Revised alkenone δ13C based CO2 estimates during the Plio-Pleistocene

Abstract

Here we revisit reported alkenone d13C (d13CC37) based CO2 records during the Plio-Pleistocene and apply a refined approach to better constrain the dynamic range of CO2 during the time. Specifically, we consider ways to correct for regional differences in physical oceanographic factors. As a result of our relatively simple approach we find that offsets of ~150 ppm between reported d13CC37 CO2 records from different sites can be significantly reduced. This confirms that better constraints 10 on environmental variables, including physical oceanographic controls on depth and season of production are key aspects for improving d13CC37 based CO2 estimates. The revised d13CC37 CO2 datasets suggest that Plio-Pleistocene CO2 levels are 180350 ppm, which is consistent with the most of reported CO2 reconstructions, though their upper end of Pliocene CO2 levels are lower than that of some CO2 estimates.