HR: 0800h
AN: PP21A-1550    [Abstracts]
TI: Examining the Response of Tropical Terrestrial Vegetation to Paleoenvironmental Variability: an Organic and Isotopic Geochemical Record from Lake Malawi, East Africa
AU: * Castaneda, I S
EM: cast0150@umn.edu
AF: Large Lakes Observatory, University of Minnesota Duluth 10 University Dr., 109 RLB, Duluth, MN 55812 United States
AU: Werne, J P
EM: jwerne@d.umn.edu
AF: Large Lakes Observatory, University of Minnesota Duluth 10 University Dr., 109 RLB, Duluth, MN 55812 United States
AU: Johnson, T C
EM: tcj@d.umn.edu
AF: Large Lakes Observatory, University of Minnesota Duluth 10 University Dr., 109 RLB, Duluth, MN 55812 United States
AU: Filley, T R
EM: filley@purdue.edu
AF: Purdue University, Dept. of Earth and Atmospheric Sciences 550 Stadium Mall Dr., West Lafayette, IN 47907 United States
AB: In this study, molecular biomarkers and compound-specific carbon isotopes are used to investigate terrestrial vegetation change in East Africa since the Last Glacial Maximum (LGM). Lake Malawi, located in the southern hemisphere between 9° S and 14° S, provides a particularly interesting and sensitive location to examine the response of terrestrial vegetation to climatic change as the lake is presently situated within a C{3} dominated vegetation zone (tree savannah) but C{4} dominated vegetation zones (grass savannah) are present to both the north and south of the lake. Additionally, Lake Malawi has been shown to respond to both southern and northern hemisphere climatic forcings, including the Antarctic Cold Reversal, the Younger Dryas, and the 8.2 cal ka cold event (Powers et al., 2005; Filippi and Talbot, 2005; Johnson et al., 2002). Climatic variability in East Africa is often expressed as hydrological fluctuations (Gasse, 2000), which typically lead to changes in the primary productivity of both terrestrial and aquatic ecosystems. It is hypothesized that during colder and more arid intervals, grass savannah vegetation zones expanded while tree savannah vegetation zones contracted, resulting in increased inputs of C{4} biomass to Lake Malawi. The ratio of cinnamyl to vanillyl lignin phenols (C/V ratio), indicative of non-woody vs. woody tissue input (Goñi, 1997), correlates closely with bulk δ ¹³C{org} values in Lake Malawi and suggests a terrestrial influence on bulk carbon isotopic values. Combined C/V ratios and bulk δ ¹³C values suggest a greater contribution of C{4} grasses to Lake Malawi during the LGM followed by a gradual shift to more C{3} vegetation until approximately 13 cal ka, and a shift back to greater contributions of C{4} grasses between 4 cal ka and the present.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1055 Organic and biogenic geochemistry
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 4914 Continental climate records
DE: 4942 Limnology (0458, 1845, 4239)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005