Inventory of water masses and carbonate system from Brazilian's northeast coast: Monitoring ocean acidification

This manuscript presents an inventory of the carbonate system from the main water masses comprising the marine current system on Brazil's northeast coast (South Atlantic Ocean). For this purpose, four transects were conducted with an approximate length of 357 km (each one) through the platform and continental slope of the Sergipe-Alagoas sedimentary basin. Water samples were then collected in vertical profiles measuring from 5 to 1,799 meters depth, totaling 34 stations. Total alkalinity, calcium, and total boron were obtained analytically from these samples and by relationships with salinity. Speciation and concentration of the carbonate system were obtained by means of thermodynamic modeling. The results revealed that the empirical models used to calculate the concentrations of TA, calcium and total boron showed relevant variation when compared to the analytical values (TA: 5.0-6.5%; Ca: 0.4-4.8%; B-T: 7.0-18.9%). However, the speciation and concentration of the carbonate system (CA, DIC, CO32-, CO2(aq), omega(Calc), and omega???????(Arag)) obtained from the empirical values of TA, calcium and total boron did not differ significantly from those obtained analytically (0.0-6.1%). On the other hand, the parameters of pH, HCO3-, CO3(aq)2-, CO2(aq), rho CO2, omega???????(Calc), and omega???????(Arag) varied significantly within the different water masses (p < 0.05). This study supports and encourages acidification monitoring projects in the South Atlantic Ocean, based on modeling the carbonate system parameters generated in real-time.