North Atlantic Ocean circulation and deep water formation under warmer climate conditions in EC-Earth3-HR

Abstract In this study, we analyze the impact of increased atmospheric CO₂ concentrations on the Atlantic Meridional Overturning Circulation (AMOC) and its dependence on North Atlantic Deep Water Formation (DWF), using the high-resolution version of the global coupled model EC-Earth3. The analyzed experiments include a pre-industrial control and two fixed CO₂ concentration scenarios, representative of stable warmer climate conditions and designed to investigate the long-term adjustments of the Earth system. Within this framework, we assess DWF using a novel method based on horizontal volume convergence in the main convective regions of the North Atlantic: the Labrador, Greenland-Iceland-Norway, and Irminger Seas. Our results suggest that under warmer climate conditions surface warming and freshening in the North Atlantic lead to disrupt deep convection, reduce DWF, and thereby weaken the AMOC. The reduction of DWF in the Labrador Sea emerges as the primary driver of AMOC weakening. In contrast, the Irminger Sea plays a central role in sustaining AMOC. The strengthened export of deep water from the Arctic Ocean also provides a stabilizing influence, though its effect is secondary to the sustained DWF in the Irminger Sea.