HR: 11:05h
AN: U52A-04    [Abstracts]
TI: Climatological, hydrological and vegetation change for the past 15,000 years based upon a new network of high resolution lake sites in the Sierra Nevada and Unita Mountains
AU: * MacDonald, G M
EM: macdonal@geog.ucla.edu
AF: Department of Geography, UCLA, Los Angeles, CA 90095-1524 United States
AU: Moser, K A
EM: katrina.moser@csbs.utah.edu
AF: Department of Geography, University of Utah, Salt Lake City, UT 84112-9155 United States
AU: Porinchu, D F
EM: porinchu.1@osu.edu
AF: Department of Geography, The Ohio State University, Columbus, OH 43210-1361 United States
AU: Bloom, A
EM: amy.bloom@geog.utah.edu
AF: Department of Geography, University of Utah, Salt Lake City, UT 84112-9155 United States
AU: Potito, A
EM: potito@ucla.edu
AF: Department of Geography, UCLA, Los Angeles, CA 90095-1524 United States
AU: Petel, A
EM: apost@ucla.edu
AF: Department of Geography, UCLA, Los Angeles, CA 90095-1524 United States
AB: Instrumented lake and watershed climatic data along with lake sediment surface samples and cores are being used to develop and apply paleolimnological transfer functions to reconstruct climate change and ecosystem response in the eastern Sierra Nevada Mountains of California and the Unita Mountains of Utah. The selection of the two ranges provides a circum Great Basin perspective on natural climate variability in the western mountains. The California study sites are located in the eastern Sierra Nevada. Surface sediment samples and water samples have been analyzed from 57 lakes extending across an altitudinal gradient of 1360 m. Transfer functions that estimate water temperature, salinity and depth on the basis of lake diatom flora or chironomid fauna have been developed and published. Long cores have been obtained from 8 lakes that provide a transect from treeline down to the sagebrush dominated Great Basin. The lake records extend back between 9000 and 15,000 Cal yr BP. Pronounced warming of ~ 4.5 degrees C and development of modern conifer forest started by ~13,800 Cal yr BP. At ~11,000 Cal yr BP temperatures were as warm or warmer than today. High resolution analysis shows that the general glacial to interglacial warming was interrupted by a climatic reversal at approximately 13,000 Cal yr BP during which time summer temperatures at mid-elevation lakes cooled by 4 to 6 degrees C. There was a pronounced three part hydrological shift during this temperature reversal. The temperature reversal corresponds in timing with Younger Dryas Stadial typical of circum North Atlantic records. There was only a muted response to this episode at higher elevations and in the terrestrial vegetation. The cooling is synchronous with the Younger Dryas Stadial. Between ~8000 and 4000 Cal yr BP there was pronounced drying and lake drawdown at lower elevations. The period from 4000 Cal yr BP to the present has been typified by shifts between relatively moist conditions, like the present, and drier multi-decadal intervals. Dry intervals observed in low elevation records correspond in time to the Stine events which have been deduced from radiocarbon dated stumps in lakes and river valleys in the eastern Sierra Nevada. At present, 35 lakes in the Uintas have been sampled for surface sediments and two long cores have been obtained. One of the cores is laminated throughout and offers the potential for sub-decadal to annual resolution of past climatic variability. The records obtained show that the ecosystems of the western mountains have experienced pronounced millennial to centennial/decadal scale climatic and hydrologic variability as a natural component in their development and persistence. It is possible that centennial/decadal scale shifts similar to those evident over the past 4000 years would occur in the future.
DE: 1655 Water cycles (1836)
DE: 1620 Climate dynamics (3309)
SC: Union [U]
MN: 2004 AGU Fall Meeting