HR: 1340h
AN: PP13C-1421    [Abstracts]
TI: Speleothem-based Holocene Climate History in Southwestern Oregon
AU: * Ersek, V
EM: ersekv@geo.oregonstate.edu
AF: Department of Geosciences, Oregon State University, Corvallis, OR 97331, United States
AU: Clark, P U
EM: clarkp@geo.oregonstate.edu
AF: Department of Geosciences, Oregon State University, Corvallis, OR 97331, United States
AU: Mix, A C
EM: mix@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Science, Oregon State University, Corvallis, OR 97331, United States
AU: Cheng, H
EM: cheng021@umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, United States
AU: Edwards, L R
EM: edwar001@umn.edu
AF: Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, United States
AB: We present a high-resolution reconstruction of Holocene climate using stable isotopes in speleothems from Oregon Caves National Monument (OCNM) in southwestern Oregon, USA (42°N, 123°W). OCNM is strongly influenced by air masses originating in the Pacific Ocean and is strategically situated in an area where storm tracks are entering North America. The age control of the speleothem record is given by 9 U-series dates with an average analytical error of 123 years. Preliminary δ\¹⁸O measurements of meteoric waters collected above the cave site indicate a temperature-dependent fractionation of 1.3‰°C^-1, which is higher than the fractionation between water and calcite (-0.2‰°C^-1), suggesting that the δ\¹⁸O of OCNM speleothems is strongly influenced by temperature. Because of precipitation seasonality in southwestern Oregon (wet winters and dry summers) and the rapid transit time of meteoric water through the karst aquifer, our speleothem record reflects mostly changes in cool season climate. The speleothem-based temperature reconstruction indicates that for the past 9000 years the climate of southwestern Oregon was characterized by a general warming trend, consistent with an increase in winter insolation at 45°N. Superimposed on this trend there is higher frequency variability at centennial to multi-decadal timescales. Prolonged cool periods are centered around 7.2 ka, 6.2 ka 5.3, 3.5 ka and 1.9 ka, while warm intervals are centered around 6.1 ka, 5.1 ka 4 ka and 1.1 ka. We note that the period corresponding to the Medieval Warm Period (~800 to 1300 AD) has the highest δ\¹⁸O values in our record and is characterized by two warm periods interrupted by a cooler period. The Little Ice Age period (~1350 to 1850 AD) is not very clearly expressed in our record as a cold interval, this period being characterized by significant decadal and centennial variability with both warmer and cooler intervals.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 3344 Paleoclimatology (0473, 4900)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting