HR: 16:30h
AN: PP34B-03    [Abstracts]
TI: Paleoclimatic Inferences From a High Resolution Bristlecone Pine δ¹⁸O Chronology
AU: * Berkelhammer, M
EM: berkelha@usc.edu
AF: Department of Earth Sciences, University of Southern California, 3651 Trousdale Pkwy., Los Angeles, CA 90089, United States
AU: Stott, L
EM: stott@usc.edu
AF: Department of Earth Sciences, University of Southern California, 3651 Trousdale Pkwy., Los Angeles, CA 90089, United States
AB: This study presents a comprehensive high resolution 400-year chronology of tree-ring α cellulose δ¹⁸O values of Pinus longaeva (Bristlecone Pine) from the White Mountains of California. The δ18O_VSMOW stratigraphy exhibits a distinctive bidecadal oscillation during the 20th century with peak excursions of 4‰. The cellulosic δ¹⁸O values appear to correlate both with growing season temperatures and the isotopic composition of regional precipitation. Because there is not a good instrumental record of δ¹⁸O in precipitation for this region, the latter statistic was estimated by calculating the percentage of each year's precipitation that had a subtropical origin by the use of daily NCEP Reanalysis data and a recently developed catalog of Pineapple Express storms. The subtropical influence on the region exhibits large interannual variability, ranging from years where no such storm occurs to years where close to 15% of the total water budget has a subtropical origin. Precipitation in this region falls predominately during the winter months and the growing season is restricted to late spring through early fall, so it can be stated that the average annual δ18O value integrates a distinct summer and winter signal. The δ¹⁸O variability during the instrumental period is dwarfed by a dramatic enrichment (~10‰) in cellulosic δ¹⁸O values between 1905 and 1855 AD. This mid 19th century isotopic shift correlates with major climatic changes across the Northern Hemisphere that have been documented in a wide-range of proxy records. Both the magnitude and direction of the Bristlecone Pine isotopic excursion suggest it is not likely the result of post-Little Ice Age warming but rather a major change in the dominant storm tracks striking this region. We hypothesize that the large isotopic shift in the mid-19th century is evidence for a change in mean storm trajectories brought about by a more southerly position of the mid-latitude jet and changes in the strength and zonality of Pacific wind fields. Dramatic and coincident changes in atmospheric circulation have been noted in both ice cores (i.e. Mt. Logan) and marine sediment records (i.e. Santa Barbara and Santa Monica Basins) and these findings thus offer insight onto the dramatic hydroclimatic changes that occurred in western North America at the terminus of the Little Ice Age.
DE: 4914 Continental climate records
DE: 4920 Dendrochronology
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting