14 



STUIVER 



E 

 * 2 



X 



h- 



Q. 



§^r— i r 



■D-- 



~o--, 



V, 



*fc 



V77/7Z777777, 



1.9 2.0 2.1 2.2 2.3 



TOTAL C0 2 , millimoles/kg 



2.4 



2.5 



Fig. 4 Total C0 2 content as a function of depth in the Pacific Ocean at 

 28°29'N, 121°38'W. The solid curve was calculated for a B/w value of 0.047, 

 with B constant. From Craig and Weiss. 1 9 



the boundary between the mixed layer and deep ocean. The net 14 C flux 

 between the deep-water and mixed-layer reservoirs through the standard 

 advection— diffusion exchange appears, surprisingly, to be about zero or even 

 directed upward. 1 8 Although the specific 14 C activities are highest in the mixed 

 surface layer, the increase in total C0 2 for the deeper waters results in a total 

 amount of 14 C transported from the deep reservoir to the mixed layer at least 

 equal to the amount transported downward (biotic transport not included). The 

 transport of particulate carbon to the deep waters would then provide almost 

 entirely for radioactive-decay losses in these waters. 



Since the gradients in specific C0 2 concentration are often large compared 

 to the gradients in specific 14 C activity, the use of specific 1 C concentrations 

 ( 14 C atoms per cubic centimeter) gives a better approximation of reality for 

 box-model calculations 1 8 than the traditionally used specific 1 C activity 

 ( 14 C/carbon). These effects have been taken into account in a diffusion— 

 advection model with particulate flux, recently discussed by Craig. With the 

 use of Craig's description, this model is outlined in the following paragraphs. 



