Indian Ocean description. Temperature, salinity and density of surface waters
The Indian Ocean is the first ocean to be discovered by great pioneers. Today Indian Ocean covers about 20% of the Earth's water surface and is considered the third largest basin of the World Ocean. Most of the Indian Ocean is located in the Southern Hemisphere. The Indian Ocean washes the shores of Africa, Asia, Antarctica and Australia.
The Indian Ocean includes several seas and gulfs - the Red, Arabian, Andaman Seas, as well as the Persian, Oman, Great Australian, Aden and Bengal Bays. World-famous tourist islands such as Madagascar, Sri Lanka, Seychelles and Maldives are also part of the Indian Ocean.
The first voyages to the Indian Ocean were made back in the days of the most ancient centers of civilization. It is believed that the first written civilization, the Sumerians, were the first to conquer the Indian Ocean. Back in the 4th millennium BC, the Sumerians, who lived in the southeast of Mesopotamia, made voyages to the Persian Gulf. In the 6th century BC, the Phoenicians were the conquerors of the ocean. With the advent of our era, the Indian Ocean began to be explored by residents of India, China and Arab countries. In the 8th-10th centuries, China and India established constant trade relations with each other.
The first attempt to explore the Indian Ocean during the Great Geographical Discoveries was made by the Portuguese navigator Peru da Covilha (1489-1492). The Indian Ocean owes its name to one of the most famous navigators of the era of great geographical discoveries - Vasco da Gama. His expedition crossed the Indian Ocean in the spring of 1498 and arrived on the southern coast of India. It was in honor of the rich and beautiful India that the ocean was named Indian. Until 1490, the ocean was called the Eastern Ocean. And the ancient people, believing that this large sea, called the ocean the Erythraean Sea, the Great Gulf and the Indian Red Sea.
The average temperature of the Indian Ocean is 3.8 degrees Celsius. The highest water temperature is observed in the Persian Gulf - over 34 degrees. In the Antarctic waters of the Indian Ocean, the temperature surface waters drops to 1 degree. The ice of the Indian Ocean is seasonal. Permanent ice found only in Antarctica.
The Indian Ocean is rich in oil and gas deposits. The largest geological reserves of oil and gas are located in the waters of the Persian Gulf. There are also several oil fields on the shelves of Australia and Bangladesh. Gas deposits have been identified in almost all seas included in the Indian Ocean basin. In addition, the ocean is rich in deposits of other minerals.
The Indian Ocean is interesting because amazing luminous circles appear on its surface from time to time. Scientists cannot yet explain the nature of the appearance of these phenomena. Presumably, these circles arise as a result of a large concentration of plankton, which tends to float up and form luminous circles on the surface.
The Second World War did not spare the Indian Ocean either. In the spring of 1942, a military operation known as the Indian Ocean Raid took place in the waters of the Indian Ocean. During the operation, the Imperial Japanese Navy defeated the Eastern Fleet of the British Empire. These are not the only military battles that took place in the ocean waters. In 1990, a battle took place in the waters of the Red Sea between the Soviet artillery boat AK-312 and Eritrean armed boats.
The history of the Indian Ocean is rich and interesting. The waters of the ocean contain many mysteries and secrets that have never been solved throughout the rich history of mankind.
Bookmark this page:The Indian Ocean is the third largest ocean. Geologically it is largely a relatively young ocean, although it should be noted, as with other oceans, that many aspects of its earliest geological history and origins are not yet understood. Western border south of Africa: along the meridian of Cape Agulhas (20° E) to Antarctica (Donning Maud Land). Eastern border south of Australia: along the western border of Bass Strait from Cape Otway to King Island, then to Cape Grim (North-West Tasmania) and from the south-eastern tip of the island of Tasmania along 147° E. to Antarctica (Fisher Bay, George V Coast). There has been much debate regarding the eastern border north of Australia, due to the fact that some scientists attribute the Arafura Sea, and some even the Timor Sea
sea to the Pacific Ocean, although this is not entirely logical, since the Timor Sea, by the nature of the hydrological regime, is inextricably linked with the Indian Ocean, and the Sahul shelf, geologically, is clearly part of the North-West Australian Shield, connecting the area of the once existing Gondwana with the Indian ocean Most geologists draw this boundary along the narrowest (western) part of the Torres Strait; according to the definition of the International Hydrographic Office, the western border of the strait runs from Cape York (11° 05" S, 142° 03" E) to the mouth of the Bensbeck River ( New Guinea) (141° 01" E), which also coincides with the eastern border of the Arafura Sea.
The northeastern border of the Indian Ocean runs (from island to island) through the Lesser Sunda Islands to the islands of Java, Sumatra and then to the islands of Singapore. About the marginal seas of the Indian Ocean, located along its northern border. The area south of the Cape Agulhas-Cape Louin line (Western Australia) is sometimes considered the southern sector of the Indian Ocean.
Indian Ocean area within the boundaries excluding the Arafura Sea 74,917 thousand km2, with the Arafura Sea 75,940 thousand km. Average depth 3897 m; maximum recorded depth 7437 m3. Volume of Indian Ocean waters 291,945 thousand km3.
Bottom relief
Bathymetrically, the Indian Ocean can be divided into five morphological units.Mainland margins
The Indian Ocean shelves are on average slightly narrower than the Atlantic Ocean shelves; their width ranges from a few hundred meters around some oceanic islands to 200 km or more in the Bombay area. The bend that forms the outer edge of the shelves of Africa, Asia and Australia has an average depth of 140 m. The boundary of the continental platform is formed by the continental slope, steep marginal scarps and the slopes of the trenches.
The continental slope is cut through by numerous underwater canyons. Particularly long underwater canyons lie along the continuation of the mouths of the Ganges and Indus rivers. The continental foot has slopes from 1:40 at the border with the continental slope to 1:1000 at the border with the abyssal plains. The relief of the continental foot is characterized by isolated seamounts, hills and canyons. Submarine canyons at the foot of the continental slope are usually narrow in diameter and difficult to detect, so few of them have been well surveyed. The areas around the mouths of the Ganges and Indus rivers have large accumulations of sediment known as archipelagic fans.
