Global marine anthropogenic CO2 inventories have traditionally emphasized the North Atlantic’s role in the carbon cycle, while Southern hemisphere processes are less understood. The South Subtropical Convergence (SSTC) in the South Atlantic, a juncture of distinct nutrient-rich waters, offers a valuable study area for discerning the potential impacts of climate change on the ocean’s biological carbon pump (Csoft). Using discrete observations from GLODAPv2.2022 and BGC-Argo at 40°S in the Atlantic Ocean, an increase in dissolved inorganic carbon (DIC) of +1.44 ± 0.11 μmol kg-1 yr-1 in surface waters was observed. While anthropogenic CO2 played a role, variations in the contribution of Csoft were observed. Discrepancies emerged in assessing Csoft based on the tracers employed: when using AOU, Csoft(AOU) recorded an increase of +0.20 ± 0.03 μmol kg‑1 yr-1, whereas, using nitrate as the reference, Csoft(NO3) displayed an increase of +0.85 ± 0.07 μmol kg-1 yr-1. Nonetheless, our observations at 40°S indicate a significant intensification of Csoft, which, scaled to the entire ocean, represents an additional 23% to 35% of organic carbon degradation within the water column. Key processes such as water mass composition shifts, changes in oxygenation, remineralization in the Southern Ocean, and the challenges they pose in accurately representing the evolving Csoft are discussed. These findings highlight that while global studies primarily attribute DIC increase to anthropogenic CO2, observations at 40°S reveal an intensified biological carbon pump, showing that regional DIC changes are more complex than previously thought and challenging the dominance of anthropogenic sources in global DIC change.
