Marine Biology

Currents

The sea is in continuous circulation.  Air temperature differences between poles and equator set up strong winds which create definite currents in the oceans.  Due to currents, the cool dense water from the pole moves towards the equator and it gradually becomes warmer as it reaches the equator.  From the equator, water again moves towards the pole and becomes cooler and dense as it reaches the pole.  Because of the circulation, oxygen depletion or stagnation so common in freshwater lakes, is rare in the oceans.

          Currents transport food materials and remove waste materials.  Currents also distribute the planktonic larvae to the different parts of the world.  They also break the temperature barriers in the ocean by constantly circulating the waters.

Currents can be divided into three kinds:- 

a.    Density currents

b.    Tidal currents

c.    Wind currents

          Density currents are produced by the heating action of sun on the ocean water.  As the warm water rises up and spreads on the surface, the cold water sinks down for the cold region and spreads downwards.  Tidal currents are produced by the gravitational pull of moon and sun on oceanic waters. Wind currents are caused by the effect of winds blowing on the waters in a slanting manner.  These currents affect only the surface waters.