HR: 11:35h
AN: PP42B-06    [Abstracts]
TI: Early-Holocene Fire, Vegetation, and Climate Linkages in the Mid-Latitudes of Western North and South America
AU: * Whitlock, C
EM: whitlock@montana.edu
AF: Montana State Univ., Dept. Earth Sciences, Bozeman, MT 59715 United States
AU: Bartlein, P
EM: bartlein@uoregon.edu
AF: Univ. Oregon, Dept. Geography, Eugene, OR 97403 United States
AU: Markgraf, V
EM: markgraf@colorado.edu
AF: Univ. Colorado, INSTAAR , Boulder, CO 80903 United States
AU: Bianchi, M
EM: mariam@crub.uncoma.edu.ar
AF: CONICET, CONICET-Univ. Nacional del Comahue, Bariloche, 08400 Argentina
AB: High-resolution fire history data from temperate forests of western North and South America permit examination of regional and hemispheric linkages between Holocene climate, fire, and ecosystem response. Both regions show striking differences in the seasonality of precipitation that influence fire regimes at present, and evidence from the paleorecord suggests that the intensity of these precipitation regimes was affected by large-scale changes in the climate system. At present, summer-dry areas in both hemispheres are dominated by subtropical high pressure systems, and subsidence in these areas suppresses summer precipitation. Summer-wet areas are influenced by onshore flow of moisture from the subtropical Pacific and Atlantic, and monsoonal precipitation increases convectional activity and fire activity east of the Rockies and Andes. In the western U.S., paleoenvironmental data, including vegetation, fire, and lake-level records, suggest that the summer-dry area became drier in the early Holocene with the expansion of the subtropical high-pressure system. Fire and pollen records from summer-wet areas, in contrast, are consistent with wetter-than-present conditions, presumably because summer insolation strengthened summer monsoonal circulation. The network of South American fire records show: (1) an abrupt increase in fire activity at the Pleistocene/Holocene transition at high-latitudes; (2) widespread fire activity and drought in the early Holocene despite the summer-insolation minimum; (3) north-south differences in fire activity in the mid-Holocene suggesting the onset of the current dipole climate, and (4) locally variable fire signals and a shift to smaller surface fires in the late Holocene consistent with cooler conditions and greater interannual variability. Widespread fire activity in southern South America in the early Holocene is consistent with recent model simulations that suggest warmer SSTs, a weakened pole-to-equator temperature gradient, and a southward shift of westerly storm tracks as a result of the strong obliquity forcing (Liu et al., Paleoceanography 18, 2003).
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
DE: 4934 Insolation forcing
DE: 4938 Interhemispheric phasing
DE: 4950 Paleoecology
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005