Ocean Science www.ocean-sci.net 1812-0784 1812-0792 3 1 2007 10.5194/os-3-129-2007 http://www.ocean-sci.net/3/129/2007/ http://www.ocean-sci.net/3/129/2007/os-3-129-2007.html http://www.ocean-sci.net/3/129/2007/os-3-129-2007.pdf 129 147 2007-02-23 Three decades of research on the greater Agulhas Current J. R. E. Lutjeharms johann.lutjeharms@uct.ac.za Department of Oceanography, University of Cape Town, 7700 Rondebosch, South Africa The greater Agulhas Current has been shown to be a key link in the global thermohaline circulation and an increased understanding of this current system is therefore of more than just local interest. Knowledge on the Agulhas Current system has in fact increased enormously over the past 30 years. This review covers some aspects of what has been learnt on the northern and the southern parts of the Agulhas Current proper and their influence on the waters and circulation of the adjoining continental shelf. It also discusses the Natal Pulse and new information that has been gained on how it is triggered and what influence it has. It deals with the Agulhas retroflection, the shedding of Agulhas rings and the movement and characteristics of these rings that contributes to the meridional overturning circulation of the global ocean. The Agulhas Return Current forms part of the final outflow of the system and current knowledge on that current is appraised. The sources of the Agulhas Current have been a controversial subject for many years and this dispute continues. This is described and discussed, based on what information has been gained from research over the past three decades. Building on what is currently known, some suggestions are given on the most important remaining knowledge gaps and how these could most efficaciously be filled. Anderson, F. P., Gründlingh, M. L., and Stavropoulos, C. C.: Kinematics of the southern Natal coastal circulation: some historic measurements 1962–63, S. Afr. J. Sci., 84, 857–860, 1988. Arhan, M., Mercier, H., and Lutjeharms, J. R. E.: The disparate evolution of three Agulhas rings in the South Atlantic Ocean, J. Geophys. Res., 104, 20 987–21 005, 1999. Bang, N. D.: Major eddies and frontal structures in the Agulhas Current retroflexion (sic) area in March, 1969, in: Symposium "Oceanography South Africa 1970", South African National Committee for Oceanographic Research, 16 pp., 1970a. Bang, N. D.: Dynamic interpretations of a detailed surface temperature chart of the Agulhas Current retroflexion (sic) and fragmentation area, S. Afr. geogr. J., 52, 67–76, 1970b. Bang, N. D.: Characteristics of an intense ocean frontal system in the upwell regime west of Cape Town, Tellus, 25, 256–265, 1973a. Bang, N. D.: Oceanography: Oceanographic Environment of Southern Africa, in: Standard Encyclopaedia of Southern Africa, edited by: Spies, J. J. and du Plessis, P. C., vol. 8, Nasou, Cape Town, pp. 282–286, 1973b. Beal, L. M. and Bryden, H. L.: Observations of an Agulhas Undercurrent, Deep-Sea Res. I, 44, 1715–1724, 1997. Beal, L. M. and Bryden, H. L.: The velocity and vorticity structure of the Agulhas Current at 32° S, J. Geophys. Res., 104, 5151–5176, 1999. Beckley, L. E.: Sea-surface temperature variability around Cape Recife, South Africa, S. Afr. J. Sci., 79, 436–438, 1983. Beismann, J.