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 atmosphere^1,2,3. 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/s41598-018-35054-7

2. Lamarche-Gagnon et al. (2019) DOI 10.1038/s41586-018-0800-0

3. Burns et al. (2018) DOI 10.1038/s41598-018-35253-2

4. Christiansen et al. (2021) DOI 10.1029/2021JG006308

5. Sapper et al. (2022) DOI:10.5194/egusphere-egu22-9972