South Atlantic interbasin exchanges of mass, heat, salt and anthropogenic carbon

- We construct an inverse box model of the South Atlantic sector, south of 24°S.
- Exchanges of mass, heat, salt and anthropogenic carbon are estimated.
- The region as a whole is a substantial anthropogenic carbon sink.
- Freshwater transport associated with meridional overturning is southward.
- Significant westward flow of Antarctic Bottom Water occurs at 30°E.

The exchange of mass, heat, salt and anthropogenic carbon (Cant) between the South Atlantic, south of 24°S, and adjacent ocean basins is estimated from hydrographic data obtained during 2008-2009 using an inverse method. Transports of anthropogenic carbon are calculated across the western (Drake Passage), eastern (30°E) and northern (24°S) boundaries. The freshwater overturning transport of 0.09 Sv is southward, consistent with an overturning circulation that exports freshwater from the North Atlantic, and consistent with a bistable Meridional Overturning Circulation (MOC), under conditions of excess freshwater perturbation. At 30°E, net eastward Antarctic Circumpolar Current (ACC) transport, south of the Subtropical Front, is compensated by a 15.9 ± 2.3 Sv westward flow along the Antarctic boundary. The region as a whole is a substantial sink for atmospheric anthropogenic carbon of 0.51 ± 0.37 Pg C yr−1, of which 0.18 ± 0.12 Pg C yr−1 accumulates and is stored within the water column. At 24°S, a 20.2 Sv meridional overturning is associated with a 0.11 Pg C yr−1 Cant overturning. The remainder is transported into the Atlantic Ocean north of 24°S (0.28 ± 0.16 Pg C yr−1) and Indian sector of Southern Ocean (1.12 ± 0.43 Pg C yr−1), having been enhanced by inflow through Drake Passage (1.07 ± 0.44 Pg C yr−1). This underlines the importance of the South Atlantic as a crucial element of the anthropogenic carbon sink in the global oceans.