[1] Methane is one of the important greenhouse gases accumulating in the atmosphere today. The increased loading over the past 2 centuries is thought to be the result of increased anthropogenic emissions. Here we present records of the d 13 C of CH 4 in firn air from the South Pole and in trapped bubbles in a short ice core from Siple Dome, Antarctica, that help constrain historical emissions of various sources throughout the last 2 centuries. Using two firn air samplings in 1995 and 2001 we calculate that d 13 CH 4 has increased by an average of 0.06 ± 0.02%/yr over the 6 years between samplings. Our ice core results suggest the d 13 C of atmospheric CH 4 has increased by 1.8 ± 0.2% between 1820 A.D. and 2001 AD. The d 13 CH 4 changes in both data sets are the result of an increase in the relative proportion of CH 4 sources with elevated 13 C/ 12 C isotope ratios. One explanation for observed trends involves a 16 Tg/yr increase in CH 4 emissions associated with biomass burning over the past 2 centuries.
Abstract.The atmospheric trend of methane isotopic ratios since the mid20th century has been reconstructed from Antarctic firn air. High volume air samples were extracted at several depth levels at two sites in East Antarctica.
Methane concentration and its
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