IS THERE AN IMBALANCE IN THE GLOBAL BUDGET OF BOMB-PRODUCED RADIOCARBON

Several recent studies of the global inventory of radiocarbon produced by above ground nuclear weapons testing have brought into question ou r understanding of the global cycle of bomb-produced radiocarbon. Radi ocarbon produced from these explosions has provided a unique test for global carbon cycle models used in the analysis of emission scenarios for carbon dioxide. We employ a globally aggregated model for the glob al cycles of carbon and its isotopes (C-13 and C-14) to examine these studies, and find several modeling approximations or assumptions which could be responsible for the differences between analyses. In light o f the considerable uncertainty in both model-based and data-based esti mates of global inventories, we conclude that the global budget of bom b-produced radiocarbon cannot be shown to be out of balance. Uncertain ties limit the utility of C-14 as a tracer for determining the flow of carbon dioxide within the atmosphere-ocean-terrestrial-biosphere syst em of carbon cycle. Our model-based analyses suggest that improved ana lysis of past nuclear tests and their production of radiocarbon, as we ll as additional measurements of C-14 in the biosphere and oceans, cou ld reduce uncertainties in model studies of the evolution of C-14 in t he carbon cycle system.