• Andrews, W. R. H., and L. Hutchings, 1980: Upwelling in the southern Benguela Current. Prog. Oceanogr., 9 , 18.

  • Armstrong, E., and J. Vazquez, 2001: A new global satellite-based sea surface temperature climatology. Geophys. Res. Lett., 28 , 41994202.

    • Search Google Scholar
    • Export Citation
  • Bakun, A., 1973: Coastal upwelling indices, west coast of North America, 1946-71. NOAA Tech. Rep. NMFS SSRF-671, 103 pp.

  • Bang, N., and W. Andrews, 1974: Direct current measurements of a shelf-edge frontal jet in the southern Benguela system. J. Mar. Res., 32 , 405417.

    • Search Google Scholar
    • Export Citation
  • Barange, M., and S. Pillar, 1992: Euphausiacea in the northern Benguela upwelling system. Cont. Shelf Res., 12 , 10271042.

  • Barnier, B., L. Siefridt, and P. Marchesiello, 1995: Thermal forcing for a global ocean circulation model using a three-year climatology of ECMWF analysis. J. Mar. Syst., 6 , 363380.

    • Search Google Scholar
    • Export Citation
  • Blanke, B., S. Speich, A. Bentamy, C. Roy, and B. Sow, 2005: Modeling the structure and variability of the southern Benguela upwelling using QuikSCAT wind forcing. J. Geophys. Res., 110 , C07018. doi:10.1029/2004JC002529.

    • Search Google Scholar
    • Export Citation
  • Boebel, O., J. Lutjeharms, C. Schmid, W. Zenk, T. Rossby, and C. Barron, 2003: The Cape Cauldron: A regime of turbulent inter-ocean exchange. Deep-Sea Res. II, 50 , 5786.

    • Search Google Scholar
    • Export Citation
  • Boyd, A. J., J. Taunton-Clark, and G. Oberholzer, 1992: 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 , 189206.

    • Search Google Scholar
    • Export Citation
  • Capet, X. J., P. Marchesiello, and J. C. McWilliams, 2004: Upwelling response to coastal wind profiles. Geophys. Res. Lett., 31 , L13311. doi:10.1029/2004GL020123.

    • Search Google Scholar
    • Export Citation
  • Carr, M-E., and E. Kearns, 2002: Estimation of potential productivity in eastern boundary currents using remote sensing. Deep-Sea Res. II, 49 , 5980.

    • Search Google Scholar
    • Export Citation
  • Colas, F., X. Capet, X. Jin, J. Molemaker, D. Chelton, and J. McWilliams, 2008a: Wind stress and sea surface temperature coupling in eastern boundary upwelling systems. Proc. Eastern Boundary Upwelling Ecosystems Symp., Las Palmas, Canary Islands, 107.

    • Search Google Scholar
    • Export Citation
  • Colas, F., X. Capet, J. C. McWilliams, and A. Shchepetkin, 2008b: 1997–1998 El Niño off Peru: A numerical study. Prog. Oceanogr., 79 , 138155.

    • Search Google Scholar
    • Export Citation
  • Colberg, F., and C. J. C. Reason, 2006: A model study of the Angola Benguela Frontal Zone: Sensitivity to atmospheric forcing. Geophys. Res. Lett., 33 , L19608. doi:10.1029/2006GL027463.

    • Search Google Scholar
    • Export Citation
  • Conkright, M., R. Locarnini, H. Garcia, T. O’Brien, T. Boyer, C. Stephens, and J. Antonov, 2002: World Ocean Atlas 2001: Objective analyses, data statistics and figures. National Oceanographic Data Center Internal Rep. 17, 21 pp.

    • Search Google Scholar
    • Export Citation
  • Da Silva, A., C. Young, and S. Levitus, 1994: Atlas of surface marine data 1994. Vol. 1: Algorithms and procedures. NOAA Tech Rep., 117 pp.

    • Search Google Scholar
    • Export Citation
  • Debreu, L., and E. Blayo, 2008: Two-way embedding algorithms: A review. Ocean Dyn., 58 , 415428.

  • de Ruijter, W., A. Biastoch, S. Drijfhout, J. Lutjeharms, R. Matano, T. Pichevin, P. van Leeuwen, and W. Weijer, 1999: Indian-Atlantic interocean exchange: Dynamics, estimation and impact. J. Geophys. Res., 104 , (C9). 2088520910.

