Salinity Distribution: Hemispherical and Latitudinal

Salinity Distribution!!! In the previous post, we have discussed, Salinity and Factors affecting salinity. So, here we will discuss salinity distribution in the following respect,

  • Hemispherical Distribution,
  • Latitudinal Distribution and
  • Salinity distribution along with the depth of the ocean.

Salinity Distribution: Reasoned Account


The northern hemisphere has lower salinity (34.5) than the southern hemisphere (35.6). It is because of the continental cover of the northern hemisphere.

Northern Hemisphere has 2/3 of the continents of the world. Thus the influx of river water and ice melt enforce dilution process in the Northern Hemisphere.

Whereas in Southern Hemisphere high-pressure belt and winds are so constant that it increases the rate of evaporation. So, rate of evaporation results in the increase of salinity.


Along the 15°N-10°S, the average salinity is 34.5, which is lower than the global average. This is because of the high precipitation and low pressure in this particular latitudinal stretch.

The freshwater thickness of 5meter in this region reduces the salinity. But below, this layer of 5meters salinity is higher, around 36. Salinity is maximum at tropics.

Salinity distribution in Northern Hemisphere

In the northern hemisphere, between 15°N-40°N, the salinity is maximum ie 36.7-37. This is because of the fact that this latitudinal stretch comes under the high-pressure zone and trade winds.

Because of the high-pressure and trade winds, the compressibility of water increases which in result increases dissolving capacity of salts. This leads to an increase in the salinity of the water.

In the Northern Hemisphere between 40°N-55°N, salinity is 33-34. This is because of the mixing of cold and warm ocean currents. This region also receives cyclonic rainfall of 100-125cms.

Between the 55°N-70°N, salinity is 31-33 due to the ice melt.

Salinity distribution in Southern Hemisphere

But in the southern hemisphere, salinity distribution varies as follows, between,

  • 10°S-30°S, it is 36.5,
  • 30°S-40°S, it is 35-36,
  • 40°S-50°S, it is 34-35 and
  • between 50°S-60°S, it is 33-34.

In the southern hemisphere, salinity distribution depends on the westerlies winds.

Along the polar fringes, we see the dualistic character of salinity.

  • During winters, salinity is higher because of the process of freezing in which ice releases salt.
  • During summers, the salinity is lower because of the ice melts.
Salinity Distribution: Double Maxima Graph
Salinity Distribution: Double Maxima Graph

Distribution of Salinity with depth

Along the equator, the top 5meters of the freshwater thick layer has low salinity. Far 100 fathoms the salinity is high. Afterwards, it decreases again below the thermocline layer. Because of the cold water has less holding capacity along the tropics

The highest salinity is along the surface where the rate of evaporation is high and the dense saline water is sinking. Up to the depth of 200 fathoms, the salinity remains high, but then it decreases with depth.

Along the poles, the surface has lower salinity because the ice-melt water is present. So, here (on poles) Salinity increases with depth. But in general, salinity decreases with the depth because of the lower temperature.

So, this was all about the salinity distribution. In the upcoming post, we shall read about the salinity of some important water bodies.

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