Pressure
Learning Objective:
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Identify the function and properties of seawater that control pressure,
and the unit used to measure pressure.
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Pressure beneath (al di sotto di) the sea surface is measured
in decibars. The pressure exerted by 1 meter of seawater very nearly equals 1
decibar (1/10 of a bar) or 100,000 dynes per square centimeter.
The farther one descends in the sea, the greater the pressure, and since
pressure in the ocean is essentially a function of depth, the numerical value of
pressure in decibars approximates the ocean depth in meters. Therefore, pressure
ranges from zero at the surface to over 10,000 decibars in the deepest parts of
the oceans. The pressure is created by the weight of the seawater above. The
weight per unit volume of seawater, in turn, varies with the temperature and
salinity.
In a column of water of constant depth, the pressure increases as the
temperature of the sea decreases, or the salinity increases, or both.
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