Ocean Currents

Introduction (Ocean Currents)

The general movement of a mass of oceanic water in a definite direction is called oceanic current which is more or less similar to water streams (rivers) flowing on the land surface of the earth. Ocean currents are the most powerful of all the dynamics of oceanic waters because these drive oceanic waters thousands of kilometers away. Ocean currents are divided based on temperature into (i) warm currents and cold currents.

They are divided based on velocity, dimension, and direction into energy by solar radiation. The transformation of solar radiation into heat in the atmosphere and the reverse are also at the sea surface and in this way, the sea surface becomes one of the most important interfaces of the earth, it is the starting point of both the atmospheric and oceanic circulation.  The  forward movement of surface water of the oceans under  the influence of prevailing winds is called drift.

Origin of Ocean Currents 

According to the general cause, mentioned above, of steady water movements in the sea, two fundamental factors stand in question:

a) the internal field of force of the mass structure, and b) the external field of force due to the winds.

The factors, in fact, controlling the origin and other characteristics of ocean currents, are related to different characteristics of ocean waters, rotational mechanism of the earth, external factors or atmospheric  factors, topographic characteristics of the coasts and ocean basins. Besides, there are some factors which modify ocean currents.

The factors relating to the earth’s  nature and its rotation include i) Gravitational force, and defective force by earth’s rotation.  Oceanic factors include i) pressure gradient, ii) temperature gradient, temperature variations and ii) Precipitation. Current modifying  factors include i) directing and shape of coastlines, ii) bottom reliefs of the ocean basins, iii) seasonal filtrations and iv) rotation of the earth.

Factors related to the Rotation of the earth  

The rotating of the earth on its axis from west to east results in the genesis of Coriolis forces which deflects the general directing of ocean currents. For example, the currents flowing from equator towards the north south and south north in the southern hemisphere are disaffected towards their left. The rotational force of the earth causes movement of ocean water near the equator in opposite direction to ‘the west to seats rotation’ of the earth and thus equatorial currents are generated.

These currents flow from east to west. Some ocean water moves in the direction of the rotation of the earth and thus equatorial currents are generated. These currents flow from east to west. Some ocean water moves in the direction of the rotation of the earth i.e. from west ti east and thus counter equilateral currents are formed.

Factors related to the Oceans (Ocean currents)

Local variations in the physical properties of the ocean e.g. pressure gradient, temperature differences, salinity differences, density variations etc. generate ocean currents.

Temperature Difference: The amount of insulting received at the earth’s surface and consequent temperature decreases from equator towards the poles. Due to high temperature in the equatorial region the water density decreases because of greater expansion of water particles whereas the density of sea water becomes comparatively greater expansion of water particles whereas the density of sea water becomes comparatively greater in the polar areas. Consequently water moves due to expansion of volume from equatorial region of higher temperature to polar areas colder areas of relatively very low temperature the Gulf Stream and Kuroshio warm currents moving from equator towards north are example of such currents.

Salinity Difference: Oceanic salinity affects the density of ocean water and density variation causes ocean currents. Salinity increases the density of ocean water. If two areas having equal temperature are characterized by varying salinity the area of high salinity will have greater density than the area of low salinity. Ocean current of the water surface are generated from the areas of less salinity to the area of greater salinity. Such system of surface and sub-surface currents caused by salinity variation is originated in open and enclosed seas.

Density Difference: In fact, the difference in the density of oceanic water is the main cause of the movement of ocean water as ocean currents. Water density depends on a number of factors e.g. temperature, salinity, pressure etc. In other words density is a function of temperature, air pressure and salinity.