Origin of CO2, CH4, and N2O trapped in ice wedges in central Yakutia and their relationship

Permafrost thawing as a result of global warming is expected to foster the biological remineralization of intact organic carbon and nitrogen and release greenhouse gas (GHG) into the atmosphere, which will have positive feedback for future global warming. However, GHG budgets and their controls in permafrost ground ice are not yet fully understood. This study aims to better understand the control mechanisms of GHG in ground ice by using new gas and chemistry data. In this study, we present new data on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) mixing ratios in three different ice wedges, Churapcha, Syrdakh, and Cyuie, located in central Yakutia, Siberia. The GHG mixing ratios in the studied ice wedges range from 0.0% to 13.8% CO2, 1.3-91.2 ppm CH4, and 0.0-141.4 ppm N2O. In particular, all three ice wedges demonstrate that ice-wedge samples enriched in CH4 were depleted in N2O mixing ratios and vice versa. N-2-O-2-Ar compositions indicate that the studied ice wedges were most likely formed by dry snow or hoarfrost, not by freezing of snow meltwater, and the O-2-consuming biological metabolism was active. Most of the observed GHG mixing ratios cannot be explained without microbial metabolism. The inhibitory impact of denitrification products of nitrate (including N2O) could be an important control of the ice-wedge CH4 mixing ratio.