Theory question 204
Oceans and Lakes(a) Explain the term salinity. (b) Describe three factors that cause variations in the salinity of seas and oceans. (c) Outline three ways in which oceans are of importance to man.
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(a) Salinity is the amount of dissolved salts in sea water, usually expressed in parts per thousand (about 35‰ on average).
(b) Rate of evaporation: high evaporation in hot dry areas raises salinity (Red Sea); fresh water from rivers, rain and melting ice lowers it (Baltic Sea, equatorial waters); degree of mixing by currents and winds; enclosed seas cut off from the open ocean become very salty or very fresh.
(c) Fishing and food; transport and trade by sea; source of minerals and oil; moderates climate and supplies moisture for rain; tourism and recreation; salt; power from waves and tides.
Explain how each factor adds or removes water or salt.