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THERMOHALINE CIRCULATION


Published on: 12/2/2020 2:34:56 AM

There are three Main process that make the Oceans circulate: Tidal force, Wind stress, and density difference. The density of sea water is controlled by its temperature (thermo) and its salinity (haline), and the circulation driven by density difference is thus called the Thermohaline circulation.

Earth's polar regions ocean water gets very cold, forming sea ice. As a consequence, the surrounding seawater gets saltier, because when sea ice forms, the salt is left behind. As the sea water gets saltier, its density increases, and it starts to sink. Surface water is pulled in to replace the sinking water, which in turn eventually becomes cold and salty enough to sink. This initiates the deep Ocean currents driving the global conveyer belt.

In the thermohaline circulation, dense, cold, salty surface water sinks in the northern Atlantic Ocean, generating slow bottom currents that in turn cause slow upwelling in the Indian Ocean, western Pacific Ocean, and along the coast of Antarctica. Thermohaline circulation plays an important role in the carbon cycle by moving CO2 rich surface water into the ocean depths deep ocean circulation provides a conveyor belt for storage and release of CO2 in a cycle of about 1500 years duration. This allows the ocean to moderate rapid changes in atmospheric CO2 concentration, such as those produced by human activity through Fossil fuel burning.

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Energy is also transported by the oceanic thermohaline circulation. By carrying warm surface water poleward, this loop acts like a heat pump in which energy is acquired in tropical and equatorial regions and is moved northward into the North Atlantic, where it is transferred to the air. Since wind patterns moves air eastward at higher latitudes, this energy ultimately warms Europe. The amount of Energy transferred to the atmosphere is quite large. A recent calculation shows that it is equal to about 35% of the total solar energy received by the Atlantic Ocean north of 40° latitude. This type of circulation does not occur in the Pacific or Indian Ocean, which is why Europe is significantly warmer than the high-latitude regions of the North Pacific and eastern North America at the same latitude.

Some scientists have observed that thermohaline circulation could be slowed or stopped by inputs of freshwater into the North Atlantic. Such freshwater inputs could come from the sudden drainage of large lakes formed by melting ice at the close of the last Ice Age. The freshwater would decrease the density of the ocean water, keeping the water from becoming dense enough to sink. Without sinking, circulation would stop.

In turn, this would interrupt a major flow path way for the transfer of heat from equatorial regions to the northern Mid latitudes. This mechanism could result in relatively rapid climatic change and is one expla­nation for the periodic cycles of warm and cold temperatures experienced since the melting of continental ice sheets about 12,000 years ago.  The Majority of climate scientists believe that a critical change in the Thermohaline circulation is unlike­ly to occur during this century, but the question cannot be answered with certainty at present. Due to the potentially serious impact on our climate of a collapse of the Thermohaline circulation, it must be regarded as a 'low risk, high-impact' event that cannot be ignored.

Also Read | HYPSOGRAPHIC CURVE OF EARTH SURFACE GEOLOGY