We all know that India is a peninsular country (surrounded by water on three sides) but have you ever questioned yourself about what might be the reason for less salinity (salt dissolved in water) in Bay of Bengal than Arabian sea. Some of us don’t even know that Bay of Bengal is less saline than Arabian sea. Let’s find out the factors responsible for the unequal distribution of salinity.
Influx of FreshWater from Rivers:
This is one of the major factors affecting salinity distribution. Rivers are one of the major sources of freshwater on the earth. Most of the river streams in India take the path from west to east. The freshwater brought by most of the rivers will be discharged to the east coast, Bay of Bengal. While some of the largest rivers of India, like Brahmaputra (Ganga+Yamuna), Godavari, Krishna, Mahanadi, etc discharge into Bay of Bengal; Narmada, Mahi, Periyar, Tapi and Indus (through Pakistan) discharge into Arabian Sea.
This heavy influx of fresh water brought by rivers decreases the salinity level (calculated as parts per thousand PPT – ‰) of the sea. Bay of Bengal, which is recognised as the largest Bay in the world, has a salinity of 31 ppt and the Arabian sea has a salinity of 37 ppt. Based on discharge of river water, Bay of Bengal is drained by 77% and Arabian sea by 23% of river streams.
Precipitation from Tropical Cyclones:
Bay of Bengal, familiar with the tag – “World’s hotbed of tropical cyclones” is the origin place for worlds deadliest cyclones. As tropical region receives direct insolation (incoming solar radiation) a Low pressure will be formed in the entire tropical belt, which means both Bay of Bengal and Arabian sea receives an equal amount of heat (forming a Low Pressure).
Bay of Bengal receives High pressure winds not only from India but also from neighbouring countries like Myanmar, Indonesia, Thailand, etc. As winds move from High pressure to low pressure, Bay of Bengal’s sea surface temperature increases, making it an intense Low pressure area. As the sea surface temperature intensifies, it results in ascending of warm and moist air (evaporation) which is absorbed by clouds.
Cyclones formed here are now intensified and pound the eastern coast of India with an average velocity of 180 km/hr. However, the velocity, wind and precipitation of the cyclone decreases while moving from west to east. As these cyclones bring menacing winds and rains along with them, the heavy downpour taking place on its journey from Bay of Bengal to eastern coast is another reason for salinity dissimilarity.
We cannot say that cyclones do not form in Arabian sea but since most of its sea surface temperature is blown away by strong Summer monsoon winds coming from South-west direction, it gives fewer chances for formation. Recently, cyclones at Arabian sea are increasing and becoming more deadly. Scientists attributed this to increased water temperatures because of global warming. They also mentioned that historically, cyclones in Arabian sea are averaged by two or three in a year, which are typically weak.
The minor factors which handle the salinity dissimilarities are existence of ocean currents and winds associated with it. Almost 75% of the seawater comprises salinity of 34 to 35 ppt but the salinity of Bay of Bengal is as low as 31 ppt. Finally, these are some of the major reasons for salinity in differences between Bay of Bengal and Arabian sea.