body of salt water
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16-02-2011, 03:09 PM
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body of salt water; covering approximately one-fifth of the total ocean area of the world. It is the smallest, youngest, and physically most complex of the world's three major oceans. Stretching for more than 10,000 km, between the southern tips of Africa and Australia and, without its marginal seas, it has an area of about 73,440,000 sq km. The Indian Ocean's average depth is 3,890 m and, its deepest point, in the Sunda Deep of the Java Trench off the southern coast of Java, is 7,450 m.
The Indian Ocean is bounded by Iran, Pakistan, India, and Bangladesh to the north; the Malay peninsula, the Sunda Islands of Indonesia, and Australia to the east; Antarctica to the south; and Africa and the Arabian peninsula to the west. In the southwest it joins the Atlantic Ocean south of the southern tip of Africa, and to the east and southeast, its waters mingle with those of the Pacific.
The Indian Ocean has the fewest seas of the major oceans. To the north are the inland Red Sea and Persian Gulf. The Arabian Sea is to the northwest, and the Andaman Sea to the northeast. The large gulfs of Aden and Oman are to the northwest, the Bay of Bengal is to the northeast, and the Great Australian Bight is off the southern coast of Australia. The Indian Ocean differs from the Atlantic and Pacific Oceans in several other respects. In the Northern Hemisphere it is landlocked, does not extend to Arctic waters, or have a temperate-to-cold zone. It has fewer islands and narrower continental shelves. It is the only ocean with an asymmetric and, in the north, semi-annually reversing surface circulation. It has no separate source of bottom water (the Indian Ocean's bottom water originates outside its boundaries) and has two sources of highly saline water (the Persian Gulf and the Red Sea). Below the surface layers, especially in the north, the ocean's water is extremely low in oxygen.
The origin and evolution of the Indian Ocean is the most complicated of the three major oceans. Its formation is a consequence of the break-up, about 150 million years ago, of the southern supercontinent Gondwana, or Gondwanaland; by the movement to the northeast of the Indian subcontinent (beginning about 125 million years ago), which began colliding with Eurasia about 50 million years ago; and by the western movement of Africa and separation of Australia from Antarctica some 53 million years ago.
By 36 million years ago, the Indian Ocean had taken on its present configuration. Although it first opened some 125 million years ago, almost the entire Indian Ocean basin is less than 80 million years old.
Oceanic ridges and fracture zones
The oceanic ridges consist of a rugged, seismically active mountain chain that is part of the world-wide oceanic ridge system and still contains centres of seafloor spreading in several places. The ridges form an inverted Y on the ocean floor, starting in the upper northwest with the Carlsberg ridge in the Arabian Sea, turning due south past the Chagos-Lakshadweep plateau, and becoming the Mid-Indian (or Central Indian) ridge. Southeast of Madagascar the ridge branches: the Southwest Indian ridge continues to the southwest until it merges into the Atlantic-Indian ridge south of Africa, and the Southeast Indian ridge trends to the east until it joins the Pacific Antarctic ridge south of Tasmania. Most striking is the aseismic (virtually earthquake-free) Ninetyeast ridge, which is the longest and straightest in the world's oceans. First discovered in 1962, it runs northward along the 90 degrees east meridian (hence its name) for 4,505 km from the zonal Broken ridge at 31 degrees south to 9 degrees north and can be traced farther under the sediments of the Bay of Bengal.
These are extinct submarine volcanoes that are conically shaped and often flat-topped. They rise abruptly from the abyssal plain to heights at least 1,006 m above the ocean floor. In the Indian Ocean, sea-mounts are particularly abundant between Reunion and Seychelles in the Central Indian basin and the Vening Meinesz group near Wharton basin. Bardin, Kohler, Nikitin, and Williams seamounts are some examples.
Ocean basins are characterized by smooth, flat plains of thick sediment with abyssal hills (less than 1,006 m high) at the bottom flanks of the oceanic ridges. The Indian Ocean's complex ridge topography led to the formation of many basins that range in width from 322 km to 9,010 km. From roughly north to south they include the Arabian, Somali, Mascarene, Madagascar, Mozambique, Agulhas, and Crozet basins in the west and the Central Indian (the largest), Wharton, and South Australia basins in the east.
Continental rise, slope, and shelf
The continental shelf extends to an average width of about 121 km in the Indian Ocean, with its widest points (306 km) off Mumbai and northwestern Australia. The island shelves are only about 305 m wide. The shelf break is at a depth of about 140 m. Submarine canyons indent the steep slope below the break. The Ganga, Indus, and Zambezi rivers have all carved particularly large canyons. Their sediment loads extend far beyond the shelf, form the rises at the foot of the slope, and contribute to the abyssal plains of their respective basins. The Ganga sediment cone is the world's widest and thickest.
The Indian Ocean has the fewest trenches of any of the world's oceans. The narrow (80 km), volcanic, and seismically active Java Trench is the world's second longest, stretching more than 2,574 km from southwest of Java and continuing northward as the Sunda Trench past Sumatra, with an extension along the Andaman and Nicobar Islands.
