Extensive subglacial hydrological network and basal temperate layer in Southwest Greenland: an integrated approach of radar analysis and ice sheet modeling

Abstract:

Meltwater storage in and beneath the ice sheet exerts strong control on ice flow velocity by modifying the ice thermal structure and basal sliding. However, observations of meltwater storage in Greenland are sparse and mostly limited to the margins of the ice sheet, providing an incomplete view on how water is distributed. To address this shortcoming, we use an integrated approach of radar analyses, and thermal and subglacial hydrology modeling to produce the first, catchment-wide characterization of the subglacial hydrological network. Our study focuses on a 1450 km² section of Russell Glacier and Isunnguata Sermia. We use the depth profiles of ice temperature from a thermal model to correct radar englacial attenuation losses, and produce maps of relative basal reflectivity from radar bed echoes. We examine the reflectivity relative to a subglacial hydrology model, and show that substantial volumes of water store in an extensive subglacial hydrological network. Data from mid-April show that subglacial water concentrates along the basal valleys in the lower catchment directly below where numerous moulins open later in the season. Additionally, we identify an unusually low apparent reflectivity feature at the catchment boundary of Russell and Isunnguata. We suggest that the apparent reflectivity anomaly is a result of high englacial attenuation losses associated with a basal temperate layer ~250 m thick and ~14 km² in area. This temperate layer was previously observed in another melt season from boreholes temperature measurements, suggesting that it is likely is a persistent and contiguous feature. Our results demonstrate the integration of observations and modeling are a powerful approach to characterize Greenland hydrology and its effect on ice sheet thermal state that may modify ice dynamics critically.