Wetland and groundwater chemistry shows evidence of aluminosilicate weathering in hyperarid Antarctic cold desert soils

Antarctic water tracks are shallow groundwater flow networks that route summer season meltwater downslope over the ice table. Water track pore fluids are highly concentrated in solutes, including silica, and water track sediments are enriched in sediment fines. However, given the extreme cold and aridity of the McMurdo Dry Valleys, it has not been clear whether aluminosilicate weathering is occurring in Dry Valleys water tracks, or whether high solute concentrations merely reflect evaporative concentration of marine or eolian-derived salts, rather than aluminosilicate weathering. Based on geochemical and isotopic analysis of water track pore fluids and freshwater snow and ice melt samples from the McMurdo Dry Valleys, coupled with flow path modeling and measurements of soil aluminum concentration, we show that silica enrichment in water tracks is not due only to silicic waters being evaporatively concentrated, but, instead, that water track composition is consistent with active and ongoing aluminosilicate weathering of water track soils. We show that water tracks connect the landscape at the hillslope scale, draining areas up to 105 m2 to 106 m2 each, and concentrating silica and other solutes from across the watershed. We find that water tracks are sites where chemical weathering products like clays and amorphous aluminum−bearing aggregates are being generated in situ, and solute concentrations are consistent with fluids in equilibrium with weathering product mineral phases. This suggests that expansion of water tracks due to regional warming, greater snowmelt, or permafrost thaw could increase the area of exposed soils in which chemical weathering can occur, altering Antarctica’s role in globally relevant soil biogeochemical processes.