HR: 1340h
AN: PP43A-0604    [Abstracts]
TI: Compound-specific hydrogen isotope ratios of sedimentary n-alkanes - a new paleoclimate proxy
AU: * Sachse, D
EM: dirk.sachse@bgc-jena.mpg.de
AF: Max Planck Institute for Biogeochemistry, Hans-Kn”ll-Str. 10, Jena, 07745 Germany
AU: Radke, J
EM: Jens.Radke@thermo.com
AF: Thermo Electron, Barkhausenstr. 2, Bremen, 28197 Germany
AU: Gleixner, G
EM: gerd.gleixner@bgc-jena.mpg.de
AF: Max Planck Institute for Biogeochemistry, Hans-Kn”ll-Str. 10, Jena, 07745 Germany
AB: Hydrogen isotope ratios (deltaD) of sedimentary biomarkers are suggested to record the hydrogen isotope composition of environmental water and to preserve it over geological timescales. Therefore, changes in earth's water cycle, like changing evapotranspiration rates or atmospheric circulation patterns, which are necessary to understand climate variability, could be reconstructed using deltaD values of biomarkers. However, so far no study exists that proves this theory for n-alkanes. Here we present the first systematic approach calibrating deltaD values of recent sedimentary n-alkanes (n-C12 to n-C31) to modern meteoric water deltaD values. deltaD values from n-alkanes (n-C17 to n-C31) extracted from lake sediments along a N-S European climatic gradient from northern Finland to southern Italy are significantly correlated with deltaD values of meteoric water. This clearly demonstrates that sedimentary n-alkanes record the source water deltaD value. The observed isotope fractionation during biosynthesis (epsilon) for the n-C17 alkane of algal origin is constant at -158 permil over a wide range of climates and lakes of different trophic states. This suggests a constant biosynthetic hydrogen fractionation driving the hydrogen isotope composition of aquatic biomarkers. Moreover, evapotranspiration enriches deuterium in terrestrial n-alkanes (n-C25 to n-C31) relative to aquatic biomarkers. This opens the additional possibility to reconstruct paleo-transpiration rates. Our results prove that deltaD values from sedimentary n-alkanes (n-C17 to n-C31) record the hydrogen isotope composition of meteoric water and may be applied to study paleohydrology of lake systems, changes in atmospheric circulation and hence climate history.
DE: 3344 Paleoclimatology
DE: 3354 Precipitation (1854)
DE: 1040 Isotopic composition/chemistry
DE: 1055 Organic geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting