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HYDROSPHERE All the Water of the Earth Including the Oceans, Lakes

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HYDROSPHERE All the Water of the Earth Including the Oceans, Lakes HYDROSPHERE All the water of the earth including the oceans, lakes, rivers, ice sheets and the water in the atmosphere is called hydrosphere and it covers about 71% of the earth's surface. The ocean predominates over land areas in the S-Hemisphere far more than that in the N- Hemisphere. Major Oceans 1. The Pacific Ocean: It is the largest and deepest ocean covering one third of the globe. Its average depth is 4200 M. The deepest parts are the Philippine Trench about 10,380 m. and the Marina Trench about 10,800 m. The Pacific Ocean has a string of volcanoes along the coastal margins of the continents known as 'The Ring of Fire'. 2. The Atlantic Ocean: Though the Atlantic is smaller than the Pacific, its total coastline is more than that of the Pacific and the Indian Ocean combined. There is a long submarine ridge running north to south in the middle of Atlantic. It is the greatest mountain chain in the world (16,000 km long). It is known as the Dolphin Ridge the North Atlantic and the Challenger Ridge in the South Atlantic. There are also continental islands such as the British Isles, Newfoundland, the West Indies etc. The Atlantic is the greatest commercial highway of the world. 3. Indian Ocean: It is small in size but has an average depth of 4,000 m. The two great bays on either side of the peninsula of India, namely the Bay of Bengal and the Arabian Sea belong to the India Ocean. The Indian Ocean is dotted with thousands of small islands some of which are of coral formation, e.g. the Maldives and Lakshadweep islands, while other like the Mauritius and the Reunions are volcanic. Sri Lanka and Malagasy are continental islands. 4. Arctic Ocean: It is found around the North Pole. It covers only one thirtieth of the sea area. It is almost completely covered with ice to a depth of about 3 m. 5. Antarctic Ocean: The remaining area of the sea is included in the Ant- arctic Ocean surrounding the Antarctic Continent. Profile of Ocean Floor: The ocean basins are in many ways similar to the land surface. There are submarine ridges, plateau, canyons; plains and trenches. The great variety of relief is largely due to the interaction of tectonic, volcanic, erosional and depositional processes. In general the ocean floor can be divided into four major divisions -the continental shelf, the continental slope, the continental rise and the Abyssal Plain. a) Continental Shelf: It is the land portion, submerged under sea water and is a transitional zone between the land and the actual sea bottom. 1. The isobath of 100 fathoms (around 2OOm) demarcates the continental shelf. 2. The average width is about 70 km and the mean slope is less than 1°. 3. About 7.5 per cent of the total ocean area is covered by it. 4. It is almost absent in the eastern Pacific ocean, especially in South America. 5. At the eastern coast of USA it is about 120 km wIde and also very wide on the eastern coast of India. 6. Individually it covers about 13.3% part of Atlantic Ocean, 5.7% of Pacific Ocean and 4.2% of Indian Ocean. 7. It is the area of terrigenous deposits i.e. sediments are derived from land. 8. They provide the richest fishing ground in the world. 9. About 20% of world petroleum and natural gas are found here. b) Continental Slope: It lies at the edge of the continental shelf, generally up to the depth of 2000 fathoms (3660 m) from the mean sea level. 1. It has a steep slope with the angle of slope varying from 2° to 5°. 2. It covers about 8.5% of the total oceanic area and individually about 12.4% of the Atlantic Ocean, 7.1 % of the Pacific Ocean and 6.5% of the Indian Ocean. 3. The continental blocks are supposed to end at the site of continental slope. 4. The continental slope along the many coasts of the world is furrowed by deep canyons like trenches terminating as fan-shaped deposits at the base. c) Continental Rise: The place where the continental slopes end, the gentle sloping continental rise begins. The average slope is between 0.5° and 1° & its general relief is low. With increasing depth the Continental Rise becomes virtually flat and it merges with abyssal plain. d) Abyssal / Deep Sea Plains: Beyond Continental Rise, it is found at the depth of 3000 to 6000 m. They cover about 40% of the total ocean floor arid generally are bounded by hills (ridges) on the seaward side. They are almost flat with a gradient less than 1:100. The irregular topography of the abyssal plain are buried forming relatively flat areas due to large supply of sediments. e) Submarine Ridges: These are the mountain ranges on the ocean floor and some of them are the largest mountain system on the earth. 