Neutrally buoyant SOFAR floats at nominal depths of 800, 1800, and 330
0 m were tracked for 21 months in the vicinity of tropical boundary cu
rrents in the Atlantic near 6-degrees-N and at several sites near 11-d
egrees-N as well as along the equator. Trajectories at 1800 m show a s
wift (>50 cm/s), narrow (100 km wide), southward flowing deep western
boundary current (DWBC) extending from 7-degrees-N to the equator. The
average transport per unit depth in the DWBC was estimated to be 13.8
x 10(3) m2/S. Coupling this value with mean velocities measured in th
e DWBC by current meters gave a volume transport of 15 x 10(6) m3/s be
tween depths of 900 m and 2800 m. Approximately 6 x 10(6) m3/s recircu
lated northward between the DWBC and the Mid-Atlantic Ridge, leaving 9
x 10(6) m3/s as cross-equatorial transport. No obvious DWBC nor swift
equatorial current was observed by the 3300-m floats; a low mean velo
city at this depth lay between F-11 and higher velocity cores above an
d below. The 1800-m trajectories also suggest that at times (February-
March 1989) the North Atlantic Deep Water in the DWBC turned eastward
and flowed along the equator and at other times (August-September 1990
) the DWBC crossed the equator and continued southward. The velocity n
ear the equator, calculated by grouping floats in a box along the equa
tor, was eastward at 4.1 cm/s from February 1989 to February 1990 and
westward at 4.6 cm/s from March 1990 to November 1990. Thus the amount
of cross-equatorial flow in the DWBC appeared to be finked to low-fre
quency variability of the structure of the equatorial current system.
Floats in Antarctic Intermediate Water at 800 m revealed a northwestwa
rd western boundary current, although flow patterns were complicated.
Three floats that significantly contributed to the northwestward flow
looped in anticyclonic eddies that translated up the coast at 8 cm/s.
Six 800-m floats drifted eastward along the equator between 5-degrees-
S and 6-degrees-N at a mean velocity of 11 cm/s; one reached 5-degrees
-W in the Gulf of Guinea, suggesting that the equatorial currents at t
his depth extended at least 35-degrees-40-degrees along the equator. T
hree of these floats reversed direction near the end of the tracking p
eriod.