Seasonal and Interannual Variability of Antarctic Bottom Water Downstream of the Four Key Formation Regions

Abstract

Antarctic Bottom Water (AABW) is a cold, dense water mass formed around Antarctica that ventilates the global abyssal ocean. Recent studies have reported widespread warming, freshening, and thinning of AABW, yet its temporal variability remains poorly constrained because of sparse observations. This limits our ability to distinguish trends induced by climate change from natural variability. We address this limitation by examining seasonal and interannual AABW variability using passive dye‐like tracers in the high‐resolution ocean–sea ice model ACCESS‐OM2‐01. The tracers are released in four key AABW formation regions: the Ross and Weddell Seas, Prydz Bay and the shelf adjacent to Adélie Land. We find pronounced differences in the magnitude and time scales of AABW variability across formation regions. AABW from the narrow‐shelf regions (Prydz Bay and Adélie Land coast) is characterized by high seasonal variability, reaching about 0.16 tracer units (equivalent to 100% of its local time‐mean tracer concentration) along the continental slope. By contrast, seasonal variability of AABW formed on the wide shelves (Ross and Weddell Seas) remains below 50% of its local time‐mean concentration. Interannual variability is strongest in the Weddell Sea, where it reaches 0.12–0.15 tracer units (40%–50% of its local time‐mean concentration) along the continental slope. Advective timescales show that AABW from narrow‐shelf sources ventilates the abyss on much shorter time scales (1 year) than AABW from wide shelves (2 years). These findings provide new context for interpreting observed deep‐ocean changes, helping to distinguish anthropogenic trends from natural variability and sampling limitations.