Multi-proxy reconstruction of Holocene and Late Glacial climate variability using precisely dated speleothems from the Herbstlabyrinth, central Germany
Zusammenfassung der Projektergebnisse
Three stalagmites from the Herbstlabyrinth, central Germany, were precisely dated by MC-ICPMS 230Th/U-dating, and high-resolution stable isotope and trace element records were determined. The combined multi-proxy record covers the entire Holocene. On the millennial time scale, the stable oxygen isotope (δ18O) values are in agreement with the δ18O record of a Greenland ice core, indicating that speleothem δ18O values at the Herbstlabyrinth reflect large-scale climate variability in the North Atlantic area. For instance, the prominent 8.2 ka event is visible as a pronounced negative excursion in the δ18O values. During the Younger Dryas, stalagmite growth at the Herbstlabyrinth stopped, probably in response to the very cold surface temperatures. We used correlation and principal component analysis to disentangle the processes influencing the stable isotope and trace element signals. This revealed that phases with elevated P, Ba and U concentrations and more negative δ13C values reflect a more productive vegetation above the cave. Furthermore, a negative correlation of Mg with P, Ba and U and a positive correlation with δ13C values indicate increased rainfall during phases of a more productive vegetation. The majority of the observed phases of reduced vegetation productivity and drier climate coincide with cooler periods in the polar North Atlantic (the Bond events). This suggests a close relationship between terrestrial climate in Central Europe and the polar North Atlantic during the Holocene. In addition, a detailed cave monitoring program was set up at the Herbstlabyrinth. In the framework of a cave monitoring program, various parameters (e.g., temperature and precipitation above the cave and temperature and drip rate inside the cave) are determined in order to relate changes in the proxy signals recorded in the speleothems to climate change above the cave. The cave monitoring data show that recharge of the aquifer at the HL cave system mainly occurs during winter months. Winter climate of the cave region is strongly influenced by a large scale atmospheric climate phenomenon, the North Atlantic Oscillation (NAO). Cave drip water and speleothem δ18O values from the Herbstlabyinth should, thus, be a sensitive proxy for reconstruction of the NAO. In order to test this hypothesis, we developed two drip water δ18O models for the Herbstlabyrinth, which show a good agreement with the monitoring data. These models also enabled us to determine the mean residence and transmission time of the water in the aquifer above the cave. Based on the model, the rainfall δ18O data from the cave monitoring program and a long-term dataset from the meteorological station Frankfurt am Main, we modelled the δ18O values of the cave drip water for the last 144 years. Despite of the favourable conditions of the Herbstlabyrinth for NAO reconstruction, the modelled drip water δ18O time series only shows a moderate correlation with the winter NAO index. The major reason for this is the substantial contribution of precipitation from the remaining seasons to the drip water, for instance, due to heavy precipitation events occurring during summer. Thus, reconstructing the NAO from speleothems is generally challenging, even for caves located in areas strongly influenced by the NAO, such as the Herbstlabyrinth. In order to handle the extensive trace element datasets, we developed a script for data reduction in the statistical language R (TERMITE). Data evaluation using TERMITE is much faster than with all other currently available software. In collaboration with Prof. Dr. T. Hoffmann (Institute of Inorganic and Analytical Chemistry, University of Mainz), we developed a novel method for analysis of low molecular weight fatty acids in cave drip water and speleothems in order to investigate the potential of fatty acids in speleothems as a climate proxy. Finally, in collaboration with colleagues from the University of Bochum, cryogenic calcites from the Herbstlabyrinth were studied, which are an indicator for freezing conditions inside the cave and may provide information on past cold periods in central Europe.
Projektbezogene Publikationen (Auswahl)
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2011. Zerbrochene Höhlensinter und Kryocalcite als Indikatoren für eiszeitlichen Permafrost im Herbstlabyrinth-Adventhöhle-System bei Breitscheid-Erdbach (N-Hessen). Die Höhle 062, 31–45
Richter, D. K., Mischel, S. A., Dorsten, I., Mangini, A., Neuser, R. D., Immenhauser, A.
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2014. Quantification of fatty acids in cave drip water and speleothems using HPLC-ESI- IT/MS - Development and validation of a selective method. Analytical and Bioanalytical Chemistry 406, 3167-3177
Bosle, J., Mischel, S. A., Schulze, A.-L., Scholz, D., and Hoffmann, T.
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2015. δ18O values of cave drip water - a promising proxy for the reconstruction of the North Atlantic Oscillation? Climate Dynamics 45, 3035-3050
Mischel, S. A., Scholz, D., and Spötl, C.
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Holocene climate variability in Central Germany and a potential link to the polar North Atlantic: A replicated record from three coeval speleothems. Holocene, 27(4), 509-525, 2017
Mischel, S. A., Scholz, D., Spötl, C., Jochum, K. P., Schröder-Ritzrau, A., and Fiedler, S.
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TERMITE: An R script for fast reduction of laser ablation inductively coupled plasma mass spectrometry data and its application to trace element measurements. Rapid Communications in Mass Spectrometry 31,13, 15 July 2017, Pages 1079-1087
Mischel, S. A., Mertz-Kraus, R., Jochum, K. P., and Scholz, D.
