Fa. Schott et al., TRANSPORTS AND PATHWAYS OF THE UPPER-LAYER CIRCULATION IN THE WESTERNTROPICAL ATLANTIC, Journal of physical oceanography, 28(10), 1998, pp. 1904-1928
The mean warm water transfer toward the equator along the western boun
dary of the South Atlantic is investigated, based on a number of ship
surveys carried out during 1990-96 with CTD water mass observations an
d current profiling by shipboard and lowered (with the CTD/rosette) ac
oustic Doppler current profiler and with Pegasus current profiler. The
bulk of the northward warm water flow follows the coast in the North
Brazil Undercurrent (NBUC) from latitudes south of 10 degrees S, carry
ing 23 Sv (Sv = 10(6) mf s(-1)) above 1000 m. Out of this, 16 Sv are w
aters warmer than 7 degrees C that form the source waters of the Flori
da Current. Zonal inflow from the east by the South Equatorial Current
enters the western boundary system dominantly north of 5 degrees S, a
dding transport northwest of Cape San Rogue, and transforming the NBUC
along its way toward the equator into a surface-intensified current,
the North Brazil Current (NBC). From the combination of moored arrays
and shipboard sections just north of the equator along 44 degrees W, t
he mean NBC transport was determined at 35 Sv with a small seasonal cy
cle amplitude of only about 3 Sv. The reason for the much larger near-
equatorial northward warm water boundary current than what would be re
quired to carry the northward heat transport are recirculations by the
zonal current system and the existence of the shallow South Atlantic
tropical-subtropical cell (STC). The STC connects the subduction zones
of the eastern subtropics of both hemispheres via equatorward boundar
y undercurrents with the Equatorial Undercurrent (EUC), and the return
flow is through upwelling and poleward Ekman transport. The persisten
t existence of a set of eastward thermocline and intermediate counterc
urrents on both sides of the equator was confirmed that recurred throu
ghout the observations and carry ventilated waters from the boundary r
egime into the tropical interior. A strong westward current underneath
the EUC, the Equatorial Intermediate Current, returns low-oxygen wate
r westward. Consistent evidence for the existence of a seasonal variat
ion in the warm water flow south of the equator could not be establish
ed, whereas significant seasonal variability of the boundary regime oc
curs north of the equator: northwestward alongshore throughflow of abo
ut 10 Sv of waters with properties from the Southern Hemisphere was fo
und along the Guiana boundary in boreal spring when the North Equatori
al Countercurrent is absent or even flowing westward, whereas during J
une-January the upper NBC is known to connect with the eastward North
Equatorial Countercurrent through a retroflection zone that seasonally
migrates up and down the coast and spawns eddies. The equatorial zone
thus acts as a buffer and transformation zone for cross-equatorial ex
changes, but knowledge of the detailed pathways in the interior includ
ing the involved diapycnal exchanges is still a problem.