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2. Measuring the Properties of Seawater


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

Oceanographers measure three fundamental properties of seawater, (1) salinity, or salt content, (2) temperature, both of which control the (3) density of seawater; so salt is dissolved in seawater. The variation in seawater density controls the layering of water on the ocean (as we will learn in this expedition)

Measuring Temperature and Density to Determine Salintiy in Water sample on Bay Voyage

Measuring Temperature and Density of Water Sample on Bay Voyage to Determine Salinity

Photo of Water bottle Rosette and CTD

Using a CTD (Conductivity, Temperature and Depth) instrument to Determine Salinity
(remember that we used this instrument in our quest to find active hydrothermal vents in one of our previous expeditions).

Is there salt dissolved in seawater? Of course there is -- why else would there be a salty taste.......

All water, both fresh and sea water, contains dissolved chemicals in the form of salts. Water is considered fresh or salty according to individual taste, but detailed measurements prove otherwise, since even rain water contains a small concentration of salt that it absorbs while falling through the atmosphere.

Dissolved Sodium and  Chloride Ions in Water
Used with Permission of Matthias Tomczak ©Copyright 1997

As the picture above illustrates, sea water is composed of, by weight, a mixture of approximately 96.5% pure water molecules (H2O molecules in diagram) and 3.5% of salts, dissolved gases, organic materials, and undissolved particles

The salty taste associated with sea water comes from the two of the most common ions in the salt, chloride (Cl-) and sodium (Na+), which are surrounded by water (H2O) molecules in the diagram above. 

(Remember that ions are atoms or combinations of atoms with charges, either negative or positive, depending on the difference in the number of electrons and protons; ions with more protons than electrons will result in a positive charge, more electrons than protons will produce a negative charge).

Cargill salt - SF Bay

Salt Pile from Evaporation Ponds Next to the San Francisco Bay
Photo from


salt.jpg (5984 bytes)

Indeed, the oceans may contain as much as 50 quadrillion tons (50 million billion tons) of dissolved solid, which if removed, would spread evenly over the Earth's land surface in the form of a layer more than 500 feet thick, about the height of a 40-story office building -- "now that's  a lotta salt."


©Copyright 1999
March 13, 1999

Send to Don Reed

Department of Geology
San Jose State University

  What do you mean "Ions of Salt Dissolved in Water"?