1. Jet Propulsion Lab, California Institute of Technology, USA
2. NASA Goddard Space Flight Center, Oceans and Ice Branch, Code 971, Greenbelt, Maryland 20771, USA
3. Complex Systems Research Center, Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, New Hampshire 03824, USA
4. Present address: Polar Science Center, Applied Physics Laboratory, University of Washington, 1013 NE 40th Street, Seattle, Washington, 9810-6698, USA

Correspondence to: Ian Joughin^1,4 Email: ian@apl.washington.edu

Abstract

It is important to understand recent changes in the velocity of Greenland glaciers because the mass balance of the Greenland Ice Sheet is partly determined by the flow rates of these outlets. Jakobshavn Isbræ is Greenland's largest outlet glacier¹, draining about 6.5 per cent of the ice-sheet area, and it has been surveyed repeatedly since 1991 (ref. 2). Here we use remote sensing data to measure the velocity of Jakobshavn Isbræ between 1992 and 2003. We detect large variability of the velocity over time, including a slowing down from 6,700 m yr^-1 in 1985 to 5,700 m yr^-1 in 1992, and a subsequent speeding up to 9,400 m yr^-1 by 2000 and 12,600 m yr^-1 in 2003. These changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter³. Our observations indicate that fast-flowing glaciers can significantly alter ice discharge at sub-decadal timescales, with at least a potential to respond rapidly to a changing climate.

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