The immense load of suspended sediments from the rivers emptying into the Indian Ocean is the highest of the three oceans, and nearly half of it comes from the Indian subcontinent alone. These terrigenous sediments occur mostly on the continental shelves, slopes, and rises, and they merge into abyssal plains. Cones of thicknesses of over one km are found in the Bay of Bengal, the Arabian Sea, and the Somali and Mozambique basins. Wharton basin off northern Australia has the oldest sediments. In the Ganga-Brahmaputra cone, sediments exceed 11 km in thickness and extend to 10 degrees south. Brown and red clay sediments dominate in the deep sea between 10 degrees north and 40 degrees south away from islands and continents and are 305 m thick. In the equatorial zone, an area of high oceanic productivity, calcareous and siliceous oozes are abundant.
Several well-defined coastal configurations are found in the Indian Ocean: estuaries, deltas, salt marshes, mangrove swamps, cliffs, coral reefs, and complexes of barrier islands, lagoons, beaches, and dunes. A particularly important estuarine system is the Hugli (Hooghly) complex, formed by three branches of the Hugli river on the Bay of Bengal near Kolkata. Pakistan combines one of the most tectonically active coasts in the world with the 193 km-wide Indus river delta, the mud flats and salty wastes of which are often flooded. The Indian subcontinent has the most extensive beach area (more than half of its coastline). Mangroves are found in most estuaries and deltas. The Sundarbans, the lower part of the Ganga river delta, contain the largest mangrove forests in the world. Coral reefs - in either fringing, barrier, or atoll form - are abundant around all the islands in the tropics and are also found along the southern coasts of Bangladesh, Myanmar (Burma), and India, and along the eastern coast of Africa.
The Indian Ocean has few islands. Madagascar - the fourth largest island in the world, the Maldives, Seychelles, Socotra, and Sri Lanka are continental fragments. The other islands - including Amirante, Andaman-Nicobar, Chagos, Lakshadweep (Laccadive, Minicoy, and Amindivi islands), Christmas, Cocos, Comoros, Crozet, Farquhar, Kerguelen, Mauritius, Prince Edward, Reunion, St. Paul and Amsterdam, and the Sunda Islands - are of volcanic origin. The Andamans and Sundas are island arc-trench subduction systems, with the trench on the oceanic side of the arc.
The Indian Ocean can be subdivided into four general latitudinal climatic zones based on atmospheric circulation.
The first zone, extending north from 10 degrees south, has a monsoon climate (characterized by semi-annual reversing winds). In the Northern Hemisphere "summer" (May to October), low atmospheric pressure over Asia and high pressure over Australia result in the southwest monsoon, with wind speeds up to 45 km per hour and a wet season in South Asia. During the northern "winter" (November to April), high pressure over Asia and low pressure from 10 degrees south to northern Australia bring the northeast monsoon winds and a wet season for southern Indonesia and northern Australia. The region is subject to destructive cy-clones that form over the open ocean and head for shore in a generally westward direction.
The second zone - that of the trade winds - lies between 10 and 30 degrees south. There, steady southeasterly trade winds prevail throughout the year and are strongest between June and September. Cyclones also occur east of Madagascar between December and March. In the northern part of the zone the air temperature averages 25ºC during the southern winter (May to October) and slightly higher the rest of the time.
Subtropical and temperate zone
The third zone lies in the subtropical and temperate latitudes of the Southern Hemisphere, between 30 and 45 degrees south. In the northern part of the zone the prevailing winds are light and variable, while in the southern area moderate to strong westerly winds prevail. The average air temperature decreases with increasing southern latitude: from 20º to 22ºC down to 10ºC in the Austral summer (December through February) and from 16 to 17ºC to 6 to 7ºC in winter. Rainfall is moderate and uniformly distributed.
ubantarctic and Antarctic zone
Finally, the fourth, or subantarctic and Antarctic zone occupies the wide belt between 45 degrees south and the continent of Antarctica. Steady westerly winds prevail, reaching gale force at times with their passage through deep Antarctic low-pressure zones. The average winter air temperature varies from 6º to 7ºC in the north to -16ºC near the continent. The corresponding summer temperatures vary within the limits of 10º to -4ºC.
The hydrological characteristics of the Indian Ocean are derived from the interaction of atmospheric conditions - rain, wind, and solar energy - with the surface, the sources of its water, and the deep (ther-mohaline) circulation, all of which combine to form generally horizontal layers of water. Each layer has different temperature and salinity combinations that form discrete water masses of different densities, with lighter water overlying denser water. Surface-water temperature varies with season, latitude, and surface circulation; surface salinity is the balance between precipitation, evaporation, and river runoff.
