Mechanisms Controlling the Past, Present, and Future Trends in the South Atlantic Ocean’s Heat Storage in a Set of CESM2 Large Ensemble Simulations

The South Atlantic Ocean is projected to warm under the increase in greenhouse gas emissions. How much of this warming is due to the ocean or the atmosphere has been an open question. With the hypothesis that changes in the Atlantic meridional overturning circulation (AMOC) are the main mechanism explaining the South Atlantic Ocean warming, this work aims to understand the changes in the components of the heat budget in the South Atlantic Ocean (08–348S) during the historical and future transient periods. We examine the simulations performed as part of the Community Earth System Model (CESM), version 2, Large Ensemble project (LENS2) that follow the Coupled Model Intercomparison Project phase 6 protocols. Specifically, we analyze the heat budget between 1850 and 2100 and investigate the relationship between changes in the heat budget and changes in AMOC. Our analysis reveals that from 1850 to the 1990s, the surface heat fluxes are partially in equilibrium with the heat exchanged laterally at 348S and the equator. Consequently, no significant trends in the heat storage rate are seen for that period. However, during the 2015–2100 future period, under the shared socioeconomic pathways 3-7.0 scenario, the heat storage rate significantly increases due to reduced northward heat transport at the equator. This reduction is attributed to the weakening of the AMOC upper cell transport. This article emphasizes the crucial role of the AMOC in regulating the heat balance in the South Atlantic and its potential to alter the basin temperature in a warming climate.