The Java Trench stretches along the Indonesian arc from Burma to Australia. On the Indian Ocean side it is bordered by a gently sloping outer ridge.
ocean bed
The most characteristic elements of the relief of the ocean floor are the abyssal plains. The slopes here range from 1: 1000 to 1: 7000. With the exception of isolated peaks of buried hills and mid-ocean canyons, the height of the relief of the ocean floor does not exceed 1-2 m. The abyssal plains of the northern and southern parts of the Indian Ocean are very clearly expressed, but near Australia they are less pronounced. The seaward margins of abyssal plains are usually characterized by abyssal hills; Some areas are characterized by low, linearly elongated ridges.
Microcontinents
The most characteristic feature of the bottom topography of the Indian Ocean are microcontinents elongated from north to south. In the northern part of the Indian Ocean, in the direction from west to east, the following aseismic microcontinents can be identified: Mozambique Ridge, Madagascar Ridge, Mascarene Plateau, Chagoss-Laccadive Plateau, Ninetiest Ridge. In the southern part of the Indian Ocean, the Kerguelen Plateau and the asymmetrical Broken Ridge, which extends from east to west, have a noticeable meridional linearity. Morphologically, microcontinents are easily distinguished from a mid-ocean ridge; they usually represent higher areas of massifs with more leveled relief.
A clearly defined microcontinent is the island of Madagascar. The presence of granites in the Seychelles also suggests that at least the northern part of the Mascarene Plateau is of continental origin. The Chagos Islands are coral islands rising above the surface of the Indian Ocean in the area of the vast, gently curved Chagos-Laccadive Plateau. The Ninetiest Ridge is perhaps the longest and most linear ridge discovered in the World Ocean during the International Indian Ocean Expedition. This ridge was traced from 10° N. w. up to 32° S
In addition to the microcontinents mentioned above, there is a distinct Diamantina fault zone in the Indian Ocean for 1,500 miles west of the southwestern tip of Australia. Broken Ridge, which forms the northern boundary of this fault zone, at 30° S. w. connects to the Ninetyist Ridge, which runs at right angles to the Diamantina fault zone in a north-south direction.
Mid-ocean ridge
The most pronounced feature of the Indian Ocean floor is the Central Indian Ridge, part of the global mid-ocean ridge, which in the central Indian Ocean is shaped like an inverted V. Along the axis of this mid-ocean ridge runs a seismically active depression, or rift. The entire ridge has a generally mountainous topography with strikes parallel to the axis ridge.
Fracture zones
The Indian Ocean is dissected by several clearly defined fault zones that displace the axis of the mid-ocean ridge. To the east of the Arabian Peninsula and the Gulf of Aden is the Owen Fracture Zone, which shifts the axis of the mid-ocean ridge approximately 200 miles to the right. The recent formation of this displacement is indicated by the Whatli Trench, a well-defined depression with depths more than 1000 m greater than the depths of the Indian Abyssal Plain.
Several small right-lateral strike-slip faults displace the axis of the Carlsberg Ridge. In the Gulf of Aden, the axis of the mid-ocean ridge is displaced by several sinistral strike-slip faults running almost parallel to the Owen Fracture Zone. In the southwestern Indian Ocean, the axis of the mid-ocean ridge is offset by a series of left-lateral fault zones that have approximately the same orientation as the Owen Fracture Zone. The Malagasy Fracture Zone, which lies east of the Madagascar Ridge, is likely a southern extension of the fault zone Owen. In the area of the islands of Saint-Paul and Amsterdam, the axis of the mid-ocean ridge is displaced by the Amsterdam Fracture Zone. These zones run parallel to the Nintyist Ridge and have approximately the same meridional orientation as the fault zones in the western Indian Ocean. Although the Indian Ocean is most characterized by meridional strikes, the Diamantina and Rodriguez fault zones extend approximately from east to west.
The highly dissected tectonic relief of the mid-ocean ridge generally presents a noticeable contrast with the very leveled relief of the continental foot and the almost completely smoothed relief of the abyssal plains. In the Indian Ocean, there are areas of smooth-wavy or wavy relief, apparently due to a thick cover of pelagic sediments. The slopes of the mid-ocean ridge south of the polar front are flatter than those north of the polar front. This may be a consequence of higher rates of pelagic sediment deposition due to increased organic productivity in the Southern Ocean.
The Crozet Plateau has an extremely smooth topography. In this region, the narrow zone of the mid-ocean ridge typically has a highly dissected topography, while the ocean floor in this area is extremely smooth.
Indian Ocean climate
Air temperature. In January, the thermal equator for the Indian Ocean is slightly shifted south of the geographic one, in the area between 10 s. w. and 20 U. w. air temperature above 27° C. In the northern hemisphere, the 20° C isotherm, which separates the tropical zone from the temperate zone, runs from the south of the Arabian Peninsula and the Gulf of Suez through the Persian Gulf to the northern part of the Bay of Bengal almost parallel to the Tropic of Cancer. In the southern hemisphere, the 10°C isotherm, which separates the temperate zone from the subpolar zone, runs almost along the parallel of 45°S. In the mid-latitudes (southern hemisphere (between 10 and 30° S), isotherms of 27-21° C are directed from WSW to ENE, from South Africa through the Indian Ocean to Western Australia, indicating that the temperature of the western sector in some and at the same latitudes the temperature of the eastern sector is 1-3° C. Near the western coast of Australia, the isotherms of 27-21° C fall to the south due to the influence of the strongly heated continent.In May, the highest temperatures (above 30°C) are observed in the interior of the southern Arabian Peninsula, Northeast Africa, Burma and India. In India it reaches more than 35° C. The thermal equator for the Indian Ocean lies about 10° N. w. Isotherms from 20 to 10°C occur in the southern hemisphere between 30 and 45°S. w. from ESE to WNW, indicating that the western sector is warmer than the eastern one. In July, the zone of maximum temperatures on land moves north of the Tropic of Cancer.
Temperatures over the Arabian Sea and the Bay of Bengal have been decreasing slightly since May, and in addition, the air temperature in the Arabian Sea region is lower than over the Bay of Bengal. Near Somalia, the air temperature due to the rise of cold deep waters drops below 25 ° C. The lowest temperatures are observed in August. In the southern hemisphere, the area west of South Africa is slightly warmer than the central part at the same latitudes. Temperatures off the west coast of Australia are also much higher than inland.
In November, the thermal equator with a small zone of temperatures above 27.5° C almost coincides with the geographic equator. In addition, over the Indian Ocean region north of 20° S. w. the temperature is almost uniform (25-27 C) except for a small area over the central Indian Ocean.
Annual air temperature amplitudes for the central part, between 10° N. w. and 12° S. latitude, less than 2.5 C, and for the area between 4 ° N. w. and 7° S. w. - less than 1 C. In the coastal areas of the Bay of Bengal and the Arabian Sea, as well as in the area between 10 and 40 ° S. w. west of 100° W. d. annual amplitude exceeds 5° C.
Pressure field and surface winds. In January, the meteorological equator (minimum atmospheric pressure 1009-1012 mbar, calm and variable winds), like the thermal equator, is located about 10° south. w. it separates the northern and southern hemispheres, which differ in meteorological conditions.
The predominant wind north of the meteorological equator is the northeast trade wind, or more precisely the northeast monsoon, which changes direction to north at the equator and northwest (northwest monsoon) and the southern hemisphere. South of the meteorological equator, due to the heating of continents in the summer of the southern hemisphere, minimum pressure (less than 1009 mbar) is observed over Australia, Africa and the island of Madagascar. Region high pressure southern subtropical latitudes is located along 35° S. the maximum pressure (above 1020 mbar) is observed over the central part of the Indian Ocean (near the islands of Saint-Paul and Amsterdam). The northern bulge of the 1014 mbar isobar in the central Indian Ocean is caused by the effect of more low temperatures air and surface waters, in contrast to the South Pacific, where a similar bulge is observed in the eastern sector of South America. South of the high pressure area there is a gradual decrease in pressure towards a subpolar depression near 64.5°S. sh., where the pressure is below 990 mbar. This pressure system creates two types of wind systems south of the meteorological equator. In the northern part, the southeast trade winds cover the entire Indian Ocean, with the exception of areas near Australia, where they change direction to the south or southwest. South of the trade wind region (between 50 and 40° S) there are westerly winds from the Cape of Good Hope to Cape Horn, in an area called the "Roaring Forties". The significant difference between westerly winds and trade winds is not only that the former have higher speeds, but also that the daily variations in direction and speed for the former are also much greater than for the latter. In July, for a wind field from the north of 10° S. w. The opposite picture to January is observed. An equatorial depression with pressure values below 1005 mbar is located over the eastern part of the Asian continent.
South of this depression the pressure gradually increases from the 20s. w. to 30° south sh., i.e. to the area of the southern borders of the “horse” latitudes. The southern trade winds cross the equator and become the southwest monsoons in the northern hemisphere, very intense, characterized by strong storms off the coast of Somalia in the Arabian Sea.
This area is good example a complete shift of winds with an annual cycle in the northern trade wind zone, which is a consequence of the strong heating and cooling effect of the Asian continent. In the middle and high latitudes of the southern hemisphere, the moderating effect of the Indian Ocean reduces the differences in pressure and wind fields in June and January.
However, at high latitudes, westerly winds increase significantly, and fluctuations in their direction and speed also increase. The frequency distribution of storm winds (more than 7 points) showed that in the winter of the Northern Hemisphere over most of the Indian Ocean north of 15° S. w. storm winds are virtually not observed (their frequency is less than 1%). In the area of 10° south. latitude, 85-95° east. (northwest of Australia) from November to April, tropical cyclones sometimes form, moving to the southeast and southwest. South of 40°S w. The frequency of storm winds is more than 10% even in the summer of the southern hemisphere. In the northern hemisphere summer, from June to August, the southwest monsoons in the western Arabian Sea (off the coast of Somalia) are always so strong that approximately 10-20% of the winds are force 7. During this season, calm zones (with a frequency of storm winds of less than 1%) shift to the area between 1° south. w. and 7° N. w. and west of 78° E. d. In the area of 35-40° S. w. The frequency of storm winds increases by 15-20% compared to the winter season.
Cloud cover and precipitation. In the northern hemisphere, cloud cover is significant seasonal changes. During the northeast monsoon period (December-March), cloudiness over the Arabian Sea and Bay of Bengal is less than 2 points. However, in summer the southwest monsoons bring rainy weather to the region of the Malay Archipelago and Burma, with average cloudiness already 6-7 points. The area south of the equator, the southeastern monsoon zone, is characterized by high cloudiness throughout the year - 5-6 points in the summer of the northern hemisphere and 6-7 points in the winter. Even in the southeast monsoon zone there is a relatively large cloud cover and there are extremely rare areas of cloudless sky characteristic of the southeast Pacific monsoon zone. Cloudiness in areas west of Australia exceeds 6 points. However, near the coast of Western Australia it is quite cloudless.
In summer, sea fog (20-40%) and very poor visibility are often observed off the coast of Somalia and the southern part of the Arabian Peninsula. The water temperature here is 1-2°C lower than the air temperature, which causes condensation, enhanced by dust brought from deserts on the continents. The area south of 40° S. w. also characterized by frequent sea fog throughout the year.
Total annual precipitation for the Indian Ocean is high - more than 3000 mm at the equator and more than 1000 mm in the western zone of the southern hemisphere. Between 35 and 20° S. w. in the trade wind zone, precipitation is relatively rare; the area near the area is especially dry western shores Australia - precipitation less than 500 mm. The northern boundary of this dry zone is parallels 12-15° S, that is, it does not reach the equator, as in the South Pacific Ocean. The northwest monsoon zone is generally the boundary region between the northern and southern wind systems. To the north of this area (between the equator and 10° S) is the equatorial rainy zone, which stretches from the Java Sea to the Seychelles. In addition, very high rainfall is observed in the eastern part of the Bay of Bengal, especially in the Malay Archipelago region. The western Arabian Sea is very dry, and the rainfall in the Gulf of Aden and the Red Sea is less than 100 mm. Maximum precipitation in rainy zones is in December-February between 10 and 25° S. w. and in March-April between 5 s. w. and 10th south. w. in the western part of the Indian Ocean. Maximum values in the summer of the northern hemisphere are observed in the Bay of Bengal. The heaviest rains almost throughout the year are observed west of the island of Sumatra.
