Short essay on the Various Sources of Oceanic Salts

Through the complex processes of rock disintegration and chemical changes the running water is supplied with a mineral load which ultimately reaches the ocean. Thus, a part of the sea – salt is derived from rivers. Various kinds of salts derived from the earth’s crust are dissolved in rain water and the rivers carry them to the ocean in solution.

The addition of salt to ocean water by the running water has been taking place since the very beginning of the cooling down and solidification of the earth’s crust. The composition of the dissolved substances in the river water depends largely on the amount of precipitation and the nature of rocks over which the rivers flow.

According to an estimate by F.W. Clark (1924), about 2.73 x 10¹⁹ metric tons of dissolved substances are carried to the oceans annually by all the rivers of the world.

Assuming that originally the ocean basins were filled with fresh water and the rivers were the only agency to carry salt into seawater, it would be only concentrated river water. That whole of the salt in the seawater has been brought by rivers is, therefore, wholly wrong.

Chemical analysis of ocean water and river water makes it amply clear that the proportion of salts in both the types of water is not the same. For example, carbonate of lime (60%) is the most important constituent of fresh water, whereas sodium chloride is present in very negligible quantity (2%).

On the other hand, silica, commonly present in fresh water, is found in ocean water only in minute quantity. Besides, the most abundant salts found in the ocean such as, the chlorides (75%) sulphates, and bromides are not common either in the rocks of the earth’s crust or in river water.

However, the dearth of more common substances like silica and carbonate of lime in ocean water is mainly due to two reasons:

1. Marine organisms like coral polyps, molluscs, oysters etc. extract carbonate of lime from the seawater to form their shells or skeletons. The result is the diminution of the total amount of carbonate of lime in ocean-water.

2. Sea weeds and other marine plants also consume a certain amount of calcium carbonate extracted from sea water. The above two facts account for the difference in the relative abundance of carbonates and chlorides in the water of the seas and the rivers.

Thus, such substances as are not needed for marine organisms continue to be accumulated in the oceans.

The difference in the amount of salts present in excessive quantity in ocean-water and only in minute quantity in river-water can easily be understood. Although the rivers continually bring salts to the ocean, the evaporation taking place constantly at the sea surface results in the loss of pure water leaving behind the salts.

This causes the gradual accumulation of salts in the ocean water. In this way, the rivers may be considered to be the most powerful agent of bringing salts to the oceans.

However, it is noteworthy that rivers contribute only a negligible fraction of the total dissolved solids in the ocean. There are other agencies like glaciers, wind and even the waves and tides in the ocean itself that contribute their little bit in adding to the dissolved substances in the ocean.

Submarine volcanic eruption also supplies some kinds of mineral salts to ocean water. But its share is very small. To conclude, it is undoubtedly true that the question regarding the origin or source of salts in the sea-water still remains unsolved.