A record of atmospheric CO₂ during the last 40,000 years from the Siple Dome, Antarctica ice core

We have measured the CO 2 concentration of air occluded during the last 40,000 years in the deep Siple Dome A (hereafter Siple Dome) ice core, Antarctica. The general trend of CO 2 concentration from Siple Dome ice follows the temperature inferred from the isotopic composition of the ice and is mostly in agreement with other Antarctic ice core CO 2 records. CO 2 rose initially at ∼17.5 kyr B.P. (thousand years before 1950), decreased slowly during the Antarctic Cold Reversal, rose during the Younger Dryas, fell to a local minimum at around 8 kyr B.P., and rose continuously since then. The CO 2 concentration never reached steady state during the Holocene, as also found in the Taylor Dome and EPICA Dome C (hereafter Dome C) records. During the last glacial termination, a lag of CO 2 versus Siple Dome isotopic temperature is probable. The Siple Dome CO 2 concentrations during the last glacial termination and in the Holocene are at certain times greater than in other Antarctic ice cores by up to 20 ppm (μmol CO 2 /mol air). While in situ production of CO 2 is one possible cause of the sporadic elevated levels, the mechanism leading to the enrichment is not yet clear.