Banda Sea. A new water mass appears.

Deep waters occur below 1000 m from the surface. It is believed that they are formed in the northern latitudes of the Atlantic, and penetrate into the Indian Ocean from the Atlantic through a wide passage between Africa and Antarctica north of the polar front. Spreading throughout the ocean, they slightly change their properties and thus enter the Pacific Ocean.

Bottom water masses are brought from the Antarctic circumpolar current from the Atlantic Ocean or are formed on the shelves of the Indo-Ocean sector of Antarctica. Heavy cold and salty waters sink to the bottom of the continental slope and, pouring over the low thresholds of the mid-ocean ridges, head north almost to the coast of Asia.

The temperature properties of water are subject to the same laws of latitudinal zonality as air temperature. Average long-term water temperatures gradually decrease from the equator to high latitudes. Cold waters off the coast of Antarctica (-1.8 ° C), warm (28 ° C) occupy large spaces along the equator. The highest temperatures are found in the semi-enclosed waters of the Persian Gulf (34°C) and the Red Sea (31°C). Sufficiently warm (30 ° C) water masses of the Arabian Sea and the Bay of Bengal.

The latitudinal temperature distribution is disturbed in the region of the Somali and Arabian peninsulas, where the direction of the isotherms is parallel to the coastline. This anomaly is caused by the upwelling of deep waters under the action of southwestern winds blowing along the coast.

The salinity of the waters depends on the ratio of precipitation and evaporation. In the Southern Hemisphere, the subtropical area of ​​high atmospheric pressure corresponds to a closed area of ​​high salinity (35.8 ‰). In the Northern Hemisphere, especially in the northwestern part of the Arabian Sea, where evaporation exceeds the amount of precipitation and runoff by 2500 mm, salinity reaches 36.5 ‰, and in semi-enclosed water bodies - more than 40 ‰. Between these areas of high salinity lies a spacious equatorial region of lower salinity (34.5% o), which adjoins a part of the tropical belt also of low salinity in the northeast. The lowest salinity (31.5 ‰) is in the Bay of Bengal.

Another area of ​​low salinity is Antarctica. During the melting of sea ice and icebergs, salinity on the surface decreases to 33.7 ‰.

Important physical characteristics of water are also its transparency and color. Let clear waters in the southern subtropical region. Between 20 and 36°S sh. this area reaches 20-40 m. In some places even 50 m. This is an area of ​​blue water without vegetation. To the north and south of it, the transparency decreases, and the color acquires a greenish tint. Green is usually a sign of organic life.

organic world. In tropical areas, unicellular algae trichodysmia are common. They develop so intensively, causing the water to become cloudy and change its color. In addition, there are many organisms in the ocean that glow at night. These are some jellyfish, ctenophores, etc. Brightly colored siphonophores, including poisonous physalia, are common here. In temperate latitudes, copepods, diatoms, and others are common.

There are three areas of planktonic algae in the Indian Ocean. The first of them covers the entire water area of ​​the Arabian Sea, the Bay of Bengal and the Andaman Sea. In each of these reservoirs, the distribution of phytoplankton is quite complex. The second region occupies the zone of deep waters rising, stretching across the entire ocean between 5 and 8 °S. sh. and is connected with the Intertrade countercurrent. The third area is the waters of Antarctica, among which the zone of collision of warm and cold waters is characterized by a special productivity.

Between the areas of high productivity are two areas of low productivity (deserts). The former occupies a narrow strip in the northern part of the ocean, in the convergence zone, while the latter occupies almost the entire central part of the ocean within the limits of the anticyclonic circulation. Phytoplankton biomass ranges from 0.1 mg/m 3 in aquatic deserts to 2,175 mg/m 3 near Java. The main role in the formation of biomass belongs to diatoms.

The distribution of zooplankton depends on the food supply. Most of it, especially the surface one, consumes phytoplankton, so its distribution is the same pattern as in the development of phytoplankton. Most zooplankton in the waters of Antarctica, the equatorial countercurrent, the Arabian and Andaman Seas in and the Bay of Bengal.

The distribution of benthos in general resembles the distribution of plankton. At the same time, it differs in quantity and quality composition, it is noticeably manifested in the coastal strip. The phytobenthos of tropical regions is characterized by the exuberant development of brown (Sargasso, turbinarium) and green (caulerpa) algae. Lush calcareous algae - lithotamnia and chalimeda - develop magnificently. Together with corals, they are involved in the formation of reef structures. A special phytocenosis is formed in the coastal zone with mangroves. In temperate latitudes, red (porphyra, helidium) and brown algae are most common, mainly from the group of fucus and kelp.

Zoobenthos is represented by various mollusks, limestone and silicon sponges, echinoderms (urchins, starfish, brittle stars, holothurians), numerous crustaceans, hydroids, bryozoans, and coral polyps.

The tropical zone is characterized by very poor and very rich organic areas. Sandy beaches of continents and islands, well warmed by the sun, but poor in organic matter, inhabited by extremely poor fauna. Also poor benthos of muddy areas of lagoons and estuaries due to stagnant water and the development of anaerobic processes. At the same time, in mangroves, benthos biomass reaches its maximum values ​​(up to 5-8 kg/m2). Very high coral reef biomass. In areas where there are no corals and coralobiontiv fauna accompanying them, the biomass of benthos is relatively low (3 g/m2).

The biomass of the zoobenthos of tropical latitudes averages 10-15 g/m2, while the biomass of the phytobenthos is much higher. Sargasso and red algae sometimes give 20 kg, and sea grasses - from C to 7 kg of biomass per 1 m 2.

An important role in the formation of the life groups of the Indian Ocean belongs to NEKTON - fish, squid, cetaceans and some other groups of ocean animals. The distribution of non-ton animals is subject to latitudinal and Circum-continental zonality, and areas rich in fish, squid and cetaceans located in bioproductive areas. More nekton animals are not near the coasts and not in the zone of upwelling or divergence, but at some distance from them. This is explained by the fact that in the zones of the emergence of deep waters, the maximum generation of phytoplankton occurs, and its main mass is carried away by the current and eaten by young zooplankton here. The maximum number of predatory forms of zooplankton shifts even further downstream. The same trend is typical for nekton. In unproductive areas of the open ocean, the number of fish and squid drops sharply. There are also very few cetaceans (sperm whales, giants, dolphins).