The Shallow and Deep Western Boundary Circulation of the South Atlantic at 5°–11°S
Journal of Physical Oceanography
Repeated shipboard observation sections across the boundary flow off northeastern Brazil as well as acoustic Doppler current profiler (ADCP) and current-meter records from a moored boundary array deployed during 2000-04 near 11°S are analyzed here for both the northward warm water flow by the North Brazil Undercurrent (NBUC) above approximately 1100 m and the southward flow of North Atlantic Deep Water (NADW) underneath. At 5°S, the mean from nine sections yields an NBUC transport of 26.5 Ϯ 3.7
... sport of 26.5 Ϯ 3.7 Sv (Sv ϵ 10 6 m 3 s Ϫ1 ) along the boundary; at 11°S the mean NBUC transport from five sections is 25.4 Ϯ 7.4 Sv, confirming that the NBUC is already well developed at 11°S. At both latitudes a persistent offshore southward recirculation between 200-and 1100-m depth reduces the net northward warm water flow through the 5°S section (west of 31.5°W) to 22.1 Ϯ 5.3 Sv and through the 11°S section to 21.7 Ϯ 4.1 Sv (west of 32.0°W). The 4-yr-long NBUC transport time series from 11°S yields a seasonal cycle of 2.5 Sv amplitude with its northward maximum in July. Interannual NBUC transport variations are small, varying only by Ϯ1.2 Sv during the four years, with no detectable trend. The southward flow of NADW within the deep western boundary current at 5°S is 25.5 Ϯ 8.3 Sv with an offshore northward recirculation, yielding a nine-section mean of 20.3 Ϯ 10.1 Sv west of 31.5°W. For Antarctic Bottom Water, a net northward flow of 4.4 Ϯ 3.0 Sv is determined at 5°S. For the 11°S section, the moored array data show a pronounced energy maximum at 60-70-day period in the NADW depth range, which was identified in related work as deep eddies translating southward along the boundary. Based on a kinematic eddy model fit to the first half of the moored time series, the mean NADW transfer by the deep eddies at 11°S was estimated to be about 17 Sv. Given the large interannual variability of the deep near-boundary transport time series, which ranged from 14 to 24 Sv, the 11°S mean was considered to be not distinguishable from the mean at 5°S.