    • Search Google Scholar
    • Export Citation
  • Estrade, P., P. Marchesiello, A. Colin de Verdiere, and C. Roy, 2008: Cross-shelf structure of coastal upwelling: A two-dimensional expansion of Ekman’s theory and a mechanism for innershelf upwelling shut down. J. Mar. Res., 66 , 589616.

    • Search Google Scholar
    • Export Citation
  • Gan, J., and J. S. Allen, 2002a: A modeling study of shelf circulation off northern California in the region of the Coastal Ocean Dynamics Experiment: Response to relaxation of upwelling winds. J. Geophys. Res., 107 , 3123. doi:10.1029/2000JC000768.

    • Search Google Scholar
    • Export Citation
  • Garzoli, S., and A. Gordon, 1996: Origins and variability of the Benguela Current. J. Geophys. Res., 101 , (C1). 897906.

  • Gordon, A., 2003: The brawniest retroflection. Nature, 421 , 904905.

  • Gordon, A., J. Lutjeharms, and M. Grundlingh, 1987: Stratification and circulation at the Agulhas Retroflection. Deep-Sea Res., 34 , 565599.

    • Search Google Scholar
    • Export Citation
  • Gordon, A., R. Weiss, W. Smethie, and M. Warner, 1992: Thermocline and intermediate water communication between the South Atlantic and Indian Oceans. J. Geophys. Res., 97 , (C5). 72237240.

    • Search Google Scholar
    • Export Citation
  • Huyer, A., R. Smith, and T. Paluszkiewicz, 1987: Coastal upwelling off Peru during normal and El Niño times, 1981–1984. J. Geophys. Res., 92 , 1429714307.

    • Search Google Scholar
    • Export Citation
  • John, H-C., V. Mohrholz, and J. Lutjeharms, 2001: Cross-front hydrography and fish larval distribution at the Angola-Benguela Front. J. Mar. Syst., 28 , 91111.

    • Search Google Scholar
    • Export Citation
  • Johnson, A., and G. Nelson, 1999: Ekman estimates of upwelling at Cape Columbine based on measurements of longshore wind from a 35-year time-series. S. Afr. J. Mar. Sci., 21 , 433436.

    • Search Google Scholar
    • Export Citation
  • Kostianoy, A., and J. Lutjeharms, 1999: Atmospheric effects in the Angola-Benguela frontal zone. J. Geophys. Res., 104 , 2096320970.

  • Kundu, P. K., 1990: Fluid Mechanics. Academic Press, 639 pp.

  • Large, W., J. McWilliams, and S. Doney, 1994: Oceanic vertical mixing: A review and a model with a nonlocal boundary layer parameterization. Rev. Geophys., 32 , 363403.

    • Search Google Scholar
    • Export Citation
  • Lett, C., J. Veitch, C. D. van der Lingen, and L. Hutchings, 2007: Assessment of an environmental barrier to the transport of ichthyoplankton from the southern to the northern Benguela ecosystems. Mar. Ecol., 347 , 247259.

    • Search Google Scholar
    • Export Citation
  • Lutjeharms, J., 1996: The exchange of water between the south Indian and South Atlantic Oceans. The South Atlantic: Past and Present Circulation, G. Wefer et al., Eds., Springer-Verlag, 125–162.

    • Search Google Scholar
    • Export Citation
  • Lutjeharms, J., and J. Meeuwis, 1987: The extent and variability of south-east Atlantic upwelling. S. Afr. J. Mar. Sci., 5 , 5162.

  • Lutjeharms, J., and P. Stockton, 1987: Kinematics of the upwelling front off southern Africa. S. Afr. J. Mar. Sci., 5 , 3549.

  • Lutjeharms, J., and R. van Ballegooyen, 1988: The retroflection of the Agulhas Current. J. Phys. Oceanogr., 18 , 15701583.

  • Lutjeharms, J., F. Shillington, and C. M. Duncombe-Rae, 1991: Observations of extreme upwelling filaments in the southeast Atlantic Ocean. Science, 253 , 774776.

    • Search Google Scholar
    • Export Citation
  • Lutjeharms, J., D. Webb, B. de Cuevas, and S. Thompson, 1995: Large-scale modelling of the south-east Atlantic upwelling system. S. Afr. J. Mar. Sci., 16 , 205225.

