HR: 09:30h
AN: C41D-07    [Abstracts]
TI: Extracting Accumulation And Vertical Strain Rate Information From Internal Layering in Ice Penetrating Radar Profiles Over the Greenland Ice Sheet: Basic Assumptions, Recognition of Potential Errors, and Techniques for Large-Area Retrievals
AU: * Fahnestock, M A
EM: mark.fahnestock@unh.edu
AF: CSRC/EOS, University of New Hampshire, 236A Morse Hall Universtiy of New Hampshire, Durham, NH 03824 United States
AB: Tracing of internal layering in aircraft-based-radar profiles of the upper 1500 meters of the ice in the Greenland Ice Sheet allows extension of the age-depth information at deep ice core sites to other parts of the ice sheet. The fitting of a simple model, based on continuity and the assumption of constant rates of strain and accumulation (but not knowledge of ice thickness), allows an estimation of both of these parameters at any point along these profiles where internal layering is well developed. This has been reported on in several places. In this paper, we address the issues behind the use of the relationship between accumulation rate and vertical strain rate at a site to constrain the ice flow responsible for the vertical strain, with a view toward both the potential and limitations of the technique. For example, with the addition of information about the ice thickness from the same radar data, it is possible to show that large areas of the northeast quadrant of the ice sheet are sliding over the bed, and that there are localized areas of sliding in the northwest as well. This method provides a constraint on basal conditions that is useful in modeling the evolution of the ice sheet over time. While there are complications to the layer-tracing approach related to the assumptions of constant accumulation and strain rates, the impact of violations of these assumptions can be constrained from the data. A comparison of 10,000 line kilometers of internal-layer-derived accumulation rate with the NASA PARCA program surface-based accumulation map shows strong agreement in both accumulation rate and spatial variations in that rate, in spite of the longer sampling interval in the internal-layer based estimates.
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting