HR: 0830h
AN: B11C-0705    [PDF]
TI: Potential use of Oxygen Isotopes From $\alpha$-Cellulose in Tree Rings to Examine Climate Trends, El Malpais National Monument, New Mexico, USA
AU: * Kocis, W N
EM: wnelson@utk.edu
AF: University of Tennessee Department of Earth and Planetary Sciences, 306 Earth and Planetary Sciences Building, Knoxville, TN 37996 United States
AU: Mora, C I
EM: cmora@utk.edu
AF: University of Tennessee Department of Earth and Planetary Sciences, 306 Earth and Planetary Sciences Building, Knoxville, TN 37996 United States
AU: Grissino-Mayer, H
EM: grissino@utk.edu
AF: University of Tennessee Department of Geography, Burchfiel Geography Building, Knoxville, TN 37996 United States
AU: Uhle, M
EM: muhle@utk.edu
AF: University of Tennessee Department of Earth and Planetary Sciences, 306 Earth and Planetary Sciences Building, Knoxville, TN 37996 United States
AB: The development of high-resolution geological proxies is key to understanding long-term climate variability. Tree-ring studies have shown the potential to provide a uniquely high resolution, precisely dated record of climate change. The oxygen isotope composition of $\alpha$-cellulose in tree rings may provide a high resolution, dateable proxy for examining precipitation source, variability, and other long-term climate trends and parameters. We are examining the potential of tree ring $\alpha$-cellulose oxygen isotopes to record changes in precipitation activity in the southwestern United States, at a site within El Malpais National Monument. Here, more than half of the annual precipitation is derived from the North American Monsoon (NAM). It has been previously suggested that the precipitation sources for the NAM may change on long-term scales. Tree rings from El Malpais that have already been subject to a 2129 -year precipitation reconstruction and are absolutely dated in time are the basis of this study. We hypothesize that a change in the precipitation source should be reflected in the oxygen isotope composition of the $\alpha$-cellulose within the tree rings. Intra-annual latewood and earlywood $\alpha$-cellulose samples were extracted and analyzed by pyrolysis-IRMS for the period 1992-1964. The oxygen isotope analysis revealed $\delta$ $^{18}$O values ranging from $\sim$ 33-37$\permil$ for the earlywood and $\sim$ 33-38$\permil$ for the latewood. Latewood samples are generally 0.5 to 2$\permil$ heavier than earlywood. Inter-annual trends are also observed, in particular, the average $\delta$ $^{18}$O values are $\sim$ 2$\permil$ heavier after the mid-1970's. Numerous other proxies, including tree-ring width analysis, show changes in the mid-1970's that are inferred to be related to a shift in the Pacific Decadal Oscillation. While further work must be done to better understand the factors influencing the tree ring oxygen isotopes, they appear to record a major change coincident with that shift.
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
DE: 1055 Organic geochemistry
DE: 1620 Climate dynamics (3309)
DE: 3344 Paleoclimatology
SC: Biogeosciences [B]
MN: 2003 Fall Meeting