We have measured the CO₂ 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 CO₂ 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 CO₂ records. CO₂ 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 CO₂ 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 CO₂ versus Siple Dome isotopic temperature is probable. The Siple Dome CO₂ 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 CO₂/mol air). While in situ production of CO₂ is one possible cause of the sporadic elevated levels, the mechanism leading to the enrichment is not yet clear.Keywords: Siple Dome, paleoclimate, CO
