Records of the D 13 C of atmospheric CH 4 over the last 2 centuries as recorded in Antarctic snow and ice

[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 dC of CH4 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 dCH4 has increased by an average of 0.06 ± 0.02%/yr over the 6 years between samplings. Our ice core results suggest the dC of atmospheric CH4 has increased by 1.8 ± 0.2% between 1820 A.D. and 2001 AD. The dCH4 changes in both data sets are the result of an increase in the relative proportion of CH4 sources with elevated C/C isotope ratios. One explanation for observed trends involves a 16 Tg/yr increase in CH4 emissions associated with biomass burning over the past 2 centuries.

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