| The
physical properties of seawater are very important to scientist.
They include
water density, temperature, salinity, chlorophyll concentration, particulate level,
and many more. These water properties can be measured in a number of ways. The
method that is used depends on the property being measured. Temperature for instance
is the most commonly measured property of seawater, and some may argue the most
important. Sea surface temperature was key in discovering and tracking the 1998
El Niño storm phenomenon. Measurements of chlorophyll concentrations can
tell scientist if there is an Algal Bloom occurring, and measurement of particulate
levels, along with salinity can be helpful in identifying hard to see sediment
plumes. Here
are a few brief descriptions of important water properties
Temperature
The temperature of a water column can give scientists a
number of clues about what kinds of organisms might be living in the water column,
where the water came from, or how the properties of the water are changing. Temperature
is almost always measured by using a device known as a CTD. The CTD measures the
temperature of the water column using an electronic temperature sensor. Differences
in temperature at various depths can indicate the level of mixing and amount of
stratification in a water column.
Salinity
Salinity is another important property of seawater. As with
temperature, salinity can give scientists a number of clues about where the water
came from. It is not only an indication of how salty the water is but also how
many solid particles are in a given amount of water. Salinity is expressed as
grams of solids in 1000 grams of seawater. The average ocean salinity is 35. This
means that there are, on average, 35 grams of solid matter in every 1000 grams
of seawater. Salinity is also measured by the CTD device. The CTD runs a current
of electricity through the water and measures the voltage of this current. For
water of the same temperature, the higher the salinity the more electrically conductive
the water column is. So if the CTD measures a high voltage current the water has
a high salinity, and if the voltage is low it has a lower salinity. Sedimentation
The amount of sediment suspended in a particular body of water, sometimes called
the sediment load, is a property that can be measured in a number of different
ways. One particularly sensitive measure for the sediment load is Silica concentration
in the water column. Scientists measure two types of silica in Plumes and Blooms
project, Lithogenic Silica and Biogenic Silica. Lithogenic Silica comes from the
land, also called the lithosphere, and Biogenic Silica comes from the shells of
marine animals. In the Plumes and Blooms data sets these two attributes are abbreviated
as Lsi and Bsi. Chlorophyll
concentration
Phytophankton pigment biomass can be quantified using the
Chlorophyll core. Chlorophyll measurements are done in a number of different ways.
One way is to quantify the color of the ocean with a radiometer and relate the
color ratio (blue to green light)to the Chlorophyll concentration. The more green
light the higher the Chlorophyll concentration. Another
method is to collect water samples from specific sites that are of interest to
the scientists. Once they have the water samples they want, then they are taken
to the laboratory and run through a filtering machine. There are a number of different
kinds of filtering processes. Most all of them filter the water through a small
disc shaped piece of paper with microscopic holes. When the filtering is complete
everything that was in that sample of water is now in the filter paper. This paper
is then run through another machine called a fluorometer. The fluorometer shines
light through the filtered sample. The amount of light absorbed by the sample
can tell the scientist how much chlorophyll is in the sample.
Top
of Page
| 
