Why are there differences in salinity of oceans?

Differences in the salinity of the ocean is caused by following factors -

• Ice melting causes fresh water to get mixed into the salt water of the ocean. This dilutes the water.

• River water which gets mixed into the ocean water also increases the freshwater content.

• Evaporation only causes the fresh water to evaporate out leaving behind the salt. This increases the concentration of salt water in the ocean.

• Rain increases the freshwater content in the ocean.

• Currents move the salt water from the equator to higher latitudes thus averaging the salt water ratio.