CS27 Paleolimnology and Paleooceanography
Date: Tuesday, June 11, 2002
Location: Poster Session - VCC
 
StoneJR, University of Nebraska-Lincoln, Lincoln, USA, jstone@unlserve.unl.edu
Fritz, S, C, University of Nebraska-Lincoln, Lincoln, USA, sfritz2@unl.edu
Stevens, L, R, University of Nebraska-Lincoln, Lincoln, USA, lstevens@unl.edu
 
LATE HOLOCENE PERSISTENT DROUGHT SEQUENCES RECONSTRUCTED FROM A HIGH-RESOLUTION DIATOM RECORD OF FOY LAKE, MONTANA
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Sub-decadal diatom analyses of varved sediments from sub-alpine Foy Lake, Montana in the Rocky Mountains indicate threshold-like responses of the lake to persistent drought throughout the late Holocene. During the decade-long drought of the 1930's, a suite of benthic diatoms, dominated by Craticula halophila and Anomoeoneis costata, rapidly replaced a population of the planktonic diatom Cyclotella bodanica, which was typically 90% or more of the diatom assemblage. A regular series of nearly identical responses in fossil diatom assemblages throughout the late Holocene suggest that persistent drought may have occurred with periodic frequency. Threshold-like responses from the diatom assemblages recovered from Foy Lake are likely the result of the asymmetric lake basin, which is shaped in such a way that a wide littoral bench, proximal to the deepest part of the lake, probably existed during extended periods of lowered lake levels. Preliminary chronological constraints suggest that extreme, decade-long droughts within the region may be closely related to solar variation and large-scale ocean-atmospheric interactions.