HR: 17:30h
AN: C34A-07    [Abstracts]
TI: Warming-induced glacial advance in Taylor Valley?
AU: * Neumann, T
EM: tneumann@uvm.edu
AF: University of Vermont, Geology Department Delehanty Hall, 180 Colchester Ave, Burlington, VT 05405 United States
AU: Fountain, A
AF: Portland State University, Departments of Geology and Geography, Portland, OR 97207 United States
AB: Changes in the extent of the polar alpine glaciers in Taylor Valley, Antarctica, are important for understanding past climates and changes in ice-dammed lakes. Glacier length changes are slow compared to surface energy balance changes (which govern lake levels) due to the relatively long response time of glaciers. Lyons and others (1998) infer a draw-down 1200 years ago of the lakes in Taylor Valley, when conditions were colder by about 3$^{\circ}$ C compared with today (Clow, pers. comm.). Presumably, colder temperatures reduced melt water production from the glaciers and lake levels dropped. Air temperatures warmed following the drawdown, and increased melt refilled the lakes. Ground-based photography taken over a 20-year period, combined with field survey measurements, show thinning and a 2 to 100m advance for three glaciers in Taylor Valley. While these advances seem to indicate cooler conditions in this part of Antarctica compared to other areas of Antarctica, we propose that long-term climate warming can explain the observed advances through ice softening. We test this hypothesis by using a flow-band model that includes a temperature-dependent softness term and apply the model to Commonwealth Glacier. Results show that a 2$^{\circ}$ C warming 2000 years ago can cause a 25m advance and thinning in the ablation zone, consistent with observations. Increasing the accumulation rate in the accumulation zone by 10% also explains the advance, but predicts 7m of thickening in the ablation zone. Our observations of thinning in the ablation zone thus support a temperature-driven glacial advance rather than an accumulation-driven advance. Our findings indicate that the dynamic behavior of temperate glaciers in response to temperature changes cannot be directly applied to polar glaciers. The sluggish behavior of polar glaciers is a consequence of the ice temperature and small magnitude of mass exchange. These conditions mask an intriguing and complex response to temperature change.
DE: 4540 Ice mechanics and air/sea/ice exchange processes
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting