HR: 1340h
AN: PP43A-0606    [Abstracts]
TI: Variations in Composition and Preservation of Peat Deposited Since 27 ka in the Baoxiu Basin, Southwestern China: Implications for Environmental and Climatic Changes
AU: * Lu, Y
EM: luyuehan@umich.edu
AF: Department of Geological Sciences, The University of Michigan, 425 East University Avenue, Ann Arbor, Mi 48109-1063 United States
AU: Sun, Y
AF: Guangzhou Institute of Geochemistry, Guangzhou, Guangdong, 510640 China
AU: Meyers, P A
EM: pameyers@umich.edu
AF: Department of Geological Sciences, The University of Michigan, 425 East University Avenue, Ann Arbor, Mi 48109-1063 United States
AU: Weng, H
AF: Department of Geoscience,Zhejiang University, Hangzhou, Zheijiang, 310027 China
AB: Multi-proxy organic geochemical paleoclimate records have been obtained from a 200-cm peat core extending back to about 27 ka cal from the Baoxiu Lake Basin, Yunnan Province of southwestern China. Relatively low del 13C values (-26.3 to -24.3 per mil) of total organic carbon (TOC) and of n-fatty acids (-30.4 to -33.0 per mil), high TOC/TN ratios (17 to 64), and the presence of p-hydroxyphenyl, guaiacyl, and syringyl phenylpropanyl lignin units in pyrolysates show that the source of organic matter is dominated by terrestrial C3 grasses (herbaceous angiosperms) throughout this peat profile. Decomposition of peat is indicated by shortening of alkyl side-chains of methoxyphenols, an increase of oxidation products, and demethylation of methoxy groups of the lignin/polyphenol fraction. Lower amounts of these decomposition proxies below 100 cm indicate good preservation of peat from 26.8 to 22.6 ka and imply good reliability of climatic information derived from this time range in the peat profile. From 26.8 to 23.3 ka , lower inputs of terrestrial plants and lower aquatic productivity are suggested by relatively low concentrations of TOC and phosphorus, mirroring decreased precipitation. Relatively heavier carbon isotopic compositions of plant wax n-fatty acids (C24 - C30) indicate larger contributions of C4 plants, providing a further hint of dry climate. Intermediate del 13C values of TOC and of mid-chain n-fatty acids (C20 - C22) result from an overprint of organic matter from aquatic algae. From 23.3 to 22.6 ka, a rapid increase of precipitation and a resultant C3 land-plant expansion is documented by maxima in concentrations of TOC and phosphorus, a minimum in TOC del 13C, and relatively negative del 13C values of plant-wax n-fatty acids. Since 22.6 ka, climate reconstruction is not reliable because of disturbance of the peat layers. The disturbance is most likely caused by human activities, a conclusion that is supported by a rapid increase in peat decomposition as indicated by more phenol proxies and higher concentrations of phosphorus.
DE: 3344 Paleoclimatology
DE: 1833 Hydroclimatology
DE: 1040 Isotopic composition/chemistry
DE: 1055 Organic geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting