Indian Ocean

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Indian Ocean,

third largest ocean, c.28,350,000 sq mi (73,427,000 sq km), extending from S Asia to Antarctica and from E Africa to SE Australia; it is c.4,000 mi (6,400 km) wide at the equator. It constitutes about 20% of the world's total ocean area. The Indian Ocean is connected with the Pacific Ocean by passages through the Malay Archipelago and between Australia and Antarctica; and with the Atlantic Ocean by the expanse between Africa and Antarctica and by the Suez Canal. Its chief arms are the Arabian Sea (with the Red Sea, the Gulf of Aden, and the Persian Gulf), the Bay of Bengal, and the Andaman Sea. The continental shelf of the Indian Ocean is narrow. Madagascar and Sri Lanka, the largest islands in the ocean, are structurally parts of the continents as are Socotra, the Andaman Islands, and the Nicobar Islands; the Seychelles and the Kerguelen Islands are exposed tops of submerged ridges. The Laccadives, the Maldives, and the Chagos are low coral islands, and Mauritius and Réunion are high volcanic cones. The floor of the Indian Ocean has an average depth of c.11,000 ft (3,400 m). The Mid-Oceanic Ridge, a broad submarine mountain range extending from Asia to Antarctica, divides the Indian Ocean into three major sections—the African, Antardis, and Australasian. The ridge rises to an average height of c.10,000 ft (3,000 m), and a few peaks emerge as islands. A large rift, an extension of the eastern branch of the Great Rift Valley that runs through the Gulf of Aden, extends along most of its length (see seafloor spreadingseafloor spreading,
theory of lithospheric evolution that holds that the ocean floors are spreading outward from vast underwater ridges. First proposed in the early 1960s by the American geologist Harry H.
..... Click the link for more information.
). The Mid-Oceanic Ridge, along with other submarine ridges, encloses a series of deep-sea basins (abyssal plains). The greatest depth (25,344 ft/7,725 m) is in the Sunda, or Java, Trench, S of Java, Indonesia. The Indian Ocean receives the waters of the Zambezi, Tigris-Euphrates, Indus, Ganges-Brahmaputra, and Irrawady rivers. The surface waters of the ocean are generally warm, although close to Antarctica pack ice and icebergs are found. The Indian Ocean has two water circulation systems—a regular counterclockwise southern system (South Equatorial Current, Mozambique Current, West Wind Drift, West Australian Current) and a northern system, the Monsoon Drift, whose currents are directly related to the seasonal shift of monsoon winds. The southwest monsoon draws moisture from the Indian Ocean and drops heavy rainfall on the Indian subcontinent and Southeast Asia.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Indian Ocean


the third largest ocean on earth (after the Pacific and the Atlantic). It lies for the most part in the southern hemisphere between Asia on the north, Africa on the west, Australia on the east, and Antarctica on the south. It is joined to the Atlantic Ocean in the southwest and the Pacific Ocean in the east and southeast. Its area, with its seas, is 74,917,000 sq km, its average depth is 3,897 m, and its average water volume is 291,945,000 cu km (without the seas, the corresponding figures are 73,442,700 sq km, 3,963 m, and 291,030,000 cu km).

The Indian Ocean has the smallest number of seas of all the world oceans. The largest seas are found in the northern part: the Red Sea and the Persian Gulf, which are inland seas, the partially enclosed Andaman Sea, and the outlying Arabian Sea. The Arafura and Timor seas are in the eastern part of the ocean.

Islands.. There are relatively few islands. The largest are continental and are located off coasts; they include Madagascar, Sri Lanka, and Socotra. Volcanic islands (including the Mascarene Islands, Crozet Islands, and Prince Edward Islands) are in the open parts of the ocean. Coral islands (including the Maldive Islands, Laccadive Islands, Chagos Islands, and Cocos Islands and most of the Andaman Islands) rise from volcanic piles in tropical latitudes.

