i. There are three different layers of the ocean from top to bottom in the tropics.
ii. Epilimnion – First layer, extended up to 500 m in the top most layer with temperature ranging between 20-25°C. It is a zone of fresh water of relatively warm water in which mixing occurs as a result of wind action and convection currents.
iii. Thermocline layer – below the first layer in which the temperature decreases with depth is greater than t hat of the oVerlying and underlying water. It is also called as Metalimnion.
iv. Hyplomnion – The third layer, the lower layer of water characterised by a uniform temperature that is coolef than other layers.
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v. Oceans are great moderating agents on the Earth.
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vi. The freezing of ocean water forces the salt ions out of the water, so the ice that forms is almost freshwater ice. Ocean ice is generally no thicker than 3 m.
vii. The ice insulates the water under it from the colder air temperature above; therefore, the water below the ice never gets cold enough to freeze.
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viii. The water immediately below the ice is not only cold but it also contains a high concentration of salts. This high concentration of salt makes the water denser than surface water.
ix. The denser water sinks to the bottom of the ocean, causing a vertical circulation of the ocean water. This type of circulation is called thermohaline referring to both temperature (thermo) and salinity (haline). Because of this circulation, the deep water of the oceans has about the same temperature as the coldest surface water.
x. In tropical regions the ocean is wanned by the Sun. Ocean waters near the equator may have a surface temperature as high as 30°C. Near the poles the surface water temperature is about 0°C.
xi. The surface layer of water, which is penetrated by solar radiation, is about 100 m deep. This water is warmer and less dense than the colder water below. Because of this temperature difference, there is little mixing between the two.
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xii. The zone separating the warm surface water and the cold water below is called the thermocline.