Variations in oceanic salinity and its multi-dimensional effects

14. Account for variations in oceanic salinity and discuss its multi-dimensional effects.  (250 words)                      15M

Ans. Ocean salinity refers to the dissolved amount of salts in the ocean water. It is measured in ppt (parts per thousand). Ocean salinity varies 

• at different latitudes, in different oceans, 
• at different locations in the same ocean. 

Many factors play a major role in the variation of ocean salinity like

• In Precipitation : It affects the ocean salinity in a way that it decreases the salanity as precipitation brings more water and dilutes the ocean water. That is why the salinity at the equatorial region is less than the tropics because tropics have less rainfall than equator.

• Evaporation: It takes up the water and concentrates the ocean water, this increases the salinity. Evaporation is affected by the temperature of the region along with the winds (mainly advection). More the temperature of the region, more will be the evaporation and more will be the salinity. It is because of this effect that different latitudes and regions in the oceans have different salinity. It is because of more evaporation and temperature, tropics have more salinity than the equatorial regions.

• In Flow of Fresh Water: Flow of fresh water either by the draining river or by the thawing of the glaciers affects salinity mainly by decreasing it. It is because of this effect Bay of Bengal observes less salinity than Arabian Sea and North Caspian Sea observes less salinity than the Southern Caspian sea.

• Variation at Latitudes : Salinity decreases as we move from equator to poles due to decrease in the insolation and evaporation.

• Salinity is also affected by the upwelling and the downwelling of the ocean water. This happens under the influence of ocean currents.

• Effects of Oceanic Salinity: Salinity affects sea water density, which in turn governs ocean circulation and climate. We know that the wind drives upper ocean currents, however ocean current can also flow deep below the surface. These deep ocean currents are driven by the differences in sea water density.

• As sea water density is controlled by temperature and salinity, these factors make the oceans very dynamic in nature. The thermohaline circulation is the principle mechanism by which the oceans store and transport heat. Since salinity is a key ingredient in the global thermohaline circulation, its measured value will help to discover how its variation induces changes in global circulation.

• Salinity is a major factor in ocean and atmospheric science because it affects the ocean currents that further control the climate of the planet.