ATMOSPHERIC CARBON DIOXIDE AND RADIOCARBON: I 



69 



STRATOSPHERE 



— ^ 



N u (t) 



N,(t) 



-F- 



TROPOSPHERE 

 ATMOSPHERE 



SURFACE LAYER 



M 



m 



i 



N d (t) 

 DEEP LAYER 



WORLD 

 OCEANS 



COSMIC-RAY 

 PRODUCTION 



-*r(t) 



TIME- 

 VARYING 

 SOURCES 



■Ht) 



INDUSTRIAL 

 PRODUCTION 



LONG ,' SHORT 



T 



i ; 



LIVED i LIVED/ 

 l v N e (t) i 



N b (t) 



LAND 

 BIOTA 



Fig. 13 Six-reservoir model of the carbon cycle. The mass of inactive carbon in each 

 reservoir is represented by N;(t) (replaced by *N;(t) for radiocarbon), and the transfer 

 coefficients between reservoirs are given by /; and k; (replaced by */; and *k; for 

 radiocarbon). In addition, the radiocarbon in each reservoir undergoes radioactive decay at 

 the rate *\*Nj. 



are significantly less than predicted by models that take into fuller account the 

 known properties of the natural carbon cycle. 



For this demonstration we use a six-reservoir model (Fig. 13) that specifies 

 the sinks for atmospheric x C0 2 as the land biota, divided into long-lived and 

 short-lived carbon pools, and the oceans, divided into surface and deep layers. 

 Also, the lower atmosphere is distinguished from the stratosphere (where the 

 1 C source occurs), and carbon exchange is recognized to take place in both 

 directions between all adjacent reservoirs. The justification for the division of 

 the carbon cycle into these pools and pathways is discussed in greater detail in 

 the next paper 1 and will not be duplicated here. The six-reservoir model, we 

 note however, makes use of practically all available global observational data, 

 and is clearly a more realistic attempt at modeling than the one-parameter model 

 of Grey and Damon. 2 5 



The distribution of C among the various reservoirs for the six-reservoir 

 model is described by a set of six first-order (linear) differential equations, one 

 for each reservoir. As with the one-reservoir model, we decompose the time- 

 dependent mass of 14 C in each reservoir, *N;, and the 14 C source term, *T(t), 

 into steady-state terms and the first-order time-varying perturbations, yielding a 

 set of steady-state and time-dependent perturbation equations analogous to 



