Atmospheric Methane and Nitrous Oxide of the Late Pleistocene from Antarctic Ice Cores.

The European Project for Ice Coring in Antarctica Dome C ice core enables us to extend existing records of atmospheric methane (CH[sub 4]) and nitrous oxide (N[sub 2]O) back to 650,000 years before the present. A combined record of CH[sub 4] measured along the Dome C and the Vostok ice cores demonstrates, within the resolution of our measurements, that preindustrial concentrations over Antarctica have not exceeded 773 ± 15 ppbv (parts per billion by volume) during the past 650,000 years. Before 420,000 years ago, when interglacials were cooler, maximum CH[sub 4] concentrations were only about 600 ppbv, similar to lower Holocene values. In contrast, the N[sub 2]O record shows maximum concentrations of 278 = 7 ppbv, slightly higher than early Holocene values. [ABSTRACT FROM AUTHOR]