Trends in Salinity of Ocean Water
Salinity of the ocean water is between 3.3-3.7 percent. The maximum amount of salt is common salt i.e. Sodium Chloride, which is followed by Magnesium Chloride. The major salts are as follows:
| Salt | %0 (parts per thousand) |
|---|---|
| Sodium Chloride | 2.6 |
| Magnesium Chloride | 0.3 |
| Magnesium Sulphate | 0.2 |
| Calcium Sulphate | 0.1 |
| Potassium Chloride | 0.1 |
| Potassium Bromide | 0.001 |
| Others | 0.001 |
Most of the salinity of the sea comes from the dissolved material that originates from land and was carried by the rain, running water, ground water, wind, sea waves, glaciers etc. Some of the salts come from the deeper layers of earth. Volcanic lava, dead organic matters also contribute in the Ocean salinity. The salinity of the ocean water depends upon the following:
Evaporation
Higher the rate of evaporation, higher is salinity. The Highest evaporation has been recorded along the tropic of Cancer and that is one of the reasons that region of Red Sea and Persian Gulf has one of the highest salinity. Another reason is that enclosed seas tend to have more salinity in their water.
Temperature
There is a direct relationship between ocean temperature and salinity. So the warmer parts are more saline and frigid parts are less saline.
Precipitation
Precipitation is inversely related to salinity. Higher is the precipitation, lower is the proportion of salinity. The equatorial region records highest rainfall and that it is why it has low salinity in comparison to those which are near to tropics.
Influx of Freshwater
Low salinity will be found at the mouth of rivers. This salinity is minimum in the raining season.
Atmospheric Pressure
High pressure areas have high salinity and vice versa.
Circulation of Ocean water
Ocean currents play a major role in distribution of salinity.
Horizontal Distribution of Salinity of Ocean Water
As a general rule, the salinity of the oceans decreases on both sides from the tropic of Cancer. This is attributed to the high occurrence of precipitation on equator. Highest salinity of the seawater has been recorded between 20°N to 40°N. The average salinity of the Northern and Southern hemisphere is 3.5 and 3.4 %0 respectively. This also because of the fact that the Northern Hemisphere is land dominated.
Vertical Distribution of Salinity of Ocean Water
There is no definite trend in the vertical distribution of salinity in the oceans, so there are no generalizations. However, it has been noted that the salinity of the ocean increases with increasing depth in the higher latitudes and polar areas. In the middle latitudes also, the same trends is seen but ONLY up to a depth of 370 meters after that it decreases with increasing depth.
