Aircraft measurements of the stable carbon isotopic ratio of atmospheric methane over Siberia

Air samples collected using aircraft during the Siberian Terrestrial Ecosystem-Atmosphere-Cryosphere Experiments (STEACE) in the summer of 1993 and 1994 were analyzed for the carbon isotopic ratio, delta(13)C, of atmospheric CH4 as well as for the CH4 concentration. The CH4 concentrations and delta(13)C values observed in the lower troposphere over wetlands in the West Siberian Lowland varied considerably, showing a clear negative correlation between the two components. From the relationships between measured values of the CH4 concentration and delta(13)C, values of delta(13)C Of CH4 released from wetlands into the atmosphere were estimated to be -75 to -67 parts per thousand. The results observed over oil wells and pipelines showed isotopic evidence for leakage of natural gas. Mean values of delta(13)C measured in the middle and upper troposphere over Siberia in the summer season were -47.9+/-0.3 and -47.8/-0.2 parts per thousand for 1993 and 1994, respectively, which are quite similar to each other.