A zonal asymmetry is noted in the surface-water temperature distribution in summer north of 20 degrees south. Summer surface temperatures are higher in the eastern part of this region than in the west. In the Bay of Bengal the maximum temperature is around 28ºC. The minimum temperature is about 22ºC in the area of Cape Gwardafuy (Guardafui), on the Horn of Africa, and is associated with the upwelling off the African coast.
Ice is formed in the extreme south during the Antarctic winter. Between January and February the melting ice along the Antarctic coast is broken up by severe storms and, in the form of large blocks and broad floes, is carried away by wind and currents to the open ocean. In some coastal areas the tongues of ice-shelf glaciers break off to form icebergs. West of the 90 degrees east meridian the northern limit for floating ice lies close to 65 degrees south. To the east of that meridian, however, floating ice is commonly encountered to 60 degrees south; icebergs are sometimes found as far north as 40 degrees south.
Examples of all three tidal types - diurnal, semidiurnal, and mixed - can be found in the Indian Ocean, although semidiurnal (twice daily) are the most widespread. Semidiurnal tides prevail on the coast of eastern Africa as far north as the Equator and in the Bay of Bengal. The tides are mixed in the Arabian Sea and the inner part of the Persian Gulf. The southwestern coast of Australia has a small area of diurnal (daily) tides, as do the coast of Thailand in the Andaman Sea and the south shore of the central Persian Gulf.
The Persian Gulf is the largest oil-producing region in the world and exploration for offshore oil and natural gas has also been under way in the Arabian Sea and the Bay of Bengal, both of which are believed to have large reserves. Other sites of exploration activity are: off the northwestern coast of Australia, in the Andaman Sea, off the coast of Africa south of the Equator, and off the southwestern coast of Madagascar. Other than the countries of the Persian Gulf, only India produces commercial quantities of oil from offshore areas, with a large proportion of its total production coming from fields off the coast of Mumbai (formerly Bombay). Some natural gas also is produced from fields off the northwestern coast of Australia.
Another potentially valuable mineral resource is contained in manganese nodules, which abound in the Indian Ocean. Sampling sites throughout the central part of the ocean, as far south as South Africa, and east in the South Australian basin have yielded nodules; the manganese content has been highest in the east and lowest towards the northwest. The difficulty in mining and processing these minerals, despite advances in technology, has precluded their commercial extraction. Other minerals of potential commercial value are ilmenite (a mixture of iron and titanium oxide), tin, monazite (a rare earth), zircon, and chromite, all of which are found in near shore sand bodies.
The greater part of the water area of the Indian Ocean lies within the tropical and temperate zones. The shallow waters of the tropical zone are characterized by numerous corals and other organisms capable of building, together with calcareous red algae and coral islands. These coralline structures shelter a thriving marine fauna consisting of sponges, worms, crabs, molluscs, sea urchins, brittle stars, starfish, and small but exceedingly brightly coloured reef fish.
The major portion of the tropical coasts is covered with mangrove thickets with an animal life specific to that environment. Mangroves act to stabilize the land along the coastal margin and are important breeding and nursery grounds for offshore species.
The small crustaceans, including more than 100 species of minute copepods, form the bulk of the animal life, followed by small molluscs, jellyfish, and polyps, and other invertebrate animals ranging from single-celled radiolaria to large Portuguese man-of-war jellyfish, which attain a size of several feet. The squid form large schools. Of the fishes, the most abundant are several species of flying fish, luminous anchovies, lantern fish, large and small tunnies, sailfish, and various types of sharks. Also found are sea turtles and large marine mammals, such as dugongs (or sea cows), toothed and baleen whales, dolphins, and seals. Among the birds, the most common are the albatross and frigate birds; several species of penguins populate the islands lying in the ocean's temperate zone and the Antarctic coast.
The upwellings that occur in several coastal regions of the Indian Ocean - particularly in the northern Arabian Sea and on the South African coast - cause nutrients to concentrate in surface waters. This, in turn, produces immense quantities of phytoplankton that are the basis for large populations of commercially valuable marine animals. Despite great fishery potentials, most commercial fishing is conducted on a small scale, and large areas remain undeveloped.
Shrimp is the most important commercial species for coastal countries, with India accounting for the largest catch. Lesser quantities of sardines, mackerel, and anchovies also are exploited by the littoral states. Since coastal nations can now claim sovereignty over resources within an exclusive economic zone that extends 370 km from their coasts, it has become possible for small states such as the Maldives to increase their national income by selling fishing rights in their zones to the major fishing nations that have the capital and technology to exploit pelagic resources.
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27-04-2011, 12:54 PM
All creatures salt, a substance essential to human survival. Regulates the amount of water & saltwater bodies. All cells from reaching the water itself, to work the way it regulates the moisture content inside the cell. It purifies, is there to extract the poisonous wastes of cellular metabolism. Salt forces some water to stay outside the cells. It balances the amount of water remains extracellular. Some sea water in the body; sea, the sea has been held in other cells of the body has been kept outside the cell. Lovely health is most dependent on a delicate balance between the volume of these oceans, this balance is achieved by salt - unrefined salt.
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