Rock comminution as a source of hydrogen for subglacial ecosystems

Substantial parts of the beds of glaciers, ice sheets and ice caps are at the pressure melting point. The resulting water harbours diverse subglacial microbial ecosystems capable of affecting global biogeochemical cycles. Such subglacial habitats may have acted as refugia during Neoproterozoic glaciations. 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 depleted. 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 0ºC 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.