78 



The Sea-w'oter ami its Physical and Chemical Properties 



Table 31. Variations of pH with depth at constant carbon dioxide 

 content due to the change in pressure 

 (After Wattenberg, 1936 ) 



Depth (m) 



2000 



4000 



6000 



8000 



10,000 



atmosphere (see p. 72). Down to 50 m there is a slight reduction in the carbon dioxide 

 content due to the assimilatory activities of the phytoplankton. Then follows a thin 

 layer where the effects of assimilation and respiration are in balance. Beneath this 

 layer the carbon dioxide pressure rises until it reaches a pronounced maximum at a 

 depth of 500-1500 m (intermediate layer) depending on the latitude; it then falls off 

 again, at first steeply and finally in the deeper layers approaches the values found at 

 the surface. This carbon dioxide inversion (see Fig. 41) is accompanied by a change in 

 the pH which is almost the exact mirror image. Figure 42, which shows the carbon di- 

 oxide pressures along a cross-section through the subtropical South Atlantic, illus- 

 trates how clearly marked these changes are. According to Wattenberg, these pro- 

 nounced variations in the carbon dioxide distribution are due principally to the follow- 

 ing factors : 



( 1 ) The strong renewal of the deep water of the oceanic stratosphere by water masses 

 of polar and subpolar origin which sink during the late autumn and winter in 



5000 



4 6 8 



CO,- pressure 



10 



20 



rc 



Fig. 41. Vertical distribution of the carbon dioxide pressure ^002 CO"* atm), the hydrogen- 

 ion concentration pH and the temperature in middle latitudes of the Atlantic (according to 



Wattenberg). 