Coasts.. The coasts in the northwest and east are original, while alluvial coasts predominate in the northeast and west. The coastline is gently indented with the exception of the northern part of the Indian Ocean. Almost all the seas and large gulfs are found here (the Gulf of Aden, Gulf of Oman, and Bay of Bengal). The Gulf of Carpentaria, Great Australian Bight, Spencer Gulf, and Gulf of St. Vincent lie in the southern part.

Relief and geological structure of the floor. A narrow continental shelf (up to 100 km), the outer periphery of which has depths of 50-200 m (up to 300-500 m only near Antarctica and northwestern Australia), extends along the shores. The continental slope consists of a steep scarp (up to 10°-30°), dissected in places by the underwater valleys of the Indus, Ganges, and other rivers. The Sunda Islands arc and the associated Sunda Trench, which has a maximum depth of 7,130 m, are in the northeastern part of the ocean. The bed of the Indian Ocean is divided by ridges, mountains, and arches into a number of basins, the most important of which are the Arabian Basin, West Australian Basin, and Atlantic-Indian Basin. The floors of these basins consist of aggradation plains and hilly plains. The former are found near mainlands in regions receiving much sedimentary material; the latter are in the central part of the ocean. Among the numerous ridges of the ocean bed the meridional East Indian Ridge, which is connected to the latitudinal West Australian Ridge in the south, is distinguished for its straightness and length (approximately 5,000 km). Large meridional ridges extend southward from the Hindustan Peninsula and the island of Madagascar. Volcanoes are widespread on the ocean floor (Mounts Bardin, Shcherbakov, Lena, and others). In certain areas they form large massifs (north of Madagascar) and chains (east of the Cocos Islands). Midoceanic ridges form a mountain system consisting of three branches that spread out from the central part of the ocean toward the north (the Arabian-Indian Ridge), the southwest (the West Indian and Atlantic-Indian ridges), and the southeast (the Mid-Indian Ridge and Australian-Antarctic Rise). This system has widths of 400-800 km and elevations of 2-3 km. It is most deeply dissected by an axial (rift) zone with deep valleys and bordering rift mountains. Transverse faults, along which horizontal displacements of the bottom for up to 400 km are found, are characteristic of this system. The Australian-Antarctic Rise, in contrast to the midoceanic ridges, is a more gently sloping arch with elevations of 1 km and widths of up to 1,500 km.

Bottom deposits of the Indian Ocean are thickest (up to 3-4 km) at the foot of continental slopes. They are least thick (approximately 100 m) in the center of the ocean, and in areas of rugged relief they are haphazardly distributed. Foraminiferal (on continental slopes, ridges, and on the floors of most basins at depths up to 4,700 m), diatomaceous (south of 50°S lat.), radiolarian (near the equator), and coral sediments are most widespread. Polygenous sediments (red mud) are found south of the equator at depths of 4.5-6 km and over. Terrigenous sediments are found near continental coasts. Chemogenic sediments consist principally of ferromanganese concretions. Riftogenic sediments are represented by products of the disintegration of abyssal rock. Outcrops of bedrock are encountered most frequently on continental slopes (sedimentary and metamorphic rock), mountains (basalt), and midoceanic ridges, where, in addition to basalt, serpentines and peridotites representing little changed substances from the upper mantle of the earth have been discovered.

Tectonic structures. A predominance of stable tectonic structures both on the bed (thalassocratons) and along the periphery (continental platforms) is characteristic of the Indian Ocean. Actively developing structures—modern geosynclines (the Sunda Islands arc) and georiftogenes (midoceanic ridges)—occupy smaller areas and are continued in corresponding structures of Indochina and the rifts of East Africa. These basic macrostructures, sharply distinguished in terms of morphology, structure of the earth’s crust, seismic activity, and volcanism, are subdivided into smaller structures: platforms, which generally correspond to floors of oceanic basins; block ridges; volcanic ridges, which in certain areas are crowned by coral islands and banks (Chagos Islands, Maldive Islands); trench-fractures (Chagos, Ob’, and others), which are frequently found at the foot of block ridges (East Indian, West Australian, Maldive); fracture zones; and tectonic scarps. The northern part of the Mascarene Ridge, which, apparently, was part of the ancient continent of Gondwanaland, is unique among structures of the floor of the Indian Ocean in terms of the presence of bedrock (the granites of the Seychelles Islands) and the continental type of the earth’s crust.

