Changes in atmospheric CO 2 and its carbon isotopic ratio during the penultimate deglaciation

Abstract

The largest natural increases in atmospheric CO 2 concentration as recorded in ice cores occur when the Earth climate abruptly shifts from a glacial to an interglacial state. Open questions remain regarding the processes at play, the sequences of events and their similarities along different glacial–interglacial transitions. Here we provide new combined data of atmospheric CO 2 and its carbon isotopic ratio (δ 13CO 2) for the penultimate glacial–interglacial transition (Termination II) from the Antarctic EPICA Dome C ice core. Together with the strongest Antarctic warming, this transition bears the largest CO 2 increase (104 ppmv) of the last nine Terminations, ending with an overshoot of 21 ppmv occurring within ∼300 y and leading to higher levels than those of the late pre-industrial Holocene. The full CO 2 rise is accompanied by an overall decrease of the δ 13CO 2 minimum values, on which three positive excursions are superimposed. Peak-to-peak δ 13CO 2 changes in our record can reach ∼1‰. The ice core atmospheric δ 13CO 2 appears more depleted by ∼0.2‰ during Termination II compared to Termination I, paralleling a similar carbon isotopic depletion recorded in marine data. During both terminations, most of CO 2 and δ 13CO 2 variations are attributed to southern ocean stratification breakdown and decreased efficiency of the biological pump. Compared to Termination I, Termination II ice core data point to different timings of decrease in iron supply and sea-ice extent, suggesting that they could account for distinct patterns of the carbon cycle.