Quantification of Antarctic Bottom Water Pathways in the Australian-Antarctic Basin

Antarctic Bottom Water (AABW) formation drives the lower limb of the meridional overturning circulation, influencing the Earth's climate, carbon cycle, and marine biological productivity. Recent findings suggest that AABW across the Southern Ocean is changing, including freshening, warming and thinning. These changes motivate the need for process-based understanding of AABW circulation and variability. However, the harsh Antarctic environment limits in-situ observations, making high-resolution models an essential tool for investigating AABW. This study examines AABW varieties from the Ross Sea and the continental shelf adjacent to the Adélie Land coast in the Australian-Antarctic Basin. We explore their interactions and pathways using passive dye-like tracers in an ocean–sea ice model. Our findings reveal that, despite higher volume transport across the shelf break, RSBW contributes less to the basin's ventilation compared to ALBW. This is due to the presence of alternative pathways that divert RSBW eastward and its significant mixing with ambient waters along the continental slope. In contrast, ALBW plays a more prominent role in ventilating the abyssal waters of the basin, a conclusion supported by recent Deep Argo observations. We also found that when RSBW first encounters ALBW along the slope, it vertically overrides ALBW due to its relatively lower density at this stage.