Interannual Variability of the South Atlantic Ocean Heat Content in a High-Resolution Versus a Low-Resolution General Circulation Model

High- and low-resolution coupled climate model simulations are analyzed to investigate the impact of model resolution on South Atlantic Ocean Heat Content (OHC) variability at interannual time scale and the associated physical mechanisms. In both models, ocean heat transport convergence is the main driver of OHC variability on interannual time scales. However, the origin of the meridional heat transport (MHT) convergence anomalies differs in the two models. In the high-resolution model, OHC variability is dominated by MHT from the south. This is in contrast to the low-resolution model, where OHC variability is largely controlled by MHT from the north. In the low-resolution simulation, both the Ekman and geostrophic transports contribute to the OHC variability, whereas in the high-resolution model, the geostrophic transport dominates. These differences highlight the importance of model resolution to appropriately represent ocean dynamics in the South Atlantic Ocean and associated impacts on regional and global climate. Plain Language Summary In this study we analyze heat content changes of the upper South Atlantic Ocean and the impact of model resolution on these changes. Results from two numerical simulations are compared. One simulation with high-resolution allows smaller-scale processes directly, while the other simulation with low-resolution does not. In both simulations oceanic heat transport dominates the ocean heat content changes on interannual time scale, while atmospheric fluxes play a secondary role. The heat anomalies, however, originate from different regions in the two simulations. While the oceanic heat transport from the south dominates in the high-resolution simulation, oceanic heat transport from the north dominates in the low-resolution simulation. Furthermore, wind-induced surface heat transport plays a significant role in the low-resolution while the heat transport in the high-resolution simulation is dominated by changes in the ocean density field at depth. These results suggest fundamentally different driving mechanisms between the simulations and highlight the importance of model resolution to appropriately represent ocean dynamics in the South Atlantic Ocean and associated impacts on large-scale climate. Key Points Interannual variability of South Atlantic Ocean heat is determined by different mechanisms in high- and low-resolution simulations Signals enter from the south in the high-resolution and from the north in the low-resolution simulation Ekman heat transport contributes significantly in the low-resolution while geostrophic heat transport dominates in the high-resolution