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

The microbial process of methane (CH4) production during the back‐freezing of permafrost soils in autumn and the future fate of produced CH4 in the thawing phase of the following spring are not well understood. Long‐term CH4 flux studies in the Lena Delta (Siberia) indicate that back‐stored CH4 adds to the emission of newly‐produced CH4 at the beginning of the vegetation period. Further field analysis shows that microbial CH4 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 CH4 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 CH4 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 CH4 in the headspace of the microcosm. The data obtained contribute to the understanding of microbial processes and CH4 fluxes in permafrost environments in the autumn and early winter. Copyright © 2003 John Wiley & Sons, Ltd.