96 A TEXTBOOK OF OCEANOGRAPHY 



over before the results could exercise any effect appreciable 

 to analysis. 



The solubility of carbonic acid in 4 water is directly 

 dependent on the temperature. 



The following table gives the coefficients of absorption for 

 sea-water of salinity 35' 19 per mille at different temperatures, 

 compared with that of pure water : 



oC. 5 C. ioC. 15 C. 20 C. 25 C. 30 C. 



Salt water (after Krogh) ... 1*41 1*17 0^99 0^85 074 0*65 0-57 



Pure water (after Bohr and Bock) 171 1*19 1-19 ro2 0-88 076 0-67 



The differences in the coefficients of absorption of carbonic 

 acid decrease with a higher temperature, and at 30 C. are 

 about one-third as large as at o C. From the above it follows 

 that warm seas contain less carbonic acid than cold. 



The chief source of oceanic carbonic acid is the atmosphere. 

 There must, however, have been carbonic acid originally in 

 sea-water.* One source of carbonic acid is, according to 

 Dittmar, the ocean bottom, especially where through sub- 

 marine eruptions large quantities of gas are discharged. 

 Sources of oceanic origin for carbonic acid have not yet been 

 found, a condition probably due to the difficulty of collecting, 

 preserving, and analysing suitable water samples. The bottom 

 layers of waters in the great oceans are under a pressure of 

 several hundred atmospheres, and consequently carbonic acid 

 would be taken into solution in a liquid condition. Carbonic 

 acid liquefies at 15 C. under pressure of 52 atmospheres, at 

 10 C. with pressure of 46, at 5 C. with 40, and at o C. under 

 pressure of 35 atmospheres, and the critical point for pressure 

 is at 73 atmospheres that is, at depths of 400 fathoms. Below 

 this depth carbonic acid is not met with in the gaseous 

 condition. 



An increase of carbonic acid due to the respiration of 

 marine organisms is hardly perceptible, except in rare cases, 

 where enclosed areas are responsible. As an example Gullmar 

 Fiord in Bohuslan (Sweden) may be given. The effect of 



