HR: 1340h
AN: H33B-1385    [Abstracts]
TI: Regional Expression of the 1988 U.S. Midwest Drought in Seasonal Stable-Carbon Isotope Patterns of Tree Rings
AU: * Leavitt, S W
EM: sleavitt@u.arizona.edu
AF: Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721 United States
AB: A massive drought in 1988 strongly impacted the U.S. Midwest, but instrumental-based measurements (precipitation and Palmer Drought Severity Index [PDSI]) revealed regional variations in moisture as the drought evolved in 1988 and diminished in 1989. Plant stable-carbon isotope composition (δ¹³C) may be a useful proxy for such local climate conditions because moisture affects leaf stomatal conductance, which in turn influences the plant's ability to discriminate against ¹³CO₂ relative to ¹²CO₂. Tree rings from 3 conifer species across a network of 9 sites over 4 states around the Great Lakes were sampled to determine the effectiveness of stable-carbon isotope composition in discerning drought strength, temporal evolution, and spatial character. δ¹³C of cellulose from 4 subdivisions of the 1988 and 1989 growth rings was analyzed and compared to moisture parameters. The range of δ¹³C variation within each ring was typically 1-2% for both years, and the co-occurrence of all 3 species at a single site revealed coherent patterns for the pines (red pine and white pine) but no correlation of the white spruce with the pines. Various averaged combinations of monthly PDSI and precipitation assigned to each subdivision versus both δ¹³C and discrimination (Δ ~ δ¹³C_air - δ¹³C_plant) yielded significant correlations (generally higher with PDSI), which were even stronger when the spruce data was removed. Fraction of average monthly cumulative precipitation (relative to 1900-2001 climate data) was more strongly related to δ¹³C than either monthly precipitation or monthly fraction of average precipitation, but was not as strongly related to δ¹³C as PDSI. Furthermore, the pattern of increasing δ¹³C in 1988 observed at several sites is an indicator of the increasing moisture stress of that year, and the difference in average isotopic composition of the 3rd and 4th subdivisions between 1988 and 1989 matched the regional moisture shift well. These results support the use of stable-carbon isotopes in tree rings as an environmental moisture proxy for exploring the characteristics of modern and ancient droughts, even at these relatively mesic sites.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1812 Drought
DE: 1866 Soil moisture
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 4920 Dendrochronology
SC: Hydrology [H]
MN: Fall Meeting 2005