What Is Seawater?

Seawater is a dilute solution of several salts resulting from weathering and erosion of rocks. The salinity of seawater is expressed in terms of total dissolved salts in parts per thousand parts of water. Salinity varies from nearly zero in continental waters to about 41 parts per 1,000 in the Red Sea, a region of high evaporation, and more than 150 parts per 1,000 in the Great Salt Lake. In the main ocean, salinity averages about 35 parts per 1,000. The major nutrients, although not abundant, are extremely important in the biological output of the sea. Trace metals are of specific importance for certain organisms, but carbon, nitrogen, phosphorus, and oxygen are almost universally important to marine life.