[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

We have performed the first ever combined-element stable isotopic measurements of extraterrestrial molecules. Methane from two carbonaceous chondrites, Murchison and Cold Bokkeveld, was measured for its hydrogen and carbon isotopic compositions. The combined isotopic composition of meteoritic methane reveals information about the indigenous nature of volatile aliphatic organic matter in meteorites and its probable extraterrestrial source environment. Deuterium enrichments relative to the solar nebula 4.6 Gyr ago reflect a contribution from low-temperature chemical reactions in interstellar space. Similar carbon but different hydrogen isotopic compositions for methane in the two meteorite samples probably represent comparable primary origins but varying levels of secondary processing and exchange with isotopically light hydrogen. Our high precision laboratory-obtained measurements provide valuable reference points for observational spectroscopists undertaking astronomical investigations of the stable isotopic composition of extraterrestrial methane.