Expedition 12 Mail Buoy

Dear Jenny:

Conductivity depends on the number of ions present in a solution, so the measurement of conductivity provides a measure of salinity. It is strongly dependent on temperature, so you need to measure the temperature at the same time, and correct for temperature to get a good value of salinity.

There is a simpler tool to measure salinity that can be used in the field, although it does not have the resolution of a conductivity measurement. The tool is a refractometer, and it depends on the change in the angle of refraction of light as it passes through solutions of different salinities. It is very simple to use: A drop of the liquid is placed on a glass and held up to the light, and the angle of refraction and its conversion to salinity is read directly off a scale. It is good for measurements where there are major differences in salinity—such as between fresh and saltwater samples. And they are relatively inexpensive (less than $50).

Thanks for the question, and I hope you continue to follow along with our cruise.

Susan Humphris



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