Variations in oceanic salinity
The salinity of the oceans is controlled by evaporation and rainfall at the earth’s surface. Global warming is making some parts of the earth’s oceans much saltier while others parts are getting fresher. If the evaporation is more at a given patch of ocean, the concentration of salts increases in the seawater resulting in higher salinity.
However, in places that receive high rainfall, the water gets more diluted resulting in low salinity. Equatorial waters have lower salinity due to heavy rainfall and high humidity. Oceans lying between 20 to 30 degrees north and south have high salinity because of high temperature and low humidity.
Similarly, oceans falling in temperate regions have lower salinity due to lower temperatures and reduced evaporation. Oceans fed by large rivers like Amazon, Congo, Ganges, Mekong, etc have lower salinity.
Multi-dimensional effects of Salinity
Melting of icebergs and resultant fresh water intake into Baltic, Arctic, and Antarctic Ocean waters makes them less saline. Change in the temperature or density influences the salinity of an area because salinity, temperature, and density of water are interrelated.
Coral reefs which are important for marine biodiversity can thrive only in saline water. Evaporation is controlled by the salinity of the oceans thus the tropical cyclones which are driven by evaporation are indirectly controlled by salinity.
Salinity play important role in the formation and circulation of oceanic currents. Because of the considerable salinity of ocean water, the plankton keeps floating over the ocean surface. Reduced salinity can endanger the survival of planktons which can affect the entire marine ecosystem. Oceanic salinity, therefore, plays a crucial role in the survival of both marine and terrestrial life forms on earth.