HR: 0800h
AN: PP21A-1369    [Abstracts]
TI: The White River Ash: New Evidence From the Bona-Churchill Ice Core Record
AU: * Mashiotta, T A
EM: mashiotta.1@osu.edu
AF: Byrd Polar Research Center, The Ohio State University, 1090 Carmack Road, Columbus, OH 43210 United States
AU: Thompson, L G
EM: thompson.3@osu.edu
AF: Byrd Polar Research Center, The Ohio State University, 1090 Carmack Road, Columbus, OH 43210 United States
AU: Davis, M E
EM: davis.3@osu.edu
AF: Byrd Polar Research Center, The Ohio State University, 1090 Carmack Road, Columbus, OH 43210 United States
AB: The White River Ash (WRA) is a well-documented bi-lobate Plinian deposit covering as much as 540,000 square km of the Yukon Territory, Canada and adjoining eastern Alaska. Recent studies have identified the source of the ash as Mount Churchill in the St. Elias Mountains of southeastern Alaska by comparing pumice deposits from the summit area of Mount Churchill with more distal pumice deposits of the WRA (e.g. {\it McGimsey et al., 1990; Richter et al., 1995}). In spring 2002 a team from The Ohio State University's (OSU) Byrd Polar Research Center recovered a 460-m long ice core drilled to bedrock in the col (elevation 4420 masl) between Mount Churchill and Mount Bona (4 km southwest) to reconstruct a proxy climate history for the region. This core is also ideal to assess whether Mount Churchill is the source of the WRA. No evidence of a visible ash layer was encountered during drilling. Borehole temperatures of -24 degrees C at 10m depth and -19.8 degrees C at the ice-bedrock interface indicate the glacier is frozen to its bed. After being returned frozen to OSU the core was cut into 12,162 samples that were analyzed for stable isotopic ratios, insoluble particles and soluble chemistry. A preliminary time scale was developed using annual variations in oxygen isotopes, dust and calcium concentrations, beta-radioactivity (bomb horizons) and well-documented historic volcanic eruptions. The $\sim$1500 year long record shows elevated sulfate values at $\sim$803AD possibly associated with the second of two eruptions in the past 2000 years that produced the eastern lobe of the WRA deposit. The paleoclimate records appear to be stratigraphically continuous and show no evidence of a depositional hiatus. The absence of an ash layer in the core suggests that the WRA deposit requires further investigation, and the source and age of the WRA will be addressed.
DE: 1863 Snow and ice (1827)
DE: 0305 Aerosols and particles (0345, 4801)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting