CHAPTER XI 



THE CHEMISTRY OF THE SEA AND ITS INFLUENCE 



ON ANIMAL LIFE 



Salt content. — Sea water is a solution whose composition is not 

 everywhere exactly the same. In the open ocean the salt content at 

 300-m. depth is quite uniformly and constantly 35% *, but there are 

 differences in the composition of the surface water. In the tropics the 

 evaporation exceeds the inflow and the salt solution becomes more con- 

 centrated. In the polar regions the melting ice causes a dilution of 

 the solution in summer. The most marked deviations from the average 

 composition occur in the seas and gulfs. The intermixture of their 

 waters with the open ocean is limited by their degree of separation, 

 and differences in one direction or the other arise accordingly. Thus 

 the Mediterranean, with its relatively low influx of fresh water, has 

 a salt content of more than 37%o in its western part, 39.5%o at Crete, 

 and even 40% on the Syrian coast. The Red Sea, with no regular 

 supply of fresh water, has as much as 45.4% to 46.5%o salt. By con- 

 trast, in the western Baltic the salt content is 12% , 7.4% at Born- 

 holm, and in the Gulf of Finland only 0.6%e. The fresh water from 

 melting glaciers and icebergs dilutes the surface water of the polar 

 seas so that the salt content may fall below 15%o. As the more con- 

 centrated solution is denser, the salt content may increase with depth. 

 This is especially evident in the Baltic, where a bottom current of 

 more concentrated salt water flows in while the more dilute surface 

 water flows out; thus in the western Baltic the salinity at the surface 

 may amount to 8-12% and in the depths may reach 27%o. 



The greater part of the salts in sea water consists of the chlorides 

 of sodium, magnesium, and potassium, of which common salt (NaCl), 

 with 27.37 gm. per liter, preponderates. To these must be added the 

 sulphates of magnesium and calcium. Other elements are present in 

 much smaller amounts; some, like silver, copper, and vanadium, only 

 in traces. The question as to whether the salts of the sea water have 

 been derived from the earth by the solvent action of the rains and 

 streams touches us in this connection only in so far as it bears on the 



* Per mille (%o) has obvious advantages over per cent (%) when discussing 

 salinity of the ocean. 



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