salinitet

Salinitet, also known as salinity, is a measure of the dissolved salts in a solution, typically seawater. In oceanography, salinity is commonly expressed as practical salinity units (PSU) or as parts per thousand (ppt). The salinity of typical seawater is about 35 PSU, corresponding to roughly 3.5 percent dissolved salts by mass.

The salts in seawater are mainly sodium and chloride, with significant amounts of sulfate, magnesium, calcium, and potassium. Salinity can be defined as the total mass of dissolved inorganic solids per mass of seawater, but on the practical scale it is dimensionless and derived from conductivity calibrations (PSS-78). Measurements can be made by chemical titration of chlorinity historically, or by modern conductivity sensors and refractometry.

In the ocean, salinity varies spatially and with depth. Open oceans typically range from about 34 to 37 PSU, while freshwater inputs from rivers or rainfall produce lower salinities near coastlines and estuaries. Evaporation in warm subtropical regions increases salinity, whereas precipitation and ice melt reduce it. Haloclines can separate layers with different salinity.

Salinity affects density and water mass structure, ocean circulation, sound speed, freezing point of seawater, and the distribution of marine organisms. It is a key parameter in climate and ocean models, and is monitored by satellites, ships, and autonomous instruments. Changes in salinity patterns are linked to hydrological cycle variations and, indirectly, to climate change.