- 1Department of Chemistry, Biochemistry and Pharmaceutical Sciences and Oeschger Centre for Climate Change Research, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland (franziska.lechleitner@unibe.ch)
- 2State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China
- 3Xi'an Institute for Innovative Earth Environment Research, Xi'an 710061, China
- 4Swiss Institute for Speleology and Karst Studies, Rue de la Serre 68, 2300 La Chaux-de-Fonds, Switzerland
- 5Laboratory of Ion Beam Physics, Department of Physics, ETH Zurich, 8093, Zurich, Switzerland
- 6Department of Earth and Planetary Sciences, ETH Zurich, 8092 Zurich, Switzerland
- 7Institute of Geography and Oeschger Centre for Climate Change Research, University of Bern, Hallerstrasse 12, 3012 Bern, Switzerland
The application of organic carbon-based proxies, particularly biomarkers, to speleothem archives has greatly increased due to methodological and analytical advances. These reconstructions rely on the critical assumption that the analyzed proxy shares the same age as the surrounding archive matrix, as direct measurement of the biomarker age remains challenging due to very low concentrations.
We have developed a dataset of globally distributed bulk organic carbon radiocarbon ages from speleothems. Comparison with coupled carbonate radiocarbon ages, and where applicable, U-Th ages, shows that the speleothem organic carbon fraction is predominantly older than the depositional age (by 600 - 15,000 years). This discrepancy seems largely unaffected by climate conditions and ecosystem type, suggesting that aging of organic matter through storage and reworking is a widely occurring feature of karst systems.
Radiocarbon measurements of drip water organic carbon in a temperate karst system in Switzerland confirm that dissolved organic carbon ages in the karst system (and is not, for example, related to processes during incorporation into the speleothem carbonate matrix), with a strong influence of hydrology. Fluorescence and high resolution mass spectrometry allow us to investigate the processing and transformation of organic matter in the subsurface.
Our results remain so far constrained to the bulk organic carbon phase, and therefore we can only infer on how different biomarkers are affected by pre-aging in the karst system. Nevertheless, we highlight the complexity of carbon transport and transformation in the karst subsurface, underscoring the need for careful screening of samples and biomarkers used for paleoenvironmental reconstructions from speleothem organic matter.
How to cite: Lechleitner, F., Sarah, R., Xue, G., Huber, T., Luetscher, M., Guidobaldi, G., Haghipour, N., Endres, L., Stoll, H., Chiaia-Hernández, A. C., and Cirelli, S.: Radiocarbon evidence for aged speleothem organic matter: what does this mean for the interpretation of speleothem biomarker records?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15460, https://doi.org/10.5194/egusphere-egu25-15460, 2025.
