Editorial Type:
Article
Article Type:
Research Article

Generation of a Buoyancy-Driven Coastal Current by an Antarctic Polynya

Alexander V. Wilchinsky Centre for Polar Observation and Modelling, Department of Earth Sciences, University College London, London, United Kingdom

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Daniel L. Feltham Centre for Polar Observation and Modelling, Department of Earth Sciences, University College London, London, and British Antarctic Survey, Cambridge, United Kingdom

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Print Publication:
01 May 2008
DOI:
https://doi.org/10.1175/2007JPO3831.1
Page(s):
1011–1032
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Abstract

Descent and spreading of high salinity water generated by salt rejection during sea ice formation in an Antarctic coastal polynya is studied using a hydrostatic, primitive equation three-dimensional ocean model called the Proudman Oceanographic Laboratory Coastal Ocean Modeling System (POLCOMS). The shape of the polynya is assumed to be a rectangle 100 km long and 30 km wide, and the salinity flux into the polynya at its surface is constant. The model has been run at high horizontal spatial resolution (500 m), and numerical simulations reveal a buoyancy-driven coastal current. The coastal current is a robust feature and appears in a range of simulations designed to investigate the influence of a sloping bottom, variable bottom drag, variable vertical turbulent diffusivities, higher salinity flux, and an offshore position of the polynya. It is shown that bottom drag is the main factor determining the current width. This coastal current has not been produced with other numerical models of polynyas, which may be because these models were run at coarser resolutions. The coastal current becomes unstable upstream of its front when the polynya is adjacent to the coast. When the polynya is situated offshore, an unstable current is produced from its outset owing to the capture of cyclonic eddies. The effect of a coastal protrusion and a canyon on the current motion is investigated. In particular, due to the convex shape of the coastal protrusion, the current sheds a dipolar eddy.

Corresponding author address: Alexander Wilchinsky, CPOM, Dept. of Earth Sciences, University College London, Gower St., London, WC1E 6BT, United Kingdom. Email: aw@cpom.ucl.ac.uk

Abstract

Descent and spreading of high salinity water generated by salt rejection during sea ice formation in an Antarctic coastal polynya is studied using a hydrostatic, primitive equation three-dimensional ocean model called the Proudman Oceanographic Laboratory Coastal Ocean Modeling System (POLCOMS). The shape of the polynya is assumed to be a rectangle 100 km long and 30 km wide, and the salinity flux into the polynya at its surface is constant. The model has been run at high horizontal spatial resolution (500 m), and numerical simulations reveal a buoyancy-driven coastal current. The coastal current is a robust feature and appears in a range of simulations designed to investigate the influence of a sloping bottom, variable bottom drag, variable vertical turbulent diffusivities, higher salinity flux, and an offshore position of the polynya. It is shown that bottom drag is the main factor determining the current width. This coastal current has not been produced with other numerical models of polynyas, which may be because these models were run at coarser resolutions. The coastal current becomes unstable upstream of its front when the polynya is adjacent to the coast. When the polynya is situated offshore, an unstable current is produced from its outset owing to the capture of cyclonic eddies. The effect of a coastal protrusion and a canyon on the current motion is investigated. In particular, due to the convex shape of the coastal protrusion, the current sheds a dipolar eddy.

Corresponding author address: Alexander Wilchinsky, CPOM, Dept. of Earth Sciences, University College London, Gower St., London, WC1E 6BT, United Kingdom. Email: aw@cpom.ucl.ac.uk

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  • Aiki, H., and T. Yamagata, 2004: A numerical study on the successive formation of Meddy-like lenses. J. Geophys. Res., 109 .C06020, doi:10.1029/2003JC001952.

    • Search Google Scholar
    • Export Citation

  • Bacon, S., G. Reverdin, I. G. Rigor, and H. Snaith, 2002: A freshwater jet on the East Greenland shelf. J. Geophys. Res., 107 .3068, doi:10.1029/2001JC000935.

