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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/tc-2020-103
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2020-103
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  08 May 2020

08 May 2020

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A revised version of this preprint is currently under review for the journal TC.

Surface velocity of the Northeast Greenland Ice Stream (NEGIS): Assessment of interior velocities derived from satellite data by GPS

Christine S. Hvidberg1, Aslak Grinsted1, Dorthe Dahl-Jensen1, Shfaqat Abbas Khan2, Anders Kusk2, Jonas Kvist Andersen2, Niklas Neckel3, Anne Solgaard4, Nanna B. Karlsson4, Helle Astrid Kjær1, and Paul Vallelonga1 Christine S. Hvidberg et al.
  • 1Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
  • 2DTU-Space, Technical University of Denmark, Kgs. Lyngby, Denmark
  • 3Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, Bremerhaven, Germany
  • 4Geological Survey of Denmark and Greenland, Copenhagen, Denmark

Abstract. The Northeast Greenland Ice Stream (NEGIS) extends around 600 km upstream from the coast to its onset near the ice divide in interior Greenland. Several maps of surface velocity and topography in the interior Greenland exist, but the accuracy is not well constrained by in situ observations and limiting detailed studies of flow structures and shear margins near the onset of NEGIS. Here we present the results from a GPS mapping of surface velocity in an area located approximately 150 km from the ice divide near the East Greenland Ice-core Project (EastGRIP) deep drilling site (75°38’ N, 35°60’ W). A GPS strain net consisting of 63 poles was established and observed over the years 2015–2019. The strain net covers 35 km along NEGIS and 40 km across NEGIS, including both shear margins. The ice flows with a uniform surface speed of approximately 55 m a−1 within a > 10 km wide central flow band with strain rates in the order of 10−4 a−1. The strain rates increase in the shear margins by an order of magnitude, and 10–20 m deep shear margin troughs mark a zone with enhanced longitudinal stretching, transverse compression and shear. We compare the GPS results to the Arctic Digital Elevation Model (ArcticDEM) and a list of satellite-based surface velocity products in order to evaluate these products. For each velocity product, we determine the bias and precision of the velocity compared to the GPS observations, as well as the smoothing of the velocity products needed to obtain optimal precision. The best products have a bias and precision of ~0.5 m a−1. We combine the GPS results with satellite-based products and show that organized patterns in flow and topography emerge in the NEGIS ice stream when the surface velocity exceeds approximately 55 m a−1 and are related to bedrock topography.

Christine S. Hvidberg et al.

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Christine S. Hvidberg et al.

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Latest update: 11 Aug 2020
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Short summary
The Northeast Greenland Ice Stream (NEGIS) extends around 600 km from its onset in the interior of Greenland to the coast. Several maps of surface velocity and topography in Greenland exist, but the accuracy is limited due to the lack of validation data. Here we present results from a 5-year GPS survey in an interior section of NEGIS. We use the data to assess a list of satellite derived ice velocity and surface elevation products and discuss the implications for the ice stream flow in the area.
The Northeast Greenland Ice Stream (NEGIS) extends around 600 km from its onset in the interior...
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