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Summary of Proposal HYD0377

TitleOutlet glacier and ice stream dynamics
Investigator Joughin, Ian - University of Washington, Polar Science Center
Team Member
Dr Joughin, Ian - University of Washington, Polar Science Center
Dr Smith, Ben - University of Washington, Polar Science Center
Dr Howat, Ian - The Ohio State University, Byrd Polar
Das, Sarah - Woods Hole Oceanographic Institution, Dept. Of Geology and Geaphysics
SummaryGreenlandís mass balance, the difference between annual snowfall and ice loss from melting and iceberg calving, has changed dramatically over the last several years. Estimates of Greenlandís contribution to sea level in the mid-1990ís ranged from slightly positive to a mass loss of up to 50 Gtons/yr (0.14 mm/yr of sea level change) [e.g. Thomas, et al., 2006; Zwally, et al., 2005]. One of the first large changes was the rapid disintegration and near-doubling in speed of Jakobshavn Isbrae, Greenlandís largest outlet glacier (see Figure 1) [Joughin, et al., 2004; Thomas, 2004]. Large speedups soon followed on Greenlandís second and third largest outlet glaciers, Kangerdlugssuaq and Helheim [Howat, et al., 2005; Luckman, et al., 2006]. Over the same period nearly all of the glaciers along Greenlandís southeast coast sped up by 50% or more [Rignot and Kanagaratnam, 2006]. Collectively, these accelerations have increased discharge of ice to the ocean by just over 101 Gtons/yr (0.28 mm/yr) [Rignot and Kanagaratnam, 2006]. The highly-variable dynamics of outlet glaciers suggest that recent Greenland observations provide only isolated snapshots of mass balance [Howat, et al., in press]. Therefore, special care must be taken in how these and other mass-loss estimates are evaluated, particularly when extrapolating to the future, since short-term spikes could yield erroneous long-term trends. Rather than yielding a well-defined trend, recent results are significant in that they show Greenland mass balance can fluctuate rapidly and unpredictably. Therefore, accurate estimates of Greenlandís mass-balance and a firm understanding of the dynamics that drive mass balance will require annual-to-sub-annual observations of outlet glacier variability to avoid aliasing of this rapidly varying signal. Our project will use TerraSARX data to measure ice velocity on several fast-moving glaciers in Greenland, continuing our ongoing studies in these areas. Specifically, we will build time series of velocity on rapidly changing glaciers to help determine the link between these changes and climate. Such links are currently poorly understood, which led to large uncertainties in the recent IPCC report.

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