The causes of the ∼80 ppmv increase of atmospheric carbon dioxide (CO2) during the last glacial.interglacial climatic transition remain debated. We analyzed the parallel evolution of CO2 and its stable carbon isotopic ratio (δ13CO2) in the European Project for Ice Coring in Antarctica (EPICA) Dome C ice core to bring additional constraints. Agreeing well but largely improving the Taylor Dome ice core record of lower resolution our δ13CO2 record is characterized by a W shape, with two negative δ13CO2 excursions of 0.5% during Heinrich 1 and Younger Dryas events, bracketing a positive δ13CO2 peak during the Bølling/ Allerød warm period. The comparison with marine records and the outputs of two C cycle box models suggest that changes in Southern Ocean ventilation drove most of the CO2 increase, with additional contributions from marine productivity changes on the initial CO2 rise and δ13CO2 decline and from rapid vegetation buildup during the CO2 plateau of the Bølling/Allerød. Copyright 2010 by the American Geophysical Union.