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HR: 12:05h
AN: C52A-08
TI: Origin, Evolution, and Preservation of Cold Based Debris Covered Glaciers: Quantifying Sublimation Rates of Ancient Buried Ice in Antarctica
AU: * Kowalewski, D E
AF: Boston University, Department of Earth Sciences, 675 Commonwealth Ave., Boston, MA 02215, United States
AU: Marchant, D R
AF: Boston University, Department of Earth Sciences, 675 Commonwealth Ave., Boston, MA 02215, United States
AB: Growing interest in our planet's climate history has placed a premium on acquiring detailed records of past climate change. Of considerable interest are archives of ancient atmosphere trapped within the debris-covered alpine glaciers of the western Dry Valleys region of Antarctica. The Mullins Valley debris-covered glacier (~8 km in length) is sourced from local snowfall at the steep headwall of the valley. The first 1.2 km of this glacier is generally free of overlying debris except for isolated cobbles and boulders. Thereafter, the ice surface is covered with a thin, continuous sheet of dolerite-rich rubble. Factors that influence the origin and modification of this ice include atmospheric temperature and relative humidity, precipitation, incoming solar radiance, surface albedo, till texture, winds, surface roughness, salts, and secondary ice lenses. We applied a diffusion model to track vapor flux within a sublimation till overlying the Mullins Valley debris-covered glacier, purportedly the world's oldest debris-covered alpine glacier. As input, we used meteorological data from HOBO data loggers that captured climate change and till temperatures. Results show that vapor flows into and out of the sublimation till at rates dependent on the non-linear variation of soil temperature with depth. Sublimation rates along the Mullins Glacier varied as a function of till thickness, local climate (using a calculated regional lapse rate of 0.88C per 100 m), and till texture. Ice loss during the study interval (November 27, 2006 to December 24, 2006) ranged from as high as 2.12 mm for exposed glacier ice in the upper ablation zone, to as low as 0.01 mm for buried ice beneath till >50 cm in thickness. Averaged over the entire ablation zone (6.7 km2), this yields a net ice-surface lowering of 0.32 mm during the study interval. Numerical modeling suggests that a modest ice accumulation rate at the headwall of ~1 cm a-1 appears sufficient to maintain current ice volumes. Overall, our model results are consistent with an inferred Miocene age for distal portions of the Mullins Valley debris-covered glacier and suggests that ancient atmosphere may be preserved in buried glaciers in the western Dry Valleys region.
DE: 0702 Permafrost (0475)
DE: 0722 Rock glaciers
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1823 Frozen ground
DE: 9310 Antarctica (4207)
SC: Cryosphere [C]
MN: 2007 Fall Meeting

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