The ocean bomb radiocarbon inventory revisited

in Radiocarbon (in press)

Large discrepancies exist among data-based estimates and model reconstructions of the ocean bomb radiocarbon inventory. In order to resolve this gap, it has been proposed that the CO2 piston veloc- ity ... [more ▼]

Large discrepancies exist among data-based estimates and model reconstructions of the ocean bomb radiocarbon inventory. In order to resolve this gap, it has been proposed that the CO2 piston veloc- ity should be revised downward (Sweeney et al., 2007; Müller et al., 2008). Here we compare the transient 14C distributions in the ocean obtained with different formulations of the isotopic ratio commonly used in modeling studies. It is found that both the CO2 increase and the air-sea CO2 flux significantly contribute to the 1990 ocean bomb radiocarbon inventory, by around 10% each. Moreover, these two processes explain more than 25% of the inventory difference be- tween 1974 and 1990. These results imply that, as already argued by Naegler (2009), inventories based on observations which lack infor- mation about CO2 invasion are underestimated. Further, this work allows to gain insight into the reasons for discrepancies among model results. It suggests that while a comprehensive isotopic formulation is needed when addressing the global radiocarbon cycle, a simplified form is more relevant for model calibration and piston velocity assess- ment based on currently available bomb radiocarbon inventories. [less ▲]