-O., Käse, R. H., and Lutjeharms, J. R. E.: On the influence of submarine ridges on translation and stability of Agulhas rings, J. Geophys. Res., 104, 7897–7906, 1999. Biastoch, A. and Krauss, W.: The role of mesoscale eddies in the source regions of the Agulhas Current, J. Phys. Oceanogr., 29, 2303–2317, 1999. Boebel, O., Duncombe Rae, C., Garzoli, S., Lutjeharms, J., Richardson, P., Rossby, T., Schmid, C., and Zenk, W.: Float experiment studies interocean exchanges at the tip of Africa, Eos, Trans. Am. geophys. Un., 79(1), 7–8, 1997. Boebel, O., Lutjeharms, J., Schmid, C., Zenk, W., Rossby, T., and Barron, C.: The Cape Cauldron: a regime of turbulent inter-ocean exchange, Deep-Sea Res. II, 50, 57–86, 2003a. Boebel, O., Rossby, T., Lutjeharms, J., Zenk, W., and Barron, C.: Path and variability of the Agulhas Return Current, Deep-Sea Res. II, 50, 35–56, 2003b. Belkin, I. M. and Gordon, A. L.: Southern Ocean fronts from the Greenwich meridian to Tasmania, J. Geophys. Res., 101, 3675–3696, 1996. Boudra, D. B., Maillet, K. A., and Chassignet, E. P.: Numerical modeling of Agulhas retroflection and ring formation with isopycnal outcropping, in: Meso-scale/Synoptic Coherent Structures in Geophysical Turbulence, edited by: Nihoul, J. C. J. and Jamart, B. M., Elsevier, Amsterdam, pp 315–335, 1989. Boyd, A. J., Tromp, B. B. S., and Horstman, D. A.: The hydrology of the South African south-western coast between Cape Point and Danger Point in 1975, S. Afr. J. Mar. Sci., 3, 145–168, 1985. Boyd, A. J., Taunton-Clark, J., and Oberholster, G. P. J.: Spatial features of the near-surface and midwater circulation patterns off western and southern South Africa and their role in the life histories of various commercially fished species, S. Afr. J. Mar. Sci., 12, 189–206, 1992. Byrne, D. A., Gordon, A. L., and Haxby, W. F.: Agulhas Eddies: a synoptic view using Geosat ERM data, J. Phys. Oceanogr., 25, 902–917, 1995. Carter, R. and d'Aubrey, J.: Inorganic nutrients in Natal continental shelf waters, in: Coastal Ocean Studies off Natal, South Africa, edited by: Schumann, E. H., Lecture Notes on Coastal and Estuarine Studies 26, Springer-Verlag, Berlin, pp. 131–151, 1988. Carter, R. A. and Schleyer, M. H.: Plankton distributions in Natal coastal waters, in: Coastal Ocean Studies off Natal, South Africa, edited by: Schumann, E. H., Lecture Notes on Coastal and Estuarine Studies 26, Springer-Verlag, Berlin, pp 152–177, 1988. Chapman, P., DiMarco, S. F., Davis, R. E., and Coward, A. C.: Flow at intermediate depths round Madagascar based on ALACE float trajectories, Deep-Sea Res. II, 50, 1957–1986, 2003. Cheney, R. A., Marsh, J. G., and Beckley, B. D.: Global mesoscale variability from collinear tracks of SEASAT altimeter data, J. Geophys. Res., 88, 4343–4354, 1983. Christensen, M. S.: Sea-surface temperature charts for Southern Africa, south of 26° S, S. Afr. J. Sci., 76, 541–546, 1980. Crimp, S. J., Lutjeharms, J. R. E., and Mason, S. J.: Sensitivity of a tropical-temperate trough to sea-surface temperature anomalies in the Agulhas retroflection region, Water SA, 24, 93–101, 1998. De Ruijter, W.: Asymptotic analysis of the Agulhas and Brazil Current systems, J. Phys. Oceanogr., 12, 361–373, 1982. De Ruijter, W. P. M. and Boudra, D. B.: The wind-driven circulation in the South Atlantic-Indian Ocean – I. Numerical experiments in a one-layer model, Deep-Sea Res., 32, 557–574, 1985. De Ruijter, W. P. M., van Leeuwen, P. J., and Lutjeharms, J. R. E.: Generation and evolution of Natal Pulses: solitary meanders in the Agulhas Current, J. Phys. Oceanogr., 29, 3043–3055, 1999a. De Ruijter, W. P. M., Biastoch, A., Drijfhout, S. S., Lutjeharms, J. R. E., Matano, R. P., Pichevin, T., van Leeuwen, P. J., and Weijer, W.: Indian-Atlantic inter-ocean exchange: dynamics, estimation and impact, J. Geophys. Res., 104, 20 885–20 911, 1999b. De Ruijter, W. P. M., Ridderinkhof, H., Lutjeharms, J. R. E., Schouten, M. W., and Veth, C.: Observations of the flow in the Mozambique Channel, Geophys. Res. Lett., 29, 1401–1403, 2002. De Ruijter, W. P. M., van Aken, H. M., Beier, E. J., Lutjeharms, J. R. E., Matano, R. P., and Schouten, M. W.: Eddies and dipoles around South Madagascar: formation, pathways and large-scale impact, Deep-Sea Res. I, 51, 383–400, 2003. De Ruijter, W. P. M., Ridderinkhof, H., and Schouten, M. W.: Variability of the southwest Indian Ocean. Phil. Trans. Roy. Soc. London, A363, 63–76, 2005. De Ruijter, W. P. M., Brummer, G.