Have you been to a beach? For swimming in the sea? What is the taste of sea water? It is salty. Why is it salty?
There are many chemical substances in the seawater and presence of those chemicals is the reason sea water is salty. Most of those chemicals are carried by rivers which get chemicals from rocks and soil.
The major compound in sea water is sodium chloride, which is commonly known as salt. Generally, seawater has about 35 grams of salt per liter of water. Salinity of sea water is measured in parts per thousand (ppt) which tells us about the amount of salt in 1 liter of water. Salinity of ocean varies between 34 ppt to 36 ppt. Properties of water changes when there is salt dissolved in it. Sea water has more density as compared to freshwater. Due to the high salt content of Dead Sea (Israel), people can even float over there. Freezing point of water is lowered when there is salt dissolved in it.
The salinity of the ocean is not equal at all places. It varies according to the location, especially at the surface. There is a balance between water being removed by evaporation and freshwater added by rivers and rain. This balance helps to control the amount of salinity at various locations of the ocean. There are locations where annual rainfall is very less and with very warm and dry winds, which causes a lot of evaporation. Due to this evaporation process and lack of rainfall, salinity of sea water increases in these areas. Because of this, seawater becomes denser. The northern and southern regions of Atlantic Ocean have very high salinity. This is because of the presence of strong winds and less rainfall in these regions. The Mediterranean Sea has 38 ppt of salinity which is very high. Even there the evaporation rate is high and addition of fresh water is less because of low rainfall.
There are regions of ocean which have a lot of rainfall. Rain, which helps to add freshwater at the surface, dilutes the seawater, which helps to reduce the salinity and density of water. Main land area, where rivers add fresh water to sea, the salinity and density is less. The ocean near the Antarctic regions has a low salinity, which is around 34 ppt and the one near the Arctic region has salinity as low as 30 ppt.
Aquarius mission initiated by NASA aims to map the salinity at the surface of the ocean. This will help to improve our understanding of the Earth’s climate system. The mission has produced a map that demonstrates the salt levels in the oceans around the globe. Data collected by Aquarius mission has shown the varying salinity patterns across different places. The Arabian Sea appears to have higher salt content than the Bay of Bengal because it is nestled up against the dry Middle East. Bay of Bengal gets more rain fall due to intense monsoon rains and also it receives freshwater from the Ganges and other large rivers from India. Similarly, the Amazon river releases a large amount of freshwater which heads towards east and reaches Africa or it moves northwards to reach the Caribbean, depending upon seasonal currents. This large discharge of freshwater current makes the ocean to be less salty around its vicinity.
Aquarius project team member Prof. Arnold Gordon, who is a professor of oceanography at Columbia University in Palisades, New York, said that the Aquarius project has exposed a pattern of salinity across the ocean surface which varies to a large extent across different locations. Also, he said that the first image showing the variation of salinity marks a great moment in the history of oceanography. The Aquarius salinity data shows much higher quality information than the researcher’s expected data. The team expects that the Aquarius project will soon allow researchers to explore the connections between ocean currents, global rainfall, ocean currents and climate variations.