Following are the causes of currents:
i. Prevailing winds: Prevailing winds influence the ocean currents more than any other single factor. These winds blow in a particular direction and drag the surface water due to the force of friction. This leads to the formation of ocean currents.
ii.Temperature difference: Warm water is lighter and rises but the cold water is denser and sinks. This makes the difference in the levels of a sea. Warm equatorial water moves polewards along the surface while the cold water from the poles move along the bottom towards the equator.
iii. Difference in salinity: Waters of high salinity are denser and heavier while the waters of low salinity are lighter. As a result light water with less salinity rushes towards the high salinity water and a current is formed.
iv. Coriolis effect: Due to the Coriolis effect the moving water turns and flows elliptical path known as gyre. Water circulates in these gyres in clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere.
