Description: Fast flowing ice streams are known to contribute in a large proportion to continental ice sheet discharge and contribute therefore to sea level variability. In this study we investigate internal layering, stratigraphy and bedrock topography of an active ice stream in North East Greenland. In conjunction with data of physical properties of the EastGRIP Ice Core it enables us to expand insights from a selective data set over a broader area to gain insights into the complex mechanisms governing ice streams. We acquired airborne radar data at the North East Greenland Ice Stream in the vicinity of EastGRIP Drill Site. The data has been recorded in May 2018 in different acquisition modes with AWI’s Ultra-wideband multichannel radar installed on the AWI Polar6 Basler BT-67 aircraft. A total area of 16000 km^2 has been mapped with profiles along and perpendicular to ice flow direction. The area in direct vicinity to the drill site is has been covered with a profile spacing of 5 km, further downstream and upstream the profile distance is10 km. The survey area reaches from 150 km upstream to 150 km downstream of the drilling sites, and also includes both shear margins and parts of the slow flowing areas adjacent to the ice stream. The data have been processed and are currently evaluated for bedrock topography and 3D shape of distortion of internal layers. Our high resolution radargrams provide detailed insights into the bedrock topography, including the ~500 m step just upstream of the drill site and flow parallel bed ridges within the ice stream. Moreover, we mapped the distortion of internal reflectors within the shear margins of the ice stream in great detail, and captured the radar stratigraphy signature of a shift in the north-western shear margin. Outside of the ice stream large scale fold structures parallel to the main trunk of NEGIS were mapped.

Description: Antarctic ice shelves often contain narrow, curvilinear tracts of thin ice, termed ice-shelf channels, that impact ice-shelf stability. Their surface depressions appear prominently in satellite imagery and form an interesting morphology of unknown origin, the more so because the processes leading to ice-shelf channel formation are unclear. Here we investigate the origin of ice-shelf channels at the Roi Baudouin Ice Shelf, which have previously been attributed to ice overriding sediment ridges formed by long-term deposition in subglacial water conduits. However, due to a limited radar dataset at the time, the shape and upstream extent of the basal obstacles was unclear, making it difficult to pinpoint the exact type of the subglacial landform. In 2019, we revisted this location with an improved airborne ultra-wideband radar and collected a number of across-flow profiles upstream of the grounding line. Consistent with previous suggestions, we find that the basal obstacles shrink in size with increasing distance from the grounding line until they are invisible about 10 km upstream. However, the change in size is gradual in the first 8 km, and then very abrupt in the last 2 km. Variations in basal reflectivity indicate the existence of patches of subglacial water in all profile lines. Once fully evaluated, this rich dataset has the potential to classify the basal landform and hence shed light on the origin of ice-shelf channels and their impact on ice-shelf stability.

Description: In connection with the East Grip ice core drilling project airborne and groundbased multichannel radar systems were used to look in detail at the internal structures inside and outside of the Northeast Greenland Icestream. While the icestream margins surface expression is just delineated by slight depressions their internal structures are characterized by rather complicated multifold elements. These features hopefully can be used to better characterize the dynamics inherent in icestream systems.

Description: Ice streams are fast moving regions within the large ice sheets of Greenland and Antarctica. Recent developments of high resolution ice sounding radar systems for deployment from an aircraft or on the ground allow a detailed view of internal structures associated with the particular stress and strain fields related to the particular flow fields across the margins between slow and fast moving ice. Exemplary data will be shown from the margins of the North-East Greenland ice stream which were obtained in association with the EASTGRIP icecore drilling project.

Description: The internal layer architecture and crystal anisotropy in ice are two main parameters to take into account for analysing particle signals within the IceCube and follow-on arrays. Using airborne and ground-based radar measurements we present a new approach to especially define the horizontal anisotropy of the bulk fabric in ice and suggest implementation during pre-site surveys in particular for the RNO-G test array near Summit, Greenland.

