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 our understanding of the global cycle of bomb-produced radiocarbon. Radiocarbon 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 global cycles of carbon and its isotopes (¹³C and ¹⁴C) to examine these studies, and find several modeling approximations or assumptions which could be responsible for the differences between analyses. In light of the considerable uncertainty in both model-based and data-based estimates of global inventories, we conclude that the global budget of bomb-produced radiocarbon cannot be shown to be out of balance. Uncertainties limit the utility of ¹⁴C as a tracer for determining the flow of carbon dioxide within the atmosphere-ocean-terrestrial-biosphere system of carbon cycle. Our model-based analyses suggest that improved analysis of past nuclear tests and their production of radiocarbon, as well as additional measurements of ¹⁴C in the biosphere and oceans, could reduce uncertainties in model studies of the evolution of ¹⁴C in the carbon cycle system.