Ultra-wideband radar data upstream of the northern catchment of the Nioghalvfjerdsbrae (79°North Glacier), Northeast Greenland

Here we present ultra-wideband radio-echo sounding data in northeast Greenland upstream of the northern catchment of the Nioghalvfjerdsbrae (79°North Glacier; 79NG). The radar data were acquired with AWI's multi-channel ultra-wideband (UWB) radar system in 2018. Most radar lines are located close to the ice divide; where ice flow velocity is almost zero and increases eastwards to as much as 15 meters per year. The survey was designed to closely investigate a set of folds. Twelve RES profiles were flown, at 7.5 km spacing, and oriented perpendicular to the 100° true North trend of the fold axes. The radar data has been used to decipher the regional ice-flow history of the northeastern Greenland Ice Sheet based on its internal stratigraphy. We applied a three-dimensional reconstruction of time-equivalent horizons to map folds deep below the surface that we then attribute to the deformation caused by now-extinct ice streams. We propose that locally this ancient ice flow regime was much more focused and reached much further inland than today's and was deactivated when the main drainage system was reconfigured and relocated southwards. The insight that major ice streams in Greenland might start, shift or abruptly disappear will affect future approaches to understanding and modeling the response of Earth's ice sheets to global warming.