-J. A., Drijfhout, S. S., Lutjeharms, J. R. E., Peeters, F., Ridderinkhof, H., van Aken, H., and van Leeuwen, P. J.: Observations of the inter-ocean exchange around South Africa, Eos, Trans. Am. Geophys. Un., 87, 97, 99, 101, 2006. De Steur, L., van Leeuwen, P. J., and Drijfhout, S. S.: Tracer leakage from modeled Agulhas rings, J. Phys. Oceanogr., 34, 1387–1399, 2004. Dijkstra, H. A. and de Ruijter, W. P. M.: Barotropic instabilities of the Agulhas Current system and their relation to ring formation, J. Mar. Res., 59, 517–533, 2001a. Dijkstra, H. A. and de Ruijter, W. P. M.: On the physics of the Agulhas: steady retroflection regimes, J. Phys. Oceanogr., 31, 2971–2985, 2001b. DiMarco, S. F., Chapman, P., and Nowlin, W. D.: Satellite observations of upwelling on the continental shelf south of Madagascar, Geophys. Res. Lett., 27, 3965–3968, 2000. Donohue, K. A., Firing, E., and Beal, L.: Comparison of three velocity sections of the Agulhas Current and Agulhas Undercurrent, J. Geophys. Res., 105, 28 585–28 593, 2000. Duncombe Rae, C. M.: Agulhas retroflection rings in the South Atlantic Ocean; an overview, S. Afr. J. Mar. Sci., 11, 327–344, 1991. Flemming, B. W.: Sand transport and bedform patterns on the continental shelf between Durban and Port Elizabeth (Southeast African Continental Margin), Sediment. Geol., 26, 179–205, 1980. Flemming, B. and Hay, R.: Sediment distribution and dynamics of the Natal continental shelf, in: Coastal Ocean Studies off Natal, South Africa, edited by: Schumann, E. H., Lecture Notes on Coastal and Estuarine Studies 26, Springer-Verlag, Berlin, pp 47–80, 1988. Garzoli, S. L. and Goni (sic), J.: Combining altimeter observations and oceanographic data for ocean circulation and climate studies, in: Satellites, Oceanography and Society, edited by: Halpern, D., Elsevier Oceanography Series 63, Elsevier, Amsterdam, pp. 79–97, 2000. Gill, A. E. and Schumann, E. H.: Topographically induced changes in the structure of an inertial coastal jet: application to the Agulhas Current, J. Phys. Oceanogr., 9, 975–991, 1979. Gordon, A. L., Horai, K.-I., and Donn, M.: Southern hemisphere western boundary current variability revealed by GEOS 3 altimeter, J. Geophys. Res., 88, 755–762, 1983. Gordon, A. L.: Indian-Atlantic transfer of thermocline water at the Agulhas retroflection, Science, 227, 1030–1033, 1985. Gordon, A. L.: Inter-ocean exchange of thermocline water, J. Geophys. Res., 91, 5037–5046, 1986. Gordon, A. L., Lutjeharms, J. R. E., and Gründlingh, M. L.: Stratification and circulation at the Agulhas Retroflection, Deep-Sea Res., 34, 565–599, 1987. Goschen, W. S. and Schumann, E. H.: Ocean current and temperature structures in Algoa Bay and beyond in November 1986, S. Afr. J. Mar. Sci., 7, 101–116, 1988. Goschen, W. S. and Schumann, E. H.: An Agulhas Current intrusion into Algoa Bay during August 1988, S. Afr. J. Mar. Sci., 14, 47–57, 1994. Gründlingh, M. L.: A description of inshore current reversals off Richards Bay based on airborne radiation thermometry, Deep-Sea Res., 21, 47–55, 1974. Gründlingh, M. L.: Drift of a satellite-tracked buoy in the southern Agulhas Current and Agulhas Return Current, Deep-Sea Res., 25, 1209–1224, 1978. Gründlingh, M. L.: Observation of a large meander in the Agulhas Current, J. Geophys. Res., 84, 3776–3778, 1979. Gründlingh, M. L.: On the volume transport of the Agulhas Current, Deep-Sea Res., 27, 557-563, 1980. Gründlingh, M. L.: On the course of the Agulhas Current, S. Afr. Geogr. J., 65, 49–57, 1983. Gründlingh, M. L.: Altimetry in the southwest Indian Ocean, S. Afr. J. Sci., 84, 568–573, 1988. Gründlingh, M. L., Stavropoulos, C. C., and Watt, L. J.: The R. V. Meiring Naudé: Two decades of support to physical oceanography, S. Afr. J. Sci., 84, 746–748, 1988. Gründlingh, M. L. and Pearce, A. F.: