Study on the formation process of ice wedges and origin of occluded greenhouse gas at Zyryanka, Northeastern Siberia

다국어 초록 (Multilingual Abstract)

Multiple geochemical analyses may provide important implication about 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). To constrain the age of the ice wedge, plant residues and CO₂ gas in the ice were analyzed for 14C dating and we obtained ~ 4000 and ~ 1000 years before 1950 CE for the side and center parts of the ice wedge, respectively. The δ(N2/Ar) of the ice wedges ranges from -43.9 to -1.8% with regard to modern air, indicating that the Zyryanka ice wedge was formed by both liquid water and dry snow. Using the δ(N₂/Ar) we calculate the melting fraction of gas species. The melting fraction is well supported by bubble shapes and orientation: In areas where melting fractions are relatively high the bubble are elongated with preferred orientation. The δ(O₂/Ar) value of the Zyryanka ice wedges ranges from -99.1 to -37.6% with regard to modern air, implying oxygen gas might have been consumed considerably by respiration of microorganisms in the ice wedge ice. We observe a negative correlation between CO₂ and O₂ gas concentrations (r=-0.92, p=0.01), indicating microbial respiration within the ice wedge ice. N₂O and CO₂ concentrations shows a weak positive correlation (r = 0.23, p = 0.0003), as does the correlation between CH₄ and CO₂ correlation (r = 0.35, p = 0.0007). We also observe a weak negative correlation between N₂O and CH₄ (r =-0.39, p = 0.04). The δ<SUP>18</SUP>O of ice melt ranges from -28.6 to -19.1‰, and the horizontal profile shows a symmetric structure with high δ<SUP>18</SUP>O values in the side parts and low in the center part. We will continue to scrutinize ice wedge formation process with additional stable water isotope data of modern precipitates at Zyryanka. Our study shows that the gas mixing ratios in ice wedges and stable water isotope analysis may help better understanding the biogeochemical environments during and after the formation of ice wedges.