HR: 10:20h
AN: PP52B-01    [Abstracts]
TI: Stable Hydrogen Isotopes of Terrestrial n-alkanes record the Mid Younger Dryas Event in European Lakes
AU: * Muegler, I
EM: imuegler@bgc-jena.mpg.de
AF: Max Planck Institute for Biogeochemistry, Hans-Knoell Str. 10, Jena, 07745, Germany
AU: Gleixner, G
EM: ggleix@bgc-jena.mpg.de
AF: Max Planck Institute for Biogeochemistry, Hans-Knoell Str. 10, Jena, 07745, Germany
AU: Sachse, D
EM: dsachse@u.washington.edu
AF: University of Washington, School of Oceanography, 1501 NE Boat Street, Seattle, WA 98195, United States
AU: Grafenstein, U v
EM: Ulrich.von-Grafenstein@cea.fr
AF: Laboratoire des Sciences du Climat et de l’environment, Point courrier 129, Gif- sur-Yvette, F-91191, France
AB: Compound-specific hydrogen isotope measurements (expressed as δD values) on lacustrine long- chained n-alkanes are a potentially promising means of reconstructing variations in the isotopic composition of continental precipitation in the geological past. Long-chain n-alkanes are produced in the leaf waxes of terrestrial higher plants and have been shown to preserve the hydrogen isotope composition of precipitation being influenced by atmospheric moisture source, evaporation as well as plant physiology. Since δD values are determined directly on carbon-bound hydrogen, which is non-exchangeable even at higher temperatures biological and environmental source conditions can be preserved over geological timescales. Here, we present a record of n-alkane δD values, \( nC₂₇ - nC₃₁ \), from the Ammersee, southern Germany and Lac d'Annecy, French Alps spanning the time period from the Oldest Dryas to Preboreal (14 ka to 11 ka BP). We compare biomarker hydrogen isotopic signatures to oxygen-isotope ratios of precipitation inferred from deep-lake ostracods from the Ammersee as well to GRIP \(δ¹⁸\)O values. The remarkable climate shift at the onset of the Younger Dryas (YD) (12.9 to 11.6 ka BP) is recorded in the \(δ¹⁸\)O values as well as the hydrogen isotope signal with a pronounced drop of approx. - 40‰ in D at the Ammersee and a minor negative excursion of - (20‰) in D at Lac d'Annecy. This depletion is consistent with a colder and dryer climate and the expansion of grasslands in the lake catchments as recorded in a significant increase of grass-derived \( nC₃₁ \). A sudden remarkable deuterium enrichment of about 100‰ in D is apparent in both lakes and marks the mid-Younger Dryas event (MYDE), which is also reflected in the GRIP and Ammersee \(δ¹⁸\)O values. δD values during this event reach or even exceed the following Holocene level. The simultaneous appearance of this event in different locations suggests a climate driven by mechanisms like the thermohaline circulation known for the Holocene. The transition to the Preboreal following the decline of the D content after the MYDE is characterized by a positive δD shift of approx. 60‰. This increase is most likely the onset ot the Holocene which is characterized by 10‰ heavier δD values compared to the Oldest Dryas. In general, hydrogen isotope ratios of n-alkanes cover a wide range of values implying a great sensitivity to precipitation as well as vegetation changes and thus wide ranging climate driven fluctuations. Furthermore, the similarity of both lake sediment records suggests that profound regional climatic changes have occurred during the YD, particularly during the MYDE. δD values of Lac d'Annecy are about 40‰ enriched throughout the whole record either suggesting a higher level of continentality or higher evaporation rates within the catchment. The timing and magnitude of the MYDE at three far distant locations over the northern hemisphere supports the suggestion that the Holocene-type thermohaline circulation started at this point with a rapid climate change followed by weakening mechanisms and terminating into warmer Holocene conditions.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1051 Sedimentary geochemistry
DE: 1620 Climate dynamics (0429, 3309)
DE: 9604 Cenozoic
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting