High resolution subglacial topography from airborne swath radar beneath the Northeast Greenland Ice Stream (NEGIS)

Here we present an extensive swath radar dataset collected in the onset region of the Northeast Greenland Ice Stream, surrounding the East Greenland Ice Core Project site (EGRIP). We produce a new digital elevation model (DEM) of the subglacial topography at a resolution of 25 m, covering a study area of 40 km by 60 km. The data was collected using the AWI airborne ultra-wideband radar system, in profiles mainly perpendicular to the ice flow direction with a spacing of 2 km so that the swaths overlapped.

The high-resolution subglacial topography DEM shows subglacial landforms beneath an active ice stream, located approximately 600 km into the interior of the ice sheet. These landforms indicate spatially variable bed conditions which are partly reflected in the surface velocity field. Some features appear to be crag and tail formations up to 4 km in length, with steep stoss-side slopes and tapering lee-side tails which are oriented in the direction of ice flow. Megascale glacial lineations up to 7 km in length are evident, but appear restricted to the inner ice stream within the modern shear margins, where the ice flow velocity increases from approximately 11 m/a to 58 m/a. Meltwater channels curve around a high point in the topography, which are on the scale of tunnel valleys formed from subglacial meltwater incision. Seismic data located in a channel at the eastern shear margin indicates soft sedimentation inflow. In summary, differences in landform morphology can be seen within and outside of the ice stream shear margins, indicating that NEGIS ice flow may have been transitory in this region.

This survey provides a new insight into the active subglacial environment of a Greenlandic ice stream, matching in quality surveys from ice-free land surface or marine areas. Further analysis will contribute to the understanding of how glacially sculpted landscapes are formed, as well as the effects of small-scale topography on the dynamics and the surface of the overlying ice sheet, in particular ice streams. Moreover, the dataset emphasises the usage of swath radar mapping of bedforms and thus a more widespread application of this method in all radar surveys.