Minerals in shelf areas include oil and gas (particularly in the Persian Gulf) and monazite (offshore area near southwestern India). In rift zones there are chrome, iron, manganese, copper, and other ores, and on the ocean floor there are vast concentrations of ferromanganese concretions.


Climate. The northern part of the Indian Ocean has a monsoon climate. In the summer, when low-pressure regions develop over Asia, southwest flows of equatorial air prevail here. In winter there are northeast flows of tropical air. South of 8°-10° S lat. atmospheric circulation is distinguished by much greater uniformity. Here at tropical latitudes (and even in subtropical latitudes in the summer) stable southeast trade winds prevail, and in temperate latitudes, nontropical cyclones moving from west to east. In the summer and fall there are hurricanes in tropical latitudes in the western part. The average air temperature in the northern part of the ocean in the summer is 25°-27°C, and near Africa it is up to 23°C. In the southern part the temperature decreases during the summer to 20°-25°C at 30° S lat., to 5°-6°C at 50° S lat., and to below 0°C south of 60° S lat. In the winter the air temperature varies from 27.5°C at the equator to 20°C in the northern part, to 15°C at 30° S lat., to 0°-5°C at 50° S lat., and to below 0°C south of 55°-60° S lat. Owing to the effect of the warm Madagascar Current the temperature year round in southern subtropical latitudes is 3°-6°C higher in the west than in the east, where the cold West Australian Current passes. Cloudiness in the northern monsoon part of the Indian Ocean is 10-30 percent in the winter and up to 60-70 percent in the summer. The largest amount of precipitation also falls during the summer. The average annual precipitation in the eastern part of the Arabian Sea and the Bay of Bengal is more than 3,000 mm; near the equator precipitation is 2,000-3,000 mm; and in the western part of the Arabian Sea, up to 100 mm. In the southern part of the ocean average annual cloudiness is 40-50 percent, and south of 40° S lat. it is up to 80 percent. Average annual precipitation in the subtropics is 500 mm in the east and 1,000 mm in the west. In temperate latitudes precipitation is more than 1,000 mm, and near Antarctica it decreases to 250 mm a year.

Hydrologic conditions. Circulation of surface waters in the northern part of the Indian Ocean is monsoonal. In summer there are northeastern and eastern currents, and in winter there are southwestern and western currents. During the winter months the Intertradewind (Equatorial) Countercurrent develops between 3° and 8° S lat. In the southern part of the Indian Ocean the water circulation has an anticyclonic circulation pattern, which is formed by warm currents (the Tradewind, or South Equatorial, Current and the Madagascar and Cape Needle currents in the west) and cold currents (South Indian Ocean Current in the south and West Australian Current in the east). Several weak cyclonic water circulation patterns enclosed by the Antarctic Circumpolar Current near the coasts of Antarctica develop south of 55° S lat.

The thermal balance is predominantly positive and amounts to 3.7-6.5 gigajoules/(m2, yr), or 88-156 kilocalories/(cm2.yr), between 10° and 20° N lat.; 1.0-1.8 gigajoules/(m2.yr), or 25-43 kilocalories/(cm2.yr), between 0° and 10° S lat.;—0.67-0.38 gigajoules/(m2.yr), or from—16 to 9 kilocalories/(cm2.yr), between 30° and 40° S lat.; 2.34-3.3 gigajoules/(m2• yr), or 56-80 kilocalories/(cm2.yr), between 40° and 50° S lat.; and from— 1.0 to—3.6 gigajoules/(m2.yr), or from—24 to—86 kilocalories/(cm2.yr), south of 50° S lat. The balance of thermal expenditures north of 50° S lat. results principally from heat loss owing to evaporation, and south of 50° S lat., from heat exchange between the ocean and the atmosphere.

