Search

Hydrogen (δ2H) and oxygen (δ18O) isotopes of water extracted from speleothem fluid inclusions are important proxies used for paleoclimate reconstruction. In our study we use a cavity ring-down laser spectroscopy system for analysis and modified the approach of Affolter et al. (2014) for sample extraction. The method is based on crushing of small sub-gram speleothem samples in a heated and continuously water-vapour purged extraction line. The following points were identified: Injection of reference water shows a precision (1σ) of 0.4–0.5 ‰ for δ18O values and 1.1–1.9 ‰ for δ2H values for water amounts of 0.1–0.5 μl, which improves with increasing water amount to 0.1–0.3 ‰ and 0.2–0.7 ‰, respectively, above 1 μl. The accuracy of measurements of water injections and water-filled glass capillaries crushed in the system is better than 0.08 ‰ for δ18O and 0.3 ‰ for δ2H values. The reproducibility (1σ) based on replicate analysis of speleothem fluid inclusion samples with water amounts >0.2 μl is 0.5 ‰ for δ18O and 1.2 ‰ for δ2H values, respectively. Isotopic differences between the water vapour background of the extraction system and the fluid inclusions have no significant impact on the measured fluid inclusion isotope values if they are within 10 ‰ for δ18O and 50 ‰ for δ2H values of the background. Tests of potential adsorption effects with inclusion free spar calcite confirm that the isotope values are unaffected by adsorption for water contents of about 1 μl (fluid inclusion) water per g of carbonate or above. Fluid inclusion analysis on three different modern to late Holocene speleothems from caves in northwest Germany resulted in δ18O and δ2H values that follow the relationship as defined by the meteoric water line and that correspond to the local drip water. Yet, due to potential isotope exchange reactions for oxygen atoms, hydrogen isotope measurements are preferentially to be used for temperature reconstructions. We demonstrate this in a case study with a Romanian stalagmite, for which we reconstruct the 20th century warming with an amplitude of approximately 1 °C, with a precision for each data point of better than ±0.5 °C.

Speleothems from well-monitored Cloşani Cave (Romania), have provided excellent records of past rainfall amount and European winter hydro-climate variability (Warken et al., 2018). Here we present new data allowing to extend the precipitation history of Central-Eastern Europe back to the Last Glacial Maximum (LGM) as well as MIS 3. High-precision 230Th/U ages show that the two analysed speleothems (C09-1 and C09-2) grew nearly continuously during the past 20 ka, with only one growth interruption between c. 11 and 9.7 ka BP. In addition, C09-2 also covers the Dansgaard/Oeschger (D/O) Stadials/Interstadials 16 to 14 between 60 and 52 ka BP. Consistently with previous results, the speleothem proxies (δ18O and δ13C values, as well as laser ablation ICPMS trace element profiles) provide a comprehensive picture of local and regional hydro-climate variability on centennial to glacial/interglacial timescales.Over the course of the record, all proxies reveal millennial-scale features associated with prominent transitions during MIS 3, i.e., D/O events 16 to 14, as well as during the deglaciation, i.e., the Bølling-Allerød (BA) and Younger Dryas (YD). Local wetness as indicated by Mg/Ca ratios exhibits large variability, including pronounced swings between dry conditions during MIS 3 interstadials, and wetter conditions during stadials. After speleothem growth re-initiated at 20 ka BP, Mg/Ca ratios indicate a progressive drying until 15 ka BP, followed by an interval with enhanced variability from the Late Glacial to the Early Holocene. During the subsequent mid to late Holocene, from 8 ka BP to present, the local hydroclimate was characterized by relatively stable conditions. This dataset thus provides new insights into Central-Eastern European precipitation variability, and possibly also into its linkages to the North Atlantic realm.References:Warken, S.F., Fohlmeister, J., Schröder-Ritzrau, A., Constantin, S., Spötl, C., Gerdes, A., Esper, J., Frank, N., Arps, J., Terente, M., Riechelmann, D.F.C., Mangini, A., Scholz, D., (2018). Reconstruction of late Holocene autumn/winter precipitation variability in SW Romania from a high-resolution speleothem trace element record. Earth and Planetary Science Letters 499, 122-133. DOI: 10.1016/j.epsl.2018.07.027