Reply on RC2

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> 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 to investigate the potential for subglacial erosion to generate H₂O₂ and release bio-utilisable organic carbon and nutrients (N, Fe). Samples were crushed using a ball mill, water added to rock powders within gastight vials, and samples incubated in the dark at 4 &deg;C. Headspace and water samples were taken immediately after the addition of water and then again after 5 and 25 h. Samples generated up to 1.5 &micro;mol H₂O₂ g^-1. The total sulphur content, a proxy for the sulphide content, did not correlate with H₂O₂ generation, suggesting that the pyrite content was not the sole determinant of net H₂O₂ production. Other factors, including the presence of carbonates, Fe-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 H₂O₂. Further, we found erosion can provide previously unaccounted sources of bio-utilisable energy substrates and nutrients, including up to 880 nmol CH₄g^-1, 680 nmol H₂ g^-1, volatile fatty acids (up to 1.7 &micro;mol acetate g^-1) and 8.2 &micro;mol NH₄⁺ g^-1 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.