Southern Ocean heat and momentum uptake are sensitive to the vertical resolution at the ocean surface

The Southern Ocean plays a leading oceanic role in Earth's changing climate, accommodating over two thirds of the excess anthropogenic heat to date. In spite of this, climate and ocean models exhibit substantial variability in Southern Ocean heat uptake and storage, reflecting the modelling challenges of representing the responsible mechanisms. Here, Southern Ocean heat uptake is investigated in a suite of global ocean-sea-ice simulations run over a range of vertical and horizontal resolutions and forced with an idealized thermal perturbation. It is found that the ocean surface speed is sensitive to the vertical resolution at the ocean surface. Subsequently, the wind stress and its curl, which are important factors for Southern Ocean heat uptake, are also sensitive to the vertical resolution at the ocean surface, tending to decrease with refined surface resolution. It follows that the Southern Ocean heat uptake itself is sensitive to the vertical resolution at the surface; indeed, the simulations here with relatively coarse surface resolution (10m) exhibit heat content changes at rates nearly double that of simulations with finer surface resolution (1m). There is relatively little sensitivity of Southern Ocean heat uptake to the horizontal resolutions examined here (1 degrees and 0.25 degrees), although the higher resolution simulations exhibit increased wind-driven upwelling. Importantly, all simulations demonstrate that the location of the zero wind stress curl determines the location of the maximum heat uptake. These findings offer guidance for examining Southern Ocean heat uptake and storage in future modelling studies and observations.