Frontal features of the Agulhas Current in the Natal Bight, S. Afr. Geogr. J., 72, 11–14, 1990. Gründlingh, M. L.: Agulhas Current meanders: review and a case study, S. Afr. Geogr. J., 74, 19–28, 1992. Harris, T. F. W.: Planetary-type waves in the South West Indian Ocean, Nature, 227, 1043–1044, 1970. Harris, T. F. W.: Sources of the Agulhas Current in the spring of 1964, Deep-Sea Res., 19, 633–650, 1972. Harris, T. F. W., Legeckis, R., and van Forest (sic), D.: Satellite infra-red images in the Agulhas Current system, Deep-Sea Res., 25, 543–548, 1978. Jacobs, S. S. and Georgi, D. T.: Observations on the Southwest Indian/Antarctic Ocean, Deep-Sea Res., 24 (supplement), 43–84, 1977. Kamenkovich, V. M., Leonov, Y. P., Nechaev, D. A., Byrne, D. A., and Gordon, A. L.: On the influence of bottom topography on the Agulhas eddy, J. Phys. Oceanogr., 26, 892–192, 1996. Katsman, C. A., van der Vaart, P. C. F., Dijkstra, H. A., and de Ruijter, W. P. M.: Stability of multilayer ocean vortices: a parameter study including realistic Gulf Stream and Agulhas Rings, J. Phys. Oceanogr., 33, 1197–1218, 2003. Kostianoy, A. G., Ginzburg, A. I., Frankignoulle, M., and Delille, B.: Fronts in the southern Indian Ocean as inferred from satellite sea surface temperature data, J. Mar. Syst., 45, 55–73, 2004. Lee-Thorp, A. M., Rouault, M., and Lutjeharms, J. R. E.: Cumulus cloud formation above the Agulhas Current, S. Afr. J. Sci., 94, 351–354, 1998. Lee-Thorp, A. M., Rouault, M., and Lutjeharms, J. R. E.: Moisture uptake in the boundary layer above the Agulhas Current: a case study, J. Geophys. Res., 104, 1423–1430, 1999. Llido, J., Garçon, V. Lutjeharms, J. R. E., and Sudre, J.: Event-scale blooms drive enhanced primary productivity at the Subtropical Convergence, Geophys. Res. Lett., 32, L5611, doi:10.1029/2005GL022880, 2005. Luther, M. E. and O'Brien, J. J.: Modelling the variability in the Somali Current, in: mesoscale/Synoptic Coherent Structures in Geophysical Turbulence, edited by: Nihoul, J. C. J. and Jamart, B. M., Elsevier, Amsterdam, pp 373–386, 1989. Lutjeharms, J. R. E.: Retroflection; When the current turns, Oceans, 13, 31, 1980. Lutjeharms, J. R. E.: Features of the southern Agulhas Current circulation from satellite remote sensing, S. Afr. J. Sci., 77, 231–236, 1981. Lutjeharms, J. R. E., Bang, N. D., and Duncan, C. P.: Characteristics of the currents east and south of Madagascar, Deep-Sea Res., 28, 879–899, 1981. Lutjeharms, J. R. E. and Valentine, H. R.: Southern Ocean thermal fronts south of Africa, Deep-Sea Res., 31, 1461–1476, 1984. Lutjeharms, J. R. E. and van Ballegooyen, R. C.: Topographic control in the Agulhas Current system, Deep-Sea Res., 31, 1321–1337, 1984. Lutjeharms, J. R. E., Mey, R. D., and Hunter, I. T.: Cloud lines over the Agulhas Current, S. Afr. J. Sci., 82, 635–640, 1986a. Lutjeharms, J. R. E., Allanson, B. R., and Parker, L.: Frontal zones, chlorophyll and primary production patterns in the surface waters of the Southern Ocean south of Africa, in: Marine Interfaces Ecohydrodynamics, edited by: Nihoul, J. C. J., Elsevier, Amsterdam, pp 105–117, 1986b. Lutjeharms, J. R. E.: Die Subtropiese Konvergensie en Agulhasretrofleksievaart (SCARC), S. Afr. J. Sci., 83, 454–456, 1987. Lutjeharms, J. R. E. and Gordon, A. L.: Shedding of an Agulhas Ring observed at sea, Nature, 325, 138–140, 1987. Lutjeharms, J. R. E. and Meeuwis, J. M.: The extent and variability of the South East Atlantic upwelling, S. Afr. J. Mar. Sci., 5, 51–62, 1987. Lutjeharms, J. R. E. and Stockton, P. L.: Kinematics of the upwelling front off Southern Africa, S. Afr. J. Mar. Sci., 5, 35–49, 1987. Lutjeharms, J. R. E.: Examples of extreme circulation events of the Agulhas Retroflection, S. Afr. J. Sci., 84, 584–586, 1988a. Lutjeharms, J. R. E.: Meridional heat transport across the Sub-Tropical Convergence by a warm