Fig. 1: Southern Ocean circulation dynamics.

a Seawater O₂ concentrations (in µmol/kg) at 3 km water depth according to the Global Ocean Data Analysis Project version 2 (GLODAPv2)⁴⁸. White lines (from south to north) indicate the Polar Front (PF) and the South Antarctic Front (SAF)⁸³. Blue arrows show the flow of Antarctic Bottom Water (AABW) from its source regions⁸. b Simulated present-day AABW tracer concentrations at the model bottom cell (after 61 model years) emerging from the Weddell Sea (upper color bar) and the Ross Sea (lower color bar) based on the ACCESS-OM2-01 model²⁵ with green and pink contours showing areas where tracer concentrations are larger than 0.02, respectively, highlighting the dispersal of AABW varieties in the Southern Ocean controlled by bathymetry. Light gray regions in a, b indicate bathymetry shallower than 3 km water depth. Blue areas in Antarctica highlight major ice shelves. c Water column transects in the Pacific (AA’ in a, b) and Atlantic Southern Ocean (BB’ in a, b) of seawater O₂ concentrations (shading) and neutral densities (white and red contours) (GLODAPv2)⁴⁸. The neutral density γ_n = 28.27 kg/m³ separating Circumpolar Deep Water (CDW) from AABW is shown in red⁸. Arrows indicate the flow paths of CDW (stippled) and AABW (solid). The locations of IODP Site U1540, ODP Site 1094, ODP Site 1123 and core PS75/059-2 are indicated with stars. Figure was created using Ocean Data View⁸⁴.