How Do Temperature and Salinity Affect Mixing in the Oceans?
ES2202  A Graph to Determine Density

Both salinity and temperature affect the density of seawater.

A liter of seawater has a higher mass than a liter of freshwater due to the added mass of the dissolved salts. As density measures mass per unit volume, saltwater has a higher density than freshwater. Increasing the amount of salt dissolved in water increases the water’s density.

Temperature affects the density of seawater by changing the volume of the water itself. Higher temperatures actually cause water to expand, increasing the amount of space it takes up. The mass of warmer water is spread over a larger volume than a similar amount of cooler water, so the warmer water has a lower density. Increasing the temperature of water results in a decrease in the water’s density.

This graph allows you to estimate the density of any mass of seawater based on its salinity and temperature. To estimate density, find the point where the temperature and salinity values for the water intersect. The blue line on the graph nearest the point of intersection indicates the density of the water.

Mixing in the oceans depends on the densities of water masses. When water masses of differing density meet, the mass with the higher density will sink to the bottom and the mass with the lower density will float on top of it.

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