Description: There is widespread, but often indirect, evidence that a significant fraction of the bed beneath the Greenland Ice Sheet is thawed (at or above the pressure melting point for ice). This includes the beds of major outlet glaciers and their tributaries and a large area around the NorthGRIP borehole in the ice-sheet interior. The ice-sheet scale distribution of basal water is, however, poorly constrained by existing observations. In principle, airborne radio-echo sounding (RES) enables the detection of basal water from bed-echo reflectivity, but unambiguous mapping is limited by uncertainty in signal attenuation within the ice. Here we introduce a new, RES diagnostic for basal water that is associated with wet-dry transitions in bed material: bed-echo reflectivity variability. This technique acts as a form of edge detector and is a sufficient, but not necessary, criteria for basal water. However, the technique has the advantage of being attenuation-insensitive and suited to data combination enabling combined analysis of over a decade of Operation IceBridge survey data. The basal water predictions are compared with existing analyses of the basal thermal state (frozen and thawed beds) and geothermal heat flux. In addition to the outlet glaciers, we demonstrate widespread water storage in the northern and eastern interior. Notably, we observe a quasi-linear 'corridor' of basal water extending from NorthGRIP to Petermann glacier that spatially correlates with elevated heat flux predicted by a recent magnetic model. Finally, with a general aim to stimulate regional- and process-specific investigations, the basal water predictions are compared with bed topography, subglacial flow paths, and ice-sheet motion. The basal water distribution, and its relationship with the thermal state, provides a new constraint for numerical models.

Description: Dielectric Profiling (DEP) of the North Greenland Eemian (NEEM) core were recorded in the field during the 2008-2011field seasons with the DEP device described by Wilhelms et al. (1998). The permittivity and conductivity of DEP data are calculated by their respective densities and conductivities (Wilhelms, 2005). The resolution of DEP data is 5 mm depth intervals. The DEP was not processed at a consistent temperature due to the varying temperature in the field seasons. The upper 100 m is measured on NEEM–2008–S1 core, which was the NEEM pilot core. For more information on the calibration procedure see Mojtabavi et al, 2020.

Description: The FINEGIS F3 data set is located in Northern Greenland upstream of the northern branch of the 79° North close to the ice divide. On average the 3D horizon spans an area of approximately 85 x 60 km and has an age of 60.0 ± 4.0 ka (thousand years). The data resemble two cylindrical fold units, which are located in the lower third of the ice column.

Description: Dielectric Profiling (DEP) of the East GReenland Ice core Project (EGRIP) core were recorded in the field during the 2017, 2018 and 2019 field seasons with the DEP device described by Wilhelms et al. (1998). The permittivity and conductivity of DEP data are calculated by their respective densities and conductivities (Wilhelms, 2005). The resolution of DEP data is 5 mm depth intervals. The DEP was not processed at a consistent temperature due to the varying temperature in the field seasons. For more information on the calibration procedure see Mojtabavi et al, 2020.

Description: The FINEGIS F1 data set is located in Northern Greenland upstream of the northern branch of the 79° North close to the ice divide. On average the 3D horizon spans an area of 105 x 65 km and has an age of 45.5 ± 2.5 ka (thousand years). The data resemble two cylindrical fold units, which are located in the lower third of the ice column.

Description: The FINEGIS F2 data set is located in Northern Greenland upstream of the northern branch of the 79° North close to the ice divide. On average the 3D horizon spans an area of 105 x 65 km and has an age of 52.2 ± 2.7 ka (thousand years). The data resemble two cylindrical fold units, which are located in the lower third of the ice column.