Temporal variations of the carbon isotopic ratio of atmospheric methane observed at Ny Alesund, Svalbard from 1996 to 2004

Systematic observations of the atmospheric CH4 mole fraction and its carbon isotope ratio delta(CH4)-C-13 have been carried out at Ny Alesund, Svalbard (78 degrees 550'N, 11 degrees 56'E) since 1991 and 1996, respectively. The CH4 and delta(CH4)-C-13 showed clear seasonal cycles with respective peak-to-peak amplitudes of 48 ppb and 0.42 parts per thousand. By comparing the anomalies in the increase rate of the CH4 with those of delta(CH4)-C-13, it is suggested that the cause of the rapid increase in the CH4 mole fraction observed at Ny Alesund in 1998 could be attributable to an enhanced CH4 release from wetland and biomass burning.