320 



THE DEEP SEA 



as was the case with tritium, bomb production greatly enhances 

 the use of C^^ without introducing any important disadvantages. 

 Having shown that the model selected provides a reasonable 

 approximation to the true large-scale mixing within the ocean- 

 atmosphere system, the model can be used to estimate the effects 

 of changes in circulation rates. Assuming that the rate of transfer 

 of COo between the ocean and atmosphere has remained constant 

 with time and that the total amount of C^^ has remained the same, 

 Table XII gives the changes in the C^^ concentration in the various 

 reservoirs for the case where oceanic mixing rates are doubled and 

 for the case where they are halved. The most interesting feature 

 of the results is the large change in the C^^ concentration of 



Table XII. Effect of Changes in Rates of Ocean Circulation on Distribution of 

 Radiocarbon between Oceans and Atmosphere 



atmospheric CO2 which would be produced by such changes. The 

 atmosphere would fall 70 per mil in concentration if ocean circu- 

 lation rates were doubled and rise 120 per mil if halved. iVIcasure- 

 ments by numerous radiocarbon laboratories of the C'^ concen- 

 tration in tree rings back to 2000 years in age suggest changes of 

 up to but probably not greater than 2 per cent either side of the 

 1890 value. On the assumption that these changes are the result 

 of variations in ocean circulation rates rather than to changes in 

 the production rate of C^^ they correspond, as shown in Fig. 11, 

 to limits of ±20% on circulation rate changes. A 15% decrease in 

 circulation rate would, after steady state was reestablished, result 

 in a 20 per mil rise in the C'^ concentration in atmospheric CO2 

 and a 20% increase in rate to a 20 per mil drop. The method is, 

 of course, sensitive only to worldwide changes of a period at least 



