Objectives, Ocean Basins, The Relief of The Ocean Basins part – 1

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Water is important for life on earth. It is required for all life processes, such as, cell growth, protein formation, photosynthesis, and absorption of materials by plants and animals. There are some living organisms, which can survive without air but can’t survive without water. All the water present on the earth makes up the hydrosphere.

Oceans are the largest water bodies in hydrosphere. We will now study about the ocean basins, their relief, causes, and effects of circulation of ocean waters, and importance of oceans for man.

Objectives

The major objectives of this chapter are:

  • To identify the various submarine relief features

  • To analyze the important factors determining the horizontal and vertical distribution of temperature in oceans

  • To give reasons for the variation in the distribution of salinity in ocean waters

  • To state the three types of ocean movements - waves, tides and currents

  • To explain the formation of waves

  • To give various factors responsible for occurrence of tides

  • To establish relationship between planetary winds and circulation of ocean currents

  • To explain with suitable examples the importance of oceans to man

Ocean Basins

Earth is the only planet in the solar system which has water in abundance. About 71 % of the earth’s surface is covered by water. Oceans form a single, large, and continuous body of water encircling all the landmass of the earth. They contain 97.2 percent of the world’s total water. On the basis of their geographical locations, there are four principal oceans in the world which are separated largely. These are the Pacific Ocean, the Indian Ocean, the Atlantic Ocean and the Arctic Ocean.

Percentage Share of the Planet’s Total Ocean Area

Percentage Share of the Planet’S Total Ocean Area

Percentage Share of the Planet’s Total Ocean Area

Percentage Share of the Planet’s Total Ocean Area

The Relief of the Ocean Basins

There are mountains, basins, plateaus, ridges, canyons, and trenches beneath the ocean water, very similar to its counterpart on the continents. These relief features found on the ocean floor are termed submarine relief. The ocean basins are broadly divided into four major sub-divisions. They are as follows:

Features of Ocean Floor Topography

Features of Ocean Floor Topography

Features of Ocean Floor Topography

Continental Shelf: Continents slope seaward from the coast to a point where the slope becomes very steep. The shallow submerged extension of continent is known as the continental shelf. The depth of this shallow sea water over the continental shelf ranges between 120-370 metres. The width of the continental shelf ranging between a few kilometres to more than 100 kilometres. The continental shelf of the eastern coast of India is much wider than that of the western coast. They are much narrower or absent in some continents, particularly where fold mountains run parallel to the coast as along the eastern Pacific Ocean.

The shallow water over the shelf enables sunlight to penetrate through water to the bottom and encourages growth of microscopic plants and animals called planktons. These planktons provide food for fishes. Continental shelves are source of fishes, minerals including sand and gravel. A large quantity of the world’s petroleum and natural gas is obtained from these shelves. The Bombay High and the recent discovery of petroleum in the Godavari basin are examples of on shore drilling on the continental shelf.

One of the striking features of the continental shelf is the presence of submarine canyons which extends to the continental slope. These canyons are steep-sided valleys cut into the floor of the seas. Godavari Canyon in front of the Godavari river mouth is 502 metres deep.

Continental Slope: The continuously sloping portion of the continental margin, seaward of the continental shelf, extending down to the deep-sea floor of the abyssal plain, is known as continental slope. It is characterised by gradients of 2.5 degrees. It extends between the depth of 180-3600 metres. In some places, such as off the shore of Philippines, the continental slope extends to a great depth.

Along the base of the continental slope there is a deposit of sediments. These sedimentary deposits form the continental rise. In some regions the rise is very narrow but in others it may extend up to 600 km in width.

Abyssal Plain: Abyssal plains are extremely flat and featureless plains of deep ocean floor. Abyssal plains covering a major portion of ocean floor between the depth of 3000m to 6000m. They have extensive submarine plateaus, hills, guyots, and seamounts.

The plains close to the continents are covered mostly by sediments brought down from land. These sediments are called oozes. Some of the open seas do not support enough life to produce ooze on the floor. They are covered with a type of sediment called red clay which is of volcanic origin and made up of tiny particles brought by wind and rivers.

Submarine Ridges: The oceanic mountains known as submarine ridges are linear belts occurring near the middle of the oceans. They are also called mid-oceanic ridges. All mid oceanic ridges constitute a world-wide system which is interconnected from ocean to ocean. The oceanic ridges are sites of frequent earthquakes. Volcanism is also common in ocean ridges and it produces several relief features.

The Mid-Atlantic Ridge is the largest continuous submerged mountain ridge which runs from north to south in the Atlantic Ocean. At some places, the peaks rise above the surface of water in the form of islands. The East Pacific Ridge and Carlsberg Ridge are some of the important submarine ridges.

Seamounts and Guyots: Thousands of submerged volcanoes with sharp tops called seamounts are scattered over the entire sea floor. Sometimes they rise above the sea as isolated Islands. Hawaii and Tahiti Islands are the exposed tops of volcanoes. Volcano rising above the ocean floor whose top has been flattened by erosion and is covered by water is known as guyot.

The Ocean Deeps: The ocean deeps are the deepest part of the ocean. They are long, narrow, steep-sided, and flat-floored depressions on the ocean floor. They are generally termed submarine trenches. Trenches are not always located in the middle of the ocean basins, but are situated very close or parallel to the continents bordered by fold mountains. They are usually found adjacent to the areas of volcanic and earthquake activity. They occur in all the major oceans. The Pacific Ocean has the largest number of trenches. The Mariana Trench in the Pacific Ocean is the deepest known part of the oceans.

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