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.
Click on image for full size
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.

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more


Almost 3/4 of the Earth is covered with water. Almost all of that water is in the oceans. Have you ever been swimming in the ocean? If you have and you accidentally got water in your mouth, you know the...more

Phoenix Mars Lander - Instruments and Mission Objectives

NASA has a new spaceship on Mars. The robot is called the Phoenix Mars Lander. Phoenix landed near the North Pole on Mars. This page tells about the mission of Phoenix. It also describes the instruments...more


An aquifer is the name for a layer of rock which is capable of holding a large amount of water. Some layers are better at holding water than others, for example a layer of sandstone can hold a good deal...more


Limestone is an example of a carbonate. Other examples of carbonates include calcite, dolomite, and marble. Limestone dissolves easily in rainwater, especially rainwater which is loaded with carbonic acid....more


Have you ever left a glass of water out for a long time? Did you notice that the water disappears after a few days? That's because it evaporated! Evaporation is when water passes from a liquid to a gas....more

Surface Ocean Currents

The water at the ocean surface is moved by powerful wind. The wind is able to move the top 400 meters of the ocean. This moving water is called surface ocean currents. Surface ocean currents form large...more


Rivers are very important to Earth because they are major forces that shape the landscape. Also, they provide transportation and water for drinking, washing and farming. Rivers can flow on land or underground...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA