HR: 0800h
AN: C51A-0272    [Abstracts]
TI: Cold Debris Entrainment at Taylor Glacier, Antarctica: Implications for Its Basal Thermal Regime
AU: * Samyn, D
EM: desamyn@ulb.ac.be
AF: Glaciology Unit, Université Libre de Bruxelles, 50, Av. F.D. Roosevelt CP160/03, Brussels, 1050 Belgium
AU: Fitzsimons, S J
EM: sjf@geography.otago.ac.nz
AF: Department of Geography, University of Otago, 85 Albany St P.O. Box 56, Dunedin, 9001 New Zealand
AU: Lorrain, R D
EM: rlorrain@ulb.ac.be
AF: Glaciology Unit, Université Libre de Bruxelles, 50, Av. F.D. Roosevelt CP160/03, Brussels, 1050 Belgium
AB: Taylor Glacier is an outlet glacier from the East Antarctic Ice Sheet, draining continental flow through Taylor Valley and toward McMurdo Sound. As is the case for most glaciers from the Dry Valleys, Taylor Glacier was less extensive than at present during the last glacial maximum and has since expanded, reaching now its maximum Holocene extension. Bonney drift, which can be followed from the valley floor up to 300 m elevation on the valley walls, affords evidence of even larger expansion of Taylor Glacier during the last interglacial period. Taylor Glacier is commonly considered as having a polythermal regime. Though this glacier be one of the most studied from the Dry Valleys and despite the remarkable opportunity that it provides to study past glacier adjustments to environmental changes in the area, little is known on its basal regime. In this perspective, we report herein the results of multi-parametric studies of a debris-laden ice sequence excavated from a 25 m-long tunnel at the snout of the glacier. The sampled basal ice sequence is 4 m-thick, of which the half presents a high debris content (> 30 % vol.), and is currently at the temperature of -15 °C. The results are three-fold: (1) gas analyses reveal the occurrence of differential dissolution of gases at structural interfaces. These gas changes are typical of water phase changes involving minute liquid water volumes; (2) stable isotope analyses show that the samples from the whole stacked sequence are aligned in a general framework along the Local Meteoric Water Line. Bulk freeze-on may thus be rejected as accounting for basal ice formation; (3) crystallographic analyses provide evidence for lattice loosening at structural interfaces, denoting strain variations and possibly slight fluctuations in interstitial liquid content. Given the subfreezing temperature of the basal ice sequence, our results point to a strong influence of intercrystalline/interfacial liquid water during the development and evolution of debris-laden ice at the base of the glacier. These results also indicate that the debris-rich ice observable in the marginal zone cannot be the result of extensive thawing and refreezing along the glacier course. Wet-based conditions were thus precluded during debris entrainment. Since basal ice dynamics are extremely slow under cold conditions and given the abundance of debris at the base of the glacier, basal ice formation must thus have spanned over a significant period of time, implying cold conditions far away up glacier. This is consistent with recent thermal and geophysical modelling of the glacier.
DE: 0776 Glaciology (1621, 1827, 1863)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 8012 High strain deformation zones
DE: 8045 Role of fluids
SC: Cryosphere [C]
MN: Fall Meeting 2005