Milankovitch as Metronome: Orchestrating Dansgaard-Oeschger Abruptness

Abstract

Earth's climate during the Quaternary period has shown profound variability across diverse timescales. While Milankovitch cycles, driven by orbital variations, are the primary pacemaker for glacial-interglacial cycles, the more abrupt, millennial-scale Dansgaard-Oeschger (DO) events represent a fundamental mode of internal climate system variability. For a long time, these two phenomena were considered largely distinct. This paper explores the hypothesis that Milankovitch cycles, rather than directly causing DO events, act as a 'metronome' orchestrating their abruptness by modulating background conditions and internal feedbacks. We review properties of both Milankovitch forcing and DO events, examining proposed internal climate mechanisms for the latter. Drawing on recent paleoclimate data and climate modeling, we propose a conceptual framework where slow, predictable orbital forcing tunes the sensitivity of the Atlantic Meridional Overturning Circulation (AMOC), ice sheet dynamics, and atmospheric circulation. This tuning influences the frequency, amplitude, and character of rapid North Atlantic climate reorganizations. This perspective suggests orbital forcing creates a 'sweet spot' or modulates the propensity for the climate system to enter or exit states favorable for abrupt millennial-scale change, providing a rhythmic backdrop against which seemingly chaotic DO abruptness unfolds.