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5. Salinity and its Variability


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

Hannes Grobe, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany;
SVG version by Stefan Majewsky

As mentioned previously, seawater is a weak, complex solution -- weak -- meaning that is highly diluted by a solvent (water) and complex because it contains at 92 different naturally occurring chemical elements -- the most common of which are listed in the table to the left .  


More elements will likely be found in the future as measuring techniques improve through advances in technology. 

Besides the water itself (H2O), here is a list of the principal chemical constituents in seawater, with their chemical symbol, and their relative The diagram at the upper left shows the principal constituents and their concentrations in a sample of sea water with a salinity of 3.5% or 35 o/oo (parts per thousand).

Chloride ion (Cl-) -- 55%
Sodium (Na+) -- 30.6%
Sulfate (SO4-2) -- 7.7%
Magnesium (Mg +2) -- 3.7%
Calcium (Ca+2) -- 1.2%
Potassium (K+) - 1.1%
And a small amount (0.7%) of other stuff..........

Oceanographers report salinity (total salt content) and the concentrations of individual chemical constituents in sea water in parts per thousand (also called parts per mil), for which the symbol o/oo is used.

Remember that % is the symbol for percent or parts per hundred -- divide % by ten or add another zero in the denominator and you have parts per thousand.

Thus, a salinity value of 35o/oo means 35 parts of dissolved salt per 1,000 parts of sea water. Similarly, a sodium (Na+) concentration of 10 o/oo means 10 pounds of sodium per 1,000 pounds of water.

  • The salinity of sea water exhibits a variation around an average value of 35.5 o/oo in the world's oceans depending on the balance between evaporation (increasing salinity) and precipitation (decreasing salinity).

©Copyright 1999
March 13, 1999

Send to Don Reed

Department of Geology
San Jose State University

#3 How many grams of dissolved salt are contained in 2000 grams of sea water with a salinity of 35o/oo?

a) 70 grams of dissolved salt
b) 140 grams of dissolved salt
c) 210 grams of dissolved salt
d) None of the above.