The South Atlantic Circulation between 34.5ºS, 24ºS and above the Mid-Atlantic Ridge from an Inverse Box Model

Abstract

The South Atlantic Ocean plays a key role in the heat exchange of the climate system, as it hosts the returning flow of the Atlantic Meridional Overturning Circulation (AMOC). To gain insights on this role, using data from three hydrographic cruises conducted in the South Atlantic Subtropical gyre at 34.5ºS, 24ºS and 10ºW, we identify water masses and compute absolute geostrophic circulation using inverse modeling. In the upper layers, the currents describe the South Atlantic anticyclonic gyre with the northwest flowing Benguela Current (26.3±2.0 Sv at 34.5ºS, and 21.2±1.8 Sv at 24ºS) flowing above the Mid-Atlantic Ridge (MAR) between 22.4ºS-28.4ºS (-19.2±1.4 Sv), and the southward flowing Brazil Current (-16.5±1.3 Sv at 34.5ºS, and -7.3±0.9 Sv at 24ºS); the deep layers feature the southward transports of Deep Western Boundary Current (DWBC; -13.9±3.0 Sv at 34.5ºS, and -8.7±3.8 Sv at 24ºS) and Deep Eastern Boundary Current (DEBC; -15.1±3.5 Sv at 34.5ºS, and -16.3±4.7 Sv at 24ºS), with the interbasin west-to-east flow close to 24ºS (7.5±4.4 Sv); the abyssal waters present northward mass transports through the Argentina Basin (5.6±1.1 Sv at 34.5ºS, and 5.8±1.5 Sv at 24ºS) and Cape Basin (8.6±3.5 Sv at 34.5ºS to 3.0±0.8 Sv at 24ºS) before returning southward (-2.2±0.7 Sv at 24ºS to -7.9±3.6 Sv at 34.5ºS), without any interbasin exchange across the MAR. In addition, we compute the upper AMOC strength (14.8±1.0 and 17.5±0.9 Sv), the equatorward heat transport (0.30±0.05 and 0.80±0.05 PW), and the freshwater flux (0.18±0.02 and -0.07±0.02 Sv) at 34.5ºS and 24ºS, respectively.