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Abstract:
We discuss two types of ice shelf firn aquifers present in coastal Antarctica: melt-derived and brine-infiltration. Mapping of melt-derived firn aquifers and regions of melt-saturated firn using both passive and active L-band microwave data has identified perennial melt-derived aquifers in the southwestern Antarctic Peninsula, and several seasonal melt-saturation regions there and in widely separated sites around the ice sheet fringe. Extensive melt aquifers are identified on the Wilkins Ice Shelf, the northern George VI Ice Shelf, and the Müller Ice shelf, and are suspected on the former Jones and Wordie ice shelves. Field work has confirmed the aquifer presence in at least two sites on both the Wilkins and Müller shelves. We also present an improved assessment of the extent of brine aquifers based on their characteristics in modern airborne ice-penetrating radar profiles. Brine aquifers are relatively widespread and are found in shelf areas with porous firn at the waterline, as was previously recognized by Cook et al.(2018). Our study also assesses the relative risk of hydrofracture for ice shelves bearing melt and brine aquifers under various scenarios of firn density, aquifer depth, and brine density. We find that ponded surface melt poses the greatest threat, but that the increased density of brine may also be an issue if the brine layer is relatively shallow in the shelf. We also discuss the likely future expansion of melt aquifers on ice shelves under warming conditions, and consider the process of transitioning from a brine aquifer to a melt aquifer.
