There are two sources of heat for the ocean water- (1) absorption of the solar radiation falling on the water surface, and (2) the convectional currents produced in the oceans because of the internal heat of the earth. In addition to the above mentioned major sources of heat, there are some other minor sources as well. These minor sources are as follows;

(a) Convection of sensible heat forms the atmosphere to the sea.

(b) Conduction of heat through the sea bottom from the interior of the earth.

(c) Conversion of kinetic energy into heat.

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(d) Heat produced by chemical and biological processes.

(e) Condensation of water vapour on the sea surface.

(f) Radioactive disintegration in the sea water.

The surface water of the oceans radiates back a part of the heat received from the solar radiation to the atmosphere. This heat loss from the sea surface is in the form of long wave radiation.

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Some of the heat is lost through the process of convection of sensible heat from the sea to the atmosphere Evaporation taking place continuously from the sea surface also consumes heat.

The above stated processes are the major factors which contribute to the cooling of the surface water of the seas and oceans. In fact, all the characteristic features of the sea surface temperatures are the result of the interaction of heating and cooling of the ocean water.

The ocean water temperature and its density are directly related. Any change in the temperature leads to a corresponding change in water density. The higher the temperature, the lower the density and vice versa.

As a matter of fact, temperature and salinity both affect the density of sea water in their own way. As we know, the density difference in the ocean water is one of the important factors controlling its movements.

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There is temporal as well as spatial variation in the temperature of sea water. Besides, below the surface water the temperature goes on decreasing with increasing depth. Latitude is another controlling factor of the distribution of surface temperature.

Because of the effect of latitudes the temperature shows a declining trend from the equator towards the poles.