Description: Advances in radio-echo sounding technology over the last two decades made it possible to map complex englacial structures in the lower part of the Greenland and Antarctic Ice Sheet. Deformation structures are made visible by distorted isochrones acting as radar reflectors. Decoding the formation history of these structures offers an excellent possibility to reconstruct past ice movements, and thus provides an additional archive about processes on the earth's surface in the past. In this study, we use ultra-wideband ice-penetrating radar data to map the deformation of the radar stratigraphy in Northern Greenland. We construct 3-dimensional horizons from folded radar layers of features which show no apparent link to the current velocity field or the regional bed topography. Furthermore, we are able to constrain the geometry and spatial extend of folds, which suggests that they were formed in several stages and in a different ice-dynamic setting than the present one in Northern Greenland.

Description: The Northeast Greenland Ice Stream (NEGIS) is an important dynamic component contributing to the total mass balance of the Greenland ice sheet, as it reaches up to the central divide and drains 12% of the ice sheet. The ice stream geometry and surface velocities in the onset region of the NEGIS are not yet sufficiently well reproduced by ice sheet models. We present an assessment of the basal conditions of the onset region in a systematic analysis of airborne ultra-wideband radar data. Our data yield a new detailed model of ice-thickness distribution and basal topography in the upstream part of the ice stream. We observe a change from a smooth to a rougher bed where the ice stream widens from 10 to 60 km, and a distinct roughness anisotropy, indicating a preferred orientation of subglacial structures. The observation of off-nadir reflections that are symmetrical to the bed reflection in the radargrams suggests that these structures are elongated subglacial landforms, which in turn indicate potential streamlining of the bed. Together with basal water routing pathways, our observations hint to two different zones in this part of the NEGIS: an accelerating and smooth upstream region, which is collecting water, with reduced basal traction, and in the further downstream part, where the ice stream is slowing down and is widening, with a distribution of basal water towards the shear margins. Our findings support the hypothesis that the NEGIS is strongly interconnected to the subglacial water system in its onset region, but also to the subglacial substrate and morphology.

Description: The effect of grain size on strain rate of ice in the upper 2207 m in the North Greenland Eemian Ice Drilling (NEEM) deep ice core was investigated using a rheological model based on the composite flow law of Goldsby and Kohlstedt (1997, 2001). The grain size was described by both a mean grain size and a grain size distribution, which allowed the strain rate to be calculated using two different model end-members: (i) the microscale constant stress model where each grain deforms by the same stress and (ii) the microscale constant strain rate model where each grain deforms by the same strain rate. The model results predict that grain-size-sensitive flow produces almost all of the deformation in the upper 2207 m of the NEEM ice core, while dislocation creep hardly contributes to deformation. The difference in calculated strain rate between the two model end-members is relatively small. The predicted strain rate in the fine-grained Glacial ice (that is, ice deposited during the last Glacial maximum at depths of 1419 to 2207 m) varies strongly within this depth range and, furthermore, is about 4–5 times higher than in the coarser-grained Holocene ice (0–1419 m). Two peaks in strain rate are predicted at about 1980 and 2100 m depth. The prediction that grain-size-sensitive creep is the fastest process is inconsistent with the microstructures in the Holocene age ice, indicating that the rate of dislocation creep is underestimated in the model. The occurrence of recrystallization processes in the polar ice that did not occur in the experiments may account for this discrepancy. The prediction of the composite flow law model is consistent with microstructures in the Glacial ice, suggesting that fine-grained layers in the Glacial ice may act as internal preferential sliding zones in the Greenland ice sheet.

Description: The North East Greenland Ice Stream (NEGIS) is one of the largest ice streams, reaching far inland and draining 12% of the interior Greenland ice mass towards the ocean. Ice flow dynamics and subglacial properties of large parts of the NEGIS are not well studied or understood but are necessary to improve the accuracy of sea-level projections. Here,we present a record of more than 8000km of radar survey lines of radio echo sounding data covering an area of 24 000km^2 centred on the drill site for the East Greenland Ice-core Project (EGRIP) in the central part of the NEGIS. The acquisition system was a multichannel ultra-wideband radar mounted on AWI’s Polar6 aircraft. Our data yield a newdetailedmodel of ice-thickness distribution and basal topography in the region. Subglacial bedrock structures and reflection patterns indicate traces of the activity of the NEGIS such as elongated structures in ice flow direction and features indicating erosion and deposition of sediments.