The water temperature at the surface of the ocean reaches a maximum (over 29°C) in May in the northern part of the ocean. In the summer the water temperature at the surface in the northern hemisphere is 27°-28°C; only near the coast of Africa does it decrease to 22°-23°C owing to the rise to the surface of cold waters from the ocean depths. At the equator the temperature is 26°-28°C, and it decreases to 16°-20°C at 30° S lat., to 3°-5°C at 50° S lat., and to below - 1°C south of 55° S lat. In the winter the temperature in the northern hemisphere is 23°-25°C in the north, 28°C at the equator, 21°-25°C at 30° S lat., from 5° to 9°C at 50° S lat., and below 0°C south of 60° S lat. In subtropical latitudes the water temperature the year round is 3°-5°C higher in the west than in the east.

Salinity of the water depends on the water balance, which for the surface of the Indian Ocean is formed by evaporation (— 1,380 mm/yr), precipitation (1,000 mm/yr), and continental drainage (70 cm/yr). The main freshwater drainage is contributed by the rivers of southern Asia (Ganges, Brahmaputra, and others) and Africa (Zambezi, Limpopo). The highest salinity is observed in the Persian Gulf (37-39 parts per thousand [%c]), the Red Sea (41 %c), and the Arabian Sea (more than 36.5%e). In the Andaman Sea and the Bay of Bengal salinity decreases to 32.0-33.0%c, and in the southern tropics it decreases to 34.0-34.5%c. In southern subtropical latitudes salinity exceeds 35.5%o (a maximum of 36.5%? in the summer and 36.0%c in the winter). South of 40° S lat., salinity decreases to 33.0-34.3%c.

The greatest water density is found at antarctic latitudes (1,027) and the lowest, in the northeastern part of the ocean and in the Bay of Bengal (1,018 and 1,022, respectively). In the northwestern part of the Indian Ocean the water density is 1,024. The oxygen content in the surface layer of water increases from 4.5 ml/l (milliliters per liter) in the northern part of the Indian Ocean to 7-8 ml/l south of 50° S lat. At depths of 200-400 m the oxygen content in terms of absolute quantity is considerably less and varies from 0.21-0.76 in the north to 2-4 ml/l in the south. At greater depths the oxygen content again gradually increases, and in layers near the bottom it equals 4.03-4.68 ml/l. The water color is for the most part dark blue, at antarctic latitudes the water is light blue, and in certain areas it has greenish tinges.

As a rule, tides in the Indian Ocean are small. (Off coasts of the open part of the ocean and for islands they vary from 0.5 to 1.6 m.) Only at the tips of certain gulfs do they reach 5-7 m. In the Gulf of Cambay tides are 11.9 m. Tides are primarily semidiurnal.

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

Deep-sea circulation and the vertical structure of the Indian Ocean are produced by waters that sink in subtropical (subsurface waters) and antarctic (middle waters) zones of convergence and along the continental slope of Antarctica (benthal waters), as well as by waters that enter from the Red Sea and the Atlantic Ocean (deep-sea waters). Subsurface waters at depths from 100-150 m to 400-500 m have temperatures of 10°-18°C and a salinity of 35.0-35. l%c Middle waters are found at depths ranging from 400-500 m to 1,000-1,500 m; their temperatures vary from 4° to 10°C and the salinity is 34.2-34.6%c. Deep-sea waters at depths from 1,000-1,500 m to 3,500 m have temperatures of 1.6°-2.8°C and a salinity of 34.68-34.78%o. In the south benthal waters below 3,500 m have temperatures of from—0.07° to—0.24°C and a salinity of 34.67-34.69 %c\ and in the north the figures for benthal waters are approximately 0.5°C and 34.69-34.77%c, respectively.


