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The absolute salinity is based on density, where it uses the mass off all non-H 2 O molecules. Conductivity-based salinity is calculated directly from conductivity measurements taken by (for example) buoys. [5] The GSW beta(SA,CT,p) function can calculate β when the absolute salinity (SA), conserved temperature (CT) and the pressure are known.
The handling of salinity was one of the novelties in TEOS-10. It defines the relationship between Reference Salinity and Practical Salinity, Chlorinity or Absolute Salinity and accounts for the different chemical compositions by adding a regionally variable 𝛿SA (see Figure). [7]
Temperature and salinity combine to determine the potential density of seawater; contours of constant potential density are often shown in T-S diagrams. Each contour is known as an isopycnal, or a region of constant density. These isopycnals appear curved because of the nonlinearity of the equation of state of seawater.
where S T, T T denote the salinity and temperature at top layer, S B, T B denote the salinity and temperature at bottom layer, Ra is the Rayleigh Number, and Pr is the Prandtl Number. The sign of Ra S and Ra T will change depending on whether it stabilizes or destabilizes the system.
The mathematical relationship between vertical and horizontal velocities can be derived by expressing the idea of conservation of angular momentum for a fluid on a rotating sphere. This relationship (with a couple of additional approximations) is known to oceanographers as the Sverdrup relation. [3]
Using this model, if the temperature of the seawater is known from external sources, then measurements of the brightness temperature can be used to compute the salinity of surface seawater directly. Figure 1 shows an example of the brightness temperature curves associated with sea surface salinity, as a function of sea surface temperature .
Because the vast majority of the world ocean's volume is deep water, the mean temperature of seawater is low; roughly 75% of the ocean's volume has a temperature from 0° – 5 °C (Pinet 1996). The same percentage falls in a salinity range between 34 and 35 ppt (3.4–3.5%) (Pinet 1996). There is still quite a bit of variation, however.
The density depends more on the temperature than on the salinity, as can be deduced from the exact formula and can be shown in plots using the GODAS Data. [4] In the plots regarding surface temperature, salinity and density, it can be seen that locations with the coldest water, at the poles, are also the locations with the highest densities.