Eddy-Induced Subduction of the Subantarctic Mode Water in the Southern Ocean from 2004 to 2023

Abstract Subantarctic Mode Water (SAMW) originates from the austral winter deep mixed layer north of the Antarctic Circumpolar Current, which is characterized by energetic mesoscale eddy activities. However, the effects of mesoscale eddies on SAMW subduction remain poorly quantified. The present study evaluates eddy-induced subduction of SAMW between 2004 and 2023 based on multiple datasets and the Gent and McWilliams parameterization with spatiotemporally varying eddy diffusivity. For the mean state, eddy-induced SAMW subduction prevails on the northern flank of the deep mixed layer pools. In particular, eddy-induced subduction contributes 3.01 ± 1.10 Sv (1 Sv ≡ 10 6 m 3 s −1 ) (34.7%) to total subduction of SAMW in the southeast Indian Ocean (SEISAMW), only slightly smaller than temporal induction (3.14 ± 0.47 Sv; 36.2%). For the long-term variability since 2004, mesoscale eddy effects are also important. Dominated by changes in eddy-induced subduction and temporal induction, the SEISAMW subduction has shifted to lighter isopycnals, and the volumetric subduction of the lighter layer of SEISAMW (26.40–26.65 kg m −3 ) has increased significantly. Our results indicate that mesoscale eddies play a crucial role in both the mean state and long-term variability of the SEISAMW subduction, with important implications for oceanic heat and carbon uptake in the Southern Ocean.