94 A TEXTBOOK OF OCEANOGRAPHY 



Nevertheless, there are sea areas in which the water does 

 not contain sufficient oxygen to support fish or other animal 

 life. Thèse are, for the most part, seas in which there is some 

 hindrance to tlie free circulation of the water. 



As examples we find certain Norwegian liords, the Black 

 and Caspian Seas, and to a lesser extent certain deep areas of 

 the Baltic. 



Russian scientists hâve shown that animal life is not 

 présent, or indeed possible, at the greatest depths in the Black 

 and Caspian Seas. In the Black Sea sulphuretted hydrogen 

 is met with in sea-water at depths of loo fathoms, whereas in 

 the Caspian it is the lack of oxygen which is responsible for 

 the absence of life in the lower layers. In the Caspian the 

 greatest depth at which life was found was 218 fathoms, where 

 a species of worm (Oligochœta) was met with. In certain 

 Norwegian fiords — e-g-, Mofïord — there is no circulation 

 between the waters of the fîord and those of the open sea, and 

 consequently the lower layers are so déficient in oxygen as 

 to be unable to support life. At the depths of 5J fathoms 

 there are 7"5 ce. of oxygen per mille, at 27 fathoms only 

 o"86 ce. 



The Challenger results show that oxygen is found in excess 

 in the surface layers of water in high southern latitudes, a 

 phenomenon attributable to the prépondérance of vegetable 

 life in the plankton. Below 50 fathoms a diminution of oxygen 

 becomes noticeable, and this becomes greater with the depth 

 until at 800 fathoms oxygen is at its minimum. There is also 

 a remarkable déficit of oxygen in the bottom waters of the 

 North Pacific between 40° and 35° N. Lat, and 150° and 180" 

 W. Long. 



The estimation of carbonic acid in sea-water is a much 

 more difficult matter. According to récent investigations, such 

 as those of Fox, it would appear that the earlier troubles were 

 due to the fact that it is difficult to get ail the carbonic acid out 

 of sea-water which is slightly alkaline. 



Tlie earlier analyses gave very différent percentages of 



