The relative importance of methane sources and sinks over the Last Interglacial period and into the last glaciation

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 (δ13CO2) 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 (104ppmv) of the last nine Terminations, ending with an overshoot of 21ppmv occurring within ∼300y 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 δ13CO2 minimum values, on which three positive excursions are superimposed. Peak-to-peak δ13CO2 changes in our record can reach ∼1‰. The ice core atmospheric δ13CO2 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 CO2 and δ13CO2 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. © 2010 Elsevier Ltd.