Understanding formation of ice wedges and origin of trapped greenhouse gas at Zyryanka, Northeastern Siberia

Multiple geochemical analyses may help us better constrain the ice-wedge formation and in-situ greenhouse gas (GHG) production mechanisms. Here we present new results from ice-wedge ice sampled at Zyryanka, Northeastern Siberia (65°93’N, 150°89’E). The plant remains and CO₂ gas were analyzed for ¹⁴C dating, and we obtained from 810 to 1750 years before 1950 CE for the Zyryanka ice wedge. δ(N₂/Ar) of the ice wedges ranges from -17.51 to -3.53 % with regard to modern air, indicating that the Zyryanka ice wedge was formed by both liquid water and dry snow. On the other hand, the δ(O₂/Ar) value of the Zyryanka ice wedges ranges from -72.88 to -37.58 % with regard to modern air, implying oxygen gas was consumed considerably by respiration of microorganisms in the ice-wedge ice. We also observed correlations among the three greenhouse gas species and oxygen gas concentrations. N₂O and CO₂ concentrations show a strong positive correlation (r = 0.94, p=0.01). We also found that the melting fraction (estimated from N₂/Ar) is positively correlated with CO2 (r=0.81, p=0.01) and CH₄ (r=0.87, p<0.05). Furthermore, O₂ concentration is negatively correlated with the CH₄ concentrations (r = -0.41, p<0.05) which may imply that CH₄ production is associated with biological oxygen consumption. The δ¹⁸O of ice melt ranges from -28.6 to -19.1 ‰ for the ice wedge and adjacent soil samples, showing a symmetric structure with low δ¹⁸O values in the ice wedge parts and high in the adjacent soils. Comparing with the δ¹⁸O value of modern precipitation in the Zyryanka region, it can be inferred that the ice wedge was mainly formed by filling with cold seasonal precipitation. Our study shows that the gas mixing ratios in ice wedges and water stable isotope analysis may help better understanding the biogeochemical environments during and after the formation of ice wedges.