During March 1994 a survey of the western boundary of the tropical Atl
antic, between 10 degrees N and 10 degrees S, was carried out by condu
ctivity-temperature-depth and current profiling using shipboard and lo
wered acoustic Doppler current profilers. In the near-surface layer, a
bove sigma. = 24.5, the inflow into the boundary regime came dominantl
y from low latitudes; out of the 14 Sv that crossed the equator in the
upper part of the North Brazil Current (NBC), only 2 Sv originated fr
om south of 5 degrees S, while 12 Sv came in from the east at 1 degree
s-5 degrees S with the South Equatorial Current (SEC). After crossing
the equator near 44 degrees W, only a minor fraction of the near-surfa
ce NBC retroflected eastward, while a net through flow of about 12 Sv
above sigma. = 24.5 continued northwestward along the boundary, By con
trast, in the isopycnal range sigma. = 24.5-26.8 encompassing the Equa
torial Undercurrent (EUC), the source waters of the equatorial circula
tion were dominantly of higher-latitude South Atlantic origin. While o
nly 3 Sv of eastern equatorial water entered the region through the SE
C at 3 degrees-5 degrees S, there was an inflow of 10 Sv of South Atla
ntic water in the North Brazil Undercurrent (NBUC) along the South Ame
rican coast that originated south of 10 degrees S, The transport of 14
Sv arriving at the equator along the boundary in the undercurrent lay
er was almost entirely retroflected into the EUC with only marginal no
rthern water additions along its path to 35 degrees W. The off-equator
ial undercurrents in the upper thermocline, the South and North Equato
rial Undercurrents carried only small transports across 35 degrees W,
of 5 Sv and 3 Sv, respectively, dominantly supplied out of SEC recircu
lation rather than out of the boundary current. Still deeper, three zo
nal undercurrents were observed: the westward-flowing Equatorial Inter
mediate Current (EIC) in the depth range 200-900 m below the EUC, and
two off-equatorial eastward undercurrents, the Northern and Southern I
ntermediate Countercurrents (NICC, SICC) at 400-1000 m and 1 degrees-3
degrees latitude. In the lower part of the NBUC there was an Antarcti
c Intermediate Water (AAIW) inflow along the coast of 6 Sv, and there
was a clear connection at the AAIW level to the SICC by low salinities
and high oxygens and a weaker suggestion also that some supply of the
NICC might be through AAIW out of the deep NBUC.