The correct answer is option 2, i.e Increasing salinity of seawater causes its density to increase.
Salinity is the term used to define the total content of dissolved salts in sea water.
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 or ppt.
The relation between salinity of sea water with depth and its density are as follows:
Salinitychanges with depth, but the way it changes depends upon the location of the sea. Hence, Option 1 is NOT correct.
Salinityat the surface varies as it increases by the loss of water to ice or evaporation, or decreased by the input of fresh waters, such as from the rivers.
Salinity at depth is very much fixed, because there is no way that water is ‘lost’, or the salt is ‘added.’ Hence, Option 3 is NOT correct.
The lower salinity water rests above the higher salinity dense water.
Salinity in general increases with depth and there is a distinct zone called the halocline where salinity increases sharply.
Other factors being constant, increasing salinity of seawater causes its density to increase. Hence, Option 2 is correct.