Sea-air CO 2 fluxes along the Brazilian continental margin

Abstract

Ocean and Coastal ResearchMeasurements of the marine carbonate system on tropical and subtropical continental margins are poorly distributed in space and time, with many uncertainties persisting regarding the role of carbon exchanges at the ocean-atmosphere interface in these areas. To calculate sea-to-air CO 2 fluxes in Marine Ecoregions along the Brazilian continental margin (4°N to 34°S), we used data from the Surface Ocean CO 2 Atlas (SOCAT v2020), collected up to 400 km from the coast, at the surface (5 m), between 1991 and 2018, with the aim of investigating the role of ecoregions as potential sinks or sources of atmospheric CO 2 . The temperature and salinity of seawater presented variability in the north-south direction mainly because of the broad latitudinal range, reflecting typical patterns of tropical (T = 27.4°C ±1.49; S = 36.4 ±1.91) and subtropical waters (T = 22.8°C ±3.41; S = 35 ±2.91), in addition to the greater or lesser influence of river inputs in each ecoregion. The pCO 2 values in the surface waters varied from 121.81 (Amazon) to 478.92 µatm (Eastern), differing significantly between ecoregions and showing an expected decadal increasing trend, both in the atmosphere and in the seawater. The calculated values of CO 2 fluxes showed non-homogeneous spatio-temporal variations, from -24.37 mmol m -2 d -1 (Rio Grande) to 9.87 mmol m -2 d -1 (Southeastern). Throughout the analyzed time series, we observed that the Northeast, Amazon and Eastern ecoregions acted predominantly as sources of CO 2 and the Southeastern ecoregions and, mainly, Rio Grande, acted predominantly as sinks of atmospheric CO 2 .

Environmental variability and hazards in the coastal and continental shelf regions of South America and the Caribbean

“…In this special issue of Ocean and Coastal Research, readers will find an interesting new by Soares et al (2023a) investigating how precipitation over the Brazilian state of Maranhão responds to ENSO-forced zonal teleconnection and its impacts on sea surface temperature patterns in the Western Equatorial Atlantic Ocean. Affe et al (2023), on the other hand, computed airsea fluxes of carbon dioxide (CO 2 ) in five different marine ecoregions of the Brazilian continental margin from 4 o S to 34 o S. These authors used surface water data from the Surface Ocean CO 2 Atlas (SOCAT v2020) from 1991 to 2018 and noticed that air-sea CO 2 fluxes depend on the biogeographic characteristics of the study area, which, in turn, depends on the effects of local upwelling, freshwater outflow from rivers, water mass and the variability of currents in the different ecoregions. The authors also observed a positive trend in the partial pressure of CO 2 in water and air during the study period and emphasized the meridional gradient in the direction of air-sea fluxes, in which the northern areas off the coast of Brazil tend to be sources of CO 2 , while the southern regions tend to be sink areas for atmospheric CO 2 .…”