Evaluation of the mechanisms acting on the Atlantic Meridional Overturning Circulation in CESM2 for the 1pctCO2 experiment

Abstract

The Atlantic Meridional Overturning Circulation (AMOC) is a crucial component of the Earth's climate system due to its fundamental role in heat distribution, carbon and oxygen transport, and the weather. Other climate components, such as the atmosphere and sea ice, influence the AMOC. Evaluating the physical mechanisms of those interactions is paramount to increasing knowledge about AMOC's functioning. In this study, the authors used outputs from the Community Earth System Model version 2 and observational data to investigate changes in the AMOC and the associated physical processes. Two DECK experiments were evaluated: piControl and 1pctCO2 , with an annual increase of 1% of atmospheric CO2 . The analysis revealed a significant decrease in the AMOC, associated with changes in mixed layer depth and buoyancy in high latitudes of the North Atlantic, resulting in the shutdown of deep convection and potentially affecting the formation of North Atlantic Deep Water and Antarctic Bottom Water. A vital aspect observed in this study is the association between increased runoff and reduced water evaporation, giving rise to a positive feedback process. Consequently, the rates of freshwater spreading have intensified during this period, which could lead to an accelerated disruption of the AMOC beyond the projections of existing models.