Collapse of the Atlantic Meridional Ocean Circulation Induced by Precession: Sensitivity to Orbital Acceleration

While orbital forcing-induced weakening of the Atlantic meridional overturning circulation (AMOC) potentially facilitated glacial initiation during the Quaternary glacial-interglacial cycles, this mechanism has remained to be confirmed by atmosphere-ocean general circulation models (AOGCMs). Our simulations with an AOGCM demonstrate that without any freshwater hosing, a complete AMOC collapse can be achieved through precessional forcing alone under high eccentricity and relatively low atmospheric CO₂ level (pCO₂). Crucially, the multi-millennial timescale required for full AMOC response to precessional forcing suggests that the orbital acceleration techniques in AOGCM simulations, often adopted to save computation time, likely obscured detection of these abrupt AMOC transitions in previous studies.