THE 14 C CYCLE AND ITS IMPLICATIONS 



FOR MIXING RATES 



IN THE OCEAN-ATMOSPHERE SYSTEM 



MINZE STUIVER 



Departments of Geological Sciences and Zoology, University of Washington, 

 Seattle, Washington 



ABSTRACT 



Residence times and exchange rates for carbon in major carbon reservoirs are derived from 

 box-model studies of ' 4 C activity ratios. A diffusion-advection model gives information on 

 oceanic mixing processes and the oceanic transport of carbon of biological origin. This paper 

 summarizes literature associated with this type of "global" study of carbon transfer and 

 storage. 



Considerable information on the carbon transfer in nature can be obtained from 

 the differences in the specific activity of 14 C in the various reservoirs found on 

 earth. The knowledge of the distribution of the 14 C isotope in these reservoirs 

 provides insight into the patterns and rates of large-scale circulation in the 

 oceans as well as in the atmosphere. Box models that describe reservoir 

 properties are used to assess the transfer of radiocarbon between the various 

 reservoirs. Various simplifying assumptions have to be made for a rigorous 

 mathematical treatment of the model. Such studies occasionally give the 

 impression that a precise calculation provides a screen for an imprecise 

 assumption, and the models should be considered a crude approximation only of 

 the gross features of carbon transfer in nature. 



In these models the ocean— atmosphere— biota system is divided into a series 

 of independent, well-mixed reservoirs. Carbon dioxide, with a specific C 

 activity representative for the reservoir under consideration, is exchanged with 

 adjacent reservoirs. The exchange rates required to maintain a fixed steady-state 

 14 C distribution between the reservoirs are computed. 



In this discussion of mean residence times, a reservoir with a steady-state 

 fixed number of molecules, N, and a continuous flux into and out of the 

 reservoir of molecules per year is considered. 1 The number of particular 



