Why are there differences in the salinity of oceans?

The salinity of Oceans is due to the foll reasons :

a. For over million of years rain, rivers and streams washed away the salt compound from rocks and carried it to the seas.

b. Some salinity in the oceans is due to undersea volcanoes.

c. When the water evaporates the salt is left behind.

The above processes continued for millions of years and resulted in salinity of the seas.

Causes for the difference in salinity level:

a. there are regions on earth that have scanty rainfall and dry winds cause lots of evaporation, as we know evaporation tends to increase the salinity. Hence the sea water nearer to that regions is salty and denser. Example: North and South Atlantic regions.

b. Then there are some regions that have an abundance of rainfall, so as the rain is a source of freshwater it dilutes the sea water and reduces the salinity.