Factors Affecting Salinity of Oceans and Seas

The variations of salinity in the various sea and oceans is affected by the following factors :-

• The rate of evaporation - The water fringing the High Pressure Belts of the Trade Wing Deserts, between 20 degree and 30 degree N and S, have salinity because of the high rate of evaporation caused by high temperature and low humidity. The temperate oceans have lower salinity due to the lower temperature and a lower rate of evaporation.
• The amount of fresh water added by precipitation streams and icebergs - Salinity is lower than the average 35% in equatorial waters because of the heavy daily rainfall and high relative humidity. Oceans into which huge rivers like the Amazon, Congo, Ganges, Irrawaddy and Mekong frain, have much of their saltness diluted and have a lower salinity. The Baltic, Arctic and Antarctic waters have a salinity of less than 32% because of the colder climate with little evaporation and because much fresh water is added from the melting of icebergs, as well as by several large poleward-bound rivers, e.g. Ob, Lena, Yenisey, and Mackenzine.
• The degree of water mixing by currents - In wholly or partially enclosed seas such as the Caspian Sea, Mediterranean Sea, Red Sea and Persian Gulf, the waters do not mix freely with the ocean water and they are not penetrated by ocean currents. Salinity is high, often over 37%. In areas of inland drainage without links with the oceans, continuous evaporation under an almost cloudless sky causes the accumulation of salts around the shores. In the open oceans where currents freely flow, salinity tends to be near the average 35% or even a little lower. The range of salinity is negligible where there is free mixing of water by surface and sub-surface currents.

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