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    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

    Salinity ranges:

    • 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) 

    Global Surface Salinity

    • 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)

    Precipitation and evaporation influence surface salinity


    • 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

    Profiles 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