HR: 09:00h
AN: PP41B-05    [Abstracts]
TI: Seasonally Resolved Oxygen Isotope Paleoclimate Proxy in Tree-Ring Cellulose from the Southeastern U.S.
AU: * Miller, D L
EM: dmiller9@utk.edu
AF: Earth and Planetary Sciences, University of Tennessee 306 Earth and Planetary Sciences, Knoxville, TN 37996-1410 United States
AU: Mora, C I
EM: cmora@utk.edu
AF: Earth and Planetary Sciences, University of Tennessee 306 Earth and Planetary Sciences, Knoxville, TN 37996-1410 United States
AU: Grissino-Mayer, H D
EM: grissino@utk.edu
AF: Department of Geography, University of Tennessee 304 Burchfiel Bldg, Knoxville, TN 37996-0925 United States
AU: Mock, C J
EM: mockcj@sc.edu
AF: Department of Geography, University of South Carolina Callcott Social Sciences Bldg 709 Bull Street, Columbia, SC 29208 United States
AB: Stable isotopes in precipitation reflect changes in climate, moisture source, and extreme events such as tropical cyclones, and an oxygen isotope proxy record of these changes through time and space is preserved in tree-ring cellulose. Extreme climate events such as droughts and hurricanes are formidable natural disasters in the southeastern United States, and considerable efforts have been made to understand factors controlling their frequency, whether natural or anthropogenic. Tree rings offer an unusually well-resolved, dateable record of climate events extending beyond modern or historical (documentary) records. Oxygen isotopes in alpha-cellulose of shallowly-rooted conifers predominately reflect the composition of precipitation. Tropical storm convection results in marked $^{18}$O depletion in storm precipitation, to -15$\permil$ relative to source seawater (~0$\permil$). The depletion increases towards the eyewall of the cyclone, however, isotopically depleted precipitation may extend outward many 100's of km. Storm water $^{18}$O depletion translates to soil water $^{18}$O depletion that may persist for many weeks until ameliorated by soil water evaporation. Tree growth during that time will take up the anomalous isotopic compositions. Distinctive earlywood (EW ~March-June) versus latewood (LW ~July-October) growth allows the rings to be resolved at an intra-annual (seasonal) scale. By comparison to average soil water, droughts result in $^{18}$O-enriched soil water compositions. Seasonal drought or years of continued drought will be similarly captured in the isotope compositions of tree-ring cellulose. A 227-year (1770-1997) seasonally-resolved record of tropical cyclone and drought activity was obtained from cross-sections of felled slash pines ({\it Pinus elliottii} Engelm.) and remnant longleaf pines ({\it Pinus palustris} Mill.) from southern Georgia. Interpretations of drought or hurricane events were tested by comparison with recent, detailed meteorological records. The 227-year record reveals most previously established hurricane events, including Florence (1953) and the Great Hurricane of 1780. Newly recognized tropical storms such as 1857 are also evident. Significant seasonal droughts such as 1955, 1927, 1904 and 1896, are observed for southeastern Georgia. Larger-scale climate oscillations appear to overprint the EW and LW isotope series, displaying periods of relatively large or small differences in EW and LW $\delta$$^{18}$O values. The oscillations are interpreted to reflect dominant climate modes that influence moisture source or seasonal temperature variation. The tree-ring record potentially extends many centuries. A preliminary record through a portion of the North American "Little Ice Age" (1580-1650) indicates a significant reduction in tropical cyclone activity.
DE: 4808 Chemical tracers
DE: 3344 Paleoclimatology
DE: 1845 Limnology
DE: 1045 Low-temperature geochemistry
DE: 1615 Biogeochemical processes (4805)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting