Abstract
Abstract. Methane (CH4) and nitrous oxide (N2O) compositions in ground ice may provide information on their production mechanisms in permafrost. However, existing gas extraction methods have not been well tested. We tested conventional wet and dry gas extraction methods using ice wedges from Alaska and Siberia, finding that both methods can extract gas from the easily extractable parts of the ice (e.g. gas bubbles) and yield similar results for CH4 and N2O mixing ratios. We also found insignificant effects of microbial activity during wet extraction. However, both techniques were unable to fully extract gas from the ground ice, presumably because gas molecules adsorbed onto or enclosed in soil aggregates are not easily extractable. Estimation of gas production in a subfreezing environment of permafrost should consider such incomplete gas extraction.
Highlights
Permafrost preserves large amounts of soil carbon (C) and nitrogen (N) in a frozen state (e.g. Hugelius et al, 2014; Salmon et al, 2018), temporarily removing this frozen C and N from active global cycles
Future projections of permafrost stability are of great interest, because thawing permafrost may lead to decomposition and/or remineralisation of the buried soil C and N and their abrupt emission into the atmosphere in the form of greenhouse gases (GHGs) such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), which in turn can trigger positive feedbacks (e.g. Salmon et al, 2018)
Assuming that activation of microbial metabolism is unlikely during dry extraction at a temperature of −37 ◦C in the extraction chamber for < 1 h, our findings may imply that wet extraction does not stimulate microbial reactivation to a measurable extent
Summary
Permafrost preserves large amounts of soil carbon (C) and nitrogen (N) in a frozen state (e.g. Hugelius et al, 2014; Salmon et al, 2018), temporarily removing this frozen C and N from active global cycles. Future projections of permafrost stability are of great interest, because thawing permafrost may lead to decomposition and/or remineralisation of the buried soil C and N and their abrupt emission into the atmosphere in the form of greenhouse gases (GHGs) such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), which in turn can trigger positive feedbacks The processes responsible for in situ C and N remineralisation and GHG production in ground ice are poorly understood, despite the fact that ground ice accounts for a substantial portion (up to ∼ 40–90 % by volume) of Pleistocene ice-rich permafrost, or Yedoma (e.g. Kanevskiy et al, 2013; Jorgenson et al, 2015). Boereboom et al (2013) utilised the conventional melting– refreezing method (wet extraction) used in polar ice core The relevant analytical methods remain poorly scrutinised. Boereboom et al (2013) utilised the conventional melting– refreezing method (wet extraction) used in polar ice core
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