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The causes and factors affecting the ocean currents may be divided into two classes : Primary causes, and, Secondary causes. Primary factors are responsible for the origin whereas the secondary factors determine the direction of flow of ocean currents.  1. Primary causes :  (i) Planetary winds: Planetary winds are the principal cause of the origin of ocean currents. Such winds drive surface water along with them.  (ii) Difference of density and salinity: Difference of density and salinity in ocean water motivates denser waters to sink and move as undercurrents; whereas lighter waters move towards the denser water as surface currents. Such density differences are mainly the result of differences in temperature and salinity of ocean waters.  2. Secondary causes:  (i) The rotation of the Earth: The rotation of the Earth, which affects the direction of movement, deflects poleward current eastwards, equator wards currents westwards. It may be pointed out here that th...

Its physical characteristics like temperature, salinity, density and the external forces like the sun, the moon and the winds influence the movement of ocean water. Ocean currents are the continuous flow of huge amount of water in a definite direction. Water moves ahead from one place to another place through ocean currents. Ocean currents have direct impact on the climate and economy of the region.  Ocean currents and water masses differ in their impacts on marine life and the coastal environment in different ways:  • Impact on biodiversity:  The physical parameters of water masses are essential because they structure the water masses and determine the various habitats that provide the environmental conditions required for marine life.  These conditions influence the production and the growth of plankton and fish species. The dispersion and dwelling of larvae for many benthic and pelagic species depend on hydro-graphical factors. They also play an important role for...