Comment on “Synchronous records of pCO2 and Δ14C suggest rapid, ocean-derived pCO2 fluctuations at the onset of Younger Dryas” by Steinthorsdottir et al

Steinthorsdottir et al. (2014) used a previously published stomata-based CO2 record (Steinthorsdottir et al., 2013) to argue for a large, abrupt change in atmospheric carbon dioxide at the onset of the Younger Dryas (YD) cold interval. Their record implies a 50 ppm CO2 rise followed by a decline by 100 ppm. They compare their results to a hypothetical and highly unlikely simulation sce- nario in which vertical mixing in the ocean is increased by a factor of 100 and wind strength by a factor of 7. They furthermore compare their stomata-based CO2 record with the ice core CO2 re- cord derived from EPICA Dome C (EDC). We here question their interpretation.