    • Search Google Scholar
    • Export Citation
  • Marchesiello, P., and P. Estrade, 2010: Upwelling limitation by coastal geostrophic convergence. J. Mar. Res., in press.

  • Marchesiello, P., J. McWilliams, and A. Shchepetkin, 2001: Open boundary conditions for long-term integration of regional oceanic models. Ocean Modell., 3 , 120.

    • Search Google Scholar
    • Export Citation
  • Marchesiello, P., J. McWilliams, and A. Shchepetkin, 2003: Equilibrium structure and dynamics of the California Current system. J. Phys. Oceanogr., 33 , 753783.

    • Search Google Scholar
    • Export Citation
  • Marchesiello, P., L. Debreu, and X. Couvelard, 2009: Spurious diapycnal mixing in terrain-following coordinate models: The problem and a solution. Ocean Modell., 26 , 156169.

    • Search Google Scholar
    • Export Citation
  • Matano, R., and E. Beier, 2003: A kinematic analysis of the Indian/Atlantic interocean exchange. Deep-Sea Res., 50 , 229249.

  • Mohrholz, V., M. Schmidt, J. Lutjeharms, and H-C. John, 2001: The hydrography and dynamics of the Angola-Benguela frontal zone in April 1999. S. Afr. J. Sci., 97 , 199208.

    • Search Google Scholar
    • Export Citation
  • Monteiro, P. M. S., and A. K. van der Plas, 2006: Low oxygen water (LOW) variability in the Benguela system: Key processes and forcing scales relative to forecasting. Large Mar. Ecosyst., 14 , 7190.

    • Search Google Scholar
    • Export Citation
  • Monteiro, P. M. S., A. K. van der Plas, J-L. Mélice, and P. Florenchie, 2008: Interannual hypoxia variability in a coastal upwelling system: Ocean–shelf exchange, climate and ecosystem-state implications. Deep-Sea Res. I, 55 , 435450.

    • Search Google Scholar
    • Export Citation
  • Narimousa, S., and T. Maxworthy, 1986: Coastal upwelling on a sloping bottom: The formation of plumes, jets and pinched-off cyclones. J. Fluid Mech., 176 , 169190.

    • Search Google Scholar
    • Export Citation
  • Nelson, G., and L. Hutchings, 1983: The Benguela upwelling area. Prog. Oceanogr., 12 , 333356.

  • Peffley, M., and J. O’Brien, 1976: A three-dimensional simulation of coastal upwelling off Oregon. J. Phys. Oceanogr., 6 , 164180.

  • Penven, P., 2000: A numerical study of the Southern Benguela circulation with an application to fish recruitment. Ph.D. thesis, University of Brest, 146 pp.

  • Penven, P., C. Roy, A. Colin de Verdiere, and J. Largier, 2000: Simulation of a coastal jet retention process using a barotropic model. Oceanol. Acta, 23 , 615634.

    • Search Google Scholar
    • Export Citation
  • Penven, P., C. Roy, G. Brundrit, A. Colin de Verdiere, P. Freon, A. Johnson, J. Lutjeharms, and F. Shillington, 2001: A regional hydrodynamic model of upwelling in the southern Benguela. S. Afr. J. Sci., 97 , 472475.

    • Search Google Scholar
    • Export Citation
  • Penven, P., V. Echevin, J. Pasapera, F. Colas, and J. Tam, 2005: Average circulation, seasonal cycle, and mesoscale dynamics of the Peru Current system: A modeling approach. J. Geophys. Res., 110 , C10021. doi:10.1029/2005JC0029452.

    • Search Google Scholar
    • Export Citation
  • Penven, P., N. Chang, and F. Shillington, 2006a: Modelling the Agulhas Current using SAfE (Southern African Experiment). Geophys. Res. Abstr., 8 , 4225.

    • Search Google Scholar
    • Export Citation
  • Penven, P., L. Debreu, P. Marchesiello, and J. McWilliams, 2006b: Evaluation and application of the ROMS 1-way embedding procedure to the central California upwelling system. Ocean Modell., 12 , 157187.

    • Search Google Scholar
    • Export Citation
  • Penven, P., J. R. E. Lutjeharms, and P. Florenchie, 2006c: Madagascar: A pacemaker for the Agulhas Current? Geophys. Res. Lett., 33 , L17609. doi:10.1029/2006GL026854.

