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    • Rights: The University of Waikato
    Published 21 June 2007 Referencing Hub media
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    Dr Mike Williams from NIWA explains how the density1 of the seawater is measured, by looking at the conductivity and temperature2 of the water.

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    DR MIKE WILLIAMS
    To measure the saltiness in the water we essentially measure its conductivity and its temperature. And the conductivity is the rate at which we can pass electricity3 through a small sample of sea water. So that gives us a nice easy way to measure it. We just lower an instrument through the water, it measures the conductivity, it measures the temperature, that allows us to calculate the salinity4. And we have a nice container that we have a hole in the floor of, and we work through that, lowering our instruments to the sea floor.

    1. density: How tightly a certain amount of matter (atoms or molecules) of a substance is compacted in a given volume. Density is commonly measured in grams per millilitre (g/ml) or cubic centimetre (g/cm3).
    2. temperature: A measure of the degree of hotness or coldness of an object or substance. Temperature is measured with a thermometer calibrated in one or more temperature scales. Kelvin scale temperature is a measure of the average energy of the molecules of a body.
    3. electricity: A general term that includes a variety of phenomena resulting from the presence and flow of electrical charge.
    4. salinity: The amount of chemicals dissolved in water. In seawater, the main chemical is sodium chloride (salt), but there are many others in smaller quantities.

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    ACTIVITY

    Density

    In this activity, students are introduced to the concept of density. They calculate the volume of various materials to determine and then rank their densities. By the end of this activity ...

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    • ARTICLE

    Water density

    Water density changes with temperature and salinity. Density is measured as mass (g) per unit of volume (cm³). Water is densest at 3.98C and is least dense at 0C (freezing point). Why does ice ...

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      density

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      2. How tightly a certain amount of matter (atoms or molecules) of a substance is compacted in a given volume. Density is commonly measured in grams per millilitre (g/ml) or cubic centimetre (g/cm3).

      salinity

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      3. The amount of chemicals dissolved in water. In seawater, the main chemical is sodium chloride (salt), but there are many others in smaller quantities.

      temperature

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      4. A measure of the degree of hotness or coldness of an object or substance. Temperature is measured with a thermometer calibrated in one or more temperature scales. Kelvin scale temperature is a measure of the average energy of the molecules of a body.

      electricity

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      5. A general term that includes a variety of phenomena resulting from the presence and flow of electrical charge.

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