The last glacial period was punctuated by abrupt, millennial-scale climate changes that contain useful information about the rate at which the climate can change from one state to another. Improvement in our knowledge of the temporal and spatial character of these rapid climate changes is important for understanding their causes and effects, and provides essential observational information for modeling studies. Here, we expand the coverage of terrestrial climate records during the last glacial period, and present a series of high-resolution stalagmite records from a cave in the northern Alps (central Europe) covering parts of the period 65-35 ka (before A.D. 1950). The climatic pattern revealed by the stalagmite temperature-controlled d 18 O profiles strongly resembles that of Greenland ice cores on millennial scales, and also corresponds to the detail of decadal-scale cooling events within interstadials. This demonstrates for the first time a strong climatic similarity and/or coupling between the two regions during Marine Isotope Stage 3 (MIS 3). Furthermore, an overall long-term agreement between the northern European Alps stalagmite chronology (NALPS) presented here, and the Greenland Ice Core Chronology 2005 modelext (GICC05modelext), suggests that the central value of the Greenland chronology may be slightly too young, possibly as a result of an undercounting of layers in a younger section of the core, and that the uncertainty on the Greenland chronology may be overestimated. The synchronicity displayed here between Greenland and central Europe, especially during the period 65-49 ka, is crucial for our understanding of climate-system teleconnections that existed during the last glacial period, and will be important for developing mechanisms of abrupt climate events.

Abstract. Sub-orbital-scale climate variability of the last glacial period provides important insights into the rates at which the climate can change state, the mechanisms that drive such changes, and the leads, lags, and synchronicity occurring across different climate zones. Such short-term climate variability has previously been investigated using δ18O from speleothems (δ18Ocalc) that grew along the northern rim of the Alps (NALPS), enabling direct chronological comparisons with δ18O records from Greenland ice cores (δ18Oice). In this study, we present NALPS19, which includes a revision of the last glacial NALPS δ18Ocalc chronology over the interval 118.3 to 63.7 ka using 11, newly available, clean, precisely dated stalagmites from five caves. Using only the most reliable and precisely dated records, this period is now 90 % complete and is comprised of 16 stalagmites from seven caves. Where speleothems grew synchronously, the timing of major transitional events in δ18Ocalc between stadials and interstadials (and vice versa) are all in agreement on multi-decadal timescales. Ramp-fitting analysis further reveals that, except for one abrupt change, the timing of δ18O transitions occurred synchronously within centennial-scale dating uncertainties between the NALPS19 δ18Ocalc record and the Asian monsoon composite speleothem δ18Ocalc record. Due to the millennial-scale uncertainties in the ice core chronologies, a comprehensive comparison with the NALPS19 chronology is difficult. Generally, however, we find that the absolute timing of transitions in the Greenland Ice Core Chronology (GICC) 05modelext and Antarctic Ice Core Chronology (AICC) 2012 are in agreement on centennial scales. The exception to this is during the interval of 100 to 115 ka, where transitions in the AICC2012 chronology occurred up to 3000 years later than in NALPS19. In such instances, the transitions in the revised AICC2012 chronology of Extier et al. (2018) are in agreement with NALPS19 on centennial scales, supporting the hypothesis that AICC2012 appears to be considerably too young between 100 and 115 ka. Using a ramp-fitting function to objectively identify the onset and the end of abrupt transitions, we show that δ18O shifts took place on multi-decadal to multi-centennial timescales in the North Atlantic-sourced regions (northern Alps and Greenland) as well as the Asian monsoon. Given the near-complete record of δ18Ocalc variability during the last glacial period in the northern Alps, we also offer preliminary considerations regarding the controls on mean δ18Ocalc for given stadials and interstadials. We find that, as expected, δ18Ocalc values became increasingly lighter with distance from the oceanic source regions, and increasingly lighter with increasing altitude. Exceptions were found for some high-elevation sites that locally display δ18Ocalc values that are heavier than expected in comparison to lower-elevation sites, possibly caused by a summer bias in the recorded signal of the high-elevation site, or a winter bias in the low-elevation site. Finally, we propose a new mechanism for the centennial-scale stadial-level depletions in δ18O such as the Greenland Stadial (GS)-16.2, GS-17.2, GS-21.2, and GS-23.2 “precursor” events, as well as the “within-interstadial” GS-24.2 cooling event. Our new high-precision chronology shows that each of these δ18O depletions occurred in the decades and centuries following rapid rises in sea level associated with increased ice-rafted debris and southward shifts of the Intertropical Convergence Zone, suggesting that influxes of meltwater from moderately sized ice sheets may have been responsible for the cold reversals causing the Atlantic Meridional Overturning Circulation to slow down similar to the Preboreal Oscillation and Older Dryas deglacial events.

