NCERT notes on important topics for the UPSC civil services exam. 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 Horizontal and Vertical Distribution of Salinity
Horizontal Distribution of Salinity
- The salinity for normal Open Ocean ranges between 33o/oo and 37 o/oo.
- The highest salinity is recorded between 15° and 20° latitudes.
- Maximum salinity (37 o/oo) is observed between 20° N and 30° N and 20° W – 60° W.
- The salinity gradually decreases towards the north.
- The salinity sometimes reaches up to 70 o/oo in the hot and dry regions where evaporation is high.
- The salinity variation in the Pacific Ocean is largely due to its shape and larger areal stretch.
- In the landlocked Red Sea, the salinity is 41o/oo which considerably high.
- The salinity in the estuaries and the Arctic varies from 0 – 35 o/oo , seasonally.
- Due to the influx of melted water from the Arctic region, the salinity decreases from 35 o/oo – 31 o/oo on the western parts of the northern hemisphere.
- The North Sea records higher salinity due to more saline water brought by the North Atlantic Drift despite its location in higher latitudes.
- Due to the influx of river waters in the large amount, the Baltic Sea records low salinity.
- The Mediterranean Sea accounts for the higher salinity due to high evaporation.
- Salinity is very low in the Black Sea due to massive freshwater influx by rivers.
- The average salinity of the Indian Ocean is 35 o/oo.
- The low salinity trend in the Bay of Bengal is due to the influx of river water.
- But the Arabian Sea displays higher salinity due to the low influx of fresh water and high evaporation.
Vertical Distribution of Salinity
- Salinity changes with depth, but the way it changes relies on the position of the sea.
- Salinity at the surface of the sea is decreased by the input of fresh waters or increased by the loss of water to ice or evaporation.
- Salinity at depth is fixed as neither water nor salt can be added in it.
- There is a marked difference in the salinity between the surface zones and the deep zones of the oceans.
- The lower saline water remains above the higher saline dense water.
- Salinity, usually, increases with depth and there is a distinct zone called the halocline, where salinity increases abruptly.
- The increasing salinity of seawater causes an increase in the density of water.
- High salinity seawater, usually, sinks below the lower salinity water. This leads to stratification by salinity.
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