Question

Factors affecting salinity in surface layers of ocean include _____.
A. Evaporation and precipitation
B. Winds by transferring water to other areas
C. The ocean currents
D. Freshwater flows from rivers and freezing and thawing of ice
E. All of these

Answer 1

Hint:
Salinity is defined as the total content of dissolved salts in seawater.
It is expressed as the amount of salt (in gm) dissolved in 1,000 gm (1 kg) of seawater.
When freshwater from rivers or when water from thawing ice enters the ocean, it decreases the salinity of the ocean.

Complete answer:
Evaporation and precipitation – The surface of the ocean when exposed to the sun’s heat, gets heated up and the water starts evaporating. As water evaporates, the salts are left behind in the ocean. Hence, the salt to water ratio increases i.e. the salinity of the ocean increases. When it rains, the opposite happens. Amount of salts in the water remains the same but the amount of water increases, hence reducing the ocean’s salinity.

Winds by transferring water to other areas – Wind also influences salinity of an area by transferring water to other areas. The winds are a major cause of huge waves. These waves transfer water to different regions in the direction of the wind.

The ocean currents – The ocean currents occur due to changes in temperature. The water gets warm in the tropical region due to direct sunlight. This warm water moves toward colder water (towards the temperate region) to attain equilibrium. These ocean currents also affect the salinity of the ocean.

Freshwater flows from rivers and freezing and thawing of ice – When freshwater from rivers or when water from thawing ice enters the ocean, it decreases the salinity of the ocean. This is the reason why oceans in the polar region are less saline as compared to those in warmer places.

Therefore the correct answer is E

Note
Higher salinity is recorded in the Mediterranean Sea because of high evaporation.
However, salinity is very low in the Black Sea due to the enormous freshwater influx by rivers.

The right amount of salinity in the ocean water is essential for maintaining the osmotic balance for the organisms, the right density for optimum water currents and a favourable freezing point.