Sustained high basal motion of the Greenland ice sheet revealed by borehole deformation

Ice deformation and basal motion characterize the dynamical behavior of the Greenland ice sheet (GrIS). We evaluate the contribution of basal motion from ice deformation measurements in boreholes drilled to the bed at two sites in the western marginal zone of the GrIS. We find a sustained high amount of basal motion contribution to surface velocity of 44–73% in winter, and up to 90% in summer. Measured ice deformation rates show an unexpected variation with depth that can be explained with the help of an ice-flow model as a consequence of stress transfer from slippery to sticky areas. This effect necessitates the use of high-order ice-flow models, not only in regions of fast-flowing ice streams but in all temperate-based areas of the GrIS. The agreement between modeled and measured deformation rates confirms that the recommended values of the temperature-dependent flow rate factor A are a good choice for ice-sheet models. DOI: https://doi.org/10.3189/2014JoG13J196 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-101718 Published Version Originally published at: Ryser, Claudia; Lüthi, Martin P; Andrews, Lauren C; Hoffman, Matthew J; Catania, Ginny A; Hawley, Robert L; Neumann, Thomas A; Kristensen, Steen S (2014). Sustained high basal motion of the Greenland ice sheet revealed by borehole deformation. Journal of Glaciology, 60(222):647-660. DOI: https://doi.org/10.3189/2014JoG13J196 Sustained high basal motion of the Greenland ice sheet revealed by borehole deformation Claudia RYSER,1 Martin P. LÜTHI,1⇤ Lauren C. ANDREWS,2;3 Matthew J. HOFFMAN,4 Ginny A. CATANIA,2;3 Robert L. HAWLEY,5 Thomas A. NEUMANN,6 Steen S. KRISTENSEN7 1Versuchsanstalt für Wasserbau, Hydrologie und Glaziologie (VAW), Zürich, Switzerland E-mail: [email protected] 2Institute for Geophysics, University of Texas at Austin, Austin, TX, USA 3Department of Geological Sciences, University of Texas at Austin, Austin, TX, USA 4Fluid Dynamics and Solid Mechanics Group, Los Alamos National Laboratory, Los Alamos, NM, USA 5Department of Earth Sciences, Dartmouth College, Hanover, NH, USA 6NASA Goddard Space Flight Center, Greenbelt, MD, USA 7National Space Institute, Technical University of Denmark, Lyngby, Denmark ABSTRACT. Ice deformation and basal motion characterize the dynamical behavior of the Greenland Ice deformation and basal motion characterize the dynamical behavior of the Greenland ice sheet (GrIS). We evaluate the contribution of basal motion from ice deformation measurements in boreholes drilled to the bed at two sites in the western marginal zone of the GrIS. We find a sustained high amount of basal motion contribution to surface velocity of 44–73% in winter, and up to 90% in summer. Measured ice deformation rates show an unexpected variation with depth that can be explained with the help of an ice-flow model as a consequence of stress transfer from slippery to sticky areas. This effect necessitates the use of high-order ice-flow models, not only in regions of fast-flowing ice streams but in all temperate-based areas of the GrIS. The agreement between modeled and measured deformation rates confirms that the recommended values of the temperature-dependent flow rate factor A are a good choice for ice-sheet models.