Tuesday, 29 December 2015

Salinity of the Ocean

Almost every known chemical element can be found in varying proportions in the oceans whose most characteristic feature is their salinity, in contrast to the fresh water of lakes and streams. All sea water contains large amounts of dissolved mineral matter of which sodium chloride or common salt alone constitutes more than 77%. The other more important compounds include magnesium, calcium and potassium, while the rest are distinguishable only in traces of very minute quantites. Due to the free movement of ocean water, the proportions of different salts, remain remarkably constant in all oceans and even to great depths. But the degree of concentration of the salt solution in oceans does vary appreciably in different areas. This is expressed as salinity, the degree of saltness of water, either as a percentage or more often in parts per thousand. Variations are shown in salinity distribution maps by isohalines lines joining places having an equal degree of salinity.
Generally speaking, the average salinity of the oceans is 35.2%, about 35 parts of salt in 1,000 parts of water. In the Baltic Sea, where there is much dilution by fresh water and melting ice, the salinity is much lower, only about 7%. In the Red sea where there is much surface evaporation and fewer rivers to bring in fresh water, the average salinity increases to 39%. In enclosed seas, which are areas of inland drainage, such as the Caspian Sea, the salinity is very high, 180%, and in the Dead Sea of Palestine, a salinity of 250 % has been recorded. The highest salinity is perhaps, that of Lake Van, in Asia Minor, with 330%. It is a salt lake,k and salts are collected from its shores. The density of the water is so high that in Lake Van or the Dead Sea, it is almost impossible to sink. Beginner-swimmers will find it much easier to float here than anywhere else!

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