Dynamics of Spontaneous (Multi) Centennial‐Scale Variations of the Atlantic Meridional Overturning Circulation Strength During the Last Interglacial

Abstract

Recent reconstructions of bottom water δ13C during the last interglacial (LIG) suggest short-lived variability in the Atlantic meridional overturning circulation (AMOC). Spontaneous (multi) centennial-scale variability of the AMOC simulated in the Earth system model of intermediate complexity iLOVECLIM are investigated for that period. The model simulates abrupt AMOC transitions occurring at 300 years frequency and correspond to a switch of the AMOC vigor between a strong (∼17 Sv) and a weak (∼11 Sv) state. The onset of these abrupt transitions is associated with changes in orbital forcings resulting in the decline of summer insolation in the high latitudes of the North Atlantic and affecting the sea ice cover in two key deep convection regions: (1) the northern Nordic Seas (NNS) and (2) the northwest North Atlantic (NWNA). Northward inflow of Atlantic surface water increases the convection depth in (1) and strengthens the Greenland Iceland Norway (GIN) Seas overturning circulation. Subsequent ocean-atmosphere interactions involving sea ice, ocean heat release, anomalies of evaporation-precipitation, and wind stress over the Nordic Seas lead also to an increase in deep convection in (2), followed by increase in the AMOC strength.