Figure14.4: Oceanwateriscomposedofmanysubstances. Thesaltsincludesodiumchloride,
magnesium chloride and calcium chloride. ( 22 )
ocean through the water cycle. Salts comprise about 3.5% of the mass of ocean water.
Depending on specific location, the salt content orsalinitycan vary. Where ocean water
mixes with fresh water, like at the mouth of a river, the salinity will be lower. But where
there is is lots of evaporation and little circulation of water, salinity can be much higher.
The Dead Sea, for example, has 30% salinity—nearly nine times the average salinity of ocean
water. It is called the Dead Sea because so few organisms can live in its super salty water.
The density (mass per volume) of seawater is greater than that of fresh water because it has
so many dissolved substances in it. When water is more dense, it sinks down to the bottom.
Surface waters are usually lower in density and less saline. Temperature affects density too.
Warm water is less dense and colder waters are more dense. These differences in density
create movement of water or deep ocean currents that transport water from the surface to
greater depths.
The Water Column
In 1960, one of the deepest parts of the ocean (10,910 meters) was reached by two men in
a specially designed submarine called theTrieste(Figure14.5). This part of the ocean has
been named the Challenger Deep. In contrast, the average depth of the ocean is 3,790 meters
— still an incredible depth for sea creatures to live at and for humans to travel. What makes
it so hard to live at the bottom of the ocean? There are three major factors—the absence of
light, low temperature, and extremely high pressure. In order to better understand regions