A terrestrial U/Th-dated stable isotope record of the Penultimate Interglacial

Abstract

Here we present the first U-series dated stable oxygen isotope record in continental Europe that covers the entire tripartite Penultimate Interglacial, i.e. Marine Isotope Stages 7.5 to 7.1. This record was obtained from a U-rich stalagmite from Spannagel Cave in the Austrian Alps which is largely devoid of kinetic isotope fractionation effects which comprised previously studied flowstone from this site. Composed of dense, columnar calcite this speleothem apparently grew without significant interruption for ca. 50 ka, albeit at a very slow rate. The age model was established based on 23 individual U/Th TIMS dates using a combination of a Bayesian approach, which includes additional information using stratigraphic constraints, and the mixed-effect regression model. The resulting record shows three prominent maxima in δ 18O (MIS 7.5, 7.3 and 7.1) separated by a long earlier and a shorter later cold period (MIS 7.4 and 7.2, respectively). The mid points of the transitions into the three warm phases occurred at 240 ± 3, 215 ± 2 and 200 ± 3 ka and the MIS 7/6 transition was dated to 190 ± 3 ka. The timing of these climate transitions is supported by other samples from the same cave and agrees within analytical uncertainties with U/Th-dated evidence from corals, marine aragonitic sediments and submerged stalagmites, as well as with orbitally tuned deep-sea records. Good agreement was also found with new speleothem data from China as far as MIS 7.1 and 7.5 are concerned, whereas MIS 7.3 apparently started earlier and MIS 7.2 lasted longer than in the Alps. Comparing the European speleothem data with Antarctic ice cores reveals obvious differences in age (the latter suggesting an earlier start and a generally shorter duration of the three warm episodes). In essence, this study underscores the great potential of speleothems as accurate and precise chronometers of Pleistocene climate change and emphasizes the need for similar studies in other continents (including submerged caves) in order to improve the imperfect chronological framework of MIS 7.