Flora and fauna. The whole expanse of the Indian Ocean lies within the tropical and southern temperate zones. The shallows of the tropical zone are characterized by Zoantharia, Oc-tocorallia, and Hydrocorallia, which, together with calcareous red algae, are capable of forming islands and atolls. Rich fauna consisting of diverse invertebrates (sponges, worms, crabs, mollusks, sea urchins, ophiuroids, and starfish) and small but brightly colored coral fish dwell among the thick coral structures. Most of the coastal regions are covered with mangrove thickets, in which the mudskipper—a fish capable of existing for long periods in an air environment—is found. The fauna and flora of beaches and cliffs that dry during low tides have been quantitatively depleted as a result of the oppressive effect of the sun’s rays. In the temperate zone life in such coastal areas is much more richly represented. Thick growths of red and brown algae (Laminaria, fucuses, and macrocystis that attain vast dimensions) are well developed here, and diverse forms of invertebrates are found in great abundance. Rich flora is also characteristic of open expanses of the Indian Ocean, especially of the surface layer of open water (up to 100 m). Several species of Peridineae and diatoms (unicellular planktonic algae) predominate, and in the Arabian Sea there are blue-green algae, which frequently cause so-called water bloom under conditions of massive growth.

The animals of the Indian Ocean basically consist of Copepoda crustaceans (more than 100 species), followed by Pteropoda, jellyfish, Siphonophora, and other invertebrates. Among unicellular animals, Radiolaria are characteristic; squid are numerous. Fish are most commonly represented by several species of flying fish, lanternfish (Myctophidae), dolphin, large and small tuna, sailfish, and various sharks; there are also poisonous sea snakes. Sea turtles and large sea mammals (dugongs, toothed and whalebone whales, pinnipeds) are widespread. Most common among birds are albatrosses and frigate birds as well as several species of penguins, which inhabit the coasts of southern Africa and Antarctica and islands lying in the temperate zone of the ocean.


The history of the exploration of the Indian Ocean can be divided into three periods: (1) from ancient voyages to 1772, (2) from 1772 to 1873, and (3) from 1873 to the present. The first period was characterized by study of the distribution of ocean water and land in this part of the world. It began with the first voyages of Indian, Egyptian, and Phoenician seafarers who traveled through northern parts of the Indian Ocean in the years 3000-1000 B.C. and ended with the voyage of J. Cook, who journeyed as far as 71° S lat. in the period 1772-75. The second period was marked by the initiation of deep-water research, first undertaken by Cook in 1772 and continued by Russian and foreign expeditions. The main Russian expeditions were those of O. von Kotzebue on the Riurik (1818) and of Pallen on the Tsiklon (1858-59). The third period has been characterized by comprehensive oceanographic research. Up to 1960 such research was conducted on individual ships. The most important projects were carried out by expeditions on the ships Challenger (England) in 1873-74; Vitiaz’ (Russia), 1886; Valdivia (Germany), 1898-99; Gauss (Germany), 1901-03; Discovery II - (England), 1930-51; and the Soviet expedition on the Ob’, 1956-58. From 1960 to 1965, UNESCO’s Intergovernmental Oceanographic Commission organized the International Indian Ocean Expedition, which collected new and valuable information on the hydrology, hydrochemistry, meteorology, geology, geophysics, and biology of the Indian Ocean. Soviet and foreign scientists actively participated in this expedition on the research vessels Vitiaz’, A. I. Voeikov, and Iu. M. Shokal’skii and the nonmagnetic schooner Zaria (USSR); Natal (Republic of South Africa); Diamantina (Australia); Kistna and Varuna (India); and Zuli-quar (Pakistan).


Zenkevich, L. A. Fauna i biologicheskaia produktimost’ moria, vol. 1. Moscow, 1951.
Muromtsev, A. M. Osnovnye cherty gidrologii Indiiskogo okeana. Leningrad, 1959.
Illegible Zemli (Morfostruktura i morfoskul’pturd).Moscow, 1967.
The Oceans, 7th ed. New York, 1957.
Subsea Mineral Resources and Problems Related to Their Development, Washington, 1969.


The penetration of the basin of the Indian Ocean by Europeans (the Portuguese, then the Dutch, French, and English) dates to the 16th and 17th centuries. By the middle of the 19th century most of its coastal areas and islands had been secured by Great Britain, which exported those raw materials and foodstuffs that were most important for its economy. Naval bases (and later air bases) were set up at all entrances to the Indian Ocean: Simonstown in the Atlantic Ocean, Singapore in the Pacific Ocean, Aden in the Red Sea, and Trincomalee at approaches to India. Colonies of France, the Netherlands (Dutch India), and Portugal were located in the northeastern part of the Indian Ocean.