    • Search Google Scholar
    • Export Citation
  • Penven, P., P. Marchesiello, L. Debreu, and J. Lefèvre, 2007: Software tools for pre- and post-processing of oceanic regional simulations. Environ. Model. Software, 23 , 660662. doi:10.1016/j.envsoft.2007.07.004.

    • Search Google Scholar
    • Export Citation
  • Peterson, R., and L. Stramma, 1991: Upper-level circulation in the South Atlantic. Prog. Oceanogr., 26 , 173.

  • Preston-Whyte, R. A., and P. D. Tyson, 1993: The Atmosphere and Weather of Southern Africa. Oxford University Press, 207–249.

  • Reid, J., 1989: Geostrophic circulation of the South Atlantic Ocean. Prog. Oceanogr., 23 , 149244.

  • Rio, M-H., and F. Hernandez, 2004: A mean dynamic topography computed over the world ocean from altimetry, in situ measurements, and a geoid model. J. Geophys. Res., 109 , C12032. doi:10.1029/2003JC002226.

    • Search Google Scholar
    • Export Citation
  • Shannon, L., 1985: The Benguela ecosystem. Part 1: Physical features and processes. Oceanographic and Marine Biology: An Annual Review, M. Barnes, Ed., Vol. 23, 105–182.

    • Search Google Scholar
    • Export Citation
  • Shannon, L., and D. Hunter, 1988: Notes on Antarctic intermediate water around Southern Africa. S. Afr. J. Mar. Sci., 6 , 107117.

  • Shannon, L., and G. Nelson, 1996: The Benguela: Large-scale features and processes and system variability. The South Atlantic: Present and Past Circulation, G. Wefer, Ed., Springer, 163–210.

    • Search Google Scholar
    • Export Citation
  • Shannon, L., J. Agenbag, and M. Buys, 1987: Large- and meso-scale features of the Angola-Benguela Front. S. Afr. J. Mar. Sci., 5 , 1134.

    • Search Google Scholar
    • Export Citation
  • Shchepetkin, A. F., and J. C. McWilliams, 1998: Quasi-monotone advection schemes based on explicit locally adaptive dissipation. Mon. Wea. Rev., 126 , 15411580.

    • Search Google Scholar
    • Export Citation
  • Shchepetkin, A. F., and J. C. McWilliams, 2003: A method for computing horizontal pressure-gradient force in an oceanic model with a nonaligned vertical coordinate. J. Geophys. Res., 108 , 3090. doi:10.1029/2001JC001047.

    • Search Google Scholar
    • Export Citation
  • Shchepetkin, A. F., and J. C. McWilliams, 2005: The Regional Oceanic Modeling System (ROMS): A split-explicit, free-surface, topography-following-coordinate oceanic model. Ocean Modell., 9 , 347404.

    • Search Google Scholar
    • Export Citation
  • Shillington, F., and L. Nykjaer, 2001: Environmental conditions and fluctuations in distribution in small pelagic fish stocks (ENVIFISH) 1998–2001. Small Pelagic Fishes and Climate Change Programme, GLOBEC Rep. 16, 79–80.

    • Search Google Scholar
    • Export Citation
  • Shillington, F., W. Peterson, L. Hutchings, T. Probyn, H. Waldron, and J. Agenbag, 1990: A cool upwelling filament off Namibia, southwest Africa: Preliminary measurements of physical and biological features. Deep-Sea Res., 37 , 17531772.

    • Search Google Scholar
    • Export Citation
  • Skogen, M., 1999: Numerical modelling of the Benguela system. Some preliminary results. S. Afr. J. Mar. Sci., 21 , 235249.

  • Speich, S., J. R. E. Lutjeharms, P. Penven, and B. Blanke, 2006: Role of bathymetry in Agulhas Current configuration and behaviour. Geophys. Res. Lett., 33 , L23611. doi:10.1029/2006GL027157.

    • Search Google Scholar
    • Export Citation
  • Stenevik, E., H. Verheye, M. Lipinski, M. Ostrowski, and T. Stromme, 2008: Drift routes of cape hake eggs and larvae in the southern Benguela Current system. J. Plankton Res., 30 , 11471156.

    • Search Google Scholar
    • Export Citation
  • Strub, P. T., F. A. Shillington, C. James, and S. J. Weeks, 1998: Satellite comparison of the seasonal circulation in the Benguela and California current systems. S. Afr. J. Mar. Sci., 19 , 99112.

    • Search Google Scholar
    • Export Citation
  • Veitch, J., P. Florenchie, and F. Shillington, 2006: Seasonal and interannual fluctuations of the Angola-Benguela frontal zone (ABFZ) using 4.5 km resolution satellite imagery from 1982 to 1999. Int. J. Remote Sens., 27 , 987998.

    • Search Google Scholar
    • Export Citation
  • Veitch, J., P. Penven, and F. Shillington, 2008: The Benguela: A laboratory for comparative modeling studies. Prog. Oceanogr., 83 , 296302. doi:10.1016/j.pocean.2009.07.008.

    • Search Google Scholar
    • Export Citation
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Modeling Equilibrium Dynamics of the Benguela Current System

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  • 1 Department of Oceanography, University of Cape Town, Rondebosch, South Africa
  • | 2 Laboratoire de Physique des Oceans (UMR 6523 CNRS, IFREMER, IRD, UBO), Brest, France
  • | 3 Department of Oceanography, University of Cape Town, Rondebosch, South Africa
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Abstract

The Regional Ocean Modeling System (ROMS) is used to systematically investigate equilibrium conditions and seasonal variations of the Benguela system at a resolution of 9 km, including both the large-scale offshore flow regime and the economically and ecologically important coastal upwelling regime. A shelf-edge poleward flow exists in the northern Benguela region (i.e., north of ∼28°S) and is driven primarily by the wind stress curl via the Sverdrup relation. As such, it is strongly seasonal and is most intense during spring and summer, when the wind stress curl is most negative. The poleward flow deepens as it moves southward; between ∼25° and 27°S, much of it veers offshore because of the nature of the wind stress curl and its interaction with the northwestward path of the Benguela Current, which is influenced by alongshore topographical variations. The Benguela Current is driven by nonlinear interactions of passing Agulhas rings and eddies and does not have a striking seasonal signal. In the mean state, it is characterized by two streams. The more inshore stream is topographically controlled and follows the run of the shelf edge. The meandering nature of the offshore stream is a result of the preferential path of Agulhas rings. The model simulates all seven of the major upwelling cells within its domain. The three southernmost cells have the strongest seasonal signal and experience their greatest upwelling during spring and summer months, whereas the two northernmost cells have less seasonal variability but nevertheless have increased upwelling from autumn to spring (and least upwelling in summer), and the central Benguela upwelling cells experience year-round upwelling. The effect of topography on coastal upwelling was investigated by smoothing alongshore coastline and topography variations, which showed that, in all of the seven major upwelling cells, upwelling is enhanced on the downstream side of capes.

Corresponding author address: Jennifer Veitch, Department of Oceanography, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa. Email: jennifer.veitch@uct.ac.za

Abstract

The Regional Ocean Modeling System (ROMS) is used to systematically investigate equilibrium conditions and seasonal variations of the Benguela system at a resolution of 9 km, including both the large-scale offshore flow regime and the economically and ecologically important coastal upwelling regime. A shelf-edge poleward flow exists in the northern Benguela region (i.e., north of ∼28°S) and is driven primarily by the wind stress curl via the Sverdrup relation. As such, it is strongly seasonal and is most intense during spring and summer, when the wind stress curl is most negative. The poleward flow deepens as it moves southward; between ∼25° and 27°S, much of it veers offshore because of the nature of the wind stress curl and its interaction with the northwestward path of the Benguela Current, which is influenced by alongshore topographical variations. The Benguela Current is driven by nonlinear interactions of passing Agulhas rings and eddies and does not have a striking seasonal signal. In the mean state, it is characterized by two streams. The more inshore stream is topographically controlled and follows the run of the shelf edge. The meandering nature of the offshore stream is a result of the preferential path of Agulhas rings. The model simulates all seven of the major upwelling cells within its domain. The three southernmost cells have the strongest seasonal signal and experience their greatest upwelling during spring and summer months, whereas the two northernmost cells have less seasonal variability but nevertheless have increased upwelling from autumn to spring (and least upwelling in summer), and the central Benguela upwelling cells experience year-round upwelling. The effect of topography on coastal upwelling was investigated by smoothing alongshore coastline and topography variations, which showed that, in all of the seven major upwelling cells, upwelling is enhanced on the downstream side of capes.

Corresponding author address: Jennifer Veitch, Department of Oceanography, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa. Email: jennifer.veitch@uct.ac.za

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