Temperature–salinity diagram

In a T-S diagram, rather than plotting each water property as a separate "profile," with pressure or depth as the vertical coordinate, potential temperature (on the vertical axis) is plotted versus salinity (on the horizontal axis).

Temperature and salinity combine to determine the potential density of seawater; contours of constant potential density are often shown in T-S diagrams.

These isopycnals appear curved because of the nonlinearity of the equation of state of seawater.

The thermal expansion coefficient, αT, and the haline contraction coefficient, βS, vary with temperature and salinity because both properties affect the potential density of seawater.

In general, the depth of the water increases as you move to the bottom right corner of the graph (high salinity, low temperature), but there is some variation.