Anthropogenic CO2 and ocean acidification in Argentine Basin Water Masses over almost five decades of observations

The chemical conditions of the Argentine Basin (western South Atlantic Ocean) water masses are evaluated with measurements from eleven hydrographic cruises to detect and quantify anthropogenic and natural stressors in the ocean carbon system. The database covers almost half-century (1972-2019), a time-span where the mean annual atmospheric carbon dioxide concentration (CO2atm) increased from 325 to 408 ppm of volume (ppm). This increase of atmospheric CO2 (83 ppm, the 64% of the total anthropogenic signal in the atmosphere) leads to an increase in anthropogenic carbon (C-ant) across all thewater columnand the consequent ocean acidification: a decrease in excess carbonate that is unequivocal in the upper (South Atlantic CentralWater, SACW) and intermediate water masses (Sub Antarctic Mode Water, SAMW and Antarctic Intermediate Water, AAIW). For each additional ppm in CO2atm the water masses SACW, SAMW and AAIW lose excess carbonate at a rate of 0.39 +/- 0.04, 0.47 +/- 0.05 and 0.23 +/- 0.03 mu mol.kg(-1).ppm(-1) respectively. Modal and intermediate water masses in the Argentine Basin are very sensitive to carbon increases due lowbuffering capacity. The large rate of AAIWacidification is the synergic effect of carbon uptake combined with deoxygenation and increased remineralization of organicmatter. If CO2 emissions follows the path of business-as-usualemissions (SSP 5.85), SACWwould become undersaturated with respect to aragonite at the end of the century. The undersaturation in AAIW is virtually unavoidable. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

The study evaluates the chemical conditions of water masses in the Argentine Basin and finds that the increasing atmospheric CO2 concentration has led to ocean acidification, especially in the SACW, SAMW, and AAIW water masses. The research suggests that if CO2 emissions continue as usual, the undersaturation of aragonite in SACW is expected by the end of the century, while the undersaturation in AAIW is virtually unavoidable.