Divisions of the Ocean Floors
The ocean floors are part of the major divisions of the oceans of the world. The ocean floors can be divided into four major divisions:
(i) the Continental Shelf; (ii) the Continental Slope; (iii) the Deep Sea Plain; 4) the Oceanic Deeps.
Continental Shelf:
The continental shelf is the sediment-covered, relatively shallow part of a continent’s continental platform. The shelf provides a wide area for the fishing industry to catch fish, and preferably to do so without endangering the long term survival of the fish species involved.
The shelf typically ends at a very steep slope, called the shelf break. The average width of continental shelves is about 80 km.
The shelves are almost absent or very narrow along some of the margins like the coasts of Chile, the west coast of Sumatra, etc. On the contrary, the Siberian shelf in the Arctic
Ocean, the largest in the world, stretches to 1,500 km in width. The depth of the shelves also varies. It may be as shallow as 30 m in some areas while in some areas it is as deep as 600 m.
Massive sedimentary deposits received over a long time by the continental shelves, become the source of fossil fuels.
Continental Slope
The continental slope is the gently sloping region of the ocean floor that lies between the foot of the continental rise and a line along which the contour of the true ocean bottom has a regular rate of rise or descent. It is often called Middle Oceanographic Zone.
The gradient of the slope region varies between 2-5°. The depth of the slope region varies between 200 and 3,000 m. The slope boundary indicates the end of the continents.
Deep Sea Plain
The deep sea plains are gently sloping areas of the ocean basins. They are composed of sediments, typically clay or silt. These flat areas are the flattest and smoothest regions of the world.
The plain’s low relief means that sound waves can travel long distances through the water almost unimpeded by reflections. This is why sonar is so effective in detecting submarines.
The depths vary between 3,000 and 6,000m. These plains are covered with fine-grained sediments like clay and silt.
Oceanic Deeps or Trenches
Even deeper than trenches are the oceanic trenches. These are formed in the same way as trenches, but they are in oceanic crust rather than continental crust.
There are deep oceanic trenches, which are found on the seabed, and there is also a theory of deep oceanic trenches found under thick continental plates which can actually help create continents.
They are some 3-5 km deeper than the surrounding ocean floor. That is why they are very significant in the study of plate movements.
As many as 57 deeps have been explored so far; of which 32 are in the Pacific Ocean; 19 in the Atlantic Ocean and 6 in the Indian Ocean.