Unveiling the Abyssal Southern Ocean

Antarctic Bottom Water – the densest and most voluminous water mass in the world – has a far-reaching influence on global climate. Formed in the southernmost limb of the global overturning circulation, it stores heat and carbon in the abyssal ocean for centuries and is the main source of oxygen to most of the deep ocean. The slowdown of Antarctic Bottom Water formation, manifesting as abyssal-ocean warming in recent decades, implies changes of global significance as less heat and carbon are sequestered in, and less oxygen is supplied to, the deep ocean. Yet, it remains one of the most difficult water masses to monitor due to winter sea ice cover and the abyssal depths at which it exists. The ACCESS-OM2-01 ocean-sea ice model is the only model known to accurately represent the formation and export of Antarctic Bottom Water.

This project investigates changes in properties, circulation, and mixing of Antarctic Bottom Water – filling the gap in understanding physical processes driving deep ocean variability – in unprecedented detail by comparing output from a state-of-the-art ocean-sea ice model to year-round, full-depth, in-situ Deep Argo float observations in the Australian-Antarctic Basin. This project will also determine the response of Antarctic Bottom Water formation and export to future climate scenarios using the ACCESS-OM2-01. Model runs mimicking expected future climate states, e.g. stronger and southern-shifted westerlies over the Southern Ocean to represent a strengthened Southern Annual Mode and increased surface freshwater fluxes on the shelf to represent increased glacial melt, will isolate specific drivers of variability in AABW formation. The ACCESS model also simulates ocean biogeochemistry, allowing for a parallel investigation into the impact of future climates on carbon uptake in the ocean.