Pacing the Abrupt: Milankovitch Modulation of Dansgaard-Oeschger Events Unveiled by Coupled Ice Core-Speleothem Chronologies

Abstract

Dansgaard-Oeschger (D-O) events represent pronounced, millennial-scale abrupt climate changes that characterized the last glacial period, involving rapid warming in the North Atlantic region followed by a more gradual cooling. While their internal dynamics, often linked to oceanic circulation reorganizations and ice sheet instability, have been extensively studied, the potential role of external, orbital-scale forcing in modulating their occurrence remains a significant subject of debate. This paper presents a novel approach to investigate the long-term pacing of D-O events by Milankovitch cycles through the synthesis of high-resolution, independently dated ice core and speleothem chronologies. By combining the precise temporal resolution and North Atlantic climate signal of ice cores with the robust U-Th dating and regional climate records from speleothems, a highly synchronized and accurate chronological framework is established. Spectral analysis, wavelet transforms, and phase coherence assessments applied to the reconstructed D-O event timings reveal statistically significant periodicities aligning with key Milankovitch parameters, particularly those associated with precession and obliquity. Our findings suggest that while D-O events are fundamentally internal to the climate system, their frequency and intensity are demonstrably modulated by the slowly varying orbital configuration, which preconditions the Earth's climate system, influencing the thresholds for abrupt transitions. This integrated chronological approach provides critical insights into the complex interplay between internal climate variability and external astronomical forcing, enhancing our understanding of past abrupt climate change and its implications for future climate trajectories.