Characterizing Weathering Crust Hydrology in the Southwest Greenland Ablation Zone

The process of meltwater generation in the ablation zone of Greenland has been studied for decades, but the processes that control the storage and transport of meltwater over and through the near-surface ice are unknown. This knowledge gap prevents a realistic treatment of runoff processes in ice sheet hydrology models and potentially limits interpretation of satellite and/or airborne data aimed at measuring ice sheet mass balance via surface lowering. During a 2.5 month field campaign in the Kangerlussuaq region, southwest Greenland, we measured near-surface (<2m) ice density, ablation, porosity, hydraulic conductivity, depth to water table, and cryoconite hole filling and draining rates. In general, the near surface ice was characterized by two distinct layers of sharply contrasting density with distinct hydrologic regimes. The lower, medium density weathered ice layer contained a shallow unconfined aquifer overlain by a very low density, highly porous, unsaturated weathered crust. We propose that the majority of surface ablation, and hence lowering, likely occurs in the very low density shallow weathered crust, whereas water storage, and potentially refreezing, occurs in the deeper weathered ice layer. Further, meltwater transport from point of origin to supraglacial streams and rivers is likely controlled by shallow porous-media flow through weathered ice as opposed to surface sheet flow. Our results have implications for the interpretation of short term surface lowering observations (ground, airborne, and satellite), surface energy balance computations, and potentially alter existing conceptualizations about processes that control the timing of meltwater delivery to supra- and en-glacial hydrologic systems.