Seven speleothems from six independent cave systems in Germany were investigated on their suitability as paleoclimatic archives. The caves are located in the Jurassic Limestones of the Swabian/Franconian Alb (southern Germany) and in a small-scale Devonian (reef) complex of the Harz Mountains (northern Germany). Based on the chronological control using 234U/230Th (TIMS) ages, δ18O/δ13C timeseries of the speleothems were established and related to known paleoclimatic events.
Results of the present-day assessment of the cave systems demonstrated that the cave temperature responses; the stable isotopic abundances of the dripwater, and present-day cave calcites reflect mean annual surface air temperatures as well as established isotopic equilibrium conditions during cave calcite precipitation. However, existing biases have been monitored but most of them may be deduced to anthropogenic influences like mining operations (Zaininger-Cave, Swabian Alb) or showcave business (Hermann’s- and Baumann’s-Cave, Harz Mountains). Although the scenarios leave partially an imprint on present-day spelean calcites, like the indicated non-equilibrium conditions at the Zaininger-Cave, their temporal imprint is restricted very much to the last couple of decennial years and thus assumed not to influence the paleorecords at all. Since the δ18O compositions of present-day calcite precipitates are primarily controlled by temperature, the sites may thus be suitable for paleoclimatic investigations from a today perspective.
Since the paleorecords of the Hermann’s- and Baumann’s-Cave stalagmites (Harz Mountains) display ages, which are not in chronological order, a construction of timeseries was not possible.
Past stable isotopic equilibrium conditions of the remaining paleorecords were verified using the single layer “Hendy-Test” as well as δ18O/δ13C regression analyzes of the subsample profiles. Late Pleistocene growth periods were found in the Paleocave Hunas Stalagmite (79373 ± 8237 to 76872 ± 9686 a. B.P.; Franconian Alb) and the Cave Hintere Kohlhalde Stalagmite (44158 ± 3329 to 2709 ± 303 a B.P.; Swabian Alb). Unexpectedly, the latter displays no macroscopic visible growth hiatuses and was deposited continuously during the “cold” OIS 2 and the LGM. This has been interpreted owing to the special conditions and mode of vadose water circulation of a discontinuous permafrost zone which may have prevailed on the Swabian Alb during that time. Here, just like for the subsequent periods, principal changes in mean δ18O/δ13C and linear extension rates of the timeseries echoed the Boelling/Alleroed Interstadial and Younger Dryas cold phase. The comparison of coeval timeseries between the Cave Hintere Kohlhalde stalagmite, the Zaininger-Cave stalactite (both Swabian Alb) and the Mühlbach-Cave stalagmite (Franconian Alb) reveal some analogy such as the transitions from the Late Glacial to the Early Holocene between 10513 and 10587 cal. a B.P. for the Swabian Alb and 10227 cal. a B.P. for the Franconian Alb; the anomaly around 8.2 ka B.P. recorded in the Zaininger- and Mühlbach-Cave; and a climatic deterioration which leads to an almost simultaneous cessation of speleothem growth on the Swabian/Franconian Alb between 2.5 and 2.8 ka B.P.
Important changes of the stable isotopic composition occur together with changes in growth rate and in the macroscopic aspect of the investigated speleothems. This confirms that general climatic and environmental parameters control the recorded variations and that they are not owing to very local factors.