Abrasion of sedimentary rocks as a source of hydrogen peroxide and nutrients to subglacial ecosystems

<p>Glaciers and ice sheets are renowned for their abrasive power, yet little is known of the mechanochemical reactions which are initiated by abrasion in these environments and their effect on subglacial biogeochemistry. Here, we use sedimentary rocks representative of different subglacial environments and from a previously glaciated terrain, along with subglacial sediments, to investigate the potential for subglacial erosion to generate <span class="inline-formula">H₂O₂</span> and to release bio-utilisable organic carbon and nutrients (<span class="inline-formula">N</span>, <span class="inline-formula">Fe</span>). Samples were crushed using a ball mill, water was added to rock powders within gastight vials, and samples were incubated in the dark at 4 <span class="inline-formula">^∘C</span>. Headspace and water samples were taken immediately after the addition of water and then again after 5 and 25 <span class="inline-formula">h</span>. Samples generated up to 1.5 <span class="inline-formula">µmol H₂O₂ g⁻¹</span>. The total sulfur content, a proxy for the sulfide content, did not correlate with <span class="inline-formula">H₂O₂</span> generation, suggesting that the pyrite content was not the sole determinant of net <span class="inline-formula">H₂O₂</span> production. Other factors including the presence of carbonates, <span class="inline-formula">Fe</span>-driven Fenton reactions and the pH of the solution were also likely to be important in controlling both the initial rate of production and subsequent rates of destruction of <span class="inline-formula">H₂O₂</span>. Further, we found that erosion can provide previously unaccounted sources of bio-utilisable energy substrates and nutrients, including up to 880 <span class="inline-formula">nmol CH₄ g⁻¹</span>, 680 <span class="inline-formula">nmol H₂ g⁻¹</span>, volatile fatty acids (up to 1.7 <span class="inline-formula">µmol acetate g⁻¹</span>) and 8.2 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">µ</mi><mi mathvariant="normal">mol</mi><mspace width="0.125em" linebreak="nobreak"/><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">g</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="67pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="c1d89d58a5fb61fe1ae0ec2dbd3ff6e1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-929-2023-ie00001.svg" width="67pt" height="16pt" src="bg-20-929-2023-ie00001.png"/></svg:svg></span></span> to subglacial ecosystems. These results highlight the potentially important role that abrasion plays in providing nutrient and energy sources to subglacial microbial ecosystems underlain by sedimentary rocks.</p>