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Our understanding of climate dynamics during millennial-scale events is incomplete, partially due to the lack of their precise phase analyses under various boundary conditions. Here we present nine speleothem oxygen-isotope records from mid-to-low-latitude monsoon regimes with sub-centennial age precision and multi-annual resolution, spanning the Heinrich Stadial 2 (HS2) — a millennial-scale event that occurred at the Last Glacial Maximum. Our data suggests that the Greenland and Antarctic ice-core chronologies require +320- and +400-year adjustments, respectively, supported by extant volcanic evidence and radiocarbon ages. Our chronological framework shows a synchronous HS2 onset globally. Our records precisely characterize a centennial-scale abrupt "tropical atmospheric seesaw" superimposed on the conventional "bipolar seesaw" at the beginning of HS2, implying a unique response/feedback from low-latitude hydroclimate. Together with our observation of an early South American monsoon shift at the HS2 termination, we suggest a more active role of low-latitude hydroclimate dynamics underlying millennial events than previously thought. New cave records from monsoon regions improve the Greenland ice core chronological framework around the Heinrich Stadial 2 by an order of magnitude, suggesting a more active role of low-latitude hydroclimate in millennial-scale climate oscillations. [ABSTRACT FROM AUTHOR]

Oxygen isotope (δ18O) records of cave speleothem have played an important role in the past two decades in characterizing the Asian Monsoon (AM) variability and correlating the monsoonal events with other global climate events on millennial timescales. Of a series of millennial events occurred during the last glacial period, the Chinese Stadial-20 (CS-20, corresponding to the Greenland Stadial-20, GS-20) event around ∼73 kyr BP (thousand years before present, where present = 1950 AD) is distinctive, since it is the weakest AM event during the last glacial period and is likely linked to the Toba volcanic super-eruption. While Greenland ice core records are commonly used to correlate the last glacial millennial events, yet their absolute age uncertainties around the GS-20 is larger than 1000 years. This prohibits precise correlations of the event between global climate archives from different climate systems to investigate the underlying climatic dynamics. Here, we present three Chinese cave stalagmite δ18O records from the AM region, covering a period from 76 to 71 kyr BP, across the CS-20. All stalagmites have high uranium contents and relatively fast growth rates, allowing acquisition of high-resolution (∼10 years) δ18O records with precise 230Th age controls (≤200 years, 2σ) to precisely characterize the structure and timing of the CS-20. Our results demonstrate that the onset and termination of the CS-20 are more gradual in Chinese cave records relative to the GS-20 event in Greenland ice core records. As such, we suggest a new 'break-point' approach to correlate CS-20 with GS-20, at either the initial onset or initial termination shifts of the events, instead of the conventional 'mid-point' match. We dated the initial onset and initial termination of CS-20 to ~74.0 ± 0.2 and 72.5 ± 0.2 kyr BP, respectively, confirming the Greenland ice core chronology well within the quoted uncertainty. The 'break-point' correlation at the GS-20/CS-20 initial termination suggests a lagged onset of CS-20 relative to the onset of GS-20. The lagged onset is in line with a northern high-latitude forcing mechanism triggering the event and a central role of oceanic reorganizations in the propagation of the climate signal. An alternative 'break-point' correlation at the GS-20/CS-20 initial onset suggests that the CS-20 initial termination leads the GS-20 initial termination by a few hundred years. This apparent paradox thus calls for further empirical and theoretical studies to better understand the underlying climatic dynamics and in turn the correlation strategy. • New cave δ18O records characterize Greenland Stadial 20 events in monsoon regions. • Break-points replaced mid-points to correlate Greenland and Asian Monsoon events. • The end of the Greenland Stadial 20 event was initiated at 72.5 ± 0.2 kyr BP. • Our data lend age-benchmarks for correlating climate variability around 73 kyr BP. [ABSTRACT FROM AUTHOR]