Temperature, salinity and density of surface waters
In February, the northern Indian Ocean experiences typical winter conditions. In the interior regions of the Persian Gulf and the Red Sea, the surface water temperature is 15 and 17.5 ° C, respectively, while in the Gulf of Aden it reaches 25 ° C. Isotherms of 23-25 ° C go from southwest to northeast, and therefore , the surface waters of the western part of the Indian Ocean are warmer than the surface waters of the eastern part for the same latitudes (the same for air temperature).This difference is caused by water circulation. It is observed in all seasons of the year. In the southern hemisphere, where it is summer at this time, the zone of high surface temperatures (above 28 ° C) runs in the direction ENE from the eastern coast of Africa to the area west of the island of Sumatra and then south of Java and north of Australia, where the water temperature sometimes exceeds 29° C. Isotherms 25-27° C between 15 and 30 degrees south. w. directed from WSW to ENE, from the coast of Africa to approximately 90-100° E. etc., then they turn to the southwest, just like in the western part of the Bay of Bengal, in contrast to the South Pacific, where these isotherms are directed off the coast of South America to the ENE. Between 40 and 50° S. w. there is a transition zone between water masses of mid-latitudes and polar waters, which is characterized by thickening of isotherms; temperature difference is about 12° C.
In May, the surface waters of the northern Indian Ocean heat up to a maximum and have temperatures generally above 29 ° C. At this time, the northeast monsoons give way to the southwest, although rains and sea level rise are not yet observed at this time. In August, only in the Red Sea and the Persian Gulf the water temperature reaches a maximum (above 30 ° C), however, the surface waters of most of the northern sector of the Indian Ocean including the Gulf of Aden, the Arabian Sea and most of the Bay of Bengal, with the exception of its western regions, have lower temperatures than in May. The zone of low temperatures of the surface layer (below 25°C) stretches from the coast of Somalia to the southeastern coast of the Arabian Peninsula. The decrease in temperature is caused by the intense rise of cold deep waters due to the southwest monsoons. In addition, in August there are three characteristic features of temperature distribution south of 30°S. sh.: isotherms 20-25° C in the eastern and central parts The Indian Ocean is directed from WSW to ENE, and the isotherms are thickened between 40 and 48° S. sh., and isotherms west of Australia are directed south. In November, surface water temperatures are generally close to the annual average. The low temperature zone (below 25°C) between the Arabian Peninsula and Somalia and the high temperature zone in the western Bay of Bengal are almost disappearing. In a huge area of water north of 10° south. w. surface layer temperatures range between 27 and 27.7° C.
The salinity of surface waters of the southern Indian Ocean has the same distribution features that are characteristic of the South Pacific Ocean. To the west of Australia, the maximum salinity value is observed (above 36.0 ppm). The equatorial zone of low salinity, corresponding to the transition zone between the southeast trade winds and the monsoons, extends to 10° S. sh., but clearly expressed only in the eastern part of the Indian Ocean.
The minimum salinity values in this zone are observed south of the islands of Sumatra and Java. The salinity of surface waters in the northern Indian Ocean varies not only regionally but also seasonally. In the summer of the northern hemisphere, the salinity of surface waters has the following characteristic features: it is extremely low in the Bay of Bengal, quite high in the Arabian Sea and very high (above 40 ppm) in the Persian Gulf and the Red Sea.
The density of surface waters in the southern Indian Ocean in the summer of the southern hemisphere decreases uniformly northward from approximately 27.0 in the region of 53-54° S. w. to 23.0 at 17° S. sh.; in this case, the isopycnals run almost parallel to the isotherms. Between 20° S. w. and 0° there is a huge zone of low-density waters (below 23.0); near the islands of Sumatra and Java there is a zone with a density below 21.5, corresponding to the zone of minimum salinity in this area. In the northern Indian Ocean, density changes are influenced by salinity. In summer, the density decreases from 22.0 in the southern part of the Bay of Bengal to 19.0 in its northwestern part, while for most of the Arabian Sea it is above 24.0, and near the Suez Canal and in the Persian Gulf it reaches 28.0 and respectively. 25.0. In addition, seasonal changes in surface water density are mainly caused by changes in temperature. For example, the northern part of the Indian Ocean is characterized by an increase in density by 1.0–2.0 from summer to winter.
Indian Ocean Currents
Currents in the northern Indian Ocean, which are strongly influenced by the monsoon and vary seasonally, are called the southwest and northeast monsoon drifts for summer and winter respectively. The Southern Trade Wind Current and the Western Wind Current pass through the southern part of the Indian Ocean. In addition to these currents, closely related to wind systems, there are currents of a local nature, caused mainly by the density structure of the Indian Ocean, such as the Mozambique Current, Cape Agulhas Current, Inter-trade (equatorial) countercurrent, Somali Current and West Australian Current.The southern Indian Ocean experiences a large anticyclonic circulation similar to that in the southern Pacific and Atlantic Oceans, but is subject to greater annual variations. Its extreme southern part is the Western Winds Current (between 38 and 50° S), 200-240 miles wide, increasing in an easterly direction. This current borders the subtropical and Antarctic convergence zones. The speed of the current depends on the strength of the wind and varies seasonally and regionally. The maximum speed (20-30 miles/day) is observed near the Kerguelen Island. In the summer of the southern hemisphere, this current, when approaching Australia, turns north and connects with the current coming from the Pacific Ocean south of Australia.
In winter, the wind drift joins the southward current along the western coasts of Australia and continues into the Pacific Ocean along the southern coasts of Australia. The eastern part of the aiticyclonic circulation in the southern hemisphere is the Western Australian Current, which has a steady northerly direction only in the summer of the southern hemisphere and reaches 10-15 miles/day north of 30° S. w. This current becomes weak in winter and changes direction to the south.
The northern part of the anticyclonic gyre is the Southern Trade Wind Current, which originates in the area where the Western Australian Current exits the Tropic of Capricorn under the influence of southeastern trade winds. The maximum speed of the current (more than 1 knot) is observed in its eastern part in the winter of the southern hemisphere, when the westerly flow from the Pacific Ocean increases north of Australia. In the summer of the southern hemisphere, when this flow becomes easterly, the northern boundary of the South Trade Wind Current is between 100 and 80° E. located about 9° south. latitude, shifting slightly to the southeast from 80° east. d.; Its southern border at this time passes about 22° south. w. in the eastern sector. In the winter of the southern hemisphere, the northern boundary of this current shifts northward by 5-6°, following the northern shift of the southeast trade wind. Before the island of Madagascar, the current divides into several branches.
One of them goes north around the island of Madagascar at a speed of up to 50-60 miles/day and then turns west. It splits again into two branches at Cape Delgado. One branch turns north (East African Coastal Current), the other turns south, following through the Mozambique Channel (Mozambique Current). The speed of this current varies from almost zero to 3-4 knots during the northeast monsoon.
