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The last glacial period was punctuated by cold intervals in the North Atlantic region that culminated in extensive iceberg discharge events. These cold intervals, known as Heinrich Stadials, are associated with abrupt climate shifts worldwide. Here, we present CO₂measurements from the West Antarctic Ice Sheet Divide ice core across Heinrich Stadials 2 to 5 at decadal-scale resolution. Our results reveal multi-decadal-scale jumps in atmospheric CO₂concentrations within each Heinrich Stadial. The largest magnitude of change (14.0 ± 0.8 ppm within 55 ± 10 y) occurred during Heinrich Stadial 4. Abrupt rises in atmospheric CO₂are concurrent with jumps in atmospheric CH₄and abrupt changes in the water isotopologs in multiple Antarctic ice cores, the latter of which suggest rapid warming of both Antarctica and Southern Ocean vapor source regions. The synchroneity of these rapid shifts points to wind-driven upwelling of relatively warm, carbon-rich waters in the Southern Ocean, likely linked to a poleward intensification of the Southern Hemisphere westerly winds. Using an isotope-enabled atmospheric circulation model, we show that observed changes in Antarctic water isotopologs can be explained by abrupt and widespread Southern Ocean warming. Our work presents evidence for a multi-decadal- to century-scale response of the Southern Ocean to changes in atmospheric circulation, demonstrating the potential for dynamic changes in Southern Ocean biogeochemistry and circulation on human timescales. Furthermore, it suggests that anthropogenic CO₂uptake in the Southern Ocean may weaken with poleward strengthening westerlies today and into the future. 

Speleothems are important timekeepers of Earth’s climate history. A key advantage of speleothems is that they can be dated using U–Th techniques. Mass spectrometric methods for measuring U and Th isotopes has led to vast improvements in measurement precision and a dramatic reduction in sample size. As a result, the timing of past climate, environment, and Earth system changes can be investigated at exceptional temporal precision. In this review, we summarize the principles and history of U–Th dating of speleothems. Finally, we highlight three studies that use U–Th dated speleothems to investigate past changes to the Asian monsoon, constrain the timing of sociopolitical change in ancient civilizations, and develop a speleothem-based calibration of the 14C timescale. 

Abstract. Investigating the precise timing of regional-scale climate changes during glacial terminations and the interglacial periods that follow is key tounraveling the mechanisms behind these global climate shifts. Here, we present a high-precision time series of climate changes in the Austrian Alpsthat coincide with the later portion of Termination III (TIII), the entire penultimate interglacial (Marine Isotope Stage (MIS) 7), Termination IIIa(TIIIa), and the penultimate glacial inception (MIS 7–6 transition). Using state-of-the-art mass spectrometry techniques, we have constructed auranium-series chronology with relative age uncertainties averaging 1.7 ‰ (2σ) for our study period (247 to 191 thousand yearsbefore present, ka). Results reveal the onset of warming in the Austrian Alps associated with TIII at 242.5 ± 0.2 ka and theduration of MIS 7e warming between 241.8 and 236.7 (±0.6) ka. An abrupt shift towards higher δ18O values at216.8 ka marks the onset of regional warming associated with TIIIa. Two periods of high δ18O values (greater than−10 ‰ Vienna Pee Dee Belemnite (VPDB)) between 215.9–213.3 and 204.3–197.5 (±0.4) ka coincide with interglacial substages MIS 7c and 7a,respectively. Multiple fluorescent inclusions suggest a partial retreat of the local Alpine glacier during peak obliquity forcings at214.3 ± 0.4 ka. Two newly collected stalagmites from Spannagel Cave (SPA146 and 183) provide high-resolution replications of thelatter portion of the MIS 7a-to-6e transition. The resulting multi-stalagmite record reveals important chronological constraints on climate shifts inthe Austrian Alps associated with MIS 7 while offering new insight into the timing of millennial-scale changes in the North Atlantic realm leadingup to TIII and TIIIa.