CO2 fluxes under different oceanic and atmospheric conditions in the Southwest Atlantic Ocean

Abstract

The Southwest Atlantic Ocean (SAO) is one of the largest global carbon sink areas. Therefore, the main objective of this study is to investigate turbulent CO₂ flux behavior and quantify it in the presence of an intense horizontal sea surface temperature (SST) gradient in the SAO under different atmospheric conditions. In-situ, satellite, and reanalysis data were used from October 14 to 27, 2018 to achieve this objective. The study area was divided into four areas based on satellite observations of SST, salinity, and chlorophyll. The CO₂ flux was calculated using the eddy covariance method. During the experiment the area absorbing the most CO₂ was the Brazil Current (BC) owing to its proximity to the chlorophyll-rich and less saline waters of the La Plata River and the cold and less saline waters from the Malvinas Current (MC). Moreover, intense wind speeds increased the CO₂ flux between the ocean and atmosphere. The Brazil Malvinas Confluence (BMC) also behaved as a CO₂ sink, and the modulation of CO₂ fluxes was due to the intense horizontal gradient of SST together with the moderate surface wind and turbulence. During the experiment, the MC sequestered less carbon than other regions because of the presence of high-pressure atmospheric systems near the region, resulting in high atmospheric stability, that inhibited mass exchange between the ocean and atmosphere. Vertical mixing mechanisms were identified at the BMC on the cold side, over MC waters. However, in the BC waters, the marine atmospheric boundary layer was modulated by the high-pressure atmospheric system, which suppressed the turbulent mixing. However, the intense mass exchange between the ocean and atmosphere was inhibited, and the area behaved as a mild CO₂ sink because of the high-pressure system. This research contributes to a better understanding of the role of the SAO in the global carbon balance in a climate change scenario, and we showed that area can act as a CO₂ sink or source, depending on the large-scale atmospheric conditions acting.