eddy, Nature, 331, 251–253, 1988b. Lutjeharms, J. R. E.: On the role of the East Madagascar Current as a source of the Agulhas Current, S. Afr. J. Sci., 84, 236–238, 1988c. Lutjeharms, J. R. E.: Remote sensing corroboration of retroflection of the East Madagascar Current, Deep-Sea Res., 35, 2045–2050, 1988d. Lutjeharms, J. R. E. and Jorge da Silva, A.: The Delagoa Bight eddy, Deep-Sea Res., 35, 619–634, 1988. Lutjeharms, J. R. E. and Roberts, H. R.: The Natal pulse; an extreme transient on the Agulhas Current, J. Geophys. Res., 93, 631–645, 1988. Lutjeharms, J. R. E. and Valentine, H. R.: Eddies at the Sub-Tropical Convergence south of Africa, J. Phys. Oceanogr., 18, 761–774, 1988a. Lutjeharms, J. R. E. and Valentine, H. R.: On mesoscale ocean eddies at the Agulhas Plateau, S. Afr. J. Sci., 84, 194–200, 1988b. Lutjeharms, J. R. E. and van Ballegooyen, R. C.: Anomalous upstream retroflection in the Agulhas Current, Science, 240, 1770–1772, 1988a. Lutjeharms, J. R. E. and van Ballegooyen, R. C.: The retroflection of the Agulhas Current, J. Phys. Oceanogr., 18, 1570–1583, 1988b. Lutjeharms, J. R. E. and Connell, A. D.: The Natal Pulse and inshore counter currents off the South African east coast, S. Afr. J. Sci., 85, 533–535, 1989. Lutjeharms, J. R. E., Gründlingh, M. L., and Carter, R. A.: Topographically induced upwelling in the Natal Bight, S. Afr. J. Sci., 85, 310–316, 1989a. Lutjeharms, J. R. E., Catzel, R., and Valentine, H. R.: Eddies and other border phenomena of the Agulhas Current, Cont. Shelf Res., 9, 597–616, 1989b. Lutjeharms, J. R. E., Shillington, F. A., and Duncombe Rae, C. M.: Observations of extreme upwelling filaments in the South East Atlantic Ocean, Science, 253, 774–776, 1991. Lutjeharms, J. R. E., de Ruijter, W. P. M., and Peterson, R. G.: Interbasin exchange and the Agulhas retroflection; the development of some oceanographic concepts, Deep-Sea Res., 39, 1791–1807, 1992. Lutjeharms, J. R. E. and Thomson, J. A.: Commercializing the CSIR and the death of science, S. Afr. J. Sci., 89, 8–14, 1993. Lutjeharms, J. R. E. and Cooper, J.: Interbasin leakage through Agulhas Current filaments, Deep-Sea Res. I, 43, 213–238, 1996. Lutjeharms, J. R. E., Meyer, A. A., Ansorge, I. J., Eagle, G. A., and Orren, M. J.: The nutrient characteristics of the Agulhas Bank, S. Afr. J. Mar. Sci., 17, 253–274, 1996. Lutjeharms, J. R. E.: Coastal hydrography, in: A Field Guide to the Eastern and Southern Cape Coast, edited by: Lubke, R. and de Moor, I., The Wildlife and Environment Society of Southern Africa, Grahamstown, University of Cape Town Press, Rondebosch, pp. 50–61, 1998. Lutjeharms, J. R. E. and Machu, E.: An upwelling cell inshore of the East Madagascar Current, Deep-Sea Res. I, 47, 2405–2411, 2000. Lutjeharms, J. R. E., Valentine, H. R., and van Ballegooyen, R. C.: The hydrography and water masses of the Natal Bight, South Africa, Cont. Shelf Res., 20, 1907–1939, 2000a. Lutjeharms, J. R. E., Cooper, J., and Roberts, M.: Upwelling at the inshore edge of the Agulhas Current, Cont. Shelf Res., 20, 737–761, 2000b. Lutjeharms, J. R. E., de Ruijter, W. P. M., Ridderinkhof, H., van Aken, H., Veth, C., van Leeuwen, P. J., Drijfhout, S. S., Jansen, J. H. F., and Brummer, G.-J. A.: MARE and ACSEX: new research programmes on the Agulhas Current system, S. Afr. J. Sci., 96, 105–110, 2000c. Lutjeharms, J. R. E., Wedepohl, P. M., and Meeuwis, J. M.: On the surface drift of the East Madagascar and the Mozambique Currents, S. Afr. J. Sci., 96, 141–147, 2000d. Lutjeharms, J. R. E. and Ansorge, I.: The Agulhas Return Current, J. Mar. Syst., 30, 115–138, 2001. Lutjeharms, J. R. E., Boebel, O., van der Vaart, P. C. F., de Ruijter, W. P. M.,. Rossby, T. H., and Bryden, H. L.: Evidence that the Natal Pulse controls the Agulhas Current over its full depth, Geophys. Res. Lett., 28, 3449–3452, 