Mechanism of Ice-Wedge Formation and Mixed Origin of Trapped Greenhouse Gases in Zyryanka Permafrost, Northeastern Siberia

This study explores the mechanisms behind ice-wedge formation and the origins of greenhouse gases (GHGs) trapped in ice wedges at Zyryanka, Northeastern Siberia. The radiocarbon ages from plant remains and CO₂ gas extracted from ice wedges were found to be significantly younger (810–1750 years before 1950 ce) than those from the adjacent soils (3900–4430 years before 1950 ce). Based on the δ(N₂/Ar) values of the ice wedges, the source of ice-wedge formation was likely both infiltrating liquid water and hoarfrost. Additionally, δ(O₂/Ar) of the ice-wedge gas bubbles (with respect to modern air) suggested that the in situ O₂ consumption occurred through microbial respiration and/or mineral oxidation in semianaerobic conditions. GHG concentrations (CO₂, CH₄, and N₂O) in ice wedges were generally two to three orders of magnitude higher than Holocene atmospheric levels. We interpreted that the additional GHGs were primarily generated through microbial activity and partially stemmed from the outgassing of gases that had been dissolved in the source liquid water. Based on the δ¹⁸O–δD relationship between ice wedges and modern precipitation, we inferred that the ice wedges predominantly reflect the isotopic composition of winter precipitation. Furthermore, we reconstructed the temperatures during the formation of the ice wedges using the stable water isotope data of ice wedges and found them to be comparable to modern air temperature conditions. Gas mixing ratios and stable water isotope chemistry of the Zyryanka ice-wedge samples in this study were useful to understand the biogeochemical environments during and after the formation of ice wedges. We supplemented ice-wedge data from inland Northeastern Siberia, a region with limited research coverage, offering a unique perspective for site-specific paleoclimate interpretations.