156 



FOUNDERS OF OCEANOGRAPHY 



contained in the thousand of sea-water is the following list 

 given by Murray and others : — 



10-722 parts in 1,000 of sea-water. 



35-000 



In addition to these principal constituents of sea-salt, 

 there are a few other elements (such as silicon and phos- 

 phorus) present in smaller quantity, but still of great import- 

 ance in connection with living organisms and the general 

 metabolism of the ocean. It is obvious, when we consider 

 the life of animals and plants in the sea, that some of these 

 salts are constantly being withdrawn from the water to form 

 shells and skeletons and other hard parts, and are again later 

 on being returned to the sea by solution. There is thus a 

 perpetual interchange or circulation of such materials as 

 calcium and silica, and there may also be vast accumulations 

 formed of, for example, carbonate of lime in the deposits 

 forming on the floor of the ocean. These are by no means 

 the only materials withdrawn from the water by the action of 

 living organisms and by chemical reactions at the sea bottom. 



Three gases dissolved in sea-water — oxygen, nitrogen, and 

 carbon dioxide — are of primary importance in connection 

 with living organisms. The sea absorbs air from the atmo- 

 sphere, but dissolves a larger proportion (about 34 per cent.) 

 of oxygen than of nitrogen. Moreover, as water at a lower 

 temperature absorbs more gas, the cold polar waters may 

 contain nearly twice as much of the dissolved gases as the 

 warm tropical water. As oxygen is constantly being used 

 up by animals, it must constantly be renewed, and as it is 

 present in the water at all depths (except in the case of 



