The ¹³C/¹²C kinetic isotope effect for soil oxidation of methane at ambient atmospheric concentrations

During a survey of the Alaskan North Slope to estimate the isotopic composition and fluxes of methane (CH 4 ) from the tundra, two sites were encountered that showed net methane consumption within flux chambers. Methane concentrations decreased from ambient (1.78 ppmv) by up to 50% and the δ 13 C increased by up to 10‰ in the two chamber deployments showing CH 4 consumption. CH 4 consumption rates were measured to be 1.2 and 0.6 mg CH 4 m −2 d −1 ; the corresponding carbon kinetic isotope effects ( k 13 / k 12 ) were 0.974 and 0.984, respectively. For comparison, the carbon kinetic isotope effect for CH 4 oxidation by hydroxyl radical has been recently measured to be 0.990 (Davidson et al., 1987). These data are briefly discussed with reference to the potential effect of soil oxidation on the stable carbon isotope budget of atmospheric methane.