Abstract
The base of glaciers and ice sheets provide environments suitable for the production of methane. High pressure conditions beneath the impermeable ‘cap’ of overlying ice promote entrapment of methane reserves that can be released to the atmosphere during ice thinning and meltwater evacuation. However, contemporary glaciers and ice sheets are rarely accounted for as methane contributors through field measurements. Here, we present direct field-based evidence of methane production and release from beneath the Icelandic glacier Sólheimajökull, where geothermal activity creates sub-oxic conditions suited to methane production and preservation along the meltwater flow path. Methane production at the glacier bed (48 tonnes per day, or 39 mM CH4 m−2 day−1), and evasion to the atmosphere from the proglacial stream (41 tonnes per day, or 32 M CH4 m−2 day−1) indicates considerable production and release to the atmosphere during the summer melt season. Isotopic signatures (−60.2‰ to −7.6‰ for δ13Cch4 and −324.3‰ to +161.1‰ for Dch4), support a biogenic signature within waters emerging from the subglacial environment. Temperate glacial methane production and release may thus be a significant and hitherto unresolved contributor of a potent greenhouse gas to the atmosphere.
Highlights
The subglacial environment provides conditions suitable for the production and storage of methane
At the point of subglacial upwelling, methane appears to be of predominantly microbial origin (δ13Cch4 < −50‰) and laboratory incubation of associated subglacial sediments demonstrate a strong potential for methanogenesis
The appearance of elevated aqueous methane concentrations that are commensurate with the location and onset of subglacial drainage, suggests the environment of methane production must be beneath the glacier
Summary
The subglacial environment provides conditions suitable for the production and storage of methane. The presence of liquid water beneath temperate and polythermal ice masses, sub-oxic conditions due to poor hydrological connectivity, and carbon within basal sediments allow the survival of microbiological communities with the potential to produce biogenic methane eg.[1,2,3]. For methane to be detected in meltwater outflow, sub-oxic conditions must occur at the glacier bed, and throughout the subglacial drainage path. The subglacial hydrological system of Sólheimajökull supports extensive sub-oxic conditions throughout the summer due to deep connectivity with the geothermal zone of the active, ice covered Katla volcanic system, where release of reduced gases consume oxygen in the meltwaters[19]. Whilst the specific environmental conditions at Sólheimajökull provide ideal opportunities to investigate mechanisms of methane formation and release dynamics, they highlight the potential for methane production beneath contemporary glaciers worldwide, especially under a changing climate
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