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The Winter 2010 issue of The Earth Scientist includes a variety of educational resources, ranging from astronomy to glaciers. Check out the other publications and classroom materials in our online store.

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

When we measure the salinity of water, we look at how much dissolved salt is in the water, or the concentration of salt in the water. Concentration is the amount (by weight) of salt in water and can be expressed in parts per million (ppm). Here are the classes of water:
• Fresh water - less than 1,000 ppm
• Slightly saline water - From 1,000 ppm to 3,000 ppm
• Moderately saline water - From 3,000 ppm to 10,000 ppm
• Highly saline water - From 10,000 ppm to 35,000 ppm

Ocean water has a salinity that is approximately 35,000 ppm. That's the same as saying ocean water is about 3.5% salt. Sometimes, salinity is measured in different units. Another common unit is the psu (practical salinity units). Ocean water has a salinity of approximately 35 psu. Scientists measure salinity using a CTD instrument (CTD = conductivity, temperature, depth).

Ocean water is about 3.5% salt. That means that if the oceans dried up completely, enough salt would be left behind to build a 180-mile-tall, one- mile-thick wall around the equator. About 90 percent of that salt would be sodium chloride, or ordinary table salt. Chlorine, sodium and the other major dissolved salts of the ocean are listed in this 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

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We have beautiful specimens of banded iron formation in our online store from Nature's Own, along with many other mineral specimens.

## Cool It! Game

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

## Salinity

About 70% of the Earth is covered with water. Over 97% of that water is found in the oceans. Everyone who has taken in a mouthful of ocean water while swimming knows that the ocean is really salty! Dissolved...more

## Phoenix Mars Lander - Instruments and Mission Objectives

The Phoenix Mars Lander was a robot spacecraft that was sent to Mars. Phoenix landed near the North Pole on Mars. This page tells about the mission of Phoenix. It also describes the instruments on the...more

## Aquifer

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

## Carbonates

Carbonate is a name for rocks and minerals which contain a molecule made of both carbon and oxygen known as CO32-. (CO32- is also known as the molecule carbonate). Limestone is an example of a calcium...more

## Deep Water and the CO2 cycle

The deep ocean waters are under pressure and are much colder than layers of the ocean which are closer to the surface. Dissolved carbon dioxide seems to be absent from the deep ocean water and as a result...more

## Evaporation

One process which transfers water from the ground back to the atmosphere is evaporation. Evaporation is when water passes from a liquid phase to a gas phase. Rates of evaporation of water depend on things...more

## Surface Ocean Currents

The water at the ocean surface is moved primarily by winds that blow in certain patterns because of the Earth’s spin and the Coriolis Effect. Winds are able to move the top 400 meters of the ocean creating...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.