Instability of the Atlantic overturning circulation during Marine Isotope Stage

Abstract

Variations in the strength of the Atlantic meridional overturning circulation (AMOC) were involved in the occurrences of Dansgaard-Oeschger (D-O) events during Marine Isotope Stage 3 (MIS3). The stability of the AMOC to North Atlantic freshwater perturbations is studied using a comprehensive climatemodel under MIS3 boundary conditions. An AMOC stability diagram constructed from a series of equilibrium freshwater perturbation experiments reveals a highly nonlinear dependence of AMOC strength on freshwater forcing. The MIS3 baseline state is remarkably unstable with respect to minor perturbations. The global climate signal associated with a change in AMOC strength is consistent with a transition from an interstadial to a stadial state including an annual mean surface air temperature drop of ∼8 K in central Greenland. We suggest that minor freshwater perturbations in the hydrologic cycle, e.g., related to ice sheet processes, had the potential to trigger D-O-type climate shifts associated with a threshold in the atmosphere-ocean system.