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To investigate the role of minerals in sustaining subglacial communities the stream water chemistry and the bacterial community composition were analyzed in two catchments containing identical sedimentary formations and differing only in the extent of glaciation. The two catchments, glaciated Dryadbreen and unglaciated Fardalen, are located in Svalbard, Norway. Stream waters from both catchments were analyzed for major ions and stable isotopes and associated stream sediments were analyzed by 16S rRNA gene tagged sequencing. Sulfate was the dominant anion in both catchments, indicating that pyrite weathering and concomitant production of sulfuric acid is a significant weathering agent in both catchments. Stable isotope measurements of sulfate, together with inferences of metabolic processes catalyzed by resident microbial communities, revealed that the pyrite oxidation reaction differed between the two catchments. No δ³⁴S fractionation relative to pyrite was observed in the unglaciated catchment and this was interpreted to reflect pyrite oxidation under oxic conditions. In contrast, δ³⁴S and δ¹⁸OSO₄ values were positively correlated in the glaciated catchment and were positively offset from pyrite. This was interpreted to reflect pyrite oxidation under anoxic conditions with loss of S intermediates. These observations suggest the potential for minerals to sustain microbial metabolism under ice in the presence and absence of oxygen.

Our previous work in subglacial environments suggest the presence of an abundant population of putatively hydrogenotrophic methanogens. However, a biological source for the hydrogen supporting these communities could not be identified suggesting that the hydrogen was being supplied by abiotic mechanisms. To investigate the potential for water-rock interactions to supply the hydrogen supporting the abundant methanogen communities in subglacial environments, we mimicked the physical abrasion of silicate bedrock by glaciers in the laboratory and showed hydrogen production when rock flour was exposed to water at 0°C. The hydrogen is likely produced via the reaction of water with surface silica radicals formed during glacial rock comminution. Rates of hydrogen production from this mechanism is sufficient to support previous measured rates of hydrogenotrophic methanogenesis in these ecosystems. We conclude that H₂ generation from glacial bedrock comminution is a potentially significant source of energy that can help support a dark, cold subglacial biosphere on Earth, and possibly other planetary bodies where silicate bedrock and glacial ice exist.