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Geosciences LibreTexts

7.7: Salinity and Latitude

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    10256
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    Salinity and Latitude

    Figure 7.24 is a map of the globe comparing the rates of evaporation and precipitation. The map is a compilation of evaporation minus precipitation (E-P) values. The data basically shows the regions where there is a net gain of salinity created in surface waters by high evaporation rates. There is also a net loss of salinity where precipitation is higher than evaporation rates (Figure 7.25). In general:

    • The tropics (equatorial region) is humid and cloudy, and receives much more rain than evaporates.
    • The temperate regions receive less precipitation, so evaporation dominates.
    • The polar regions have low evaporation rates relative to the amount of precipitation they receive.

    Map showing the difference betwen average evaporation an precipitation daily, world
    Figure 7.24. Map of net evaporation minus precipitation (E-P) on oceans.

    Evaporation and Precipitation curves by latitude
    Figure 7.25. Evaporation and precipitation curves compared with latitude.

    Variability of ocean salinity: Ocean salinity is stable at depth but can be highly variable at the surface. The upper surface layers of the ocean impacted by wave energy is a mixing zone. Simply this: the more waves, the more mixing. Freshwater is less dense than seawater and without mixing freshwater will float (stratify) on top of seawater.

    Factors that decrease salinity:
    white_bar_300.jpg
    Factors that increase salinity:
    white_bar_300.jpg
    Precipitation
    Runoff
    Melting icebergs/sea ice
    Evaporation
    Freezing sea ice