Preliminary analysis of the variability of the marine carbonate system in the Brazil-Malvinas Confluence

The Brazil-Malvinas Confluence (BMC) is an important region of the South Atlantic Ocean. It is marked by high variability and instability, generated by the convergence of two currents with contrasting characteristics. The Brazil Current (BC) is associated with the South Atlantic Subtropical Gyre and is warm, saline and oligotrophic. The Malvinas Current (MC) is a branch of the Antarctic Circumpolar Current and is cold, rich in carbon dioxide (CO₂) and nutrients. In this context, this study aims to understand how the marine carbonate system behaves in three distinct parts of the confluence (BC, BMC and MC). We selected three points: MC (42°S, 56.25°W), BMC (38.25°S, 52.25°W) and BC (34.50°S, 48°W). Daily mean outputs (P1D) were extracted from the Copernicus CMEMS Global Ocean Biogeochemistry Analysis and Forecast product (GLOBAL_ANALYSISFORECAST_BGC_001_028), which has a horizontal spatial resolution of 0.25° × 0.25°, for the period from November 2021 to June 2026. The extracted surface-layer variables were potential temperature, salinity, total alkalinity (TA), pH and dissolved inorganic carbon (DIC). In addition, the partial pressure of carbon dioxide (pCO₂) was calculated from TA and DIC using the CO2SYS routines. The results suggest that each of the three regions is dominated by a different water mass; Tropical Water (BC), a mixture of waters from the Río de la Plata plume (BMC), and Malvinas Current Surface Water (MC). The DIC–TA distribution suggests conditions for surface CaCO₃ dissolution in the BC and BMC regions and for CO₂ uptake in the MC region, with strong variability in the BMC. Over the study period, the results suggest a decrease in the TA – DIC difference (μmol/L) in the MC region. This region also showed the highest Revelle factor values, which reinforces the increase in surface DIC, possibly driven by CO₂ uptake. Despite the predominant CO₂ "sink" behavior in the MC region, no CaCO₃ (aragonite) undersaturation was observed. A thorough understanding of the processes controlling the marine carbonate system requires expanding the study area and include other physical parameters, such as vorticity and the vertical structure of the water column.