| Summary: | Recent supercomputing power improvements enable us to explore climate variability and change with coupled models that resolve the ocean mesoscale, its fine-scale interactions and feedbacks. Although these processes are usually parametrised in standard resolutions, several studies have already shown that effectively resolving them leads to reduced model biases in the ocean and improved air-sea interactions. In this study, we have used control simulations with the global climate model EC-Earth3P following the HighResMIP protocol to investigate the role of fine-scale processes in large-scale ocean circulation in the Atlantic. In particular, we have worked with three configurations of the model: eddy-parameterised (~100 km nominal horizontal resolution in mid-latitudes), eddy-permitting (~25 km) and eddy-resolving oceans (~10 km). For each model configuration, we have studied the two leading modes of variability of the mixed-layer depth in the subpolar North Atlantic. We have explored their drivers and preconditioners (which include the background stratification, the local buoyancy forcing from the atmosphere, and the advection of salinity and temperature anomalies by the mean circulation). We have also investigated whether and how they eventually impact the variability of the Atlantic Meridional Overturning Circulation (AMOC) through their influence on the southward propagation of density anomalies along the western boundary current.
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