- Salinity - Definition
-
Original
definition: Salinity = total salts (ions)
in water; [‰]
35‰ = 35 g ions / kg water = 3.5% - Constancy of composition: ratio of ions remains constant at all salinities
-
Most abundant
ion, Cl-, easy to measure;
salinity estimated as
S = 1.80655 x [Cl-] ‰ - Modern definition: Salinity = ratio of conductivities of sea water to standard of 32.4356 g KCl / kg water (standard water)
- Modern unit: without (S=33.4) or with “practical salinity scale” (S=33.4 psu); sometimes 10-3; in biological literature still ‰ erlaubt
- Open ocean: 32 – 38; avg. 35
- Coastal ocean: 27 – 30
- Estuaries: 0 – 30 [brackish]
- Semi-enclosed seas (Baltic Sea): <25 [brackish]
- Hypersaline environments (Red Sea, tropical coastal lagoons, tide ponds in warm climate): >40
- Salinities between 0.1 and 30: brackish water
- Salinity variation much higher in surface waters than in deep-sea (lack of sea-air interaction)
- On average, the Atlantic Ocean exhibits a much higher salinity than the other oceans
- Highest surface salinity in the subtropical regions (20-30 deg), lower surface salinity in temperate regions and near the equator (Doldrums)
- Opposite effects of precipitation and evaporation
- Water mass of the oceans is in balance, changes only on geological time scale
- Precipitation/Evaporation balance influence surface salinity
- Precipitation is highest in Doldrums (north of equator) and temperate regions
- Evaporation is highest in subtropics
- E – P mirrors latitudinal distribution of salinity
- Salinity shows surface maximum at low and mid latitudes but surface minimum at high latitudes (related to evaporation/precipitation balance, see above!)
- Salinity in the deep sea is fairly homogeneous
- Note depression in surface salinity in the tropics due to high rainfall
- Vertical region of strong salinity gradien with depth (i.e. strongest change of salinity over a certain depth range) = halocline
Salinity ranges:
Global Surface
Salinity
Precipitation
and evaporation influence surface salinity
Profiles of
salinity
