NCERT Notes: Salinity Of Ocean Water [Geography Notes For UPSC]

NCERT notes on important topics for the IAS aspirants. These notes will also be useful for other competitive exams like banking PO, SSC, state civil services exams and so on. This article talks about the Salinity of ocean waters.

Salinity of Ocean Water (UPSC Notes):- Download PDF Here


Salinity of ocean waters
  • Salinity means the total content of dissolved salts in Sea or Ocean.
  • Salinity is calculated as the amount of salt dissolved in 1,000 gm of seawater.
  • It is generally expressed as ‘parts per thousand’ (ppt).
  • A salinity of 24.7 % has been regarded as the upper limit to fix ‘brackish water’.
  • It is a significant factor in deciding several characteristics of the chemistry of natural waters and biological processes.


Factors affecting ocean salinity
  • Salinity, temperature, and density of water are interconnected. The salinity of water in the surface layer of oceans is influenced by:
    • Evaporation
    • Precipitation
  • In the coastal regions, the surface salinity is influenced by the freshwater flow from rivers.
  • In the Polar region, the surface salinity is influenced by the processes of freezing and melting of ice.
  • The wind also influences the salinity of an area by moving water to other areas.
  • The ocean currents contribute to the salinity variations.
  • The change in the density or temperature influences the salinity of water in an area.

Highest salinity in water bodies
Lake Van in Turkey 330 o/oo
Dead Sea 238 o/oo
Great Salt Lake 220 o/oo


Dissolved Salts in Sea Water (gm of Salt per kg of Water)
Chlorine 18.97
Sodium 10.47
Sulphate 2.65
Magnesium 1.28
Calcium 0.41
Potassium 0.38
Bicarbonate 0.14
Bromine 0.06
Borate 0.02
Strontium 0.01

Share of different salts

  • Sodium chloride — 77.7%
  • Magnesium chloride—10.9%
  • Magnesium sulphate —.4.7%
  • Calcium sulphate — 3.6%
  • Potassium sulphate — 2.5%

Salinity of Ocean Water (UPSC Notes):- Download PDF Here

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Frequently Asked Questions about Salinity of Oceans


Which ocean has highest salinity?

Of the five ocean basins, the Atlantic Ocean is the saltiest. On average, there is a distinct decrease of salinity near the equator and at both poles, although for different reasons.

How does salinity affect the ocean?

Salinity can affect the density of ocean water: Water that has higher salinity is denser and heavier and will sink underneath less saline, warmer water. This can affect the movement of ocean currents. It can also affect marine life, which may need to regulate its intake of saltwater.

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