Wilma Huneke: Refining Southern Ocean lower overturning dynamics in ACCESS-OM3/CM3-25km
The Southern Ocean lower overturning circulation is poorly represented in most global ocean and coupled climate models. Australia’s ACCESS-OM2 flagship model at 1/10° resolution successfully simulates realistic Antarctic bottom water formation, driving recent advancements in understanding Southern Ocean dynamics. However, the 0.25° version failed to capture these processes effectively. In developing the next-generation ACCESS-OM3 global ocean-sea ice model and its coupled counterpart ACCESS-CM3, key insights from ACCESS-OM2 are incorporated to improve the representation of lower overturning dynamics, even at coarser grid resolutions (25 km). This study examines the promising progress made to date in representing Antarctic Bottom Water formation and reduced deep convection in the offshore Southern Ocean in ACCESS-OM3/-CM3 compared to their predecessors. Technical updates include grid resolution adjustments, revised GM parameterisation, spreading of Antarctic meltwater, at the coast and through a pseudo iceberg parameterisation and other configuration changes. As development remains ongoing, we welcome feedback and ideas to further improve the representation of the Southern Ocean lower overturning circulation.