25 Sv Benguela Current geostrophic transport,
15 Sv are drawn from the Indian Ocean. Nine Sv
(2 Sv of thermocline water warmer than 9°C and 7 Sv
of lower thermocline and Antarctic Intermediate
Water) of this Indian Ocean water pass into the
North Atlantic within the North Brazil Coastal
Current. The rest of the Indian Ocean water entering the South Atlantic follows the subtropical gyre,
eventually to return along the horizontal plane to
the Indian Ocean along a path just south of the
Agulhas Return Current. As the Indian Ocean
thermocline and intermediate layers are saltier
than the other major provider of the Benguela
Current water (the South Atlantic Current defining the polar limb of the subtropical gyre), the
Agulhas leakage also adds salt to the South Atlantic.
The leakage is also warmer than the waters of the
South Atlantic Current, and hence also adds heat to
the Atlantic Ocean.
Saunders and King (1995b), using WHP section
A11 (roughly along 40°S, ending at 30°S at Africa),
find a northward transport of 10 Sv of thermocline
water (: 0 of 26.8) drawn from the Agulhas
Retroflection and 5 Sv of AAIW. Garzoli et al.
(1996) estimate the Benguela Current transport,
based on a 16-month (1992–93) time series of Pressure and Inverted Echo Sounder (PIES) and current
meter data at 30°S, as 16 Sv. Applying the property-based estimate of the percentage of Indian
Ocean water found by Gordon et al. (1992), the
Indian Ocean influx would be on average 10 Sv,
6 Sv of which enter into the upper limb of the
Atlantic meridional overturning circulation. During
the mooring deployment discussed by Garzoli et al.
(1996), three oceanographic sections were obtained
across the Benguela Current near 30°S. While the
sample number is small, higher transport is associated with a more saline thermocline and intermediate layer, suggesting that variable Benguela Current
transport is due to a variable Agulhas leakage.
Holfort and Siedler (2001) in an inverse solution
find 9 Sv of warm surface water (Agulhas leakage)
and 6 Sv of cold AAIW pass northward across 30°S
in the South Atlantic. This is close to the values
found by Saunders and King (1995b). Their partitioning between warm and cold route contrasts
with that of Schlitzer (1996) of 2 Sv of Agulhas
leakage to 11.9 Sv of AAIW. Stutzer and Krauss
(1998) assimilate drifter trajectories into a model
for the South Atlantic. They find that the Benguela
Current, with its Indian Ocean component, directly
feeds the South Equatorial Current, with bifurcation near 10°S along the Brazilian coast. Clearly
some Indian Ocean water is deflected into the
North Brazil Current and northern hemisphere.
Agulhas eddies
The primary means by which the Agulhas injects
Indian Ocean water into the Benguela Current
occurs within large anticyclonic eddies. These energetic eddies of Agulhas (Indian Ocean) water can
be traced across the South Atlantic Ocean (Byrne
et al., 1995). Interannual variability of the width
and latitude of the transocean corridor occurs, with
expansion and contraction of the South Atlantic
subtropical gyre (Witter and Gordon, 1999).
Effects of seafloor topography on the eddy propagation is clearly evident in observations and models
(Byrne et al., 1995; Kamenkovich et al., 1996;
Florenchie and Verron, 1998). On average six
Agulhas eddies enter the South Atlantic each year,
injecting from 3 to 9 Sv into the South Atlantic
Ocean. In transit they dissipate, losing their core of
Indian Ocean water (Byrne et al., 1995) into the
Benguela Current and South Equatorial Current.
4.7.4.3 Heat and freshwater fluxes
The South Atlantic contributes to the overall high
thermocline salinity of the Atlantic Ocean in two
ways: the ACC exports fresh water from the South
Atlantic subtropics (Gordon and Piola, 1983);
warm saline Indian Ocean thermocline water is
injected into the Benguela Current (Gordon et al.,
1992). Agulhas leakage occurs in the form
of Agulhas rings shed from the Agulhas Current’s retroflection and surface water filaments
(Lutjeharms, 1996). In addition, branches of the
Agulhas Current may flow directly into the
Benguela Current between the Africa and the main
offshore corridor that carries the eddies towards
the northwest (Gordon et al., 1992; Garzoli et al.,
1996). These branches of Indian Ocean water lost
from the core of the eddies are carried into the
South Equatorial Current of the South Atlantic,
part of which passes into the northern hemisphere.
