AIRCRAFT MEASUREMENTS OF THE STABLE CARBON ISOTOPIC RATIO OF ATMOSPHERIC METHANE OVER SIBERIA

Air samples collected using aircraft during the Siberian Terrestrial E cosystem-Atmosphere-Cryosphere Experiments (STEACE) in the summer of 1 993 and 1994 were analyzed for the carbon isotopic ratio, delta(13)C, of atmospheric CH4 as well as for the CH4 concentration. The CH4 conce ntrations 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 relati onships between measured values of the CH4 concentration and delta(13) C, values of delta(13)C Of CH4 released from wetlands into the atmosph ere were estimated to be -75 to -67 parts per thousand. The results ob served over oil wells and pipelines showed isotopic evidence for leaka ge of natural gas. Mean values of delta(13)C measured in the middle an d 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, wh ich are quite similar to each other.