If the salinity of ocean waters is

If the salinity of ocean waters is analyzed, it is found to vary only
slightly from place to place. Nevertheless, some of these small changes
are important. There are three basic processes that cause a change in
oceanic salinity. One of these is the subtraction of water from the
ocean by means of evaporation--- conversion of liquid water to water
vapor. In this manner the salinity is increased, since the salts stay
behind. If this is carried to the extreme, of course, white crystals of
salt would be left behind.

The opposite of evaporation is precipitation, such as rain, by which
water is added to the ocean. Here the ocean is being diluted so that the
salinity is decreased. This may occur in areas of high rainfall or in
coastal regions where rivers flow into the ocean. Thus salinity may be
increased by the subtraction of water by evaporation, or decreased by
the addition of fresh water by precipitation or runoff.

Normally, in tropical regions where the sun is very strong, the ocean
salinity is somewhat higher than it is in other parts of the world where
there is not as much evaporation. Similarly, in coastal regions where
rivers dilute the sea, salinity is somewhat lower than in other oceanic
areas.

A third process by which salinity may be altered is associated with the
formation and melting of sea ice. When sea water is frozen, the
dissolved materials are left behind. In this manner, sea water directly
materials are left behind. In this manner, sea water directly beneath
freshly formed sea ice has a higher salinity than it did before the ice
appeared. Of course, when this ice melts, it will tend to decrease the
salinity of the surrounding water.

In the Weddell Sea Antarctica, the densest water in the oceans is formed
as a result of this freezing process, which increases the salinity of
cold water. This heavy water sinks and is found in the deeper portions
of the oceans of the world.