Salinity measures dissolved salt content. A transport model must specify its units; salt mass fraction is one convenient convention. A dilute solution's ice liquidus is often approximated by . Salt-free ice has zero salinity, and the moving interface's salt balance distinguishes salt rejection during freezing from dilution during melting.
The conservation law for salt in a reservoir: the rate of change of its salt content equals inflowing minus outflowing salt transport and any explicit salt sources. Freshwater addition changes salinity without directly adding salt. For a well-mixed fixed-volume reservoir, salt content is proportional to its volume times salinity.
The salt forcing used to represent freshwater exchange while retaining a fixed reference volume. Removing freshwater at volume flux is represented by a salt input , and adding freshwater by the opposite salt forcing, with reference salinity . Replacing the actual salinity in a compensating-flow salt budget by is an approximation when salinity contrasts are small.
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Salinity is a measure of the concentration of dissolved salts in water. It is typically expressed in parts per thousand (ppt) or as a specific gravity. Salinity is an important physical property of water bodies, influencing various biological and chemical processes. In oceans and seas, salinity is primarily derived from the weathering of rocks on land, river runoff, and the evaporation of water, which leaves salts behind.