The Cape Agulhas Current is formed from the continuation of the Mozambique Current and the southern branch of the South Trade Wind Current south of the island of Mauritius. This current, narrow and clearly defined, extends from the coast for less than 100 km. As is known, a southward flow in the Southern Hemisphere is characterized by a tilt of the water surface to the left. At a distance of 110 km from Port Elizabeth, the slope of the level towards the ocean increases by approximately 29 cm. Between Durban and 25° E. The speed of this current at the edge of the Agulhas Bank reaches 3-4.5 knots. South of Africa, the main part of the current turns sharply to the south and then to the east and thus unites with the current of the Western Winds. However, a small one continues to move into the Atlantic Ocean. Due to the change in directions and razor-sharp currents, numerous eddies and gyres develop along the coast of South Africa, the position of which changes throughout the year.
North of 10° S. w. There is strong variability in Indian Ocean surface currents from winter to summer. During the northeast monsoon, from November to March, the Northern Trade Wind Current (drift of the northeast monsoon) develops. The southern boundary of this current varies from 3-4° N. w. in November up to 2-3° S. w. in February. In March, the current turns north again and disappears with the advent of the southwest monsoon drift. With the onset of the northeastern monsoon (from November), the Intertrade Countercurrent begins to develop. It is formed under the combined influence of the current running southwest of the coast of Somalia and the East African Coastal Current running north from the cape. Delgado. The countercurrent is narrow and reaches almost to the island of Sumatra. Its northern boundary in November passes north of the equator, and in February it shifts to 2-3° S. Later, the current rises again to the north and then disappears. The southern boundary of the current lies between 7 and 8° S. w. Current speed between 60 and 70° E. d. reaches 40 miles/day, but further east it decreases.
During the period of the southwest monsoon, from April to October, the Northern Trade Wind Current (the drift of the northeast Monsoon disappears and is replaced by the drift of the southwest monsoon, going east south of India. South of the island of Sri Lanka its speed is 1-2 knots, and sometimes reaches 3 knots. The branches of this current create a clockwise circulation in the Arabian Sea, following the contours of the coastline. The speed of the southeasterly flow off the western coast of India reaches 10-42 miles / day. During this season, the Somali Current along the coast of Somalia in the region of 10 ° S latitude is directed north, and the waters of the South Trade Wind Current cross the equator.An intense rise of water occurs off the coast of Somalia, causing cooling of surface waters over a large area.
Subsurface currents in the Indian Ocean north of 10°S. w. were measured at horizons of 15, 50, 100, 200, 300, 500 and 700 m during the 31st voyage of the Vityaz (January-April 1960), at approximately 140 deep-sea stations.
As established, at a depth of 15 m, the distribution of currents turned out to be almost similar to the surface one in the winter of the northern hemisphere, with the exception that, according to observational data, the Intertrade Countercurrent originates at 60° E. and covers the area between 0 and 3° S. those. its width is much smaller than on the surface. On the horizon 200 m of current south of 5° N. w. have the opposite direction to the currents at a horizon of 15 m: they are directed to the east under the Northern and Southern Trade Wind Currents and to the west under the Inter-Trade Wind Countercurrent east of 70° E. d. At a depth of 500 m, the current is between 5° N. w. and 10° S. w. in general they have an eastern direction and form a small cyclonic gyre centered at 5°S. latitude, 60° east. d. In addition, direct current measurements and dynamic calculation data for the period November-December 1960, obtained during the 33rd voyage of the Vityaz, indicate that the observed current system does not yet correspond to the current system characteristic of the winter monsoon , despite the fact that northwest winds are already beginning to prevail here. At a depth of 1500 m south of 18° S. w. An easterly current was detected at a speed of 2.5-45 cm/s. About 80° E. This current combines with the southern flow, which has a speed of 4.5–5.5 cm/s and its speed is rapidly increasing. About 95°E. This current sharply turns north and then west, forming an anticyclonic gyre, the northern and southern parts of which have speeds of 15-18 and 54 cm/s, respectively.
About 20-25° S. latitude, 70-80° east. The southern branch of this current has a speed of less than 3.5 cm/s. At a horizon of 2000 m between 15 and 23° S. w. the same current has an eastern direction and a speed of less than 4 cm/s. About 68°E. d. a branch departs from it, going north at a speed of 5 cm/s. Anticyclonic gyre between 80 and 100° E. at a horizon of 1500 m covers a large area between 70 and 100° east. e. A current coming south from the Bay of Bengal meets another current coming from the east at the equator and turns north and then northwest to the Red Sea.
On the horizon 3000 m between 20 and 23° S. w. the current is directed to the east with speeds in some places up to 9 cm/s. Cyclonic gyre at 25-35° S. latitude, 58-75° E. d. becomes clearly expressed here at speeds of up to 5 cm/s. Anticyclic cycle between 80 and 100 centuries. observed at a horizon of 1500 m, here it breaks up into a number of small vortices.
Water masses
The Indian Ocean, in addition to the subantarctic water mass, is characterized by three main water masses: the central water mass of the Indian Ocean (subtropical subsurface), the equatorial water mass of the Indian Ocean, extending to medium depths, and the deep water of the Indian Ocean, below the horizon of 1000 m. There are also intermediate water masses. These are Antarctic intermediate waters, the waters of the Red Sea and others at medium depths.
The Indian Ocean ranks third in area after the Pacific and Atlantic. The average depth is about 4 km, and the maximum is recorded in the Java Trench and is 7,729 m.
The Indian Ocean washes the shores of the most ancient centers of civilization and it is believed that it was the very first to be explored. The routes of the first voyages did not go far into open waters, therefore, the ancients who lived on the ocean considered it simply a huge sea.
The Indian Ocean appears to be the most populous of animals. Fish stocks have always been famous for their abundance. Northern waters served as almost the only source of food for people. Pearls, diamonds, emeralds and others gems- all this is in the Indian Ocean.
The ocean is also rich in minerals. The Persian Gulf contains one of the largest oil fields developed by man.
Flows into the Indian Ocean a small amount of rivers, mainly in the north. These rivers carry a lot of sediment into the ocean, so this part of the ocean cannot boast of cleanliness. Things are different in the south, where the ocean has no freshwater arteries. The water appears crystal clear to the observer, with a dark blue tint.
