Ocean Ventilation Controls the Contrasting Anthropogenic CO2 Uptake Rates Between the Western and Eastern South Atlantic Ocean Basins

The South Atlantic Ocean is an important region for anthropogenic CO2 (C-anth) uptake and storage in the world ocean, yet is less studied. Here, after an extensive sensitivity test and method comparison, we applied an extended multiple linear regression method with six characteristic water masses to estimate C-anth change or increase (Delta C-anth) between 1980s and 2010s in the South Atlantic Ocean using two meridional transects (A16S and A13.5) and one zonal transect (A10). Over a period of about 25 years, the basin-wide Delta C-anth was 3.86 +/- 0.14 Pg C decade(-1). The two basins flanking the Mid-Atlantic Ridge had different meridional patterns of Delta C-anth, yielding an average depth-integrated Delta C-anth in the top 2000 m of 0.91 +/- 0.25 mol m(-2) yr(-1) along A16S on the west and 0.57 +/- 0.22 mol m(-2) yr(-1) along A13.5 on the east. The west-east basin Delta C-anth contrasts were most prominent in the tropical region (0-20 degrees S) in the Surface Water (SW), approximately from equator to 35 degrees S in the Subantarctic Mode Water (Subantarctic Mode Water (SAMW)), and all latitudes in the Antarctic Intermediate Water (AAIW). Less Delta C-anth in the eastern basin than the western basin was caused by weaker ventilation driven by SAMW and AAIW formation and subduction and stronger Antarctic Bottom Water (AABW) formation in the former than the latter. In addition to the spatial heterogeneity, C-anth increase rates accelerated from the 1990s to the 2000s, consistent with the overall increase in air-sea CO2 exchange in the South Atlantic Ocean.