Ocean Acidification

The southwestern South Atlantic Ocean is an important global sink of atmospheric carbon dioxide (CO₂), driven by increased primary productivity in a nearby region where oligotrophic warm currents converge with nutrient-rich cold waters. However, uncertainties remain regarding CO₂ dynamics and the role of physical processes in CO₂ uptake across this region. Here, we assess variations in surface partial pressure of CO₂ (pCO₂) and air–sea CO₂ fluxes in the Southwest Atlantic, along a transect from the continental shelf to the open ocean at 34.5°S during austral autumn 2018 and winter 2019. High-resolution spatial measurements of the temperature, salinity, and molar fraction of surface CO₂ were conducted. In autumn 2018, the shelf region acted as a source of CO₂ to the atmosphere (median of 3.2 mmol CO₂ m^-2 d^-1), which was partially offset by a sink (median of –2.5 mmol CO₂ m^-2 d^-1) in the open ocean. In contrast, the entire transect in winter 2019 presented median CO₂ emissions of ~1.5 mmol CO₂ m^-2 d^-1, which differs from climatological estimates. The spatial and seasonal variations in surface ocean pCO₂ were linked to variable hydrodynamic processes, including water masses and mesoscale structures. Our findings reveal that, in one of the most productive oceanic waters worldwide, pCO₂ may be influenced by distinct continental inputs (e.g., rivers, runoff, and groundwater discharge) and water masses (e.g., Tropical Water, Plata Plume Water and Subtropical Shelf Water). Therefore, the local hydrodynamic processes can modulate high spatial and seasonal variability in CO₂ exchange at the ocean–atmosphere interface, with potential implications for regional and global carbon budgets. General results, such as climatological, cannot fully capture the influence of regional upwelling and continental water input, which highlights the importance of high-resolution regional observations.

Albuquerque C., Miguel G., Lencina-Avila J. M., Pinho L., Marotta H., Fernandes A. M., Passos E. N., Amora-Nogueira L., Campos E. & Cotrim da Cunha L., 2025. Linking surface pCO₂ variability to physical processes along a continental shelf–ocean transect in the southwestern Atlantic Ocean during austral autumn and winter. Frontiers in Marine Science 12: 1623344. doi: 10.3389/fmars.2025.1623344. Article.