HR: 16:15h
AN: B44C-02    [Abstracts]
TI: Synchroneity in Background Charcoal Records From the Northwestern U.S.
AU: * Marlon, J
EM: jmarlon@uoregon.edu
AF: Dept. of Geography, University of Oregon, Eugene, OR 97403 United States
AU: Bartlein, P J
EM: bartlein@uoregon.edu
AF: Dept. of Geography, University of Oregon, Eugene, OR 97403 United States
AU: Whitlock, C
EM: whitlock@uoregon.edu
AF: Dept. of Earth Sciences, Montana State University, Bozeman, MT 59717 United States
AB: Holocene fire-histories have been reconstructed from charcoal accumulation rates (CHAR) in lakes, bogs, and forest soils. "Peaks" in the CHAR data represent discrete fire events or intervals with frequent fires, while slowly varying trends represent "background" changes in regional burning, vegetation (biomass), and/or depositional processes. Background CHAR (BCHAR) data were explored in 15 high-resolution macroscopic charcoal records from the northwestern U.S. to identify widespread patterns. BCHAR was compared with charcoal peak influx and pollen data from the same sediment cores and with geospatial data to explain the patterns. Relative charcoal abundances at different sites were largely explained by local characteristics including lake size and elevation, and watershed area and mean slope. Synchroneity in gradual BCHAR trends, abrupt changes, and variability is further evidence that background variations are controlled primarily by broad-scale forcings, such as changing climate conditions or human activity. During the Holocene, BCHAR rose steadily and reached a maximum at ca. 1600 cal yr BP (AD 400), after which values generally declined to a late-Holocene minimum during the Little Ice Age (600-100 cal yr BP). Background charcoal increased again in the last few centuries. Fire frequency inferred from CHAR peaks showed different long-term trends than the BCHAR data, however fires were very frequent at several sites at ca. 2000 cal yr BP, when BCHAR was near its maximum. Comparisons between BCHAR and arboreal pollen percentages showed that fire activity and fuel levels were highly correlated on centennial and millennial time-scales. These results complement our understanding of northwestern U.S. fire-history based on local fire frequency data. They also demonstrate the sensitivity of high-resolution macroscopic charcoal records to long-term vegetation and climate dynamics.
DE: 3344 Paleoclimatology
DE: 1699 General or miscellaneous
DE: 1812 Drought
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting