The Agulhas Current is the strong western boundary current of the South Indian Ocean. It flows southward along the east coast of southern Africa, but when it passes the southern tip of South Africa, it makes a tight turn (“retroflects”) and flows back into the Indian Ocean. However, this retroflection shortcuts every few months spawning a large column of warm and salty Indian Ocean water that drifts into the Atlantic. This process is called Agulhas Leakage (De Ruijter et al. 1999).
Studies using both conceptual 2D models (Weijer et al., 1999; Weijer et al., 2001) and a low-resolution GCM (Weijer et al., 2002) indicate that the interocean fluxes of heat and salt may exert a considerable influence on the strength and stability of the Atlantic overturning circulation. In the case of Agulhas Leakage, the salt and temperature anomalies initially cancel with respect to density. Rapid decay of the thermal anomaly leaves a density anomaly when the Indian Ocean water is advected northward. This results in a modification of the large-scale pressure distribution that tends to strengthen the overturning circulation. And since a stronger overturning circulation enhances advective feedbacks, it also becomes more stable with respect to large-amplitude perturbations.
This work was done in the group of Will de Ruijter, in collaboration with Henk Dijkstra and Peter Jan van Leeuwen, at IMAU.
Response
of the Atlantic overturning circulation to South Atlantic sources of
buoyancy
Weijer, W., W. P. M. De Ruijter, A. Sterl and S.
S. Drijfhout, 2002.
Global
and Planetary Change, 34,
293-311. Abstract
Full
text (pdf)
Stability
of the Atlantic overturning circulation: Competition between Bering
Strait freshwater flux and Agulhas heat and salt sources
Weijer,
W., W. P. M. De Ruijter and H. A. Dijkstra, 2001.
J.
Phys. Oceanogr., 31,
2385-2402. Abstract
Full
text (pdf)
Impact
of interbasin exchange on the Atlantic overturning
circulation
Weijer, W., W. P. M. De Ruijter, H. A.
Dijkstra and P. J. van Leeuwen, 1999.
J.
Phys. Oceanogr., 29,
2266-2284, 3184. Abstract
Full
text (pdf) Corrigendum
(pdf)
Indian-Atlantic
interocean exchange: Dynamics, estimation and impact
De
Ruijter, W. P. M., A. Biastoch, S.S. Drijfhout, J.R.E. Lutjeharms,
R.P.Matano, T. Pichevin, P.J. Van Leeuwen and W. Weijer, 1999.
J.
Geophys. Res., 104,
20885-20910. Abstract
Full
text (pdf)
Impact
of Interocean Exchange on the Atlantic Overturning Circulation
Ph.D.
Dissertation, Utrecht
University, 2000.
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