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Radar-sounding evidence for a subglacial groundwater table in Hiawatha Crater, Greenland
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  • Jonathan Bessette,
  • Thomas Jordan,
  • Dustin Schroeder,
  • Joseph MacGregor
Jonathan Bessette
University at Buffalo

Corresponding Author:jbessett@buffalo.edu

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Thomas Jordan
University of Bristol
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Dustin Schroeder
Stanford University
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Joseph MacGregor
Univ of TX-Inst for Geophysics
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Recent airborne radar-sounding surveys by NASAs Operation IceBridge revealed a large impact crater in the Hiawatha glacier region of northwest Greenland. The radar data used to identify the craters morphology included a 2016 survey carried out with a new ultrawideband radar system that demonstrated unprecedented levels of detail in the radar images. Notably, an unusual flat, specular reflector below the ice-bed interface was identified by visual inspection potentially as a groundwater table. However, this observation, and characterization of overlying material, has yet to be confirmed by a detailed radiometric analysis. This work analyzes four different flight segments with potential subglacial groundwater reflectors to constrain the bed geology and thermal regime, and probability that the sub-bed reflector is indeed a groundwater table. First, we exploit variation in the thickness of the subglacial layer between the ice-bed interface and the proposed ground water table to determine dielectric loss values. The bed material estimated is most likely a mixture of ice, dry sand, and air – with minuscule groundwater present in the layer between the ice-bed interface and the reflector. Lastly, we use the subglacial layer loss values to determine the radar reflectivity difference between the ice-bed interface and sub-bed reflector. The analyses are consistent with the presence of a groundwater table and are useful for providing additional geophysical constraints on the groundwater system beneath Hiawatha Crater. This detection is possible for subglacial settings that consist of a dry/frozen bed around 15 meters thick between the ice and water table in conjunction with a 150 to 520 MHz chirp radar system. Such groundwater sources are a commonly neglected but likely important component of glacier hydrology; they can drive water into till, elevate porewater pressures, reduce shear strength and significantly influence ice sheet dynamics and thus, sea level rise.