Abstract
Abstract. Investigations of sources and sinks of atmospheric CH4 are needed to understand the global CH4 cycle and climate-change mitigation options. Glaciated environments might play a critical role due to potential feedbacks with global glacial meltdown. In an emerging glacier forefield, an ecological shift occurs from an anoxic, potentially methanogenic subglacial sediment to an oxic proglacial soil, in which soil-microbial consumption of atmospheric CH4 is initiated. The development of this change in CH4 turnover can be quantified by soil-gas profile analysis. We found evidence for CH4 entrapped in glacier forefield soils when comparing two methods for the collection of soil-gas samples: a modified steel rod (SR) designed for one-time sampling and rapid screening (samples collected ∼1 min after hammering the SR into the soil), and a novel multilevel sampler (MLS) for repetitive sampling through a previously installed access tube (samples collected weeks after access-tube installation). In glacier forefields on siliceous bedrock, sub-atmospheric CH4 concentrations were observed with both methods. Conversely, elevated soil-CH4 concentrations were observed in calcareous glacier forefields, but only in samples collected with the SR, while MLS samples all showed sub-atmospheric CH4 concentrations. Time-series of SR soil-gas sampling (additional samples collected 2, 3, 5, and 7 min after hammering) confirmed the transient nature of the elevated soil-CH4 concentrations, which were decreasing from ∼100 μL L−1 towards background levels within minutes. This hints towards the existence of entrapped CH4 in calcareous glacier forefield soil that can be released when sampling soil-gas with the SR. Laboratory experiments with miniature soil cores collected from two glacier forefields confirmed CH4 entrapment in these soils. Treatment by sonication and acidification resulted in a massive release of CH4 from calcareous cores (on average 0.3–1.8 μg CH4 (g d.w.)−1) (d.w. – dry weight); release from siliceous cores was 1–2 orders of magnitude lower (0.02–0.03 μg CH4 (g d.w.)−1). Clearly, some form of CH4 entrapment exists in calcareous glacier forefield soils, and to a much lesser extent in siliceous glacier forefield soils. Its nature and origin remain unclear and will be subject of future investigations.
Highlights
Methane in the atmosphere contributes significantly to global climate change (Forster et al, 2007)
We found evidence for CH4 entrapped in glacier forefield soils when comparing two methods for the collection of soilgas samples: a modified steel rod (SR) designed for one-time sampling and rapid screening, and a novel multilevel sampler (MLS) for repetitive sampling through a previously installed access tube
Our objectives for this study were (i) to compare the two sampling instruments (MLS and SR) side by side at three locations in a siliceous and a calcareous glacier forefield to confirm the disagreement with respect to elevated CH4 concentrations, (ii) to examine the possibility of temporary CH4 release during SR sampling by performing time-series sampling, and (iii) to provide a first quantitative assessment of potentially entrapped CH4 in glacier forefield soils by disturbing miniature soil cores in the laboratory using sonication and acidification
Summary
Methane in the atmosphere contributes significantly to global climate change (Forster et al, 2007). Microbial oxidation of atmospheric CH4 has been confirmed in glacier forefield soils in Greenland and Switzerland (Bárcena et al, 2010, 2011; Nauer et al, 2012). Our objectives for this study were (i) to compare the two sampling instruments (MLS and SR) side by side at three locations in a siliceous and a calcareous glacier forefield to confirm the disagreement with respect to elevated CH4 concentrations, (ii) to examine the possibility of temporary CH4 release during SR sampling by performing time-series sampling, and (iii) to provide a first quantitative assessment of potentially entrapped CH4 in glacier forefield soils by disturbing miniature soil cores in the laboratory using sonication and acidification
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