The lack of sufficient desalination, as well as high evaporation, explains why the salinity of its waters is slightly higher compared to other oceans. The saltiest part of the Indian Ocean is the Red Sea (42%).
Climate
Since the Indian Ocean has extensive borders with continents, it climatic conditions are largely determined by the surrounding land. The status of " monsoon"The pressure contrast over land and sea causes strong winds - monsoons. In summer, when the land in the northern ocean is very hot, a large area of low pressure occurs, causing heavy precipitation over both the continent and the ocean. This is the so-called southwest equatorial monsoon".
In contrast, winter is characterized by harsher weather in the form of destructive hurricanes and flooding on land. An area of high pressure over Asia causes trade winds.
The speed of the monsoons and trade winds is so fast that they form large surface currents that change every season. The largest such current is Somali, which flows from north to south in winter and changes its direction in summer.
The Indian Ocean is quite warm. The water surface temperature in Australia reaches 29 degrees, but in the subtropics it is colder, around 20. Icebergs, which can float quite high, up to 40 degrees south latitude, have a minor but quite noticeable effect on the water temperature, as well as on its salinity. . Before this area, salinity averages 32% and increases closer to the north.
What is the area of the Indian Ocean? The very name of the water area implies enough big numbers. It is immediately worth paying attention to the fact that the Indian Ocean ranks third in size among similar bodies of water on our planet. In the widest part of the ocean, the distance is about 10 thousand km. This meaning visually connects the southern points of Africa and Australia. It is located between four continents: Antarctica, Eurasia, Africa and Australia. So, what is the area of the Indian Ocean (million km2)? This figure is 76.174 million square meters. km.
Let's look into history
The Indian Ocean in the north cuts so far into the land that people ancient world defined it as a very large sea. It was in these waters that humanity began its first long journeys.
On ancient maps it (or rather, the western part) was called the “Eritrean Sea”. And the ancient Russians called him Black. In the 4th century, a name consonant with the current one began to appear for the first time: the Greek “Indikon pelagos” - “Indian Sea”, the Arabic Bar-el-Hind - “Indian Ocean”. And already in the 16th century, the hydronym, which was proposed by a Roman scientist, was officially assigned to the ocean.
Geography
The Indian Ocean, whose area is smaller than the Pacific and Atlantic, is younger and much warmer than these bodies of water. This body of water receives many rivers in the region, the largest of which are the Limpopo, Tigris, Ganges and Euphrates. The near-continental waters of the ocean are muddy due to the abundance of clay and sand that rivers carry into them, but its open water is surprisingly clean. There are many islands in the Indian Ocean. Some of them are debris. The largest are Madagascar, Sri Lanka, Comoros, Maldives, Seychelles and many others.
The Indian Ocean has seven seas and six bays, as well as several straits. Their area is more than 11 million square meters. km. The most famous are the Red Sea (the saltiest in the world), the Arabian Sea, the Andaman Sea, the Persian Sea and
The ocean sits above ancient tectonic plates that are still moving today. Because of this, tsunamis and underwater volcanic eruptions are common in the region.
Climate indicators
The Indian Ocean, whose area is more than 76 million square meters. km, located in four climatic zones. The north of the water basin is influenced by the Asian continent, which is why frequent tsunamis with characteristic tsunamis are observed here. Thanks to high temperatures, the water heats up well, so the seas and bays there are the warmest. In the south, the southeast trade wind prevails with its cold air. Tropical hurricanes often form in the middle part.
The entire weather background is formed by monsoons - winds that change direction depending on the season. There are two of them: summer - hot and rainy and winter, with sudden changes weather, often accompanied by storms and floods.
World of flora and fauna
The Indian Ocean, whose area is quite large, has an extremely diverse fauna and flora, both on land and in the aquatic part. The tropics are rich in plankton, which, unlike the Pacific, is abundant in luminous organisms. A huge number of crustaceans, jellyfish and squid. The most common fish are flying species, poisonous sea snakes, tuna, and some types of sharks. In the waters you can see whales, seals and dolphins. The coast is favored by giant turtles and elephant seals.
Among the variety of birds, albatross and frigatebirds can be distinguished. And in southern Africa there are various populations of penguins. Corals grow in shallow waters, sometimes forming entire islands. Among these beautiful structures live many representatives of this region - sea urchin and starfish, crabs, sponges, coral fish.
Like any other body of water, the Indian Ocean abounds in numerous species of algae. For example, sargassum, which is also found in the Pacific region. There are also lush and strong lithothamnias and halimedas, which help the corals build atolls, turbinaria and caulerpas, forming entire underwater jungles. The tidal zone is favored by mangroves - dense, always green forests.
Economic characteristics of the Indian Ocean
The Indian Ocean is shared by 28 mainland and 8 island states. With some on the brink of extinction, what was once a highly developed species is fading away. Fishing takes up a small percentage of the economy of this region. Mother-of-pearl and pearls are mined off the coast of Australia, Bahrain and Sri Lanka.
The ocean is the largest transport artery for ships in the region. The main maritime transport hub is the Suez Canal, connecting the Indian Ocean with the Atlantic. From there the path to Europe and America opens. Almost most of the region's business life is concentrated in port cities - Mumbai, Karachi, Durban, Colombo, Dubai and others.
With an area of over 76 million km2, the Indian Ocean is home to a huge number of mineral deposits. Huge deposits of non-ferrous metals and ores. But the main wealth, of course, is the richest oil and gas deposits. They are concentrated mainly on the shallows of the Persian and Suez Gulfs.
Unfortunately, human activity is becoming a threat to the integrity and preservation of this world. Across the Indian Ocean large quantities tankers and industrial vessels ply. Any leak, even a small one, can become a disaster for the entire region.
The Indian Ocean has the least number of seas compared to other oceans. In the northern part there are the largest seas: the Mediterranean - the Red Sea and the Persian Gulf, the semi-enclosed Andaman Sea and the marginal Arabian Sea; in the eastern part - the Arafura and Timor Seas.
There are relatively few islands. The largest of them are of continental origin and are located near the coasts of Madagascar, Sri Lanka, Socotra. In the open part of the ocean there are volcanic islands - Mascarene, Crozet, Prince Edward, etc. In tropical latitudes, coral islands rise on volcanic cones - the Maldives, Laccadives, Chagos, Cocos, most Andaman, etc.
