The oceans, unlike the continents, merge so naturally into one another that it is hard to demarcate them. The ocean waters are always moving. The three chief movements of ocean waters are the waves, the tides and the ocean currents.
Relief of Ocean Basins
The ocean water conceals a considerable variety of landscape very similar to its counterpart on the continents. There are mountains, basins, plateaus, ridges, canyons and trenches beneath the ocean water too. These relief features found on the ocean floor are called submarine relief. The Ocean basins are broadly divided into four major sub-divisions:
- Continental shelf
- Continental slope
- Abyssal plains
- Ocean deeps
Continental shelf is the submerged portion of the continent which gradually slope seawards from the shore line. Continental slope is the steeply sloping part of the sea floor which marks the boundary between the sea floor and the continental shelf. Abyssal plains are extremely flat and featureless plains of the deep ocean floor. Long, narrow steep sided and flat floored depressions in the oceans are known as ocean deeps.
Oceans of the World
The five major oceans are:
- Pacific Ocean
- Atlantic Ocean
- Indian Ocean
- Southern Ocean
- Arctic Ocean
The various seas, bays, gulfs and other inlets are parts of these large oceans.
The Pacific Ocean is the largest and the oldest of the oceans and occupies about 50% of the entire water surface of the World Ocean. It is spread over one-third of the earth. Mariana Trench, the deepest part of the earth, lies in the Pacific Ocean. The Pacific Ocean is almost circular in shape. Asia, Australia, North and South Americas surround it.
The Atlantic Ocean, the second largest ocean, covers a little more than half of the area occupied by the Pacific. Its greatest depth is 8385 metres (Milwaukee deep). It is S shaped. It is flanked by the North and South Americas on the western side, and Europe and Africa on the eastern side.
The Indian Ocean, the third largest, stretches from Cape Comorin (Kanyakumari) in India to the Antarctic at the South Pole. The shape of ocean is almost triangular. In the north, it is bound by Asia, in the west by Africa and in the east by Australia.
The Southern Ocean encircles the continent of Antarctica and extends northward to 60 degrees south latitude.
The Arctic Ocean is strictly not an ocean. It is not navigable. It winds round the North Pole and is completely frozen in winter and covered with drifting ice for the rest of the year. It is connected with the Pacific Ocean by a narrow stretch of shallow water known as Berring strait. It is bound by northern coasts of North America and Eurasia.