100 km of the slope with maximum velocity in the
uNADW layer (the lNADW layer is not well sampled by this mooring array, and probably 5–6 Sv
of this water reaches the equator east of this
array). Circulation in the uNADW layer was also
sampled by floats (Richardson and Schmitz, 1993;
Richardson and Fratantoni, 1999), their paths
illustrating the link between the western boundary
current and the equatorial circulation. How the
interior equatorial flow connects with the western
boundary current south of the equator is not yet
clear, nor is the exact nature of the interaction
with the topography. Sections along 5°S indicate a
southward boundary transport on the order of
19 Sv, but somewhat off the continental slope, and
not necessarily closely correlated to tracer extrema.
These data have also illustrated the importance of
offshore recirculation cells, some of which are
probably permanent, so that the transport estimate
of 19 Sv taking only southward currents into
account should be viewed as an upper estimate of
the southward transport in this layer.
The circulation of Antarctic bottom water in
the equatorial Atlantic will be presented in another
chapter, and we will not comment on it here.
The available direct current data in the deep
equatorial Atlantic Ocean all suggest the presence of strong seasonal variability, both at annual
and semiannual period (Fischer and Schott, 1997;
4.3 The Tropical Ocean Circulation
231
Godfrey, Johnson, McPhaden, Reverdin and Wijffels
Freon near 1700m
70°W
6 0 °
50°
40°
30°
20°
10°
0°
10°E
30°N
20°
20°
10°
10°
0°
30°S
Fig. 4.3.7 Composite F-11 concentration near 1700 m based on measurements from the TAS (1983) and SAVE
(1987–88) expeditions (age-corrected to 1988) (Ray Weiss, personal communication). Higher concentrations have
darker shading.
8
6
4
2
0
2
4
6
8
10 12
201
172
413
529
881
1696
1364
319
79
37
5°S
0°
5°N
Number of observations
1800 m equatorial floats
Eastward velocity (cm s
–1 )
Fig. 4.3.8 Average zonal velocity at 1800 m along a
35°W section. Based on the composite of float velocities
in 1989–92. From Richardson and Fratantoni (1999).
uNADW layer (the lNADW layer is not well sampled by this mooring array, and probably 5–6 Sv
of this water reaches the equator east of this
array). Circulation in the uNADW layer was also
sampled by floats (Richardson and Schmitz, 1993;
Richardson and Fratantoni, 1999), their paths
illustrating the link between the western boundary
current and the equatorial circulation. How the
interior equatorial flow connects with the western
boundary current south of the equator is not yet
clear, nor is the exact nature of the interaction
with the topography. Sections along 5°S indicate a
southward boundary transport on the order of
19 Sv, but somewhat off the continental slope, and
not necessarily closely correlated to tracer extrema.
These data have also illustrated the importance of
offshore recirculation cells, some of which are
probably permanent, so that the transport estimate
of 19 Sv taking only southward currents into
account should be viewed as an upper estimate of
the southward transport in this layer.
The circulation of Antarctic bottom water in
the equatorial Atlantic will be presented in another
chapter, and we will not comment on it here.
The available direct current data in the deep
equatorial Atlantic Ocean all suggest the presence of strong seasonal variability, both at annual
and semiannual period (Fischer and Schott, 1997;
4.3 The Tropical Ocean Circulation
231
Godfrey, Johnson, McPhaden, Reverdin and Wijffels
Freon near 1700m
70°W
6 0 °
50°
40°
30°
20°
10°
0°
10°E
30°N
20°
20°
10°
10°
0°
30°S
Fig. 4.3.7 Composite F-11 concentration near 1700 m based on measurements from the TAS (1983) and SAVE
(1987–88) expeditions (age-corrected to 1988) (Ray Weiss, personal communication). Higher concentrations have
darker shading.
8
6
4
2
0
2
4
6
8
10 12
201
172
413
529
881
1696
1364
319
79
37
5°S
0°
5°N
Number of observations
1800 m equatorial floats
Eastward velocity (cm s
–1 )
Fig. 4.3.8 Average zonal velocity at 1800 m along a
35°W section. Based on the composite of float velocities
in 1989–92. From Richardson and Fratantoni (1999).