Changes in atmospheric CO2 and its carbon isotopic ratio during the penultimate deglaciation

The largest natural increases in atmospheric CO2 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 CO2 and its carbon isotopic ratio (delta(CO2)-C-13) 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 CO2 increase (104 ppmv) of the last nine Terminations, ending with an overshoot of 21 ppmv occurring within similar to 300 y and leading to higher levels than those of the late pre-industrial Holocene. The full CO2 rise is accompanied by an overall decrease of the delta(CO2)-C-13 minimum values, on which three positive excursions are superimposed. Peak-to-peak delta(CO2)-C-13 changes in our record can reach similar to 1 parts per thousand. The ice core atmospheric delta(CO2)-C-13 appears more depleted by similar to 0.2 parts per thousand during Termination II compared to Termination I, paralleling a similar carbon isotopic depletion recorded in marine data. During both terminations, most of CO2 and delta(CO2)-C-13 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. (C) 2010 Elsevier Ltd. All rights reserved.