2001. Lutjeharms, J. R. E. and Fillis, C. S.: Intrusion of sub-Antarctic water across the Subtropical Convergence south of Africa, S. Afr. J. Sci., 99, 173–176, 2003. Lutjeharms, J. R. E. and Kortum, G.: On the influence of German marine research on South African physical oceanography since 1890, Historisch-meereskundliches Jahrbuch, 9, 81–100, 2003. Lutjeharms, J. R. E., Penven, P., and Roy, C.: Modelling the shear-edge eddies of the southern Agulhas Current, Cont. Shelf Res., 23, 1099–1115, 2003a. Lutjeharms, J. R. E., Boebel, O., and Rossby, T.: Agulhas cyclones, Deep-Sea Res. II, 50, 13–34, 2003b. Lutjeharms, J. R. E.: The coastal oceans of south-eastern Africa, in: The Sea, volume 14B, edited by: Robinson, A. R., Brink, K. H., pp. 783–834, 2006a. Lutjeharms, J. R. E.: The Agulhas Current, Springer-Verlag, Berlin, 329 pp., 2006b. Lutjeharms, J. R. E. and Kortum, G.: German research on the Agulhas Current system between the World Wars; a lost scientific achievement, Historisch-meereskundliches Jahrbuch, 11, 73–98, 2006. Machu, E., Lutjeharms, J. R. E., Webb, A. M., and van Aken, H. M.: First hydrographic evidence of the southeast Madagascar upwelling cell, Geophys. Res. Lett., 29, 2009, doi:10.1029/2002GL015381, 2003. Malan, O. G. and Schumann, E. H.: Natal shelf circulation revealed by Landsat imagery, S. Afr. J. Sci., 75, 136–137, 1979. Matano, R. P.: A numerical study of the Agulhas retroflection: the role of bottom topography, J. Phys. Oceanogr., 26, 2267–2279, 1996. Meyer, A. A., Lutjeharms, J. R. E., and de Villiers, S.: The nutrient characteristics of the Natal Bight, South Africa, J. Mar. Syst., 35, 11–37, 2002. Michaelis, G.: Die Wasserbewegung an der Oberfläche des Indischen Ozeans im Januar und Juli, Veröffentlichungen des Instituts für Meereskunde an der Universität Berlin, n.f. A8(16): 32~pp., 1923. Morrow, R., Birol, F., Griffen, D., and Sudre, J.: Divergent pathways of cyclonic and anti-cyclonic eddies, Geophys. Res. Lett., 31, L24311, doi:10.1029/2004GLO20974, 2004. Nehring, D., Hagen, E., Jorge da Silva, A., Schemainda, R., Wolf, G., Michelsen, N., Kaiser, W., Postel, L., Gosselck, F., Brenning, U., Kuhner, E., Arlt, G., Siegel, H., Gohs, L., and Bublitz, G.: Results of oceanological studies in the Mozambique Channel in February–March 1980, Beit. Meeresk., 56, 51–63, 1987. Olson, D. B. and Evans, R. H.: Rings of the Agulhas Current, Deep-Sea Res., 33, 27–42, 1986. Olson, D. B., Fine, R. A., and Gordon, A. L.: Convective modifications of water masses in the Agulhas, Deep-Sea Res., 39 (Supplement 1): s163–s181, 1992. Paech, H.: Die Oberflächenströmungen um Madagascar in ihrem Jährlichen Gang, Veröffentlichungen des Instituts für Meereskunde an der Universität Berlin, n.f. A(16): 39~pp., 1926. Pazan, S. and Niiler, P.: New global drifter data set available, Eos, Trans. Am. Geophys. Un., 86, 17, 2004. Pearce, A. F.: Some features of the upper 500 m of the Agulhas Current, J. mar. Res., 35, 731–753, 1977. Pearce, A. F., Schumann, E. H., and Lundie, G. S. H.: Features of the shelf circulation off the Natal coast, S. Afr. J. Sci., 74, 328–331, 1978. Peeters, F. J. C., Acheson, R., Brummer, G.-J. A., de Ruijter, W. P. M., Ganssen, G. M., Schneider, R. R., Ufkes, E., and Kroon, D.: Vigorous exchange between Indian and Atlantic Ocean at the end of the last five glacial periods, Nature, 430, 661–665, 2004. Penven, P., Lutjeharms, J. R. E., Marchesiello, P., Weeks, S. J., and Roy, C.: Generation of cyclonic eddies by the Agulhas Current in the lee of the Agulhas Bank, Geophys. Res. Lett., 28, 1055–1058, 2001. Penven, P., Lutjeharms, J. R. E., and Florenchie, P.: Madagascar: a pacemaker for the Agulhas Current system? Geophys. Res. Lett., 33, L17609, doi:10.1029/2006GL 026854, 2006. Pillsbury, R. D., Bottero, J. M., Pittock, G., Root, D. C., Simpkins, J., and Still, R. E.: Benguela Source and Transport Project (BEST): Current measurements off the coast of South Africa. WOCE ACM-4, June 1992–October 1993, OSU Data Report 157, Reference 94-3, Corvallis, 69 pp., 1994. Quartly, G. D. and Srokosz, M. A.: SST observations of the Agulhas and East Madagascar retroflections by the TRMM Microwave imager, J. Phys. Oceanogr., 32, 1585–1592, 2002. Quartly, G. D. and Srokosz, M. A.: Eddies in the southern Mozambique Channel, Deep-Sea Res. II, 51, 69–83, 2004. Rau, A. J., Rogers, J., Lutjeharms, J. R. E., Giraureau, J., Lee-Thorp, J. A., Chen, M.