First measurement of methane emissions from Canadian glaciers in the Yukon

Land-terminating glaciers in Greenland and Iceland are sources of methane (CH4) to the atmosphere1,2,3. CH4 is produced through microbial methanogenesis underneath the ice, transported dissolved in subglacial meltwater to the margin where the gas is emitted to the atmosphere via degassing4. However, sparse empirical data exist about the spatial distribution of subglacial CH4 production and emission in other glaciated regions of the world, limiting our understanding of its regional and global importance in atmospheric carbon budgets and its possible role in the climate system.In August 2022, we conducted fieldwork at three outlet glaciers - Dusty, Kluane and Donjek glaciers - of the St. Elias Icefields in Yukon, Canada, to investigate if these alpine glaciers are also sources of CH4 emissions to the atmosphere. The glaciers were chosen due to the absence of proglacial lakes and the presence of meltwater upwellings at the glacier termini, which were accessed via helicopter.In-situ extracted dissolved CH4 and CO2 concentrations were measured in the field with a portable greenhouse gas analyzer. Additionally, extracted gas was collected in exetainers for concentration measurements via gas chromatography and in Tedlar gas bags for stable carbon and hydrogen isotope analyses of CH4 to decipher its origin. Further, water samples were collected for geochemical analyses. At Dusty glacier, we performed a high-intensity sampling campaign over 10 hours and continuous measurements of dissolved CH4 concentrations with a custom-made low-cost and low-power dissolved CH4 sensor5 to study changes in dissolved gas concentrations, stable isotopic signatures and water chemistry during the rising limb of the diurnal discharge curve.In-situ measured CH4 and CO2 concentrations yielded significantly elevated CH4 and depleted CO2 levels in the meltwater of all three glaciers. Discrete gas samples confirmed dissolved CH4 concentrations 45x, 135x and 250x above the atmospheric equilibrium concentration (3.6 nmol L-1) in the meltwater of Dusty, Kluane and Donjek glaciers, respectively. First measurements of stable carbon and hydrogen isotope values of CH4 showed enrichment in 13C, while 2H was depleted compared to atmospheric CH4, at all sites, likely originating from a thermogenic source or caused by bacterial CH4 oxidation. Water analyses showed an alkaline environment enriched in carbonates and DOC, in contrast to more acidic waters from glaciers in Greenland and Iceland.These first measurements demonstrate that the subglacial meltwaters from glaciers in the St. Elias Icefields are net sources of CH4 and net sinks of CO2 to the atmosphere. Our findings indicate that CH4 emissions from subglacial environments under alpine glaciers may be a more common phenomenon than previously thought, and a potential cause for remotely sensed CH4 concentrations anomalies over glaciated regions. However, more alpine glaciers and outlets from the Greenland Ice Sheet need to be studied to evaluate this link and provide the needed ground truthing for satellite sensors in high latitudes. 1. Christiansen & Jørgensen (2018) DOI 10.1038/s41598-018-35054-72. Lamarche-Gagnon et al. (2019) DOI 10.1038/s41586-018-0800-03. Burns et al. (2018) DOI 10.1038/s41598-018-35253-24. Christiansen et al. (2021) DOI 10.1029/2021JG0063085. Sapper et al. (2022) DOI:10.5194/egusphere-egu22-9972

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