Milankovitch-Driven Thresholds for Dansgaard-Oeschger Abruptness: A Coherent Ice Core-Speleothem Synthesis

Abstract

Dansgaard-Oeschger (DO) events represent some of the most dramatic examples of abrupt climate change during the last glacial period, characterized by rapid warming in Greenland followed by a more gradual cooling. While these events are well-documented in ice core records and have teleconnected impacts across the globe, the ultimate underlying mechanisms and external forcings that modulate their occurrence and abruptness remain subjects of intense research. This paper presents a coherent synthesis of high-resolution ice core and precisely dated speleothem records to investigate the potential role of Milankovitch orbital cycles in establishing thresholds that govern the abruptness of DO events. By aligning and comparing paleoclimate proxy data from both hemispheres, particularly focusing on Greenland ice isotope records and Chinese and European speleothem oxygen isotope series, we aim to identify non-linear relationships and critical orbital configurations that appear to precondition the climate system's sensitivity to abrupt shifts. Our findings suggest that variations in Northern Hemisphere summer insolation, driven by eccentricity and obliquity, may not directly trigger DO events but rather modulate the background climatic state, influencing the magnitude and rate of temperature change during these abrupt transitions. Specifically, we propose that certain Milankovitch configurations, by affecting ice sheet stability, ocean circulation strength, and atmospheric moisture transport, create windows of increased or decreased susceptibility, effectively acting as Milankovitch-driven thresholds for DO abruptness. This synthesis provides crucial insights into the complex interplay between long-term orbital forcing and internal climate variability, enhancing our understanding of past climate dynamics and informing future climate projections.