THE OCEAN 167 



In the Atlantic the temperature varies ap- 

 proximately as follows with increasing depth: — 



In the Mediterranean, where no cold cur- 

 rent flows in at the bottom of the ocean, the 

 temperature sinks rapidly to 11° at a short 

 distance below the surface, and thereafter re- 

 mains constant. This is due to the fact that 

 in winter the surface water is cooled to that 

 temperature and sinks, remaining then pro- 

 tected from the summer heat by the warmer 

 layer of less density above. 



The slight range of ocean temperatures, 

 whether with changing seasons, with chang- 

 ing depth, or with changing latitude, depends 

 primarily upon the latent heat of water, 

 especially its heat of vaporization, and upon 

 the very high freezing point, as already ex- 

 plained in the discussion of these physical 

 properties. 



Far more constant than the temperature is 

 the alkalinity of sea water. It has been stated 

 above that the extreme variation in concent ra- 