-T., and Waelbroeck, C.: A 450-kyr record of hydrographical conditions on the western Agulhas Bank slope, south of Africa, Mar. Geology, 180, 183–201, 2002. Reason, C. J. C.: Evidence for the influence of the Agulhas Current on regional atmospheric circulation patterns, J. Climate, 14, 2769–2778, 2001. Rennell, J.: An investigation of the currents of the Atlantic Ocean, and of those which prevail between the Indian Ocean and the Atlantic, J. G. and F. Rivington, London, edited by: Purdy, J., viii + 359~pp. + 2 folding maps, 1832. Richardson, P. L. and Garzoli, S. L.: Characteristics of intermediate water flows in the Benguela Current as measured with RAFOS floats, Deep-Sea Res. II, 50, 87–118, 2003. Ridderinkhof, H. and de Ruijter, W. P. M.: Moored current observations in the Mozambique Channel, Deep-Sea Res. II, 50, 1933–1955, 2003. Rouault, M. and Lutjeharms, J. R. E.: Air-sea interaction in the marine atmosphere boundary layer: a new South African research venture, S. Afr. J. Sci., 90, 11–12, 1994. Rouault, M., Lee-Thorp, A., Ansorge, I., and Lutjeharms, J.: Agulhas Current Air-Sea Interaction Experiment, S. Afr. J. Sci., 91, 493–496, 1995. Rouault, M. and Lutjeharms, J. R. E.: Air-sea exchange over an Agulhas eddy at the Subtropical Convergence, Global Atmos. Ocean Syst., 7, 125–150, 2000. Rouault, M., Lee-Thorp, A. M., and Lutjeharms, J. R. E.: The atmospheric boundary layer above the Agulhas Current during alongcurrent winds, J. Phys. Oceanogr., 30, 40–50, 2000. Rouault, M., White, S. A., Reason, C. J. C., Lutjeharms J. R. E., and Jobard, I.: Ocean-atmosphere interaction in the Agulhas Current and a South African extreme weather event, Weather Forecast., 17, 655–669, 2002. Rouault, M. and Lutjeharms, J. R. E.: Estimation of sea-surface temperature around southern Africa from satellite-derived microwave observations, S. Afr. J. Sci., 99, 489–494, 2003. Sǽtre, R. and Jorge da Silva, A.: The circulation of the Mozambique Channel, Deep-Sea Res., 31, 485–508, 1984. Schmid, C., Boebel, O., Zenk, W., Lutjeharms, J. R. E., Garzoli, S., Richardson, P. L., and Barron, C.: Early evolution of an Agulhas ring, Deep-Sea Res. II, 50, 141–166, 2003. Schmitz, W. J.: On the eddy field in the Agulhas Retroflection, with some global considerations, J. Geophys. Res., 101, 16 259–16 271, 1996. Schouten, M. W., de Ruijter, W. P. M., van Leeuwen, P. J., and Lutjeharms, J. R. E.: Translation, decay and splitting of Agulhas rings in the south-eastern Atlantic ocean, J. Geophys. Res., 105, 21 913–21 925, 2000. Schouten, M. W., de Ruijter, W. P. M., and van Leeuwen, P. J.: Upstream control of Agulhas ring shedding, J. Geophys. Res., 107, doi:10.1029/2001JC000804, 2002a. Schouten, M. W., de Ruijter, W. P. M., van Leeuwen, P. J., and Dijkstra, H.: A teleconnection between the equatorial and southern Indian Ocean, Geophys. Res. Lett., 29, 1812, doi:10.1029/2001GL014542, 2002b. Schouten, M. W., de Ruijter, W. P. M., van Leeuwen, P. J., and Ridderinkhof, H.: Eddies and variability in the Mozambique Channel, Deep-Sea Res. II, 50, 1987–2003, 2003. Schumann, E. H.: Inshore circulation of the Agulhas Current off Natal, J. Mar. Res., 40, 43–55, 1982. Schumann, E. H., Perrins, L.