All waters in nature, whether rainwater or ocean water, contain dissolved mineral salts. Salinity is the term used to define the total content of dissolved salts in seawater. It is calculated as the amount of salt (in gm) dissolved in 1,000 gm (1 kg) of seawater. It is usually expressed as parts per thousand (o/oo) or ppt. Salinity is an important property of seawater. The salinity of 24.7 o/oo has been considered as the upper limit to demarcate ‘brackish water’.
Ocean salinity is affected by the following factors :
- The salinity of water in the surface layer of oceans depends mainly on evaporation and precipitation.
- Surface salinity is greatly influenced in coastal regions by the freshwater flow from rivers, and in polar regions by the processes of freezing and thawing of ice.
- Wind also influences the salinity of an area by transferring water to other areas.
- The ocean currents contribute to the salinity variations. Salinity, temperature, and density of water are interrelated. Hence, any change in the temperature or density influences the salinity of water in an area.