Simulation of freezing‐thawing cycles in a permafrost microcosm for assessing microbial methane production under extreme conditions

The microbial process of methane (CH 4 ) production during the back‐freezing of permafrost soils in autumn and the future fate of produced CH 4 in the thawing phase of the following spring are not well understood. Long‐term CH 4 flux studies in the Lena Delta (Siberia) indicate that back‐stored CH 4 adds to the emission of newly‐produced CH 4 at the beginning of the vegetation period. Further field analysis shows that microbial CH 4 production already occurs at in situ temperatures of around 1°C in the bottom layer of the soil. Therefore, a permafrost microcosm was developed to simulate the influence of the annual freezing‐thawing cycles on the CH 4 fluxes in the active layer of permafrost soils. Two cryostats ensure independent freezing and thawing the top and the bottom of the microcosm to simulate different field conditions. The CH 4 concentration (Rhizon soil moisture samplers), the soil temperature (film platinum resistance temperature detectors [RTDs]) and the soil water content (time domain reflectometry) are analysed in different depths of the microcosm during the simulation in addition to the concentration of emitted CH 4 in the headspace of the microcosm. The data obtained contribute to the understanding of microbial processes and CH 4 fluxes in permafrost environments in the autumn and early winter. Copyright © 2003 John Wiley & Sons, Ltd.