Is there an imbalance in the global budget of bomb‐produced radiocarbon?

Abstract

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.