HR: 11:05h
AN: PP42A-04    [Abstracts]
TI: Alkenone and Isotopic Records of Holocene Climatic and Environmental Change From Laminated West Greenland Lakes
AU: * D'Andrea, W J
EM: william\_dandrea@brown.edu
AF: Department of Geological Sciences, Brown University , Providence, RI 02912 United States
AU: Huang, Y
EM: yongsong\_huang@brown.edu
AF: Department of Geological Sciences, Brown University , Providence, RI 02912 United States
AB: Long chain alkenones (LCAs) are a key class of biomarkers for paleotemperature reconstructions. These compounds are ubiquitous in ocean sediments, but rare in lake sediments. Here we report the first discovery of LCAs in a downcore profile and surface sediments of five Greenland lakes. The concentrations of LCAs in surface sediments of these lakes are one to two orders of magnitude higher than those reported previously in other lake surface sediments around the world. Alkenones are present in five Greenland lakes with elevated salinity, but absent from five freshwater lakes. The alkenones have exceptionally low \delta$^{13}$C values ranging from -40 to -43\permil, and are depleted by 10 to 15\permil relative to short-chain fatty acids and sterols within the same samples. These \delta$^{13}$C values are the lowest ever reported for alkenones in a natural setting and have important implications for tracing the alkenone producers in lakes. Using the published calibration for lake sediments, the alkenone unsaturation indices in the surface sediments of the Greenland lakes record late spring/early summer temperature when algal blooms occur, suggesting the applicability of lacustrine alkenones as a paleotemperature proxy. LCA unsaturation indices and \deltaD from sediment cores taken from these Greenland lakes will help elucidate the environmental controls on these sedimentary parameters, and will aid the reconstruction of Holocene climate variability in West Greenland. Ongoing work on the saline lakes includes determining high resolution alkenone unsaturation ratios/abundances and bulk/compound-specific isotopic values from sediment cores, algal culturing, and establishing microbial community structure in the saline lakes using DNA/RNA fingerprinting. Up-to-date results will be presented in the meeting.
DE: 4239 Limnology
DE: 1040 Isotopic composition/chemistry
DE: 1055 Organic geochemistry
DE: 0330 Geochemical cycles
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting