Haline contraction coefficient

The Haline contraction coefficient, abbreviated as β, is a coefficient that describes the change in ocean density due to a salinity change, while the potential temperature and the pressure are kept constant.

This determines the contribution of the temperature and salinity to the density of a water parcel.

The Brunt–Väisälä frequency can also be defined when β is known, in combination with α, Θ and S

This frequency is a measure of the stratification of a fluid column and is defined over depth as:[3]

β can be computed when the conserved temperature, the absolute salinity and the pressure are known from a water parcel.

Python offers the Gibbs SeaWater (GSW) oceanographic toolbox.

[4] It contains coupled non-linear equations that are derived from the Gibbs function.

This equation relates the thermodynamic properties of the ocean (density, temperature, salinity and pressure).

The absolute salinity is based on density, where it uses the mass off all non-H2O molecules.

Conductivity-based salinity is calculated directly from conductivity measurements taken by (for example) buoys.

The conserved temperature cannot be obtained directly from assimilation data bases like GODAS.

Near Antarctica, temperature is the main contributor for the high density there.

Evaporation leaves salt behind in the water, increasing salinity and therefore density.

As water temperatures are a lot higher, density in the tropics is lower than around the poles.

This is the 2020 average for the haline contraction coefficient β. At the locations where the salinity is high, in the tropics, the haline contraction coefficient is low and where the salinity is low, the haline contraction coefficient is high. This means that changing the salinity will have a large effect on the density when the haline contraction coefficient is high.
This graph shows the 2020 average salinity in an intersection in the Atlantic ocean at 30W. The salinity is low near Antarctica and high in the tropics.