How does seawater density change when salinity increases?

In the study of oceanography, the density of seawater is a fundamental physical property that increases as salinity increases.1

Because density is a function of temperature, salinity, and pressure, oceanographers often use an abbreviated density value known as sigma-t (${\sigma }_t$). This value is controlled exclusively by temperature and salinity, and it consistently rises as salinity increases or as temperature decreases.1

The relationship between these properties is critical to the movement of water in the oceans. For example, when sea ice forms, salt is largely excluded from the ice, which increases the salinity of the underlying water. This process creates very dense, cold, and saline water—such as Antarctic Bottom Water—which then sinks to the deepest parts of the ocean, driving thermohaline circulation.1