10 THE WEALTH OF THE SEA 



temperature is between 30° and 35° F. In the North 

 Atlantic and parts of the Pacific the bottom tem- 

 perature is between 35° and 45° F. Thus it is seen 

 that all deep-sea water is very cold. While the 

 temperature of the sea bottom, at depths of 2000 

 fathoms or more, does not vary more than 12° F. 

 (between 28° and 40° F.), there is no such uni- 

 formity of temperature of the surface waters. The 

 highest surface temperature, 96° F., was recorded 

 in the Persian Gulf, and the lowest on record is 

 26° F. in the polar regions. The seasonal variation 

 in the surface temperature of the sea is least in 

 Arctic and Antarctic waters and in the tropics where 

 it is less than 10° F. In the northern temperate zone 

 the variation is from 10° to 50° F., and in the 

 southern temperate zone it is from 10° to 30° F. 



In ancient times the source of the salts of the sea 

 was a great mystery. Modern geology has, however, 

 explained their origin. Time was when the ocean 

 was composed of fresh water, but all through the 

 ages the rivers have been carrying into it the dis- 

 solved salts which the rain has leached from the 

 earth. Although the rivers contain but a small per- 

 centage of saline matter, and although much of this 

 is deposited in the ocean near their mouths in the 

 form of lime and magnesium salts (limestone, etc.), 

 the total amount of salts in solution in the ocean 

 is very great. 



Since we can estimate with some exactness the 

 total amount of sodium in the sea, if we assume that 

 it has been added in a constant manner without 



