Sensitivity of Antarctic dense water formation to surface vertical resolution

Dense water formation on the Antarctic continental shelf drives the abyssal overturning circulation, being the main process by which Antarctic Bottom Waters form. Despite its importance, most ocean models cannot simulate dense water formation at the Antarctic coast and flow down the continental slope (i.e., overflow) due to the fine resolution required by these processes. While many studies have looked at the impact of horizontal and vertical resolution in the deep ocean on the overflows, no studies have investigated whether surface vertical resolution impacts dense water formation. In this work, we varied the surface ocean cell of two dense water-forming models from 1m to 5m thickness as a simple vertical resolution sensitivity test. We used the ACCESS-OM2 and the Pan-Antarctic ocean and sea ice models, each employing a different boundary layer parameterization. Thickening the surface cell to 5m in ACCESS-OM2 decreased the dense water formation at the Antarctic continental shelf by 45% (1.5 Sv) and ceased its overflow through the continental slope after 10 years of simulation. In the Pan-Antarctic, thickening the surface cell reduced the Antarctic dense water formation by 34% (1.5 Sv) and its overflow by 67% (2.5 Sv) after 10 simulation years. The dense water formation reduction in 5m experiments is explained by a southward shift in the surface Ekman transports, bringing light offshore waters to the coast and prohibiting dense water formation at the Antarctic continental shelf. This response is independent of the boundary layer scheme employed.