Shores on the north-west. and the East are indigenous, in the north-east. and in the West, alluvial deposits predominate. The coastline is slightly indented, with the exception of the northern part of the Indian Ocean. Almost all seas and large bays (Aden, Oman, Bengal) are located here. In the southern part there are the Gulf of Carpentaria, the Great Australian Gulf and the Gulfs of Spencer, St. Vincent, etc.
A narrow (up to 100 km) continental shelf (shelf) stretches along the coast, the outer edge of which has a depth of 50-200 m (only in Antarctica and northwestern Australia up to 300-500 m). The continental slope is a steep (up to 10-30°) ledge, in places dissected by the underwater valleys of the Indus, Ganges and other rivers. In the northeastern part of the ocean there is the Sunda Island Arc and the Sunda Trench associated with it, which is associated with maximum depths (up to 7130 m). The bed of the Indian Ocean is divided by ridges, mountains and swells into a number of basins, the most significant of which are the Arabian Basin, the Western Australian Basin, and the African-Antarctic Basin. The bottom of these basins is formed by accumulative and hilly plains; the former are located near continents in areas with an abundant supply of sedimentary material, the latter - in the central part of the ocean. Among the numerous ridges of the bed, the meridional East Indian Ridge, which connects in the south with the latitudinal Western Australian Ridge, stands out due to its straightness and length (about 5,000 km); large meridional ridges stretch south from the Hindustan Peninsula and the island. Madagascar. Volcanoes are widely represented on the ocean floor (Mt. Bardina, Mt. Shcherbakova, Mt. Lena, etc.), which in some places form large massifs (to the north of Madagascar) and chains (to the east of the Cocos Islands). Mid-ocean ridges are a mountain system consisting of three branches diverging from the central part of the ocean to the north (Arabian-Indian ridge), southwest. (West Indian and African-Antarctic ridges) and South-East. (Central Indian Ridge and Australian-Antarctic Rise). This system has a width of 400-800 km, a height of 2-3 km and is most dissected by an axial (rift) zone with deep valleys and rift mountains bordering them; Characterized by transverse faults, along which horizontal displacements of the bottom up to 400 km are noted. The Australian-Antarctic Rise, in contrast to the median ridges, is a more gentle swell 1 km high and up to 1500 km wide.
Bottom sediments of the Indian Ocean are thickest (up to 3-4 km) at the foot of the continental slopes; in the middle of the ocean - small (about 100 m) thickness and in places where dissected relief is distributed - intermittent distribution. The most widely represented are foraminifera (on continental slopes, ridges and on the bottom of most basins at depths of up to 4700 m), diatoms (south of 50° S), radiolarians (near the equator) and coral sediments. Polygenic sediments - red deep-sea clays - are common south of the equator at a depth of 4.5-6 km or more. Terrigenous sediments - off the coast of continents. Chemogenic sediments are represented mainly by iron-manganese nodules, and riftogenic sediments are represented by products of destruction of deep rocks. Outcrops of bedrock are most often found on continental slopes (sedimentary and metamorphic rocks), mountains (basalts) and mid-ocean ridges, where, in addition to basalts, serpentinites and peridotites, representing the slightly altered material of the Earth's upper mantle, were found.
The Indian Ocean is characterized by the predominance of stable tectonic structures both on the bed (thalassocratons) and along the periphery (continental platforms); active developing structures - modern geosynclines (Sunda arc) and georiftogenals (mid-ocean ridge) - occupy smaller areas and are continued in the corresponding structures of Indochina and the rifts of East Africa. These main macrostructures, sharply different in morphology, structure earth's crust, seismic activity, volcanism, are divided into more small structures: plates that usually correspond to the bottom of oceanic basins, block ridges, volcanic ridges, in some places topped with coral islands and banks (Chagos, Maldives, etc.), fault trenches (Chagos, Obi, etc.), often confined to the foot of block ridges (East -Indian, Western Australian, Maldivian, etc.), fault zones, tectonic ledges. Among the structures of the Indian Ocean bed, a special place (in terms of the presence of continental rocks - granites of the Seychelles Islands and the continental type of the earth's crust) is occupied by the northern part of the Mascarene Ridge - a structure that is, apparently, part of the ancient continent of Gondwana.
Minerals: on the shelves - oil and gas (especially the Persian Gulf), monazite sands (coastal region of South-West India), etc.; in rift zones - ores of chromium, iron, manganese, copper, etc.; on the bed there are huge accumulations of iron-manganese nodules.
The climate of the northern Indian Ocean is monsoonal; in summer, when an area of low pressure develops over Asia, southwestern flows of equatorial air dominate here, in winter - northeastern flows of tropical air. To the south 8-10° S. w. atmospheric circulation is much more constant; Here, in tropical (summer and subtropical) latitudes, stable southeastern trade winds dominate, and in temperate latitudes, extratropical cyclones moving from West to East dominate. In tropical latitudes in the western part there are hurricanes in summer and autumn. The average air temperature in the northern part of the ocean in summer is 25-27 °C, off the coast of Africa - up to 23 °C. In the southern part it drops in summer to 20-25 °C at 30° S. latitude, up to 5-6 °C at 50° S. w. and below 0 °C south of 60 ° S. w. In 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. latitude, up to 0-5 °C at 50° S. w. and below 0 °C south of 55-60 ° S. w. Moreover, in southern subtropical latitudes all year round the temperature in the West, under the influence of the warm Madagascar Current, is 3-6 °C higher than in the East, where the cold Western Australian Current exists. Cloudiness in the monsoon northern part of the Indian Ocean is 10-30% in winter, up to 60-70% in summer. In summer there is also greatest number precipitation. The average annual precipitation in the east of the Arabian Sea and the Bay of Bengal is more than 3000 mm, at the equator 2000-3000 mm, in the west of the Arabian Sea up to 100 mm. In the southern part of the ocean, the average annual cloudiness is 40-50%, south of 40° S. w. - up to 80%. The average annual precipitation in the subtropics is 500 mm in the east, 1000 mm in the west, in temperate latitudes it is more than 1000 mm, and near Antarctica it drops to 250 mm.
The circulation of surface waters in the northern part of the Indian Ocean has a monsoon character: in summer - northeastern and eastern currents, in winter - southwestern and western currents. In the winter months between 3° and 8° S. w. The inter-trade wind (equatorial) countercurrent develops. In the southern part of the Indian Ocean, water circulation forms an anticyclonic circulation, which is formed from warm currents - the Southern Trade Winds in the north, Madagascar and Agulhas in the West and cold currents - the Western Winds current in the South and Western Australian in the East South of 55 ° S. w. Several weak cyclonic water circulations develop, closing off the coast of Antarctica with an eastern current.
