Ventilation of the deep southern ocean and deglacial CO₂ rise

Past glacial-interglacial increases in the concentration of atmospheric carbon dioxide (CO₂) are thought to arise from the rapid release of CO₂ sequestered in the deep sea, primarily via the Southern Ocean. Here, we present radiocarbon evidence from the Atlantic sector of the Southern Ocean that strongly supports this hypothesis. We show that during the last glacial period, deep water circulating around Antarctica was more than two times older than today relative to the atmosphere. During deglaciation, the dissipation of this old and presumably CO₂-enriched deep water played an important role in the pulsed rise of atmospheric CO₂ through its variable influence on the upwelling branch of the Antarctic overturning circulation.