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Marine Isotope Stage 3 (MIS 3, 57-27 ka) was characterised by numerous rapid climate oscillations (i.e., Dansgaard-Oeschger (D/O-) events), which are reflected in various climate archives. So far, MIS 3 speleothem records from central Europe have mainly been restricted to caves located beneath temperate Alpine glaciers or close to the Atlantic Ocean. Thus, MIS 3 seemed to be too cold and dry to enable speleothem growth north of the Alps in central Europe. Here we present a new speleothem record from Bunker Cave, Germany, which shows two distinct growth phases from 52.0 (+0.8, -0.5) to 50.9 (+0.6, -1.3) ka and 473 (+1.0, -0.6) to 42.8 (+/- 0.9) ka, rejecting this hypothesis. These two growth phases potentially correspond to the two warmest and most humid phases in central Europe during MIS 3, which is confirmed by pollen data from the nearby Eifel. The hiatus separating the two phases is associated with Heinrich stadial 5 (HS 5), although the growth stop precedes the onset of HS 5. The first growth phase is characterised by a fast growth rate, and Mg concentrations and Sr isotope data suggest high infiltration and the presence of soil cover above the cave. The second growth phase was characterised by drier, but still favourable conditions for speleothem growth. During this phase, the delta C-13 values show a significant decrease associated with D/O-event 12. The timing of this shift is in agreement with other MIS 3 speleothem data from Europe and Greenland ice core data. (C) 2018 Elsevier Ltd. All rights reserved.
We report the chronological construction for the top portion of a speleothem, PC1, from southern Cambodia with the aim of reconstructing a continuous high-resolution climate record covering the fluorescence and decline of the medieval Khmer kingdom and its capital at Angkor (similar to 9th-15th centuries AD). Earlier attempts to date PC1 by the standard U-Th method proved unsuccessful. We have therefore dated this speleothem using radiocarbon. Fifty carbonate samples along the growth axis of PC1 were collected for accelerator mass spectrometry (AMS) analysis. Chronological reconstruction for PC1 was achieved using two different approaches described by Hua et al. (2012a) and Lechleitner et al. (2016a). Excellent concordance between the two age-depth models indicates that the top similar to 47 mm of PC1 grew during the last millennium with a growth hiatus during similar to 1250-1650 AD, resulting from a large change in measured C-14 values at 34.4-35.2 mm depth. The timing of the growth hiatus covers the period of decades-long droughts during the 14th-16th centuries AD indicated in regional climate records.
The precise determination of the stable C and O isotope fractionation between water and calcite (CC) and water and aragonite (AR) is of special interest for climate reconstructions, e.g. paleotemperatures. Previous studies reported results from both laboratory and field experiments, but their results are only partly consistent. Here we present C and O isotope data of a stalagmite from the Swiss Alps, which shows CC-AR transitions along individual growth layers. Using detailed analyses both laterally and perpendicular to such layers we examined the difference in the C and O isotope fractionation factor of the HCO3- - CC and the HCO3- - AR system. For O this difference is similar to the water-CC and water-AR offset provided in experimental studies. The O isotope fractionation difference in the water-CC and water-AR system is comparable to those determined in laboratory studies but shows a statistically significant correlation with the CaCO3 precipitation rate. For C we found a fractionation difference, which is independent of CaCO3 precipitation rate and with slightly smaller values for the fractionation offset between HCO3- - CC and HCO3- - AR compared to literature values. However, we also found an unexpected decrease in delta C-13 along growth layers, which contradicts the widely used concept of Rayleigh fractionation during CO2 degassing and CaCO3 precipitation. The results of this study can be used e.g., to correct stable isotope time series of stalagmites showing CC-AR transitions along their growth axes. (C) 2018 Elsevier Ltd. All rights reserved.