Salinity distribution of ocean water
Every water in nature has dissolved mineral salts in it. Salinity is defined as the amount of salt in grams dissolved in 1 kg of seawater and it is usually expressed in Part Per Thousand (PPT).
The salinity of 24.7 PPT is considered as the upper limit to mark ‘brackish water’.
The saltiest place on earth
- Lake Van (Turkey) – 330 PPT
- Dead Sea (Jordan) – 238 PPT
- Great Salt Lake (Usa) – 220 PPT
Factors of Salinity distribution of ocean water
The salinity of water, in the ocean’s surface layer, depends on evaporation and precipitation.
The salinity of seawater in coastal regions depends on freshwater flow from rivers, in the polar regions due to the freezing and thawing of ice.
Sometimes wind also influences the salinity in a particular area by transferring water from one area to another area.
The Salinity distribution is influenced also due to ocean currents.
The salinity, temperature, and density of water are interrelated. Thereby any variation in the temperature or density influences the water’s salinity.
Horizontal Distribution of Salinity
The salinity for normal open ocean ranges between 33 PPT and 37 PPT and in the case of the landlocked Red Sea, it is as high as 41 PPT.
In the estuaries and the Arctic, the salinity fluctuates from 0-35 PPT, and in the hot and dry region, where the evaporation is high, the salinity reaches 70PPT.
The salinity in the Pacific Ocean is due to its shape and large area and the Salinity decreases from 35 PPT to 31 PPT in the western parts of the Northern Hemisphere due to the influx of melted water from the Arctic region.
Similarly, in 15° – 20° south, it decreases to 33 PPT and the average salinity of the Atlantic ocean is roughly 36 PPT.
The highest salinity is recorded between 15° and 20° latitudes and maximum salinity, 37 PPT, is recorded between 20° N and 30° N and 20° W – 60° W and its gradually decreases towards the north.
The North Sea, in spite of its location in higher latitudes, records higher salinity due to more saline water which is brought by the North Atlantic Drift.
Baltic sea records low salinity due to the influx of river water in huge quantity.
The Mediterranean sea records higher salinity due to high evaporation.
Salinity is very low in the Black Sea because of the enormous freshwater influx by rivers.
Danube, Dnieper, Don, Dniester, Kuban rivers drain into the Black Sea.
The average salinity, in the Indian ocean, is 35 PPT and low salinity is observed in the Bay of Bengal because of the influx of river water.
On the other hand, salinity in the Arabian sea is higher due to high evaporation and a low influx of freshwater.
Vertical distribution of salinity in ocean UPSC
Salinity also changes with depth, also the location influences it and the salinity at the surface of the sea depends on evaporation, loss of water, the influx of water, etc.
Salinity at the depth is fixed as there is no way water is added or removal is possible and there is a remarkable difference in salinity between the zone on the surface and zones on the depth.
The less salinity water stay above and more salinity water is at the depth.
Salinity generally increases with depth and there is a distinct zone called the Halocline, where the salinity increase sharply.
And other factors being constant, increasing the salinity of seawater causes its density to increase.
Highly salinity water generally sinks below the low salinity water and this phenomenon leads to stratification by salinity.