One of the characteristics of the ocean water is its salinity or saltiness.
When we speak of salinity we have in mind not only common salt or sodium chloride but a great variety of other salts as well.
The dominant salts among these are sodium chloride & Magnesium Chloride with 77.7% & 10.9% respectively.
Due to the free movement of ocean water, the proportion of different salts remains constant in all oceans and even to great depth.
But the degree of concentration of the salt solution in oceans does vary appreciably in different seas.
The salinity of the ocean water is produced by a large number of dissolved chemical compounds.
Salinity is defined as the weight in grammes of solid material left after the evaporation of 1000 grammes of sea water.
If the weight of solid material is 35 grammes (and it is usually very near this figure), the salinity would be shown 35% (35 per thousands).
Salinity is expressed in this way rather than as percentage.
In the Baltic Sea, fresh water enters it from the surrounding land and reduce the salinity to 7% and it may fall in this sea as low as 2%.
But great evaporation combined with a very dry climate in the Red Sea region gives the water of this sea a high salinity of 41% to 42%.
In enclose sea, which are areas of inland drainage such as the Caspian Sea, the salinity is very high, 18% in the Dead Sea of Jordan. The salinity may be as high as 25%
The variation of salinity in different seas and oceans is affected by
– The rate of evaporation,
– The amount of fresh water added by streams and icebergs
– Mixing of the ocean waters