HR: 14:10h
AN: C53A-03    [Abstracts]
TI: InSAR and GPS Observations Show Seasonal Speedup of Ice Flow in Greenland Following the Onset of Summer Melting
AU: * Joughin, I
EM: ian@apl.washington.edu
AF: Polar Science Center Applied Physics Laboratory University of Washington, 1013 NE 40th Street, Seattle, WA 98105, United States
AU: Das, S B
EM: sdas@whoi.edu
AF: Department of Geology and Geophysics Woods Hole Oceanographic Institution, Woods Hole Road, Woods Hole, MA 02543, United States
AU: King, M A
EM: m.a.king@newcastle.ac.uk
AF: School of Civil Engineering and Geosciences University of Newcastle, Cassie Building, Newcastle Upon Tyne, NE1 7RU, United Kingdom
AU: Smith, B
EM: smithcommaben@gmail.com
AF: Polar Science Center Applied Physics Laboratory University of Washington, 1013 NE 40th Street, Seattle, WA 98105, United States
AU: Howat, I
EM: ihowat@apl.washington.edu
AF: Polar Science Center Applied Physics Laboratory University of Washington, 1013 NE 40th Street, Seattle, WA 98105, United States
AU: Moon, T
EM: twilap@u.washington.edu
AF: Polar Science Center Applied Physics Laboratory University of Washington, 1013 NE 40th Street, Seattle, WA 98105, United States
AB: We have assembled a comprehensive set of InSAR and GPS observations that reveal both spatial and temporal changes in velocity during the summer melt season along a several-hundred kilometer stretch of the ice-sheet margin near Jakobshavn Isbrae, Greenland. In the bare ice zone, we obtain InSAR (speckle/feature tracking) results throughout the melt season that agree well with results from two continuous GPS stations located at roughly 1000 meters elevation. Over much of the slow-moving (100 m/yr) bare-ice zone, the InSAR data show summer speedups of 50-to-100 m/yr averaged over 24 days. We also detect seasonal speedups of similar magnitude on Jakobshavn Isbrae and several smaller fast moving (> 1 km/yr) outlet glaciers. In relative terms, however, the outlet glaciers speedups represent increases of less than 10 % relative to their annual means. Thus, proportionately the slow-moving inland ice is far more sensitive to seasonal speedup than are the rapidly flowing outlet glaciers, making it unlikely that recently reported large (> 1 km/yr) speedups on Jakobshavn and other outlet glaciers can be directly attributed to enhanced basal lubrication from increased surface melt. Similarly, the GPS data also reveal a period of generally enhanced flow extending through the melt season, punctuated by shorter-term speedups lasting a few days. These shorter-term accelerations correlate well with periods of increased surface melt that we inferred from positive-degree-day values measured at the GPS sites. In addition, the short-term accelerations coincide well with GPS-measured periods of peak uplift rates of the ice-sheet surface. The strong correlation of seasonal velocity with melt and uplift rates suggests that surface melt makes its way to bed rapidly, providing enhanced lubrication to regions of the ice sheet extending up to at least 1000 meters elevation. Furthermore, the spatially uniform nature of the speedup in the upper bare-ice zone, where a sparse distribution of moulins delivers water to the bed, suggests the presence of a well distributed sub-glacial drainage network.
DE: 0720 Glaciers
DE: 0726 Ice sheets
DE: 0758 Remote sensing
DE: 0776 Glaciology (1621, 1827, 1863)
SC: Cryosphere [C]
MN: 2007 Fall Meeting