HR: 0800h
AN: B41B-0102    [Abstracts]
TI: Fire-Climate Linkages in the Northern Rocky Mountains During the Holocene
AU: * Power, M
EM: mpower@darkwing.uoregon.edu
AF: University of Oregon, Department of Geography, Eugene, OR 97403 United States
AU: Whitlock, C
EM: whitlock@montana.edu
AF: Montana State University, Department of Earth Sciences, Bozeman, MT 59717 United States
AU: Bartlein, P
EM: bartlein@uoregon.edu
AF: University of Oregon, Department of Geography, Eugene, OR 97403 United States
AB: Foy Lake, located in low elevation forests of northwestern Montana, provides records of annual-to-decadal-scale landscape change for the last 13,000 years. Sedimentary charcoal and pollen analyses were used to document fire-climate linkages in the Northern Rocky Mountains (NRM) to improve the interpretation of lake-sediment records of fire activity. This paper focuses on the climate controls that suppress and promote fire activity on seasonal-to-decadal time-scales and the ability of lake-sediment proxies from the NRM to record past fire activity occurring at different spatial and temporal scales. Annually-sampled charcoal in lake-sediment cores is compared with evidence of known fires identified from historic fire atlases and fire-scarred tree-ring studies. Historical records of fire near Foy Lake, including the AD 1910 fires that burned over two million acres in Idaho and Montana, are used as a baseline for the analysis of sedimentary charcoal influx during Holocene fire episodes. During recent drought and fire years in the NRM, anomalously higher-than-normal 500mb geopotential heights in summer extended across the Pacific and into northwestern North America and produced stronger westerlies, increased subsidence off the eastern north Pacific and western North America, and suppressed precipitation. Large fire years in the early 20th century, including AD 1910, are associated with above average spring precipitation, higher-than-normal spring temperatures, followed by lower-than normal summer precipitation. The long-term record of sedimentary charcoal and pollen at Foy Lake shows that fire activity (inferred from the frequency of charcoal peaks) was initially low during the early Holocene, increased between 7000 to 5000 cal yr BP, and then decreased from 3800 to 2200 cal yr BP. Fire frequency increased from 7 episodes/1000 years at 2200 cal yr BP to 14 episodes/1000 years at 800 cal yr BP. Fire episodes reached a maximum at ca. 500 cal yr BP and then decreased to present levels.
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting