Bathymetry is the measurement of depth in the ocean
in order to delineate (trace the outline of) the submarine (under the
sea) topography.
From the sinking of the Titanic in 1912 until the
launch in 1978 of SEASAT satellite, bathymetric measurements were primarily
made using echo sounders (sonar).
Now, satellites can observe seafloor topography by
very precise radar measurement of seasurface elevation.
Surface measurements, usually made from ships and buoys,
are extremely important for ocean science, but are very limited in space
and time.
Earth orbiting satellites have revolutionized our ability
to collect ocean data.
Pressure
Pressure, force per unit area, increases with depth
as the weight of overlying water accumulates.
The deepest part of the ocean is 11 kilometers (6.8
miles) deep. At that depth, pressure is almost 1,000 atmosphere (1,000
kilograms per square-centimeter or 14,700 pounds per square inch).
Salinity
Accurate measures of
salinity cannot be obtained by
simply evaporating the water and weighing the residue. Some salt when
heated (to cause evaporation) decompose and for gases and solid compounds
not originally present in the water sample. Because of seawater's constancy
of composition, we need to measure the concentration of only one major
constituent--chlorine ions--to find the salinity of a water sample.
Water samples are collected from different depths using
sampling bottles such as the Nansen and the Niskin.
Today's scientists use an electronic device called salinometer
that measures the electrical conductivity of seawater.
A refractometer, an optical device that compares the
degree to which light is bent by a sample of seawater to the degree of
bending for water of known salinity, is a quick way to measure salinity
in the field. It is not as accurate as a salinometer.
Temperature
Temperature is measured in degrees. One degree of Celsius
= 1.8 degrees Fahrenheit.
Celsius degrees are more important in science because
they are based on two of pure water's most significant properties: its
freezing point (0 degrees Celsius) and its boiling point (100 degrees
Celsius).
Most substances become denser (weigh more per unit of
volume) as they get colder.
Satellites measure sea surface temperature by monitoring
thermal infrared wavelengths over the ocean.
Density
Density is the expression of the relative heaviness
of a substance.
Density is defined as the mass per unit volume, usually
expressed in grams per cubic centimeter (g/cm3). The density of "pure"
water is 1 g/cm3.
Most substances become denser (weigh more per unit of
volume) as they get colder. Seawater's density increases with increasing
salinity. Ocean water tends to form into stable layers, with the heaviest
water at the bottom--a form of density
stratification. The density zones
are:
Surface zone or mixed layer (2% of ocean water)
Pycnocline--a combination of the thermocline &
halocline (18% of ocean water)
Printer
Friendly Page