After World War II (1939-45) the break-up of the colonial system of imperialism brought about fundamental changes in the political map of the basin of the Indian Ocean. The following states became independent: in Asia, Bangladesh, Bahrain, Burma, India, Qatar, Kuwait, the Maldive Republic, the People’s Democratic Republic of Yemen, United Arab Emirates, Pakistan, Sri Lanka (Ceylon), Indonesia, and Malaysia; and in Africa, Kenya, Mauritius, Malagasy Republic (Madagascar), Somali Republic, Sudan, and Tanzania. As a result of the July Revolution of 1952, Egypt freed itself from semicolonial dependence.

Freight traffic and navigation. The overall volume of goods transported by sea across the Indian Ocean is considerably lower than that across the Atlantic and Pacific oceans. It constitutes approximately 10 percent of the world’s freight turnover. In an economic sense a majority of the above-named countries are developing countries. Exports from countries of the Indian Ocean consist mainly of raw materials and foodstuffs, and imports consist of manufactured goods. Because of the lack of development of the merchant marine of these countries, longdistance shipping by sea is effected mainly by chartered foreign vessels. The most important freight, including both exports from Indian Ocean countries and transit freight, consists of oil and petroleum products, almost entirely from Persian Gulf ports to Western Europe, the United States, and Japan; iron, manganese, and chrome ores from India to Japan; tin from Malaysia and Indonesia; tungsten from Burma; copper and cobalt from Zambia; rice from Burma; cotton from India, Pakistan, and the Sudan; jute from Bangladesh (its main exporter); rubber from Malaysia, Indonesia, and Sri Lanka; spices from Indonesia, East African countries, and the Malagasy Republic; wool from Australia; and tea from India and Sri Lanka. The principal imported freights are cloth, metals, machinery, and cement. The most important transit freights of the Indian Ocean include rubber and sugar from Indonesia; rice and timber from Thailand; non-ferrous metals, wheat, and wool from Australia; and meat and dairy products from New Zealand.

All principal Indian Ocean freight traffic converges and diverges at the southern entrance to the Red Sea. Here begins Suez freight traffic, which, however, has been inactive since June 1967 owing to the aggressive actions of Israel in the Suez Canal zone. Until navigation through the canal is resumed, this freight traffic moves from the junction at the entrance to the Red Sea along the eastern coast of Africa, merging with East African freight traffic, which passes through the commercial ports of East Africa. Data for 1966 show that 241.8 million tons of freight were shipped through the Suez Canal, of which 194.1 million tons were transported from south to north (80 percent of which were oil cargoes) and 47.7 million tons, from north to south.

India-Far East freight traffic, which is joined by oil freight traffic from the Persian Gulf, has the second greatest volume (after Suez traffic) of the Indian Ocean. By the end of the 1960’s the volume of freight traffic here had significantly increased owing to oil imports by Japan (100 million tons of oil a year, that is, up to 90 percent of the oil imported by this country). This freight traffic includes considerable shipments of iron and manganese ores from India to Japan.

Southern freight traffic proceeds from the southern tip of Australia to the Cape of Good Hope. It mainly serves transport between Australia and America.

Open-sea freight traffic moves from the junction at the entrance to the Red Sea to the southern coast of Australia and from the Cape of Good Hope to the Western Channel. (This is the route followed by ships going from Europe to the Far East after the closing of the Suez Canal.)

Australian freight traffic moves along the western coast of Australia.

The route between Soviet European seas and the Soviet Far East and Kamchatka lies across the Indian Ocean. Regular passages between Soviet ports and countries of Africa, Asia, and Australia, with whom the Soviet Union maintains commercial ties, are effected along this route.

Main commercial ports. After World War II (1939-45) new oil ports and moorings that are accessible to supertankers have been built in the Persian Gulf by a number of states. These ports include Mina al-Ahmadi in Kuwait, Khark in Iran, Ra’s at Tannurah in Saudi Arabia, and Khuwr al-Amaya in Iraq. Less deep ports include Abadan, Bandar-e Shahpur, and Bandar-e Mah Shar in Iran and Basra and Fao in Iraq. The principal ports for dry freight are Dammam in Saudi Arabia and Manama in the Bahrain Islands.

