Methane emissions from subglacial meltwater of three alpine glaciers in Yukon, Canada

Subglacial meltwater of land-terminating glaciers in Greenland and Iceland are sources of methane (CH₄) to the atmosphere, but sparse empirical data exist about the spatial distribution of subglacial CH₄ production and emission from glaciers in other regions of the world. This study presents the first measurements of CH₄ emissions from the subglacial meltwater of three outlet glaciers of the St. Elias Mountains in Yukon, Canada. Dissolved CH₄ concentrations were highly elevated at 45, 135, and 250 times compared to the atmospheric equilibrium concentration in the meltwater of Dusty, Kluane, and Donjek glaciers, respectively. Dissolved CO₂ concentrations were depleted relative to the atmospheric equilibrium. This points to the meltwater being a source of CH₄ and a sink of CO₂. Stable carbon (¹³C) and hydrogen (²H) isotopic signatures of the subglacial CH₄ were depleted compared to atmospheric CH₄ at all sites, indicating both biotic and abiotic sources and possible alteration from bacterial CH₄ oxidation in the meltwater. No relation was found between CH₄ concentrations in the meltwater and the meltwater chemistry or the size of the glaciers in this study. These findings suggest that CH₄ emissions from subglacial environments under alpine glaciers may be a more common phenomenon than previously thought.