An Early Pleistocene atmospheric CO2 record based on pedogenic carbonate from the Chinese loess deposits

•The pedogenic carbonate paleobarometer was used to reconstruct pCO2 from loess deposits.•We provide the first continental documentation of early Pleistocene pCO2 record.•Our results show a successive decrease of interglacial pCO2 throughout the early Pleistocene.•Atmospheric CO2 acted as an important forcing mechanism to drive the early Pleistocene cooling.

The tight coupling between temperature and atmospheric CO2 is shown by ice core records for the past 0.8 million years (Myr). However, the modern atmospheric partial pressure of CO2 (pCO2) has exceeded previous interglacial pCO2 levels over the past 0.8 Myr, suggesting that the earlier part of the Pleistocene and Pliocene might be a better analog of today's radiative forcing of CO2. The early Pleistocene experienced a constant cooling characterized by the intensification of northern hemisphere glaciations. Existing pCO2 records developed from marine organic matter and inorganic precipitates, however, disagree with the trends and absolute values of CO2 over this time interval. Here we present quantitative interglacial pCO2 estimates from ∼2.6-0.9 Myr using the stable carbon isotopic compositions of pedogenic carbonates collected from the Chinese Loess Plateau (CLP). Our pCO2 records provide the first documentation of pCO2 from continental sedimentary deposits over the early Pleistocene. The successive decrease of our pCO2 records is broadly consistent with the increase in deep-sea δO18 and the overall decline of sea surface temperature (SST) at this time, but in contrast with the increasing peak interglacial pCO2 recorded in ice cores for the last 0.8 Myr.