Ian Joughin et al., J. Geophys. Res., 113, Continued evolution of Jakobshavn Isbrae following its rapid speedup

Journal of Geophysical Research, 113 (2008) F04006; doi: 10.1029/2008JF001023

Continued evolution of Jakobshavn Isbrae following its rapid speedup

Continued evolution of Jakobshavn Isbrae following its rapid speedup

Ian Joughin (Applied Physics Laboratory, Polar Science Center, University of Washington, Seattle, WA, U.S.A.), Ian M. Howat (Byrd Polar Research Center, School of Earth Sciences, Ohio State University, Columbus, OH, U.S.A.), Mark Fahnestock (Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH, U.S.A.), Ben Smith (Applied Physics Laboratory, Polar Science Center, University of Washington, Seattle, WA, U.S.A.), William Krabill (Cryospheric Sciences Branch, Wallops Flight Facility, Goddard Space Flight Center, NASA, Wallops Island, VA, U.S.A.), Richard B. Alley (Department of Geosciences, and Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA, U.S.A.), Harry Stern (Applied Physics Laboratory, Polar Science Center, University of Washington, Seattle, WA, U.S.A.) and Martin Truffer (Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK, U.S.A., and

Versuchsanstalt für Wasserbau, Hydrologie und Glaziologie, ETH Zürich, Zürich, Switzerland)

Abstract

Several new data sets reveal that thinning and speedup of Jakobshavn Isbrae continue, following its recent rapid increase in speed as its floating ice tongue disintegrated. The present speedup rate of ∼5% a⁻¹ over much of the fast-moving region appears to be a diffusive response to the initial much larger speedup near the front. There is strong seasonality in speed over much of the fast-flowing main trunk that shows a good inverse correlation with the seasonally varying length of a short (typically ∼6 km) floating ice tongue. This modulation of speed with ice front position supports the hypothesis that the major speedup was caused by loss of the larger floating ice tongue from 1998 to 2003. Analysis of image time series suggests that the transient winter ice tongue is formed when sea ice bonds glacier ice in the fjord to produce a nearly rigid mass that almost entirely suppresses calving. Major calving only resumes in late winter when much of this ice clears from the fjord. The collapse of the ice tongue in the late 1990s followed almost immediately after a sharp decline in winter sea-ice concentration in Disko Bay. This decline may have extended the length of the calving season for several consecutive years, leading to the ice tongue's collapse. 

Received 21 March 2008; accepted 27 August 2008; published 28 October 2008. 

Citation: Joughin, I., I. M. Howat, M. Fahnestock, B. Smith, W. Krabill, R. B. Alley, H. Stern, and M. Truffer (2008), Continued evolution of Jakobshavn Isbrae following its rapid speedup, J. Geophys. Res., 113, F04006, doi:10.1029/2008JF001023.

Link:  http://www.agu.org/pubs/crossref/2008/2008JF001023.shtml