How do scientists use temperature-salinity diagrams to study mixing between ocean water masses?

Scientists use temperature-salinity (T–S) diagrams as a powerful research tool to analyze the physical characteristics and interactions of ocean water masses.1

A water mass is defined by a distinctive, narrow range of temperature and salinity that determines its density. On a T–S diagram, samples from a single, homogeneous water mass appear as a cluster of points or an elongated zone.21

When scientists plot samples taken from different depths, the resulting T–S curve provides a visual representation of the mixing occurring between distinct water masses. If the water is fully mixed and homogeneous, it plots as a single point; however, the complex curves typically observed in vertical profiles indicate the degree and nature of the mixing taking place between different layers of the ocean. Additionally, these diagrams are highly effective for identifying potential errors in collected data.1