    • Search Google Scholar
    • Export Citation

  • Baines, P. G., and S. Condie, 1998: Observations and Modelling of Antarctic Downslope Flows: A Review. AGU Antarctic Research Series, Vol. 75, Amer. Geophys. Union, 29–49.

    • Search Google Scholar
    • Export Citation

  • Brickman, D., 1995: Heat flux partitioning in open-ocean convection. J. Phys. Oceanogr., 25 , 2609–2623.

  • Cavalieri, D. J., and S. Martin, 1985: A Passive Microwave Study of Polynyas along the Antarctic Wilkes Land Coast. AGU Antarctic Research Series, Vol. 43, Amer. Geophys. Union, 227–252.

    • Search Google Scholar
    • Export Citation

  • Cenedese, C., and J. A. Whitehead, 2000: Eddy shedding from a boundary current around a cape over a sloping bottom. J. Phys. Oceanogr., 30 , 1514–1531.

    • Search Google Scholar
    • Export Citation

  • Chapman, D. C., and G. Gawarkiewicz, 1995: Offshore transport of dense shelf water in the presence of a submarine canyon. J. Geophys. Res., 100 , 13373–13387.

    • Search Google Scholar
    • Export Citation

  • Condie, S. A., and G. N. Ivey, 1988: Convectively driven coastal currents in a rotating basin. J. Mar. Res., 46 , 473–494.

  • D’Asaro, E., 1988: Generation of submesoscale vortices: A new mechanism. J. Geophys. Res., 93 , 6685–6693.

  • Davies, P. A., and I. Ahmed, 1996: Laboratory studies of a round, negatively buoyant jet discharged horizontally into a rotating homogeneous fluid. Fluid Dyn. Res., 17 , 237–274.

    • Search Google Scholar
    • Export Citation

  • Davies, P. A., H. J. S. Fernando, F. Besley, and R. J. Simpson, 1991: Generation and spreading of a turbulent mixed layer in a rotating, stratified fluid. J. Geophys. Res., 96 , 12567–12585.

    • Search Google Scholar
    • Export Citation

  • Deleersnijder, E., and P. Luyten, 1994: On the practical advantages of the quasi-equilibrium version of the Melllor and Yamada level 2.5 turbulence closure applied to numerical modelling. Appl. Math. Modell., 18 , 281–287.

    • Search Google Scholar
    • Export Citation

  • Dewar, W. K., and P. D. Killworth, 1990: On the cylinder collapse problem, mixing, and merger of isolated eddies. J. Phys. Oceanogr., 20 , 1563–1575.

    • Search Google Scholar
    • Export Citation

  • Etling, D., F. Gelhardt, U. Schrader, F. Brennecke, G. Kühn, C. d’Hieres, and H. Didelle, 2000: Experiments with density currents on a sloping bottom in a rotating fluid. Dyn. Atmos. Oceans, 31 , 139–164.

    • Search Google Scholar
    • Export Citation

  • Ezer, T., 2005: Entrainment, diapycnical mixing and transport in three-dimensional bottom gravity current simulations using the Mellor–Yamada turbulence scheme. Ocean Modell., 9 , 151–168.

    • Search Google Scholar
    • Export Citation

  • Galperin, B., L. H. Kantha, S. Hassid, and A. Rossati, 1988: A quasi-equilibrium turbulent energy model for geophysical flows. J. Atmos. Sci., 45 , 55–66.

    • Search Google Scholar
    • Export Citation

  • Gawarkiewicz, G., 2000: Effect of ambient stratification and shelfbreak topography on offshore transport of dense water on continental shelves. J. Geophys. Res., 105 , 3307–3324.

    • Search Google Scholar
    • Export Citation

  • Gawarkiewicz, G., and D. C. Chapman, 1995: A numerical study of dense water formation and transport on a shallow, sloping continental shelf. J. Geophys. Res., 100 , 4489–4507.

