Journal cover Journal topic
The Cryosphere An interactive open-access journal of the European Geosciences Union
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
28 Jan 2011
Review status
This discussion paper is a preprint. A revision of the manuscript for further review has not been submitted.
Geophysical evidence for soft bed sliding at Jakobshavn Isbrae, West Greenland
A. E. Block1,2 and R. E. Bell2 1Department of Earth and Environmental Sciences, Columbia University, New York, New York, 10027, USA
2Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, 10964, USA
Abstract. Jakobshavn Isbrae is Greenland's fastest moving outlet glacier and a major contributor to sea level rise. We analyze new gravity and magnetic profiles across the glacier, extending from the mouth of the outlet fjord to 64 km inland of the 2008 grounding line. Our results provide new insights into Jakobshavn Isbrae's geologic underpinnings and controls on the basal velocities. Earlier studies of basal processes minimized basal slip as a fast flow mechanism. Currently, velocities are up to double those considered in these studies, necessitating a reanalysis of the basal conditions. The gravity field along the glacier's main trunk cannot be attributed to the gravitational effect of bed topography and the overlying ice sheet. We interpret the remaining gravity signal as evidence of up to 2400 m of low density sediment beneath the main trunk. Examining recent velocities, we find basal slip is a major contributor to ice flow along most of the sediment filled trough. Within 54 km of the grounding line, only isolated 1–3 km wide regions have velocities that possibly result solely from internal deformation of the ice. We conclude soft bed sliding over the thick sediment wedge beneath Jakobshavn Isbrae is the dominant mechanism of fast flow.

Citation: Block, A. E. and Bell, R. E.: Geophysical evidence for soft bed sliding at Jakobshavn Isbrae, West Greenland, The Cryosphere Discuss.,, in review, 2011.
A. E. Block and R. E. Bell
Interactive discussionStatus: closed (peer review stopped)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version      Supplement - Supplement
RC C34: 'Review of Block and Bell', Anonymous Referee #1, 28 Jan 2011 Printer-friendly Version 
RC C139: 'Review', Martin Lüthi, 10 Mar 2011 Printer-friendly Version Supplement 
RC C195: 'Refereed Review by Dr. Theresa Diehl', Theresa Diehl, 25 Mar 2011 Printer-friendly Version Supplement 
EC C204: 'Editor comment', Ian M. Howat, 26 Mar 2011 Printer-friendly Version 
AC C290: 'Review Response', Adrienne Block, 26 Apr 2011 Printer-friendly Version Supplement 
A. E. Block and R. E. Bell
A. E. Block and R. E. Bell


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