Rock comminution as a source of hydrogen for subglacial ecosystems

Microbes live under glaciers that have persisted for millions of years, without a clear energy supply. Analyses of crushed rocks suggest that interactions of glaciers with the rocks beneath can produce enough H2 to support methanogenic bacteria. Substantial parts of the beds of glaciers, ice sheets and ice caps are at the pressure melting point1. The resulting water harbours diverse subglacial microbial ecosystems2,3 capable of affecting global biogeochemical cycles4,5. Such subglacial habitats may have acted as refugia during Neoproterozoic glaciations6. However, it is unclear how life in subglacial environments could be supported during glaciations lasting millions of years because energy from overridden organic carbon would become increasingly depleted7,8. Here we investigate the potential for abiogenic H2 produced during rock comminution to provide a continual source of energy to support subglacial life. We collected a range of silicate rocks representative of subglacial environments in Greenland, Canada, Norway and Antarctica and crushed them with a sledgehammer and ball mill to varying surface areas. Under an inert atmosphere in the laboratory, we added water, and measured H2 production with time. H2 was produced at 0 °C in all silicate–water experiments, probably through the reaction of water with mineral surface silica radicals formed during rock comminution. H2 production increased with increasing temperature or decreasing silicate rock grain size. Sufficient H2 was produced to support previously measured rates of methanogenesis under a Greenland glacier. We conclude that abiogenic H2 generation from glacial bedrock comminution could have supported life and biodiversity in subglacial refugia during past extended global glaciations.