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8. Calculating Salinity



The Briny Deep

1. Introduction
2.  Salt in Seawater?
3. Ions of Salt
4. Source of the Salt?
5. Salinity Variability
6.Salinity & Precipitation
7. Salinity Summary
8. Calculating Salinity
9. Ocean Temperature
10. Solar Radiation
11. Properties
12. Light Penetration
13. Temperature
14. Thermocline
15. Density
16. Layering

In the open ocean, the principal chemical constituents in seawater have nearly the identical concentrations relative to one another and nearly constant concentrations relative to the total salinity.

Consequently by determining the concentration of one major
chemical constituent of sea water, you can calculate the total salinity of sea water and also the concentration of each individual principal chemical element.

The concentration of salinity in sea water is important to oceanographers because it can be used to:

  1. trace the origin of water masses and circulation patterns in the sea,
  2. understand the mixing of human-caused pollution with the natural chemical constituents of seawater, and
  3. assess the influence of seawater composition on biochemical reactions within marine organisms.

We have already mentioned that the proportion of any one of the principal chemical elements in seawater is constant relative to the other chemical elements in seawater. Therefore, if the salinity of seawater increases, then the concentrations of all chemical elements increase (equally).

This constancy of chemical composition is caused by the endless processes of circulation and mixing by ocean currents, wind action, water temperature, chemical solubilities, and biochemical reactions of the organisms.

Because of seawater's constancy of chemical composition, the total salinity can be determined from the concentration of the chloride ion since the ratios of sodium to chloride to magnesium to calcium and to any other major constituent remain constant.

We can construct a graph of the total salt content of sea water in parts per thousand (o/oo), or salinity (S), versus concentration of the chloride (Cl-), from which we can determine the relationship between salinity and chlorinity (concentration of Cl- ion) for sea water

From the graph, we can derive the following equation

S (o/oo)= 1.80655 x Cl-(o/oo)

Where S is salinity and Cl- is Chlorinity

ęCopyright 1999
March 13, 1999

Send to Don Reed

Department of Geology
San Jose State University

#5 If the concentration of the Cl- ion is 19.2632 in a sample of seawater, what is the salinity?

a) 37.1o/oo
b) 34.3o/oo
c) 36.5o/oo
d) 34.8o/oo
e) 35.5o/oo