-A., and Hunter, I. T.: Upwelling along the south coast of the Cape Province, South Africa, S. Afr. J. Sci., 78, 238–242, 1982. Schumann, E. H., Ross, G. J. B., and Goschen, W. S.: Cold water events in Algoa Bay and along the Cape south coast, South Africa, in March/April 1987, S. Afr. J. Sci., 84, 579–584, 1988. Shannon, L. V.: The Cape Nimbus-7 CZCS programme: An overview and preliminary results, S. Afr. J. Sci., 75, 564, 1979. Shannon, L. V., Lutjeharms, J. R. E., and Agenbag, J. J.: Episodic input of Subantarctic water into the Benguela region, S. Afr. J. Sci., 85, 317–332, 1989. Shillington, F. A., Peterson, W. T., Hutchings, L., Probyn, T. A., Waldron, H. N., and Agenbag, J. J.: A cool upwelling filament off Namibia, southwest Africa: preliminary measurements of physical and biological features, Deep-Sea Res., 37, 1753–1772, 1990. Stramma, L.: The South Indian Ocean Current, J. phys. Oceanogr., 22, 421–430, 1992. Stramma, L. and Lutjeharms, J. R. E.: The flow field of the subtropical gyre of the South Indian Ocean, J. Geophys. Res., 102, 5513–5530, 1997. Swallow, J. C., Fieux, M., and Schott, F.: The boundary currents east and north of Madagascar. Part I. Geostrophic currents and transports, J. geophys. Res., 93, 4951–4962, 1988. Swart, V. P. and Largier, J. L.: Thermal structure of Agulhas Bank water, S. Afr. J. Mar. Sci., 5, 243–253, 1987. Van Aken, H., van Veldhoven, A. K., Veth, C., de Ruijter, W. P. M., van Leeuwen, P. J., Drijfhout, S. S., Whittle, C. P., and Rouault, M.: Observations of a young Agulhas ring, Astrid, during MARE, the Mixing of Agulhas Rings Experiment, in March 2000, Deep-Sea Res. II, 50, 167–195, 2003. Van Ballegooyen, R. C., Gründlingh, M. L., and Lutjeharms, J. R. E.: Eddy fluxes of heat and salt from the southwest Indian Ocean into the southeast Atlantic Ocean: a case study, J. Geophys. Res., 99, 14 053–14 070, 1994. Van Gogh, J.: Uitkomsten van Wetenskap en Ervaring aangaande winden en zeestromingen in sommige gedeelten van den oseaan, Koninklijk Nederlandsch Meteorologisch Instituut, Bosch en Zoon, 74~pp., 1857. Van Gogh, J.: De stormen nabij de Kaap de Goede Hoop in verband beschouwd met de temperatuur der zee, Verhandelingen en Mededelingen der Koninklijke Akademie, afdeling Natuurkunde, 8, 23~pp., 1858. Van Leeuwen, P. J., de Ruijter, W. P. M., and Lutjeharms, J. R. E.: Natal Pulses and the formation of Agulhas rings, J. Geophys. Res., 105, 6425–6436, 2000. Walker, N. D. and Mey, R. D.: Ocean/atmosphere heat fluxes within the Agulhas Retroflection region, J. Geophys. Res., 93, 15 473–15 483, 1988. Walker N. D. and Lindesay, J. A.: Preliminary observations of oceanic influences on the February-March 1988 floods in central South Africa, S. Afr. J. Sci., 85, 164–169, 1989. Walker, N. D.: Links between South African summer rainfall and temperature variability of the Agulhas and Benguela Current Systems, J. Geophys. Res., 95, 3297–3319, 1990. Weeks, S. J. and Shillington, F. A.: Phytoplankton pigment distribution and frontal structure in the subtropical convergence region south of Africa, Deep-Sea Res. I, 43, 739–768, 1996. Weijer, W., de Ruijter, W. P. M., Dijkstra, H. A., and van Leeuwen, P. J.: Impact of interbasin exchange on the Atlantic overturning circulation, J. Phys. Oceanogr., 29, 2266–2284, 1999. Weijer, W., de Ruijter, W. P. M., and Dijkstra, H. A.: Stability of the Atlantic overturning circulation: competition between Bering Strait freshwater flux and Agulhas heat and salt sources, J. Phys. Oceanogr., 31, 2385–2402, 2001. Weijer, W., de Ruijter, W. P. M., Sterl, A., and Drijfhout, S. S.: Response of the Atlantic overturning circulation to South Atlantic sources of buoyancy, Global Planet. Change, 34, 293–311, 2002. Wüst, G.: Proposed International Indian Ocean Expedition, 1962–1963, Deep-Sea Res., 6, 245-249, 1960. Wyrtki, K.: Oceanographic Atlas of the International Indian Ocean Expedition, National Science Foundation, Washington, D.C., 531~pp., 1971.