The ocean current is horizontal flow of a mass of waters in a fairly defined direction over great distances.
They are like stream of water flowing through the main body of the ocean in a regular pattern.
The average speed of current is between 3.2 km to 10 km per hour.
Ocean currents with higher speed are called stream and currents with lower speed are called drift.
Ocean currents can be broadly divided into two—-
Those currents which flow from equatorial regions towards poles have a higher surface temperature and are called warm current.
Those currents which flow from Polar Regions towards equator have a lower surface temperature and are called cold currents.
The origin and the nature of circulation of the ocean currents depend on the following factors:
[A] Differences in Density
The sea water’s density varies from place to place according to its temperature and proportion of salinity.
The higher the temperature of water, the lesser will be the density.
Hence the less dense water of the equator moves towards the poles while the cold and dense waters of the poles move towards the equator.
Thus cold currents always move from the poles to the equator while the warm currents move from equator towards the poles.
Currents are also produced by changes in the salinity of ocean waters.
If the salinity of the water is more, the density of the water increases, and the water sinks.
Hence water with Lower salinity flows on the surface of the high salinity water while an undercurrent of high salinity flows towards the less dense water.
The currents caused by difference in salinity are found between the Atlantic Ocean with lower salinity and the Mediterranean Sea with higher salinity.
[B] The Earth’s Rotation
The earth’s rotation deflects air to its right in the northern hemisphere and to its left in the southern hemisphere.
Similarly, ocean water is also affected by Coriolis force and follows the Ferrel’s Law.
So all the ocean currents follow clockwise direction in the northern hemisphere and anticlockwise direction in the southern hemisphere.
[C] The Planetary Winds
The planetary winds like the trade winds and westerlies, drive the ocean water in a steady flow in front of them.
In low latitudes or in the region of the trade winds the ocean currents change their direction according to the change in the direction of summer and winter monsoon winds.