Abstract. Sub-orbital-scale climate variability of the last glacial period provides important insights into the rates that the climate can change state, the mechanisms that drive that change, and the leads, lags and synchronicity occurring across different climate zones. Such short-term climate variability has previously been investigated using speleothems from the northern rim of the Alps (NALPS), enabling direct chronological comparisons with highly similar shifts in Greenland ice cores. In this study, we present NALPS19, which includes a revision of the last glacial NALPS δ18O chronology over the interval 118.3 to 63.7 ka using eleven,newly-available, clean, precisely-dated stalagmites from five caves. Using only the most reliable and precisely dated records, this period is now 90 % complete and is comprised of 15 stalagmites from seven caves. Where speleothems grew synchronously, major transitional events between stadials and interstadials (and vice versa) are all in agreement within uncertainty. Ramp-fitting analysis further reveals good agreement between the NALPS19 speleothem δ18O record, the GICC05modelext NGRIP ice-core δ18O record, and the Asian Monsoon composite speleothem δ18O record. In contrast, NGRIP ice-core δ18O on AICC2012 appears to be considerably too young. We also propose a longer duration for the interval covering Greenland Stadial (GS) 22 to GS-21.2 in line with the Asian monsoon and NGRIP-EDML. Given the near-complete record of δ18O variability during the last glacial period in the northern Alps, we offer preliminary considerations regarding the controls on mean δ18O. We find that as expected, δ18O values became increasingly more depleted with distance from the oceanic source regions, and increasingly depleted with increasing altitude. Exceptions were found for some high-elevation sites that locally display δ18O values that are too high in comparison to lower-elevation sites, thus indicating a summer bias in the recorded signal. Finally, we propose a new mechanism for the centennial-scale stadial-level depletions in δ18O such as "pre-cursor" events GS-16.2, GS-17.2, GS-21.2, and GS-23.2, as well as the "within-interstadial" GS-24.2 event. Our new high-precision chronology shows that each of these δ18O depletions occurred shortly following rapid rises in sea level associated with increased ice-rafted debris and southward shifts in the Intertropical Convergence Zone, suggesting that influxes of meltwater from moderately-sized ice sheets may have been responsible for the cold reversals causing the AMOC to slow down similar to the Preboreal Oscillation and Older Dryas deglacial events.

SI Figure 1. Samples analysed in this study. Black scale bars = 5cm Sample U-Th ages (n)Stable isotope measurements (n) Stable isotope spatial resolution (µm) Resolution of age model (yr), average in parentheses Growth rate (mm ka -1 ), average in parentheses BA-5 7 279 250 13 -24 (19) 10 -20 (14) BA-7 16 407 500 11 -24 (15) 21 -45 (34) SCH-6 7 349 250 6 -22 (9) 11 -44 (32) HÖL-19 8 159 250 4 -5 (5) 46 -68 (53) HUN-14 34 707 250 4 -24 (10) 11 -57 (35) GAS-12 12 751 250 4 -17 (7) 26 -61 (40) GAS-13 13 692 250 3 -7 (5) 34 -81 (54) GAS-22 16 530 200 2 -16 (5) 13 -100 (45) GAS-25 17 630 250 4 -8 (6) 30 -61 (40) GAS-27 9 240 250 6 -9 (7) 29 -39 (34) GAS-29 6 256 250 7 -9 (8) 28 -36 (32) Total 145 5,000 ---SI Table 1. U-Th and stable-isotope sampling information for the samples analysed in this study SI Figure 2. δ 18 O (red) and δ 13 C (blue) for each sample measured in this study relative to distance along growth axis. Black crosses mark locations of U-Th dating locations Sample (mm dft) 238 U [ng g -1 ] 232 Th [pg g -1 ] 230 Th / 232 Th (atomic x10 -6 ) δ 234 U* (measured) 230 Th / 238 U † (activity) Uncorrected Age (a) § Corrected Age (a)# δ 234 U* (initial) BA-5