Question

The salinity of the oceans is

• A. Increasing
• B. Decreasing
• C. Constant
• D. Decreasing now but was increasing in past

Answer 1

The correct option is D Decreasing now but was increasing in past

Oceans occupy 73 percent of earths surface with salinity of 3.5 per cent (0.5 percent in Red Sea and 1 percent in Baltic sea). Throughout Earth's history, certain processes have served to make the oceans more salty eg. Weathering of rocks delivers minerals, including salt, into the ocean; Evaporation of ocean water and formation of sea ice both increase the salinity of the ocean. However these "salinity raising" factors are continually counter balanced by processes that decrease salinity such as the continuous input of fresh water from rivers, precipitation of rain and snow, and melting of ice. The fresh water rivers continuously wash salt and minerals from mountains and pour them into oceans. As this process continues for millions of years, the amount of salt and minerals brought by rivers keeps on decreasing because mountains and soil in general keep on becoming mineral and salt deficient. Hence, the balance of salinity in ocean has tilted towards decreasing salinity whereas in past it favoured increasing salinity.