HR: 10:35h
AN: U42A-02    [Abstracts]
TI: Changes in Solar Irradiance as a Possible Mechanism for Century-Scale Droughts Reconstructed From a Holocene Pollen Record, Pyramid Lake, Nevada, USA
AU: * Mensing, S A
EM: smensing@unr.edu
AF: Department of Geography, University of Nevada, Reno, Reno, NV 89557 United States
AU: Benson, L V
EM: lbenson@usgs.gov
AF: US Geological Survey, 3215 Marine Street, Boulder, CO 80303 United States
AU: Kashgarian, M
EM: kashgarian@llnl.gov
AF: Lawrence Livermore National Laboratory, PO Box 808, Livermore, CA 94550 United States
AU: Lund, S
EM: slund@usc.edu
AF: Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089 United States
AB: Pollen and algae microfossils preserved in sediments from Pyramid Lake, Nevada provide evidence for periods of persistent drought during the Holocene age. We analyzed one hundred nineteen 1-cm thick samples for pollen and algae from a set of cores that span the last 7630 years. The early middle Holocene, 7600 to 6300 cal yr B.P. was found to be the driest period, although it included one short but intense wet phase. We suggest that Lake Tahoe was below its rim for most of this period, greatly reducing the volume and depth of Pyramid Lake. Middle Holocene aridity eased between 5000 and 3500 cal yr B.P. and climate became variable with distinct wet and dry phases. Lake Tahoe probably spilled intermittently during this time. No core was recovered that represented the period between 3500 and 2600 cal yr B.P. The last 2500 years appear to have had recurrent persistent droughts. The timing and magnitude of droughts identified in the pollen record compares favorably with previously published oxygen isotope data from Pyramid Lake. The timing of these droughts also agrees with the ages of submerged rooted stumps in the Eastern Sierra Nevada and woodrat midden data from central Nevada. Prolonged drought episodes appear to correspond with the timing of ice drift minima (solar maxima) identified from North Atlantic marine sediments, suggesting that changes in solar irradiance may be a possible mechanism influencing century-scale drought in the western Great Basin.
DE: 3344 Paleoclimatology
DE: 1812 Drought
DE: 1851 Plant ecology
DE: 1600 GLOBAL CHANGE (New category)
DE: 1620 Climate dynamics (3309)
SC: Union [U]
MN: 2004 AGU Fall Meeting