Dual stable isotopic methane (δ¹³CH4 and dD(CH4)) records from four Antarctic ice cores

Here we present dual stable isotopic methane records (d13CH4 and dD(CH4)) from four Antarctic ice cores, which provide improved constraints on past changes in natural methane sources. Our isotope data show that tropical wetlands and seasonally inundated floodplains are most likely the controlling sources of atmospheric methane variations for the current and two older interglacials and their preceding glacial maxima.

The changes in these sources are steered by variations in temperature, precipitation and the water table, as modulated by insolation, (local) sea level and monsoon intensity. Based on our new dD(CH4) constraint, it appears that geologic emissions of methane may play a steady but only minor role in atmospheric CH4 changes, and that the glacial budget is not dominated by these sources. Superimposed on the glacial/interglacial variations is a marked difference in both isotope records, with systematically higher values during the last 25,000 years compared to older time periods.