HYDROSPHERE (INTRODUCTION)
INTRODUCTION :-
The abundance of water on Earth's surface is a unique feature that distinguishes the "Blue Planet" from others in the solar system. The Earth's hydrosphere consists chiefly of the oceans, but technically includes all water surfaces in the world, including inland seas, lakes, rivers, and underground waters down to a depth of 2,000 m. The deepest underwater location is Challenger Deep of the Mariana Trench in the Pacific Ocean with a depth of -10,911.4 M. The average depth of the oceans is 3,800 m, more than four times the average height of the continents.
About 3.5% of the total mass of the oceans consists of salt. Most of this salt was released from volcanic activity or extracted from cool, igneous rocks. The oceans are also a reservoir of dissolved atmospheric gases, which are essential for the survival of many aquatic life forms. Sea water has an important influence on the world's climate, with the oceans acting as a large heat reservoir. Shifts in the oceanic temperature distribution can cause significant weather shifts, such as the EI Nino-Southern Oscillation.
WATER :-
Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state. water vapor or steam. About 1.460 petatonnes (Pt) (10'21 kilograms) of water covers 71% of the Earth's surface, mostly in oceans and other large water bodies, with 1.6% .of water below ground in aquifers and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation. Saltwater oceans hold 97% of surface water, glaciers and polar ice caps 2.4%, and other land surface water such as rivers, lakes and ponds 0.6%. A very small amount of the Earth's water is contained within water towers, biological bodies, manufactured products, and food stores. Other water is trapped in ice caps, glaciers, aquifers, or in lakes, sometimes providing fresh water for life on land.
EARTH'S OCEANS: An Introduction :-
Oceans cover about 70% of the Earth's surface. The oceans contain roughly 97% of the Earth's water supply.
The oceans of Earth are unique in our Solar System. No other planet in our Solar System has liquid water (although recent finds on Mars indicate that Mars may have had some liquid water in the recent past). Life on Earth originated in the seas, and the oceans continue to be home to an incredibly diverse web of life.
The oceans of Earth serve many functions, especially affecting the weather and temperature. They moderate the Earth's temperature by absorbing incoming solar radiation (stored as heat energy). The always-moving ocean currents distribute this heat energy around the globe. This heats the land and air during winter and cools it during summer.
The Earth's oceans are all connected to one another. Until the year 2000, there were four recognized oceans: the Pacific, Atlantic, Indian, and Arctic. "In the Spring of 2000, the International Hydro graphic Organization delimited a new ocean, the Southern Ocean (it surrounds Antarctica and extends to 60 degrees latitude),"
There are also many seas (smaller branches of an ocean); seas are often partly enclosed by land. The largest seas are the South China Sea, the Caribbean Sea, and the Mediterranean Sea.
Ocean Area (square miles) Average Depth (ft) Deepest depth (ft)
Pacific Ocean 64,186,000 15,215 Mariana Trench, 36,200 ft deep
Atlantic Ocean 33,420,000 12,881 Puerto Rico Trench, 28,231 ft deep
Indian Ocean 28,350,000 13,002 Java Trench, 25,344 ft deep
Southern Ocean 7,848,300 sq. miles (20.327 million sq km) 13,100-16,400 ft deep (4,000 to 5,000 meters) the southern end of the South Sandwich Trench, 23,736 ft (7,235 m) deep
Arctic Ocean 5,106,000 3,953 Eurasia Basin, 17,881 ft deep
THE OCEAN FLOOR :-
The Ocean floor may be divided into four' parts
(1) The Continental Shelf is one of the most important relief features of the ocean bottom. It is the name given to the fringe of shallow water (upto about 100 fathoms or 180 m deep) that surrounds the continents. It is a relatively narrow platform and found especially where the mountain ranges occur close to the coasts of continents.
In these shallower parts, waves and tides constantly distribute silt and rock fragments that have been broken by waves from the shore lines. Much of the waste of the land brought by rivers is also spread over the continental shelf. Again, the shallowness of the continental shelf enables the
sunlight to penetrate through the water. This fosters growth of minute plants and microorganisms which directly or indirectly provide food for other marine life. This is one of the reasons why the world's chief fishing grounds are found in the shallow waters of the continental shelf, such as those in the North .Sea and the Grand Banks off New Foundland.
The slope of the shelf is usually gentle, but beyond the 180 meter line it descends steeply to the bed of the ocean. This line is called the continental edge.
(2) The steep which descends from the edge of the containerize shelf to the deep ocean bed is known as the continental slope.
(3) The Deep Sea Plains are wide and almost level areas forming most of the ocean floor. They are generally 3 to 5 km below sea level.
(4) In some places these plains plunge to great depths known as Ocean Deeps. Most of the deeps or Trenches. As many as 57 deeps have been explored so far; out of which 32 are in the Pacific Ocean: 19 in the Atlantic ocean and 6 in the Indian ocean. The deepest is the Mariana Trench in the Pacific, about 10,800 m. below sea level. One of the most unusual features of the sea floor is a series of underwater mountains called Mid-ocean ridges. The peaks of these ridges are higher than those of most continental mountain systems.
THE MAJOR OCEANS :-
It is customary to speak of the oceans as if they were separate bodies of water. In reality they are just sections of one great sea covering most of the earth's surface.
The major oceans of the world are the Pacific, the Atlantic, the Indian, the Arctic and the Antarctic.
The Pacific Ocean is the largest and deepest covering one third of the globe. Its average depth is 4,200 m. Its ,basin contains high and abrupt ridges, deep trenches, volcanic mountains and other features. The deepest hollows are in the Philippine Trench about 10,380 m and the Mariana Trench about 10,800 m. Some of these ridges project above sea level and form islands most of which are either volcanic or coral. The highest volcanic islands form Hawaii, Tahiti and Samoa.
The Atlantic Ocean is smaller and shallower. Its'S' shaped curve is similar to that of the coastline bordering it. This ocean also has many ridges. Though the Atlantic is smaller than the Pacific its total coastline is more than that of the Pacific and the Indian Ocean combined. It also receives many great rivers such as the Rhine, Senegal, Niger, Congo, St. Lawrence, Mississippi,' Amazon, Orinoco and La Plata.
There is a long submarine ridge running north southwards in the middle of the Atlantic. It is the greatest mountain chain in the world. it is some 16,000 km. It is known as the Dolphin Ridge in the North Atlantic and the Challenger Ridge in the South Atlantic. On each side of the central Atlantic ridge are the great deeps, the deepest is the Nares Deep (8,500 m).
The Atlantic is the greatest commercial highway of the world. Most of the world's great ports lie on its coasts.
The Indian Ocean is small in size but has an depth of 4,000 m. There is a Mid - Indian ridge which runs in a southward direction several hundred kilometers from the coast of India. The two great bays on either side of the peninsular of India, namely, the Bay of Bengal and the Arabian Sea belong to the Indian Ocean. The principal rivers draining into it are the Zambesi, the Indus, the Ganga and the Irrawaddy.
Around the north pole is the Arctic Ocean, a small ocean only one-thirtieth of the sea's area. It is almost completely covered with ice to a depth of about 3 or 4 m. The remaining area of the sea is included in the Antarctic Ocean surrounding the Antarctic Continent.