Climatic transitions across Marine Isotope Stage 10–12 in the Alps evidenced by subglacial speleothems

Late Pleistocene climate in the European Alps was marked by large, orbitally driven fluctuations in temperature, precipitation, and ice extent. Reconstructing mountain glaciation prior to the Last Glacial Maximum remains challenging, however, because glacial deposits are often eroded or reworked. Here we present a 90-kyr speleothem record from Klaus Cramer Cave (western Austria) spanning Marine Isotope Stages (MIS) 12–10. Stable-isotope and trace-element data identify intervals of subglacial speleothem growth associated with warm-based ice cover. Subglacial phases are characterized by low δ 18 O, high δ 13 C, and highly elevated sulfur concentrations, indicating enhanced sulfide oxidation from the infiltration of meltwater through glacially comminuted detritus. Sulfate δ 34 S and δ 18 O values signal that the aerobic oxidation of pyrite was the dominant sulfur source. In the absence of geomorphological evidence, we constrain the timing of warm-based ice retreat to 423.3 ± 1.6 ka and re-advance to 370.8 +2.1 / −1.8 ka, while MIS 11 remained entirely ice-free.