saliniteter

Salinitet, or salinity, is a measure of the concentration of dissolved salts in water. In oceanography and environmental science, the term describes the amount of salts present, primarily sodium and chloride, but also including ions such as sulfate, magnesium, calcium, and potassium. Salinity influences water density, buoyancy, and many chemical and biological processes.

Salinity is usually expressed in practical salinity units (PSU) or as a mass fraction. The practical salinity scale (PSS-78) estimates salinity from the electrical conductivity of water, calibrated against seawater samples. Absolute salinity can be defined in mass-based terms (grams of dissolved salts per kilogram of seawater) and is used in more detailed thermodynamic frameworks such as TEOS-10. While PSU is dimensionless, it is closely correlated with the mass-based salinity in typical seawater.

Natural salinity values vary widely. The open ocean generally has a salinity around 35 PSU. Freshwater rivers and lakes are near 0 PSU, whereas brackish waters in estuaries and coastal zones can range from about 0.5 to 30 PSU. Sea ice formation concentrates salts in the remaining liquid water, while brine rejection during freezing can locally modify salinity patterns in polar regions.

The distribution of salinity is governed by precipitation, evaporation, river discharge, ice formation and melting, and mixing with other water masses. Salinity gradients combine with temperature to drive density-driven circulation in the ocean, a key component of the global thermohaline circulation. Salinity also affects osmoregulation in marine organisms and influences habitat suitability, nutrient cycling, and water treatment applications such as desalination.

Human activities and climate change alter salinity patterns through changes in precipitation, river flow, and melting ice, making monitoring and understanding salinity important for marine science and water resource management.