1.4.2. Vertical Distribution of Temperature

It is a well-known fact that the maximum temperature of the oceans is always at their surfaces because they directly receive the heat from the sun and the heat is transmitted to the lower sections of the oceans through the process of convection. It results into decrease of temperature with the increasing depth, but the rate of decrease is not uniform throughout.

The temperature falls very rapidly up to the depth of 200 m and thereafter, the rate of decrease of temperature is slowed down. The temperature profile of oceans shows a boundary region between the surface waters of the ocean and the deeper layers. The boundary usually begins around 100-400m below the sea surface and extends several hundred of metres downward. This boundary region, from where there is a rapid decrease of temperature, is called the thermocline. About 90 per cent of the total volume of water is found below the thermoclinein the deep ocean. In this zone, temperatures approach 0°C.