A new paper, led by Jade Hatton, has been published in Geochemical Perspectives Letters, detailing how physical crushing could be key to explain subglacial silicon weathering processes and the export of isotopically light silicon to proglacial rivers.
Rock debris was collected from the proglacial plain in front of Leverett Glacier, SW Greenland, and used in a series of laboratory crushing experiments to test the impact of physical grinding (mimicking high erosion rates in the subglacial system) on silicon concentrations and isotopic composition.
Previously, it has been found that glacial rivers export dissolved silicon (DSi) with an isotopic composition much lighter than non-glacial rivers, however the source of this light DSi was unknown. This study shows that the initial dissolution of the reactive mineral surfaces in freshly crushed rock leads to isotopically light DSi. This suggests that subglacial erosion provides a clear mechanism for why glacially-derived DSi is isotopically lighter than other riverine DSi.
The experiments also show how more physical erosion leads to higher amorphous silica (ASi) concentrations. The formation mechanisms for subglacial ASi are very poorly understood and this publication highlights physical erosion could play an important part and help to explain why glacial rivers have such elevated concentrations of ASi.
Glacial meltwaters export substantial quantities of DSi and ASi, providing an essential nutrient for downstream diatoms, and this new work begins to unravel some of the questions about its subglacial source.
Hatton JE, Hendry KR, Hawkings JR, Wadham JL, Benning LG, Blukis R, Roddatis V, Ng HC, Wang T (2021) Physical weathering by glaciers enhances silicon mobilisation and isotopic fractionation. Geochemical Perspectives Letters 19:7–12 doi: 10.7185/geochemlet.2126