Nonlinear feedback of Asian summer monsoon to abrupt events in North Atlantic: Evidence from a precisely dated speleothem record during late MIS3

Millennial-scale climate oscillations, particularly Dansgaard-Oeschger (DO) events, were prevalent during Marine Isotope Stage 3 (MIS3), but their regional responses/feedbacks remain poorly understood. We present a high-resolution (∼4 years) speleothem δ¹⁸O record from the Sichuan Basin, spanning late MIS3, with 56 precise ²³⁰Th dates (∼ ± 60 years) and approximately ∼4804 fluorescence annual laminas, to constrain the Asian summer monsoon (ASM) response/feedback to the millennial-scale climate oscillations. Our results show that the varying durations of strong and weak ASM phases during DO events reinforce the important role of atmospheric CO₂ levels and orbital parameters (precession and obliquity) in shaping the nonlinear feedbacks of millennial-scale climate variability. These findings are consistent with recent climate simulations, which emphasize the influence of CO₂ and orbital factors on the balance between tropical net precipitation and subpolar sea-ice shelves in the North Atlantic. In addition, all transitions from weak to strong monsoon phases during the DO cycles extended to centennial timescales (∼153–233 years), in contrast to the abrupt, decadal-scale oxygen isotope transitions in Greenland influenced by regional sea-ice shelves changes in the North Atlantic. This observation suggests a relatively gradual change in the Atlantic Meridional Overturning Circulation during these periods, providing new insights into the dynamics of past climate transitions.