1. A large number of submarine ridges are placed centrally in the oceans. 2. At some places their summits may rise above the sea level forming islands. f) Abyssal Hills: A deep sea floor also contains numerous isolated abyssal hills, sea- mounts and guyots. 1. A submarine mountain peak rising more than 1000 m above ocean floor is known as "seamount". 2. Flat topped seamounts are known as "Guyots". 3. All the above features are volcanic in origin, very common in Pacific Ocean. g) Submarine Trenches or Deeps: A long narrow and steep sided depression on the ocean floor is called trench. These are the deepest part of the ocean. 1. They lie along the fringes of the deep sea plains and usually run parallel to the bordering fold mountains or the island claims. 2. They are believed to have resulted from faulting or down folds of the earth crust and so tectonic in origin. 3. They are most common in the pacific Ocean like "Mariana Trench" off the Guam lsland Chain which is deepest (11 km)in the world. h) Submarine Canyons: These are the deep gorges on the ocean floor and are restricted to the continental shelves, slopes and rises. 1. Some canyons begin at the edge of the continental shelf and extend down the continental slope. For example- Oceanographer Canyon " near New England. 2. Some canyons have dendritic appearance like off the east coast of Southern California. 3. Some begins at the river mouth and extends over the continental shelf as "Zaire”, "Mississippi" and "lndus" canyons. i) Bank, Shoal & Reef: Banks are almost flat topped elevation located in the continental margin. Shoals are detached. elevation with shallow depth. Reefs are the mound or rocky elevation like ridges made of organic deposit. 1. The depth of water is relatively small in banks but adequate for navigation. 2. These are sites of rich fishing e.g. "DoggerBank" (North Sea), "Grand Bank" (off Newfoundland). 3. Shoals are dangerous for navigation as they are only 8-20 m below the sea level. 4. 'Great Barrier Reef' (off Queens land, Australia) is the largest reef in the world: Atlantic Ocean Ridges: Rio Grande Ridge, Wyville- Thompson Ridge; Newfoundland Ridge, Walvis Ridge, Telegraphic Plateau, Sierra Leone Ridge, Raykjanes Ridge, Cape Swell, Dolphin Ridge, Challenger Ridge. Basins: Labrador Basin, Iberian Basin, Cape-Verde Basin, Guinea Basin, Sierra Leone Basin, Cape Basin, Argentina Basin, Agulhas Basin. Deeps & Trenches: Moseley Deep, Buchanan Deep, Valdivia Deep, Romanche Deep, Puertorico Deep, Nares Deep. Pacific Ocean Ridges: Albatross Plateau, Cocos Ridge, San-Felix-Juan Ridge" Hawaiian Swell, Marcus Necker Rise; Chatham Rise, Lord Howe Rise, Norfolk Ridge, S. Tasmania Ridge. Basins: Aleutian Basin, E&W Caroline Basin, Fiji Basin, E. Australian Basin, Jeffrey's Basin, S W Pacific Basin, S E Pacific Basin, Pacific Atlantic Basin. Trenches: Aleutian Trench, Kuril Trench, Philippine Trench, Cape-Johnson Deep, Nero Deep, Mariana Trench, Tonga-Kermadec Trench, Aldrich Deep, Brook Deep, Planet Deep. Indian Ocean Ridges: Socotra-Chagos Ridge, St. Paul Ridge, Seychelles Ridge, Crozet Ridge, Crozet Ridge, Kerguelen. Ridge, Laccadives-Chagos Ridge, Chagos St. Paul Ridge, Kergel- Gausberg Ridge, Andaman Ridge. Basins: Somali Basin, Oman Basin, Natal Basin, Mauritius Basin, Agulhas Basin, Andaman Basin, Cocos- Kelling Basin, E. Indian-Antarctic Basin. Trenches: Sunda Trench, Valdivia Deep, Jeffrey deep. Arctic Ocean Ridges and Basins: Faeroe- lceland Rise, East Jan Mayen Ridge, Spitsbergen Ridge, Greenland Basin, Norwegian Basin, N-Polar Basin. Temperature Horizontal Distribution of Temperature: The mean annual temperature of the surface water of the oceans is 25°C varying from -5°C to over 33°C. 1. The temperature decreases as we move away from the equator. The average temperature of ocean water is 26°C at the equator, 23°C at latitude 20°, 14°C at latitude 40° and 1°C at latitude 60°. 2. The coldest month in the ocean is February and the warmest month is August in the Northern Hemisphere and reverse in the Southern Hemisphere. 3. The highest temperature of ocean water is found in enclosed or partially enclosed seas in the equatorial areas e.g. a temperature of 38°C has been recorded in Red Sea though the average temperature in summer is only 29°C. 4. The temperature of the warm current is higher than the surrounding areas. Thus Gulf Stream does not allow the Norwegian coast to freeze even in winter . 5. The prevailing Winds deflect the warm and cold currents and cause change in temperature of the ocean water. So, in the tropical zone the western section of the oceans are warmer than the eastern section owing to the influence of trade winds.
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