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A student from the HIGH TIDE project turns on the CTD instrument. High school students use the CTD recorder to measure salinity, temperature and depth of the water in the Lafayette River which is a part of Chesapeake Bay.
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Image courtesy of the HIGH TIDE project

Salinity - Dissolved Salts, Measuring Salinity

Salinity is the measure of how much salt is in water. Ocean water has a high salinity and fresh water has a very low salinity.

Sometimes, salinity is measured in parts per million (ppm). Ocean water has a salinity that is about 35,000 ppm. That's the same as saying ocean water is about 3.5% salt. Sometimes, salinity is measured in different units. Ocean salinity is also about 35 psu (practical salinity units).

Ocean water has a lot of salt in it. Most of it is normal table salt (made up of chlorine and sodium). Chlorine, sodium and the other major dissolved salts of the ocean are listed in the following table:

Dissolved salts in
sea water (atoms):
55.3 % Chlorine
30.8 % Sodium
3.7 % Magnesium
2.6 % Sulfur
1.2 % Calcium
1.1 % Potassium


Last modified August 30, 2001 by Jennifer Bergman.

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The Summer 2010 issue of The Earth Scientist, available in our online store, includes articles on rivers and snow, classroom planetariums, satellites and oceanography, hands-on astronomy, and global warming.

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