Englacial diagenesis in deep Antarctic ice: implications for Martian dust oxidation

Abstract The discovery of englacial diagenesis, involving neoformation of minerals at depth within ice sheets, has the potential to reshape the interpretation of insoluble dust records in ice cores and the origin of planetary ice-bearing deposits on Mars. Mineralogical changes in deep ice involve iron geochemistry, and are driven by the circulation of acidic fluids within pre-melted ice during ice metamorphism, leading to the authigenic formation of jarosite. Here we show that englacial diagenesis is a widespread process in deep Antarctic ice and involves the authigenic growth of mineral phases like goethite (lepidocrocite) and hematite (maghemite) in addition to jarosite. The coexistence of these neoformed phases reflects micron-scale variability in pH and water activity within the englacial brine network. Englacial diagenesis has major consequences: it introduces systematic biases in bulk mineralogical proxies used to reconstruct dust source conditions, and it provides a grounded explanation for the anomalously high dust magnetization observed in deep Antarctic ice. We further propose that repeated burial of dust within planetary ice reservoirs, as expected on Mars over orbital timescales, represents a viable and previously underexplored mechanism for the oxidation, aggregation and magnetic activation of Martian airborne dust, without requiring prolonged warm and wet surface conditions.