HR: 1340h
AN: C23A-1163    [Abstracts]
TI: Resolving Accumulation-Rate Patterns Using Ice-Flow Inverse Methods
AU: * Koutnik, M R
EM: mkoutnik@ess.washington.edu
AF: University of Washington, Department of ESS Box 351310, Seattle, WA 98195 United States
AU: Waddington, E D
EM: edw@ess.washington.edu
AF: University of Washington, Department of ESS Box 351310, Seattle, WA 98195 United States
AU: Neumann, T A
EM: tneumann@uvm.edu
AF: University of Vermont, 213 Delehanty Hall Department of Geology, Burlington, VT 05405 United States
AB: Internal layers detected by ice-penetrating radar can be used to infer spatial patterns of accumulation. For upper layers (within a few percent of the total ice thickness) finite strain can be neglected ("Shallow-Layer Approximation") or approximated with a local 1-D flow model ("Local-Layer Approximation"). However, these simple methods cannot be applied to "deep" internal layers, which reflect longer-term changes in climate, because spatially variable ice strain and accumulation rate affect layer depths. We have developed a robust method that is capable of inferring patterns of accumulation from these older, deeper layers. We predict depths of internal layers with a forward model that calculates particle paths and internal-layer shapes in a flow band. Observed layer depths are assimilated using geophysical-inverse methods, in order to find robust estimates of accumulation patterns. We incorporate an objective tolerance criterion to prevent over-fitting the data. We also want to know whether the data and the model are capable of resolving the accumulation patterns. The model resolution function determines how closely the individual model parameters (i.e. accumulation-rate distribution in space and time) can be individually determined, or whether only broad averages can be resolved. We can also calculate the data importance, indicating the extent to which each data value contributes to the solution. This model has been be applied near Taylor Dome, and will next be applied near the upcoming inland West Antarctic ice-core site.
DE: 0726 Ice sheets
DE: 0774 Dynamics
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 0798 Modeling
SC: Cryosphere [C]
MN: Fall Meeting 2005