The ocean has absorbed more than one quarter of anthropogenic carbon emissions since the 1850s, acting as a critical buffer of atmospheric CO₂ increases and thus moderating climate change. Sustained oceanic CO₂ uptake requires the export of dissolved inorganic carbon (DIC) from the surface mixed layer into the ocean interior through water mass subduction, yet the magnitude, variability, and drivers of global carbon subduction remain poorly understood. Here we quantify global carbon subduction by combining observation-based estimates of water mass subduction with machine-learning reconstructions of subsurface DIC. During the Argo era (2005–2022), we estimate that approximately 270.3 ± 9.4 Pg C yr^-1 of DIC has been subducted into the ocean interior between 65°S and 65°N. About 75% of this carbon subduction is associated with mode and intermediate waters, with approximately 27% occurring in the Subantarctic Mode Water (SAMW) formation region of the Southern Ocean. We estimate that global carbon subduction has increased by 24.7 ± 8.6 Pg C yr⁻¹ since 2005, with approximately 43% of this increase occurring in the SAMW formation region, despite it occupying only ~13% of the global ocean surface area. Decomposition of carbon subduction in mode water formation regions shows that recent increases are driven primarily by intensified mode water subduction associated with winter mixed layer deepening, rather than by increases in DIC concentration. These results highlight the dominant role of SAMW in regulating recent changes in ocean carbon uptake and underscore the importance of monitoring high-latitude mixed layer dynamics for predicting future ocean carbon sequestration.

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