The positive component predominates in the heat balance: between 10° and 20° N. w. 3.7-6.5 GJ/(m2×year); between 0° and 10° S. w. 1.0-1.8 GJ/(m2×year); between 30° and 40° S. w. - 0.67-0.38 GJ/(m2×year) [from - 16 to 9 kcal/(cm2×year)]; between 40° and 50° S. w. 2.34-3.3 GJ/(m2×year); south of 50° S. w. from -1.0 to -3.6 GJ/(m2×year) [from -24 to -86 kcal/(cm2×year)]. In the expenditure part of the heat balance north of 50° S. w. the main role belongs to the loss of heat for evaporation, and south of 50° south. w. - heat exchange between the ocean and the atmosphere.
Surface water temperatures reach a maximum (over 29 °C) in May in the northern part of the ocean. In the summer of the Northern Hemisphere it is 27-28 °C here and only off the coast of Africa it decreases to 22-23 °C under the influence of cold waters coming to the surface from the depths. At the equator the temperature is 26-28 °C and decreases to 16-20 °C at 30° south. latitude, up to 3-5 °C at 50° S. w. and below -1 °C south of 55° S. w. In the winter of the Northern Hemisphere, the temperature in the north is 23-25 °C, at the equator 28 °C, at 30 ° S. w. 21-25 °C, at 50° S. w. from 5 to 9 °C, south of 60° S. w. temperatures are negative. In subtropical latitudes all year round in the West, the water temperature is 3-5 °C higher than in the East.
The salinity of water depends on water balance, which consists on average for the surface of the Indian Ocean from evaporation (-1380 mm/year), precipitation (1000 mm/year) and continental runoff (70 cm/year). The main flow of fresh water comes from the rivers of South Asia (Ganges, Brahmaputra, etc.) and Africa (Zambezi, Limpopo). The highest salinity is observed in the Persian Gulf (37-39‰), in the Red Sea (41‰) and in the Arabian Sea (more than 36.5‰). In the Bay of Bengal and the Andaman Sea it decreases to 32.0-33.0‰, in the southern tropics - to 34.0-34.5‰. In southern subtropical latitudes, salinity exceeds 35.5‰ (maximum 36.5‰ in summer, 36.0‰ in winter), and to the south 40° S. w. decreases to 33.0-34.3‰. The highest water density (1027) is observed in Antarctic latitudes, the lowest (1018, 1022) in the northeastern part of the ocean and in the Bay of Bengal. In the northwestern part of the Indian Ocean, the density of water is 1024-1024.5. The oxygen content in the surface layer of water increases from 4.5 ml/l in the northern part of the Indian Ocean to 7-8 ml/l south of 50° south. w. At depths of 200-400 m, the oxygen content in absolute value is significantly lower and varies from 0.21-0.76 in the north to 2-4 ml/l in the south; at greater depths it gradually increases again and in the bottom layer is 4.03 -4.68 ml/l. The color of the water is predominantly blue, in Antarctic latitudes it is blue, in places with greenish tints.
Tides in the Indian Ocean, as a rule, are small (off the coast of the open ocean and on the islands from 0.5 to 1.6 m), only at the tops of some bays they reach 5-7 m; in the Gulf of Cambay 11.9 m. The tides are predominantly semidiurnal.
Ice forms in high latitudes and is carried by winds and currents along with icebergs in a northerly direction (up to 55° S in August and up to 65-68° S in February).
The deep circulation and vertical structure of the Indian Ocean are formed by waters plunging in the subtropical (subsurface waters) and Antarctic (intermediate waters) convergence zones and along the continental slope of Antarctica (bottom waters), as well as coming from the Red Sea and the Atlantic Ocean (deep waters). At a depth of 100-150 m to 400-500 m, subsurface waters have a temperature of 10-18°C, a salinity of 35.0-35.7‰, intermediate waters occupy a depth of 400-500 m to 1000-1500 m, and have a temperature of 4 to 10°C, salinity 34.2-34.6‰; deep waters at depths from 1000-1500 m to 3500 m have a temperature of 1.6 to 2.8 ° C, salinity 34.68-34.78‰; Bottom waters below 3500 m have a temperature from -0.07 to -0.24 ° C in the South, a salinity of 34.67-34.69‰, in the North - about 0.5 ° C and 34.69-34.77 ‰ respectively.
Flora and fauna
The entire Indian Ocean lies within the tropical and southern temperate zones. The shallow waters of the tropical zone are characterized by numerous 6- and 8-rayed corals and hydrocorals, which, together with calcareous red algae, can create islands and atolls. Among the powerful coral structures lives a rich fauna of various invertebrates (sponges, worms, crabs, mollusks, sea urchins, brittle stars and starfish), small but brightly colored coral fish. Most of the coasts are occupied by mangroves, in which the mudskipper stands out - a fish that can exist in the air for a long time. The fauna and flora of beaches and cliffs that dry out at low tide are quantitatively depleted as a result of the inhibitory effect sun rays. In the temperate zone, life on such sections of the coast is much richer; Dense thickets of red and brown algae (kelp, fucus, reaching enormous sizes of macrocystis) develop here, and a variety of invertebrates are abundant. The open spaces of the Indian Ocean, especially the surface layer of the water column (up to 100 m), are also characterized by a rich flora. Among unicellular planktonic algae, several species of peredinium and diatom algae predominate, and in the Arabian Sea - blue-green algae, which often cause so-called water blooms when they develop en masse.
The bulk of ocean animals are copepod crustaceans (more than 100 species), followed by pteropods, jellyfish, siphonophores and other invertebrate animals. The most common unicellular organisms are radiolarians; Squids are numerous. Of the fish, the most abundant are several species of flying fish, luminous anchovies - myctophids, coryphaenas, large and small tuna, sailfish and various sharks, poisonous sea snakes. Sea turtles and large marine mammals (dugongs, toothed and toothless whales, pinnipeds) are common. Among the birds, the most typical are albatrosses and frigatebirds, as well as several species of penguins that inhabit the coasts of South Africa, Antarctica and islands lying in the temperate zone of the ocean.