    • Search Google Scholar
    • Export Citation

  • Griffiths, R. W., and P. F. Linden, 1982: Laboratory experiments on fronts. Part I: Density-driven boundary currents. Geophys. Astrophys. Fluid Dyn., 19 , 159–187.

    • Search Google Scholar
    • Export Citation

  • Griffiths, R. W., 1986: Gravity currents in rotating systems. Annu. Rev. Fluid Mech., 18 , 59–89.

  • Griffiths, R. W., and P. F. Linden, 1981: The stability of buoyancy-driven coastal currents. Dyn. Atmos. Oceans, 5 , 281–306.

  • Griffiths, R. W., P. D. Killworth, and M. E. Stern, 1982: Ageostrophic instability of ocean currents. J. Fluid Mech., 117 , 343–377.

    • Search Google Scholar
    • Export Citation

  • Grumbine, R. W., 1991: A model of the formation of high-salinity shelf water on polar continental shelves. J. Geophys. Res., 96 , 22049–22062.

    • Search Google Scholar
    • Export Citation

  • Holt, J. T., and I. D. James, 1999: A simulation of the southern North Sea in comparison with measurements from the North Sea Project. Part 1: Temperature. Cont. Shelf Res., 19 , 1087–1112.

    • Search Google Scholar
    • Export Citation

  • Holt, J. T., and I. D. James, 2001: An s coordinate density evolving model of the northwest European continental shelf. 1. Model description and density structure. J. Geophys. Res., 106 , 14015–14034.

    • Search Google Scholar
    • Export Citation

  • Ikeda, M., 1987: Wind effects on the buoyancy-driven general circulation in a closed basin using a two-level model. J. Phys. Oceanogr., 17 , 1707–1723.

    • Search Google Scholar
    • Export Citation

  • Ivanov, V. V., G. I. Shapiro, J. M. Huthnance, D. L. Aleynik, and P. N. Golovin, 2004: Cascades of dense water around the world ocean. Prog. Oceanogr., 60 , 47–98.

    • Search Google Scholar
    • Export Citation

  • Ivey, J., J. Taylor, and M. Coates, 1995: Convectively driven mixed layer growth in a rotating, stratified fluid. Deep-Sea Res. I, 42 , 331–349.

    • Search Google Scholar
    • Export Citation

  • James, I. D., 1996: Advection schemes for shelf sea models. J. Mar. Syst., 8 , 237–254.

  • Jiang, L., and R. W. Garwood Jr., 1996: Three-dimensional simulation of overflows on continental slopes. J. Phys. Oceanogr., 26 , 1214–1233.

    • Search Google Scholar
    • Export Citation

  • Johannessen, O. M., and M. Mork, 1979: Remote sensing experiment in the Norwegian coastal waters. Geophysisk Institutt, Universitetet i Bergen Tech. Rep. 3/79.

  • Killworth, P. D., 1985: A two-level wind and buoyancy driven thermocline model. J. Phys. Oceanogr., 15 , 1414–1432.

  • Kukichi, T., M. Wakatachi, and M. Ikeda, 1999: A numerical investigation of the transport process of dense shelf water from a continental shelf to slope. J. Geophys. Res., 104 , 1197–1210.

    • Search Google Scholar
    • Export Citation

  • Lane-Serff, G. F., and P. G. Baines, 1998: Eddy formation by dense flows on slopes in a rotating fluid. J. Fluid Mech., 363 , 229–252.

    • Search Google Scholar
    • Export Citation

  • Legg, S., and J. Marshall, 1993: A heton model of the spreading phase of open-ocean deep convection. J. Phys. Oceanogr., 23 , 1040–1056.

    • Search Google Scholar
    • Export Citation

  • Legg, S., R. W. Hallberg, and J. B. Girton, 2006: Comparison of entrainment in overflows simulated by z-coordinate, isopycnal and nonhydrostatic models. Ocean Modell., 1 , 69–97.

    • Search Google Scholar
    • Export Citation

  • Massom, R. A., P. T. Harris, K. J. Michael, and M. J. Potter, 1998: The distribution and formative processes of latent-heat polynyas in east Antarctica. Ann. Glaciol., 27 , 420–426.

    • Search Google Scholar
    • Export Citation

  • Mellor, G. L., 1989: Retrospective on oceanic boundary layer modelling and second moment closure. The Parameterisation of Small Scale Processes: Proc. ‘Aha Huliko‘a Hawaiian Winter Workshop, Honolulu, HI, University of Hawaii at Manoa, 251–271.

  • Mellor, G. L., 1991: An equation of state for numerical models of oceans and estuaries. J. Atmos. Oceanic Technol., 8 , 601–611.

  • Mellor, G. L., and T. Yamada, 1974: A hierarchy of turbulence closure models for planetary boundary layers. J. Atmos. Sci., 31 , 1791–1806.

    • Search Google Scholar
    • Export Citation

  • Morales Maqueda, M. A., A. J. Wilmott, and N. R. T. Biggs, 2004: Polynya dynamics: A review of observations and modeling. Rev. Geophys., 42 .RG1004, doi:10.1029/2002RG000116.

    • Search Google Scholar
    • Export Citation

  • Nof, D., 1988a: Draining vortices. Geophys. Astrophys. Fluid Dyn., 42 , 187–208.

  • Nof, D., 1988b: Eddy-wall interactions. J. Mar. Res., 46 , 527–555.

  • Pichevin, T., and D. Nof, 1995: The eddy cannon. Deep-Sea Res. I, 43 , 1475–1507.

  • Rintoul, S. R., J. R. Donguy, and D. H. Roemmich, 1997: Seasonal evolution of upper ocean thermal structure between Tasmania and Antarctica. Deep-Sea Res. I, 44 , 1185–1202.

    • Search Google Scholar
    • Export Citation

  • Sadoux, S., J. Baey, A. Fincham, and D. Renouard, 2000: Experimental study of the stubility of an intermediate current and its interaction with a cape. Dyn. Atmos. Oceans, 31 , 165–192.

    • Search Google Scholar
    • Export Citation

  • Sansón, L. Z., F. Greaf, and E. G. Pavía, 1998: Collision of anticyclonic, lens-like eddies with a meridional western boundary. J. Geophys. Res., 103 , 24881–24890.

    • Search Google Scholar
    • Export Citation

  • Shi, C., and D. Nof, 1994: The destruction of lenses and generation of wodons. J. Phys. Oceanogr., 24 , 1120–1136.

  • Smith, S. D., R. D. Muench, and C. H. Pease, 1990: Polynyas and leads: An overview of physical processes and environment. J. Geophys. Res., 95 , 9461–9479.

    • Search Google Scholar
    • Export Citation

  • Swallow, J. C., 1969: A deep eddy off Cape St. Vincent. Deep-Sea Res., 16 , 285–295.

  • Swaters, G. E., 1991: On the baroclinic instability of cold-core coupled density fronts on a sloping continental shelf. J. Fluid Mech., 224 , 361–382.

    • Search Google Scholar
    • Export Citation

  • Tanaka, K., and K. Akimoto, 2001: Baroclinic instability of density current along a sloping bottom and the associated transport process. J. Geophys. Res., 106 , 2621–2638.

    • Search Google Scholar
    • Export Citation

  • Visbeck, M., J. Marshall, and H. Jones, 1996: Dynamics of isolated convective regions in the ocean. J. Phys. Oceanogr., 26 , 1721–1734.

    • Search Google Scholar
    • Export Citation

  • Wadhams, P., A. Gill, and P. F. Linden, 1979: Transects by submarine of the East Greenland Polar Front. Deep-Sea Res., 26 , 1311–1327.

    • Search Google Scholar
    • Export Citation
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