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Only a few localised ice streams drain most of the ice from the Greenland Ice Sheet. Thus, understanding ice stream behaviour and its temporal variability is crucially important to predict future sea-level change. The interior trunk of the 700 km-long North-East Greenland Ice Stream (NEGIS) is remarkable due to the lack of any clear bedrock channel to explain its presence. Here, we present a 3-dimensional analysis of the folding and advection of its stratigraphic horizons, which shows that the localised flow and shear margins in the upper NEGIS were fully developed only ca 2000 years ago. Our results contradict the assumption that the ice stream has been stable throughout the Holocene in its current form and show that upper NEGIS-type development of ice streaming, with distinct shear margins and no bed topography relationship, can be established on time scales of hundreds of years, which is a major challenge for realistic mass-balance and sea-level rise projections. The flow of ice streams leaves traces in the stratigraphy of the ice sheets. Made visible by radar, they reveal the history of the upper North East Greenland Ice Stream. The ice stream is found to have existed in its current form for only about the last 2000 years. [ABSTRACT FROM AUTHOR]

We present a dataset of reconstructed three-dimensional (3D) englacial stratigraphic horizons in northern Greenland. The data cover four different regions representing key ice-dynamic settings in Greenland: (i) the onset of Petermann Glacier, (ii) a region upstream of the 79° North Glacier (Nioghalvfjerdsbræ), near the northern Greenland ice divide, (iii) the onset of the Northeast Greenland Ice Stream (NEGIS) and (iv) a 700 km wide region extending across the central ice divide over the entire northern part of central Greenland. In this paper, we promote the advantages of a 3D perspective of deformed englacial stratigraphy and explain how 3D horizons provide an improved basis for interpreting and reconstructing the ice-dynamic history. The 3D horizons are provided in various formats to allow a wide range of applications and reproducibility of results. [ABSTRACT FROM AUTHOR]

We present a high-resolution airborne radar data set (EGRIP-NOR-2018) for the onset region of the Northeast Greenland Ice Stream (NEGIS). The radar data were acquired in May 2018 with the Alfred Wegener Institute's multichannel ultra-wideband (UWB) radar mounted on the Polar 6 aircraft. Radar profiles cover an area of ∼24 000 km 2 and extend over the well-defined shear margins of the NEGIS. The survey area is centered at the location of the drill site of the East Greenland Ice-Core Project (EastGRIP), and several radar lines intersect at this location. The survey layout was designed to (i) map the stratigraphic signature of the shear margins with radar profiles aligned perpendicular to ice flow, (ii) trace the radar stratigraphy along several flow lines, and (iii) provide spatial coverage of ice thickness and basal properties. While we are able to resolve radar reflections in the deep stratigraphy, we cannot fully resolve the steeply inclined reflections at the tightly folded shear margins in the lower part of the ice column. The NEGIS is causing the most significant discrepancies between numerically modeled and observed ice surface velocities. Given the high likelihood of future climate and ocean warming, this extensive data set of new high-resolution radar data in combination with the EastGRIP ice core will be a key contribution to understand the past and future dynamics of the NEGIS. The EGRIP-NOR-2018 radar data products can be obtained from the PANGAEA data publisher (https://doi.pangaea.de/10.1594/PANGAEA.928569 ;). [ABSTRACT FROM AUTHOR]

We present a high-resolution airborne radar data set (EGRIP-NOR-2018) for the onset region of the Northeast Greenland Ice Stream (NEGIS). The radar data were acquired in May 2018 with Alfred Wegener Institute's multichannel ultra- wideband (UWB) radar mounted on the Polar6 aircraft. Radar profiles cover an area of ~24000 km2 and extend over the well- defined shear margins of the NEGIS. The survey area is centred at the location of the drill site of the East Greenland Ice-Core Project (EastGRIP) and several radar lines intersect at this location. The survey layout was designed to: (i) map the stratigraphic signature of the shear margins with radar profiles aligned perpendicular to ice flow, (ii) trace the radar stratigraphy along several flow lines and (iii) provide spatial coverage of ice thickness and basal properties. While we are able to resolve radar reflections in the deep stratigraphy, we can not fully resolve the steeply inclined reflections at the tightly folded shear margins in the lower part of the ice column. The NEGIS is causing the most significant discrepancies between numerically modelled and observed ice surface velocities. Given the high likelihood of future climate and ocean warming, this extensive data set of new high-resolution radar data in combination with the EastGRIP ice core will be a key contribution to understand the past and future dynamics of the NEGIS. The EGRIP-NOR-2018 radar data products can be obtained at the PANGAEA Data Publisher (https://doi.pangaea.de/10.1594/PANGAEA.928569; Franke et al. 2021a). [ABSTRACT FROM AUTHOR]

Understanding the buttressing of floating ice tongues is important to better evaluate the contribution of grounded ice streams to sea-level rise. In Greenland only few floating tongues still exist, such as the one of the 79°N Glacier, an outlet glacier fed by the North East Greenland Ice Stream. Within the project Greenland Ice Sheet Ocean Interaction (GROCE) a team of glaciologists, oceanographers, geophysicists, geodesists, and atmospheric scientists combine measurements and model studies to investigate the dynamics of the 79°N Glacier. We present a glaciological study focusing on the deformation response to ocean tidal forcing by means of observations and modeling. GPS measurements on the 79°N Glacier realized in 2017-2018 allow to analyze vertical and horizontal displacements of the glacier and its ice tongue due to ocean tides. In the hinge zone, i.e. the transition between grounded and floating ice, the tidal forcing leads to bending of the ice and a movement of the grounding line. Observations at stations situated on the fully grounded part reveal phase shifts of horizontal displacements caused by tidal forces in a distance of more than 35 km to the grounding line. In order to model the measured displacements a viscoelastic material is required using the observed vertical displacement at the ice tongue as external forcing. In a purely viscous material model the phase shift of horizontal displacements due to tides cannot be described. Using AWI's new ultrawideband radar, geometries are obtained which form the data basis for the finite element simulations. The results obtained by the viscoelastic Maxwell material model with a nonlinear Glen-type viscosity show the measured phase shift of horizontal displacements on the fully grounded part. This material model combines the typical long-term viscous behavior of ice with the short-term elastic response. Nonlinearities of basal sliding and viscous deformation result in a modified ice outflow across the grounding line and are also included in the model. [ABSTRACT FROM AUTHOR]