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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 09 May 2019

Research article | 09 May 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

Subglacial roughness of the Greenland Ice Sheet: relationship with contemporary ice velocity and geology

Michael A. Cooper1, Thomas M. Jordan1,2, Dustin M. Schroeder2,3, Martin J. Siegert4, Christopher N. Williams1,a, and Jonathan L. Bamber1 Michael A. Cooper et al.
  • 1School of Geographical Sciences, University of Bristol, Bristol, UK
  • 2Department of Geophysics, Stanford University, Stanford, CA., USA
  • 3Department of Electrical Engineering, Stanford University, Stanford, CA., USA
  • 4Grantham Institute, and Department of Earth Science and Engineering, Imperial College London, London, UK
  • anow at: British Geological Survey, Nottingham, UK

Abstract. The subglacial environment of the Greenland Ice Sheet (GrIS) is poorly constrained, both in its bulk properties, for example geology, presence of sediment, and of water, and interfacial conditions, such as roughness and bed rheology. There is, therefore, limited understanding of how spatially heterogeneous subglacial properties relate to ice-sheet motion. Here, via analysis of two decades worth of radio-echo sounding data, we present a new systematic analysis of subglacial roughness beneath the GrIS. We use two independent methods to quantify subglacial roughness: first, the variability of along- track topography—enabling an assessment of roughness anisotropy from pairs of orthogonal transects aligned perpendicular and parallel to ice flow; and second, from bed-echo scattering—enabling assessment of fine-scale bed characteristics. We establish the spatial distribution of subglacial roughness and quantify its relationship with ice flow speed and direction. Overall, the beds of fast-flowing regions are observed to be rougher than the slow-flowing interior. Topographic roughness exhibits an exponential scaling relationship with ice surface velocity parallel, but not perpendicular, to flow direction in fast-flowing regions, and the degree of anisotropy is correlated with ice surface speed. In many slow-flowing regions both roughness methods indicate spatially coherent regions of smooth bed, which, through combination with analyses of underlying geology, we conclude is likely due to the presence of a hard flat bed. Consequently, the study provides scope for a spatially variable hard bed/soft bed boundary constraint for ice-sheet models.

Michael A. Cooper et al.
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Michael A. Cooper et al.
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Subglacial bed roughness of Greenland, provided using two independent metrics M. A. Cooper and T. M. Jordan

Michael A. Cooper et al.
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