The amount of salinity in tropical regions is found to be the highest (36 per thousand). More salinity is found in this region due to the high temperature, prevailing warm and dry winds, more evaporation, lack of rainfall and lesser availability of clean water. At both the sides of tropical regions, that is, towards the equator and the poles, the amount of salinity reduces. But the amount of salinity is found to be lesser in the polar regions than the equatorial regions.
The reason for this is that there is less evaporation and more supply of melt water by glaciers in the polar regions. In the equatorial regions, both the evaporation and the availability of clean water remain high. There are also local variations in the distribution of salinity in the coastal regions of the ocean. For example, due to the availability of clean water, low salinity is found in the parts of the river basins of the Ganga, Congo, Niger, Amazon, Indus Rivers, etc.
In the Sargasso region of the North Atlantic Ocean, the salinity is 38 per thousand. The main reason for this high salinity is that the cyclic flow of ocean currents found here does not mix the intermediate water with the water of other areas. Lines joining the places with similar salinity in the oceanic regions are called Isohalines.
