HR: 0800h
AN: H51G-0448    [Abstracts]
TI: Modeling Langjokull ice cap through the Holocene
AU: * Flowers, G E
EM: gflowers@sfu.ca
AF: Department of Earth Sciences Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6 Canada
AU: Björnsson, H
EM: hb@raunvis.hi.is
AF: Science Institute University of Iceland, Sturlugata 7, Reykjavik, IS-101 Iceland
AU: Marshall, S J
EM: marshals@ucalgary.ca
AF: Department of Geography University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4 Canada
AU: Clarke, G K
EM: gclarke@eos.ubc.ca
AF: Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T1Z4 Canada
AB: Seismic studies and coring of proglacial lake Hvítárvatn, central Iceland, have revealed a detailed sedimentological history from which Holocene environmental conditions can be interpreted. These records indicate decisive shifts in sediment provenance over the last 10,000 years, which in turn provide constraints on the distribution and activity of ice in the Hvítárvatn catchment. The emerging interpretation is that the Hvítárvatn catchment was ice-free in the early Holocene, with Langjökull ice cap reaching its Holocene maximum during the Little Ice Age. To assess the validity of this interpretation from a glaciological standpoint, we use numerical models of ice dynamics and hydrology to investigate the climatic conditions under which the proposed glacial history is possible. The structure of temporal fluctuations in air temperature through the Holocene are taken from the NGRIP oxygen isotope record and referenced to a spatially-resolved 1961--1990 temperature map of the area. A reference precipitation field is derived from modern winter balance measurements. Calibration simulations of Langjökull's recent history (1600 to present) are used to tune the climate input fields and refine model parameters as a starting point for millennial-scale simulations. Because of the gentle topography underlying the ice cap, Langjökull is sensitive to small changes in temperature and precipitation, with the northern sector of the ice cap being especially mobile in response to changes in winter precipitation patterns. Due to its small size, the ice cap is also sensitive to high-frequency (interannual to decadal) temperature fluctuations. Simulations show that under certain climate scenarios, Langjökull reaches its present size from ice-free conditions in roughly 2000 years. A limited number of simulations exhibit a period of ice growth associated with the 8.2 ka BP cooling, and nearly all simulations sustain a period of 3000--6000 years of ice-free conditions in the mid-Holocene. Numerical results also reveal the lake record to be preferentially sensitive to glaciation in the northern sector of the catchment area. A complete picture of the glacial history thus requires merging of empirical and numerical modeling results.
DE: 0720 Glaciers
DE: 1621 Cryospheric change (0776)
DE: 1630 Impacts of global change (1225)
DE: 1863 Snow and ice (0736, 0738, 0776, 1827)
DE: 9315 Arctic region (0718, 4207)
SC: Hydrology [H]
MN: Fall Meeting 2005