The commercial port of Aden (People’s Democratic Republic of Yemen), which is accessible to large ships, is situated at the entrance to the Red Sea. The largest ports in India are Bombay and Calcutta (mostly imports), Madras, and Vishakhapatnam; in Pakistan, Karachi; in Bangladesh, Chittagong; in Sri Lanka, Colombo; in Burma, Rangoon; at the entrance from the Pacific Ocean, Singapore; in Australia, Fremantle; in the Republic of South Africa, Durban and Port Elizabeth; in Mozambique, Lou-renco Marques and Beira; in Kenya, Mombasa; in Tanzania, Dar es Salaam; in the Malagasy Republic, Tamatave; and in the Somali Republic, Mogadisho.

Air transport.. The basic network of Indian Ocean air routes passes over the northern part of the ocean in the region of the Persian Gulf, the Arabian Sea, and the Bay of Bengal. These routes are traveled by planes of American, British, and French companies and by planes of independent Asian and African countries. Countries in the basin of the Indian Ocean are linked through these air routes to Western Europe and the Soviet Union. The largest connecting airport is in Rome, from where airlines pass through Athens and Beirut to Cairo; from Cairo to Rangoon through Manama, Karachi, Bombay, and Calcutta (with a number of branch lines through Sri Lanka to Indonesia and Australia); and to Pretoria through Cairo, Nairobi, Khartoum, and Salisbury. The open parts of the Indian Ocean are crossed by one route that begins in Nairobi and Pretoria, passes through the islands of Madagascar, Reunion, Mauritius, and the Cocos group, and proceeds to southern Australia (Perth). There are air routes from the USSR to India, Burma, Malaysia, Sri Lanka, the Somali Republic, Tanzania, and other countries of the Indian Ocean.

Telegraph communications. There is a ramified network of radio stations along the coasts and on the islands of the Indian Ocean. Cables operate that link Great Britain with India by several parallel lines. Junction points for the cable crossing the Indian Ocean are Mahé (Seychelles Islands), the island of Mauritius, and the Cocos Islands.

Fishing and marine industry. Fishing is poorly developed (the catch does not exceed 5 percent of the world total) and is limited to local offshore zones. Tuna is caught near the equator (Japan), and there is whaling in antarctic waters. Pearl and mother-of-pearl are obtained in Sri Lanka, the Bahrain Islands, and on the northwestern coast of Australia.

There are rich oil deposits in the basin of the Persian Gulf. Oil is extracted both from land deposits and underwater deposits in shelf areas. The Indian Ocean countries also have considerable resources of other valuable types of mineral raw materials (tin, iron and manganese ores, natural gas, diamonds, and phosphorites).


Briliant, L. A. Geografiia morskikh putei. Moscow, 1966.
Morskoi Atlas, vol. 3, part 2. Moscow, 1963. Map, 54-55.
Zaleski, J. Geografiia morskogo transporta. Moscow, 1971. (Translated from Polish.)
Nadtochii, G. L. Geografiia morskikh putei. Moscow, 1972.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

Indian Ocean

[′in·dē·ən ′ō·shən]
The smallest and geologically the most youthful of the three oceans, whose surface area is 29,300,000 square miles (75,900,000 square kilometers); it is bounded on the north by India, Pakistan, and Iran; on the east by the Malay Peninsula; on the south by Antarctica; and on the west by the Arabian peninsula and Africa.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

Indian Ocean

an ocean bordered by Africa in the west, Asia in the north, and Australia in the east and merging with the Antarctic Ocean in the south. Average depth: 3900 m (13 000 ft.). Greatest depth (off the Sunda Islands): 7450 m (24 442 ft.). In December 2004 a major undersea earthquake off Sumatra triggered a tsunami which affected large areas of the ocean as far away as east Africa, and killed around 275 900 people. Area: about 73 556 000 sq. km (28 400 000 sq. miles)
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
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