ALBERT

Description: The wind-driven part of the South Atlantic Ocean is primarily ventilated through central and intermediate water formation. Through the water mass formation processes, anthropogenic carbon (C-ant) is introduced into the ocean's interior which in turn makes the South Atlantic region vulnerable to ocean acidification. C-ant and the accompanying acidification effects have been estimated for individual sections in the region since the 1980s but a comprehensive synthesis for the entire basin is still lacking. Here, we quantified the C-ant accumulation rates and examined the changes in the carbonate system properties for the South Atlantic using a modified extended multiple linear regression method applied to five hydrographic sections and data from the GLODAPv2.2021 product. From 1989 to 2019, a mean C-ant column inventory change of 0.94 +/- 0.39 mol C m(-2) yr(-1) was found. C-ant accumulation rates of 0.89 +/- 0.33 mu mol kg(-1) yr(-1) and 0.30 +/- 0.29 mu mol kg(-1) yr(-1) were observed in central and intermediate waters, accompanied by acidification rates of -0.0020 +/- 0.0007 pH units yr(-1) and -0.0009 +/- 0.0009 pH units yr(-1), respectively. Furthermore, increased remineralization was observed in intermediate waters, amplifying the acidification of this water mass, especially at the African coast along 25 degrees S. This increase in remineralization is likely related to circulation changes and increased biological activity nearshore. Assuming no changes in the observed trends, South Atlantic intermediate waters will become unsaturated with respect to aragonite in similar to 30 years, while the central water of the eastern margins will become unsaturated in similar to 10 years.

Description: Flow of dense shelf water provide an efficient mechanism for pumping CO 2 to the deep ocean along the continental shelf slope, particularly around the Antarctic bottom water (AABW) formation areas where much of the global bottom water is formed. However, the contribution of the formation of AABW to sequestering anthropogenic carbon ( C ant ) and its consequences remain unclear. Here, we show prominent transport of C ant (25.0 ± 4.7 Tg C yr −1 ) into the deep ocean (〉2,000 m) in four AABW formation regions around Antarctica based on an integrated observational data set (1974–2018). This maintains a lower C ant in the upper waters than that of other open oceans to sustain a stronger CO 2 uptake capacity (16.9 ± 3.8 Tg C yr −1 ). Nevertheless, the accumulation of C ant can further trigger acidification of AABW at a rate of −0.0006 ± 0.0001 pH unit yr −1 . Our findings elucidate the prominent role of AABW in controlling the Southern Ocean carbon uptake and storage to mitigate climate change, whereas its side effects (e.g., acidification) could also spread to other ocean basins via the global ocean conveyor belt. Plain Language Summary The Southern Ocean is thought to uptake and store a large amount of anthropogenic CO 2 ( C ant ), but little attention has been paid to the Antarctic coastal regions in the south of 60°S, mainly due to the lack of observations. Based on an integrated data set, we discovered the deep penetration of C ant and a visible pattern of relatively high concentration of C ant along the AABW formation pathway, and the concentration of C ant along the shelf‐slope is higher than that of other marginal seas at low‐mid latitudes, implying a highly effective C ant transport in AABW formation areas. We also found strong upper‐layer CO 2 uptake and a significant acidification rate in the deep waters of the Southern Ocean due to the AABW‐driven CO 2 transport, which is 3 times faster than those in other deep oceans. It is therefore crucial to understand how the Antarctic shelf regions affect the global carbon cycle through the uptake and transport of anthropogenic CO 2 , which also drives acidification in the other ocean basins. Key Points We show evidence for the accumulation of C ant along the Antarctic shelf‐slope into the deep ocean The process of AABW formation drives C ant downward transport at 25.0 ± 4.7 Tg C yr −1 , sustaining the CO 2 uptake in the surface ocean This further triggers acidification of AABW at a rate of −0.0006 ± 0.0001 pH unit yr −1 , which is faster than in other deep oceans