The water in an ocean, exclusive of the sea bed or other landforms, is referred to as the water column. The average depth of the World Ocean's water column is 12,464 feet (3,800 meters).

The term sea level refers to the average height of the sea when it is halfway between high and low tides and all wave motion is smoothed out. Sea level changes over time. Between 1930 and 1950, sea level along the east coast of the United States rose about one-fourth inch (1 centimeter) per year.

Ocean Composition

Every element known on Earth can be found in the ocean. Ocean water is 3.5 percent dissolved salts by weight, including primarily chloride, sodium, sulfur (sulfate), magnesium, calcium, and potassium. The measure of these salts determines the ocean's salinity (saltiness). One cubic mile (4.1 cubic kilometers) of sea water contains enough salt to cover all the continents with a layer...