HR: 0830h
AN: C11C-0832    [PDF]
TI: A 3-D Thermomechanical Ice-Sheet Model: Preliminary Simulation of the Antarctic Ice Sheet With the Goldsby-Kohlstedt vs. Glen Flow Laws
AU: * Lingle, C S
EM: clingle@gi.alaska.edu
AF: Geophysical Institute, University of Alaska Fairbanks, POB 757320, Fairbanks, AK 99775-7320 United States
AU: Bueler, E L
EM: ffelb@uaf.edu
AF: Dept. of Mathematical Sciences, University of Alaska Fairbanks, POB 756660, Fairbanks, AK 99775-6660 United States
AU: Kallen-Brown, J A
EM: jbrown@gi.alaska.edu
AF: Depts. of Physics and Mathematical Sciences, University of Alaska Fairbanks, POB 755920, Fairbanks, AK 99775-5920 United States
AU: Covey, D N
EM: dnc@gi.alaska.edu
AF: Geophysical Institute, University of Alaska Fairbanks, POB 757320, Fairbanks, AK 99775-7320 United States
AB: We have developed a 3-D coupled time- and temperature-dependent ice-sheet model (still in preliminary form) in which the Goldsby-Kohlstedt (2001) and Glen flow laws can be employed interchangeably. D. Goldsby and D. Kohlstedt found that the constitutive equation for ice is best represented as a nonlinear combination of 4 terms, representing (i) dislocation climb (for which the stress exponent n = 4), (ii) grain size-dependent grain boundary sliding (GBS)-accomodated basal slip (n = 1.8), (iii) basal slip-accommodated GBS (n = 2.4), and (iv) diffusional flow (n = 1). Each term is similar in form to Glen's flow law, but the 4 creep processes are characterized by differing values of material parameter, activation energy, stress exponent, etc. We have verified our model by reproducing the results of EISMINT experiment A, as summarized in Table 4 of Payne et al. (2000), for the case of Glen's flow law. In addition, new analytical solutions have been derived (by E.L.B.) for the cases of (i) a time-dependent, isothermal, circular ice sheet on a flat bed with a mass balance of zero, having all mass concentrated in a delta function at the origin at time zero, and (ii) a coupled time- and temperature-dependent circular ice sheet on a flat bed, with a non-zero distribution of mass balance. In both cases, the ice rheology is represented by Glen's flow law. We find that our model reproduces these analytical solutions, which provide a means for verifying the correctness of thermomechanical ice-sheet models without resorting to intercomparison exercises (e.g., Huybrecht et al., 1996; Payne et al., 2000). The cause of the "spoked" patterns of simulated basal melting that are characteristic of time-dependent temperature-coupled ice-sheet models with idealized geometries consisting of circular ice caps on flat beds has been identified (see e.g. Payne et al., 2000), and a method for resolving this problem has been developed (by J.A.K.-B.). Comparisons of the Goldsby-Kohlstedt vs. Glen flow laws have been carried out for the time evolution of idealized circular ice sheets on flat beds. Preliminary time- and temperature-dependent simulations of the Antarctic ice sheet using the Goldsby-Kohlstedt vs. Glen flow laws will be summarized. References: Goldsby, D.L., and D.L. Kohlstedt. 2001. Superplastic deformation of ice: experimental observations. J. Geophys. Res., 106(B6), 11017-11030. Huybrecht, P., T. Payne, and The EISMINT Intercomparison Group. 1996. The EISMINT benchmarks for testing ice-sheet models. Ann. Glaciol., 23, 1-12. Payne, A.J., and 10 others. 2000. Results from the EISMINT model intercomparisons: the effects of thermomechanical coupling. J. Glaciol., 46(153), 227-238.
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2003 Fall Meeting