Alpine speleothem records millennial-scale climate variability during Marine Isotope Stage 10

Marine Isotope Stage 10 (MIS) represents a critical period for understanding glacial climate dynamics, yet high-resolution terrestrial records from this interval remain scarce. Here, we present a precisely 230 Th-dated speleothem record documenting millennial-scale climate variability during MIS 10 (∼377 to 366 ka and ∼357 to 340 ka) from the northern European Alps. Stalagmite 7H-21 from the Sieben Hengste cave system records at least six rapid warming events characterized by abrupt δ 18 O excursions of 1-3‰. These events occurred on centennial to millennial timescales and exhibit the asymmetric structure characteristic of Dansgaard-Oeschger-type oscillations. A major growth hiatus between 366 and 357 ka corresponds, within age uncertainties, to Heinrich event 10.3, highlighting the strong sensitivity of Alpine hydroclimate to perturbations in North Atlantic circulation. The isotopic variability of 7H-21 shows coherence with Asian Monsoon speleothem records, indicating that hemispheric-scale teleconnections operated during MIS 10, most plausibly starting with changes in the Atlantic Meridional Overturning Circulation. Notably, the amplitude and recurrence of MIS 10 isotopic oscillations are comparable to those observed in Greenland ice cores during MIS 3, challenging the notion that older glacial periods were characterized by greater climatic stability.