Why Is the Ocean Salty?
The salt in the ocean comes from the earth’s crust. Since the very beginning of the earth’s history, water on its surface has been at work dissolving the rocks that make up the earth’s crust. The salt minerals in the dissolved rocks are added to the water of the oceans.
As water evaporates from the sea, it leaves all the accumulated salt behind. When rain falls upon the continents, it washes still more salt from the land and sends it by rivers to the oceans. Because this has happened for millions of years, the ocean now has a great deal of salt in it.
The salinity of ocean water varies. One cubic foot of average sea water contains 2.2 pounds of salt. The saltiest water is in the Red Sea and in the Persian Gulf, which have salinity due to very high evaporation rates and low fresh water influx.
The least salty seas are in the polar regions, where both melting polar ice and a lot of rain dilute the salinity.