Evaporation: The salinity of water in the surface layer of oceans depend mainly on evaporation. Where the evaporation is greater, the salinity is higher, for example, Mediterranean sea.
Freshwater flow influx: 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.
Where the freshwater flow into the oceans is greater, the salinity is lower.
For instance, at the mouths of rivers such as Amazon, Congo, Ganga etc., the ocean surface salinity is found to be lower than the average surface salinity.
Temperature and density: Salinity, temperature and density of water are interrelated. Hence, any change in the temperature or density influences the salinity of an area.
In general, regions with high temperatures are also, regions with high salinity.
Ocean Currents: They play an important role in the spatial distribution of dissolved salts in ocean waters.
The warm currents near the equatorial region push away the salts from the eastern margins of the oceans and accumulate them near the western margins.
Similarly, ocean currents in the temperate regions increase the salinity of ocean waters near the eastern margins. For instance, Gulf Stream in the North Atlantic Ocean increases the salinity of ocean waters along the western margins of the Atlantic Ocean.
Precipitation: Precipitation and salinity share an inverse relationship.
In general, regions with higher levels of precipitation have lower levels of salinity. This is the reason why though the equatorial region is as hot as the sub-tropics, it records lower salinity than the sub-tropics since the former receives heavy precipitation in a day.
Atmospheric pressure and Wind direction: anti-cyclonic conditions with stable air and high temperature increase salinity of the surface water of oceans
winds help is redistribution of salinity, as they drive away saline waters to less saline areas resulting into decrease of salinity in the former and increase in the latter