If there is one thing that just about everyone knows about the ocean is that it is salty. The two most common elements in sea water, after oxygen and hydrogen, are sodium and chloride. Sodium and chloride combine to form what we know as salt.
Sea water salinity is expressed as a ratio of salt (in grams) to liter of water. In sea water typically there are close to 35 grams of dissolved salts in each liter. This concentration is written as 35‰. The normal range of ocean salinity ranges between 33-37 grams per liter (33‰ - 37‰).
As in weather, where there are circumstances of high and low pressure, there are situations characterized by high as well as low salinity. Of the Earth's five ocean basins, the Atlantic Ocean is the saltiest. On average, there is a distinct decrease of salinity near the equator and at both poles, although for different reasons:
- Near the equator, the tropics receive the most rain on a consistent basis. As a result, the fresh water falling into the ocean helps decrease the salinity of the surface water in that region.
- As one move toward the poles, the regional occurrence of rain decreases and with less rain and more sunshine, evaporation increases.
Fresh water, in the form of water vapor, moves from the ocean to the atmosphere through evaporation causing the higher salinity. Toward the poles, fresh water from melting ice decreases the surface salinity once again.
The saltiest locations in the ocean are the regions where evaporation is highest or in large bodies of water where there is no outlet into the ocean. The saltiest ocean water is in the Red Sea and in the Persian Gulf region (around 40‰) due to very high evaporation and little fresh water inflow.