AUTHOR=Stone Jordan , Edgar John O. , Rutherford Johnny , Gill-Olivas Beatriz , Tranter Martyn , Gould Jamie A. , Xavier Cijo M. , Telling Jon 

TITLE=Flash heating boosts the potential for mechanochemical energy sources for subglacial ecosystems

JOURNAL=Frontiers in Geochemistry

VOLUME=Volume 1 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/geochemistry/articles/10.3389/fgeoc.2023.1180893

DOI=10.3389/fgeoc.2023.1180893

ISSN=2813-5962

ABSTRACT=Subglacial environments host diverse microbial ecosystems capable of influencing biogeochemical cycles. However, the darkness and isolation of subglacial environments set limits on the energy sources available for microbial metabolism. A recently recognized energy source for these microbes in wet-based regions is the rock-water reactions which occur after the mechanical fracturing of glacial bedrock. These mechanochemical reactions produce H2 and H2O2 at 0 ⁰C from reactions with mineral surface defects (Si• and SiO•) and release Fe from within the mineral structures, providing electron donors and acceptors for microbial metabolism. However, the production of H2O2 and H2 may be underestimated as temperatures on rock abrasion points can increase substantially above 0 ⁰C as glaciers ‘slip’ and grind rocks, potentially accelerating rates of mechanochemical reactions. Despite this, the effect of rapid heating on subsequent low temperature mechanochemical reactions has yet to be examined. Here, we investigate H2, H2O2 and Fe production during low temperature (0 °C) incubations of water with a range of ground rocks and minerals following ‘flash heating’ to 30, 60, or 121 °C. We show that transient increases (just 5-10 minutes of heating) to moderate temperatures (30 or 60 °C) can significantly increase the rate of H2 production, while short-term heating to 121 °C generates larger bursts of H2. Additionally, pyrite is easily crushed, potentially releasing high quantities of Fe2+ into subglacial systems and promoting mechanochemical reactions due to the resulting large surface area (10× larger than other materials). We provide the first evidence of H2 production from water reactions with crushed pyrite and suggest that crushed pyrite has a higher influence on subglacial H2O2 production than silicates. We conclude that electron donors in the form of Fe2+ and bursts of H2 may be produced in subglacial ecosystems which may be coupled to substantial concentrations of H2O2 produced from crushed pyrite. This suggests that water-rock mechanochemical reactions may be a larger source of energy for subglacial environments than previously recognized.