Centennial AMOC Variability of North Atlantic–Arctic Origin: Mechanism and Future State

ABSTRACT

Centennial‐scale variability in the Atlantic Meridional Overturning Circulation (AMOC) exerts far‐reaching climatic influences, yet its mechanisms remain debated and its behaviour under anthropogenic warming is underexplored. This study demonstrates that centennial AMOC variability persists in both a pre‐industrial control simulation and an abrupt‐4 × CO ₂ simulation of the IPSL‐CM6A‐LR model. While previous research on the control simulation emphasized Arctic freshwater transport (FWT), particularly through the Fram Strait, as the driver due to its phase lag, we show that from a linear feedback perspective, this component is a negative feedback that damps AMOC anomalies. Instead, North Atlantic FWT and surface freshwater flux of the deep water formation region are two essential positive feedbacks that amplify AMOC anomalies. Together, these elements constitute a more comprehensive mechanism accounting for the amplification, damping, and timescale of the centennial AMOC variability in the control simulation, suggesting the variability is more accurately characterized as being of North Atlantic–Arctic origin. Under warming, the variability persists, but reduced sea‐ice weakens surface freshwater flux variability and Arctic FWT especially through the Fram Strait, thereby diminishing the Arctic's contribution to both feedback and phase lag. Conversely, North Atlantic FWT remains active and provides a longer phase lag, sustaining the variability with a longer period. These suggest a potential mechanistic shift toward a North Atlantic origin resembling previous findings in CESM1, and indicate that centennial AMOC variability mechanisms may be linked across different models and climate states.