Why is the sea water salty?

Sea water is salty because it contains large amounts of the salt Sodium Chloride. Salts are brought to the sea through many sources like rivers and streams which collect various minerals, salts and silt on their course and drain them into the oceans. Atmospheric phenomena like evaporation also increase the salt concentration in the oceans. Apart from these, the existing sediments and minerals present in the ocean bed add to the salinity. The high salt content in the sea water makes it unfit for human consumption. To compare the salinity of fresh water and sea water, it is said that sea water is 220 times saltier than normal fresh water. And the dead sea is 8.6 times saltier than the ocean water. Read to know – what is dead sea


Origin of oceans

Studies conducted by scientists say that the oceans and seas are almost 500 million years old. There is one theory which suggests that the ocean originated because of prolonged escape of gases and water vapour from the molten igneous rocks of the earth. It must have rained for several centuries and the water got accumulated in the hollows of the earth’s surface.

Sea Water

Why is the sea water salty? (Image Source: sxc.hu)

Source of salts

Sea water contains not just salt but it is a complex solution of several mineral salts and decayed biologic matter. Mostly, the salt content of the sea is derived from the earth’s crust in which igneous rocks break up and get cooled due to weathering and erosion, through mountains, and the rains and streams dissolve all these minerals and salts and transport these contents to the seas and oceans. Other source is from the rocks and the sediments that occupy the ocean floor. The solid and gaseous materials that escape the earth’s crust via volcanic vents also contribute to make the seawater salty..


Rivers carry around 4 billion tons of salt every year. Along with this, the salts in the ocean add up to the salty taste and that is the reason why there is no difference in taste even after fresh water merges with oceans.


One more reason why the salinity of the oceans does not reduce even after river water merges with the oceans is, the process of evaporation by sun’s heat vaporizes pure water from oceans leaving the salts behind. These waters get condensed and fall back to earth as rain. This process is known as the hydrologic cycle.



Many studies were conducted to assess the composition of ocean water. But scientists are still not clear about the chemical composition. Because of the huge ocean size, it is very difficult to correctly assess its chemical composition. As per the test results that were conducted, around 72 chemical traces were seen in ocean water. Almost all the elements that occur on earth are seen in oceans as well.


Sodium chloride constitutes 85 percent of the dissolved elements in the ocean water. Other elements like magnesium, calcium, silica and bicarbonates are also present. Creatures that survive in the ocean waters also contribute to several other elements. Mollusk organisms like oysters and mussels extract calcium from the ocean and develop their shells and skeletons. Crustaceans like crabs, shrimps and lobsters also extract calcium to form their bodies. Coral reefs that are seen in warmer areas of oceans comprise of limestone.


Salinity: Why is the seawater salty?

Sea water’s salinity changes as per the geographical location of the ocean. The more away they are from land, the more saltily their waters taste. As there will not be any fresh water inflow into the ocean in such areas, the salt content will be more. Places in the oceans that experience higher temperatures have higher salinity in the water because the process of evaporation will be faster in these areas. The salt residues in the ocean water will be more in these regions. Low salinities are seen in oceans and seas which are nearer to polar areas. Here, the salty water gets diluted with the melting of glaciers.  Salinity of oceans is measured per thousand pounds of ocean water.


The Baltic Sea has less salinity with 5 to 15 parts of salts per thousand pounds of ocean water. The North Atlantic Ocean is the saltiest with 37.9 pounds of salt per thousand pounds of ocean water. (Also know about dead sea) William Dittmar, a scientist collected several samples of ocean water to detect the salinity. He conducted these tests in 1872 and continued for 4 years almost covering 68,890 nautical miles. He gave 77 samples and till today these are considered as the standard for counting the salinity ratio in ocean waters.