Dansgaard/Oeschger-like events detected in MIS 11 speleothem proxy records from Central Europe

Two stalagmites, DH_Br2 and DH_Kn6, were sampled from excavations in Dechencave, western Germany. Both were precisely dated by the ²³⁰Th/U-method (Mainz University), thin sections were investigated (Mainz University), and both stalagmites were analysed for their stable oxygen and carbon isotope composition (Mainz University and Max Planck Institute for Chemistry, Mainz) as well as various trace element concentrations (Max Planck Institute for Chemistry, Mainz).

Both stalagmites show evidence for diagenesis, such as roundish voids and mosaic calcite fabric in their lower parts. These parts were excluded from further analyses due to the alteration of the ²³⁰Th/U-ages as well as the proxy data. The discussed section of stalagmite DH_Br2 started growing at 401 ka and stopped at 379 ka, which corresponds to late Marine Isotope Stage (MIS) 11c to mid-11a. Stalagmite DH_Kn6 grew between 394 and 390 ka and overlaps with that of DH_Br2. Overall, speleothem records from MIS 11 are rare, in particular from Central Europe.

The δ¹³C and δ¹⁸O records show different levels for both stalagmites, most probably related to different amounts of prior calcite precipitation (PCP) and disequilibrium isotope fractionation during calcite precipitation at the different drip sites. The trace element records of both stalagmites can be identified as different environmental proxies with Al and Y being proxies for detrital material in the stalagmites and P and U reflecting soil microbial and vegetation activity. Strontium and Ba were influenced by leaching of soil minerals as well as changes in stalagmite growth rates. The Mg records correlate well with the δ¹³C records indicating PCP as dominant controlling factor. All trace element records, except for Al and Y, and the δ¹³C values are proxies for past precipitation. As revealed by the proxy records of stalagmite DH_Br2, drier conditions prevailed between 401-395 ka as well as between 391-379 ka, whereas wetter conditions existed between 395-391 ka, which is probably related to insolation changes. According to the δ¹⁸O values of stalagmite DH_Br2, temperature was slightly lower during 389-379 ka, i.e., after the peak warm phase of MIS 11, in agreement with marine and Antarctic ice core records. During this period 389-379 ka, we observe millennial-scale oscillations, which are most prominent in the δ¹⁸O record of stalagmite DH_Br2. They are probably Dansgaard/Oeschger-like events, not described up to now from speleothems from Central Europe during MIS 11. These millennial-scale oscillations are in good agreement with sea surface temperature changes in the North Atlantic.