Byrne et al. (1995) estimate that the average
Agulhas eddy sampled within the southeastern
South Atlantic transfers at least 0.8 Sv of Indian
Ocean water into the South Atlantic. Two newly
formed Agulhas eddies found near the retroflection
each contributed 1.4 and 1.8 Sv, respectively, of
Indian Ocean water (Byrne et al., 1995). Clement
4.7 Interocean Exchange
311
Gordon
15 Sv are drawn from the Indian Ocean. Nine Sv
(2 Sv of thermocline water warmer than 9°C and 7 Sv
of lower thermocline and Antarctic Intermediate
Water) of this Indian Ocean water pass into the
North Atlantic within the North Brazil Coastal
Current. The rest of the Indian Ocean water entering the South Atlantic follows the subtropical gyre,
eventually to return along the horizontal plane to
the Indian Ocean along a path just south of the
Agulhas Return Current. As the Indian Ocean
thermocline and intermediate layers are saltier
than the other major provider of the Benguela
Current water (the South Atlantic Current defining the polar limb of the subtropical gyre), the
Agulhas leakage also adds salt to the South Atlantic.
The leakage is also warmer than the waters of the
South Atlantic Current, and hence also adds heat to
the Atlantic Ocean.
Saunders and King (1995b), using WHP section
A11 (roughly along 40°S, ending at 30°S at Africa),
find a northward transport of 10 Sv of thermocline
water (: 0 of 26.8) drawn from the Agulhas
Retroflection and 5 Sv of AAIW. Garzoli et al.
(1996) estimate the Benguela Current transport,
based on a 16-month (1992–93) time series of Pressure and Inverted Echo Sounder (PIES) and current
meter data at 30°S, as 16 Sv. Applying the property-based estimate of the percentage of Indian
Ocean water found by Gordon et al. (1992), the
Indian Ocean influx would be on average 10 Sv,
6 Sv of which enter into the upper limb of the
Atlantic meridional overturning circulation. During
the mooring deployment discussed by Garzoli et al.
(1996), three oceanographic sections were obtained
across the Benguela Current near 30°S. While the
sample number is small, higher transport is associated with a more saline thermocline and intermediate layer, suggesting that variable Benguela Current
transport is due to a variable Agulhas leakage.
Holfort and Siedler (2001) in an inverse solution
find 9 Sv of warm surface water (Agulhas leakage)
and 6 Sv of cold AAIW pass northward across 30°S
in the South Atlantic. This is close to the values
found by Saunders and King (1995b). Their partitioning between warm and cold route contrasts
with that of Schlitzer (1996) of 2 Sv of Agulhas
leakage to 11.9 Sv of AAIW. Stutzer and Krauss
(1998) assimilate drifter trajectories into a model
for the South Atlantic. They find that the Benguela
Current, with its Indian Ocean component, directly
feeds the South Equatorial Current, with bifurcation near 10°S along the Brazilian coast. Clearly
some Indian Ocean water is deflected into the
North Brazil Current and northern hemisphere.
Agulhas eddies
The primary means by which the Agulhas injects
Indian Ocean water into the Benguela Current
occurs within large anticyclonic eddies. These energetic eddies of Agulhas (Indian Ocean) water can
be traced across the South Atlantic Ocean (Byrne
et al., 1995). Interannual variability of the width
and latitude of the transocean corridor occurs, with
expansion and contraction of the South Atlantic
subtropical gyre (Witter and Gordon, 1999).
Effects of seafloor topography on the eddy propagation is clearly evident in observations and models
(Byrne et al., 1995; Kamenkovich et al., 1996;
Florenchie and Verron, 1998). On average six
Agulhas eddies enter the South Atlantic each year,
injecting from 3 to 9 Sv into the South Atlantic
Ocean. In transit they dissipate, losing their core of
Indian Ocean water (Byrne et al., 1995) into the
Benguela Current and South Equatorial Current.
4.7.4.3 Heat and freshwater fluxes
The South Atlantic contributes to the overall high
thermocline salinity of the Atlantic Ocean in two
ways: the ACC exports fresh water from the South
Atlantic subtropics (Gordon and Piola, 1983);
warm saline Indian Ocean thermocline water is
injected into the Benguela Current (Gordon et al.,
1992). Agulhas leakage occurs in the form
of Agulhas rings shed from the Agulhas Current’s retroflection and surface water filaments
(Lutjeharms, 1996). In addition, branches of the
Agulhas Current may flow directly into the
Benguela Current between the Africa and the main
offshore corridor that carries the eddies towards
the northwest (Gordon et al., 1992; Garzoli et al.,
1996). These branches of Indian Ocean water lost
from the core of the eddies are carried into the
South Equatorial Current of the South Atlantic,
part of which passes into the northern hemisphere.
Byrne et al. (1995) estimate that the average
Agulhas eddy sampled within the southeastern
South Atlantic transfers at least 0.8 Sv of Indian
Ocean water into the South Atlantic. Two newly
formed Agulhas eddies found near the retroflection
each contributed 1.4 and 1.8 Sv, respectively, of
Indian Ocean water (Byrne et al., 1995). Clement
4.7 Interocean Exchange
311
Gordon