Carbon Isotope Constraints on the Deglacial CO₂ Rise from Ice Cores

The stable carbon isotope ratio of atmospheric CO₂ (δ¹³C atm ) is a key parameter in deciphering past carbon cycle changes. Here we present δ¹³C atm data for the past 24,000 years derived from three independent records from two Antarctic ice cores. We conclude that a pronounced 0.3 per mil decrease in δ¹³C atm during the early déglaciation can be best explained by upwelling of old, carbon-enriched waters in the Southern Ocean. Later in the deglaciation, regrowth of the terrestrial biosphere, changes in sea surface temperature, and ocean circulation governed the S¹³C atm evolution. During the Last Glacial Maximum, δ¹³C atm and atmospheric CO₂ concentration were essentially constant, which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then.