The total quantity of dissolved salts in sea water, normally expressed in parts per thousand (ppt or per mille); the average salinity of the world ocean is about 35 parts per thousand.
- Salinity is raised by high evaporation and lowered by high rainfall, river inflow of fresh water, and the melting of ice.
- It is highest in enclosed seas of dry subtropical latitudes: the Dead Sea and the Lake Van region are extreme, and the Red Sea and Persian Gulf are very saline; it is low near the equator (heavy rain) and at river mouths.
- The most abundant dissolved salt is sodium chloride (common salt); horizontal salinity generally peaks around 20 to 40° latitude where evaporation exceeds precipitation.
- Salinity, together with temperature, controls the density of sea water and so helps drive the deep thermohaline ocean circulation.
- The Bay of Bengal is less saline than the Arabian Sea because of the heavy freshwater discharge of the Ganga and Brahmaputra and high rainfall.
The average value (35 ppt), the high-salinity seas (Dead Sea, Red Sea), the equatorial low, and the Bay of Bengal versus Arabian Sea contrast are recurring oceanography facts.
Salinity is highest in the dry subtropics (high evaporation), not at the rainy equator; the Bay of Bengal is less saline than the Arabian Sea because of river inflow; the Dead Sea is extremely saline but is a lake, not part of the open ocean.
Average sea salinity is about 35 parts per thousand, highest in dry subtropical and enclosed seas, lowest near the equator and river mouths.