An oceanic origin for the increase of atmospheric radiocarbon during the Younger Dryas

Variations in carbon‐14 to carbon‐12 ratio in the atmosphere (Δ 14 C atm ) provide a powerful diagnostic for elucidating the timing and nature of geophysical and anthropological change. The (Atlantic) marine archive suggests a rapid Δ 14 C atm increase of 50‰ at the onset of the Younger Dryas (YD) cold reversal (12.9–11.7 kyr BP), which has not yet been satisfactorily explained in terms of magnitude or causal mechanism, as either a change in ocean ventilation or production rate. Using Earth‐system model simulations and comparison of marine‐based radiocarbon records from different ocean basins, we demonstrate that the YD Δ 14 C atm increase is smaller than suggested by the marine archive. This is due to changes in reservoir age, predominantly caused by reduced ocean ventilation.