Role of mesoscale eddies in ventilation pathways of South Atlantic AAIW using Lagrangian backtracking

We investigate mesoscale eddy effects on the ventilation timescales and pathways of South Atlantic Antarctic Intermediate Water (AAIW) using a high-resolution 1/10° eddy-resolving ocean model (Parallel Ocean Program) combined with a Lagrangian particle tracking algorithm (OceanParcels). AAIW sequesters a significant amount of anthropogenic carbon along its ventilation pathways through the eddy-rich Southern Ocean. The distribution of subduction zones along dynamic sections of the Antarctic Circumpolar Current, as well as the Malvinas Confluence Zone, indicates an influence of mesoscale eddies on ventilation, in addition to the zonally uniform Ekman transport. To identify eddy effects, we perform particle backtracking from the South Atlantic AAIW interior to the mixed layer, both with eddy-resolving model output velocity and its mean state, where mesoscale eddy velocities are absent. We characterise mean ages and ventilation pathways for South Atlantic AAIW originating from subduction zones located around the Drake Passage, the South Atlantic, and the South Indian Ocean. Eddy effects increase the contribution of Drake Passage waters to the South Atlantic AAIW and reduce mean age estimates, attributable to accelerated advection together with deeper and more southward subduction below the mixed layer, near the Malvinas Confluence Zone. We highlight the role of eddies in the ventilation of the South Atlantic pycnocline, which, if accurately represented, increase estimates of ventilation rates and strengthen cold water inflow, enhancing Southern Ocean carbon and heat uptake in ocean models.