GEOCHEMISTRY AND PHYSICS OF OCEAN CIRCULATION 



319 



be considered an upper limit since no account of storage of humic 

 materials in soils has been made. If these humic materials are 

 renewed each 30 years and if existing estimates of their abundance 

 are reliable, the two curves would agree. 



A potential further crosscheck method involves C^^ produced 

 by bombs. Figure 10 shows how the atmospheric C^^ concentration 

 has changed since 1850. Following a small drop resulting from the 

 addition of industrial CO2 to the system a rapid rise commenced 

 in 1955. Currently the southern hemisphere lags behind the 

 northern because the majority of the testing has taken place north 

 of the equator. This bomb C^^ is gradually being transferred to 

 the ocean. Estimates based on the model suggest that the surface 

 water should now be running about 30 per mil higher than in the 

 pre-bomb era. Estimates based on bomb production to date 

 suggest that the surface ocean will rise about 100 per mil during 

 the next 10 years. This rise will provide an extremely valuable 

 tracer for near surface ocean circulation. Rather than greatly 

 confusing attempts to apply isotopes to oceanic mixing problems, 



a-€C- 



TREE RING DATA 

 (FERGUSSON) 



1910 1915 



DATE 



Fig. 10. Variation in C^VC^" ratio in atmospheric CO2 over the last 100 years. 



