• Antonov, J. I., , R. A. Locarnini, , T. P. Boyer, , A. V. Mishonov, , and H. E. Garcia, 2006: Salinity. Vol. 2, World Ocean Atlas 2005, NOAA Atlas NESDIS 62, 182 pp.

    • Search Google Scholar
    • Export Citation
  • Cessi, P., , and M. Fantini, 2004: The eddy-driven thermocline. J. Phys. Oceanogr., 34 , 26422658.

  • Cessi, P., , and C. L. Wolfe, 2009: Eddy-driven buoyancy gradients on eastern boundaries and their role in the thermocline. J. Phys. Oceanogr., 39 , 15951614.

    • Search Google Scholar
    • Export Citation
  • Cessi, P., , W. R. Young, , and J. A. Polton, 2006: Control of large-scale heat transport by small-scale mixing. J. Phys. Oceanogr., 36 , 18771894.

    • Search Google Scholar
    • Export Citation
  • Döös, K., , and D. J. Webb, 1994: The Deacon cell and the other meridional cells of the Southern Ocean. J. Phys. Oceanogr., 24 , 429442.

    • Search Google Scholar
    • Export Citation
  • Ferrari, R., , J. C. McWilliams, , V. M. Canuto, , and M. Dubovikov, 2008: Parameterization of eddy fluxes near oceanic boundaries. J. Climate, 21 , 27702789.

    • Search Google Scholar
    • Export Citation
  • Fučkar, N. S., , and G. K. Vallis, 2007: Interhemispheric influence of surface buoyancy conditions on a circumpolar current. Geophys. Res. Lett., 34 , L14605. doi:10.1029/2007GL030379.

    • Search Google Scholar
    • Export Citation
  • Gnanadesikan, A., 1999: A simple predictive model for the structure of the oceanic pycnocline. Science, 283 , 20772079.

  • Griffies, S. M., , R. C. Pacanowski, , and R. W. Hallberg, 2000: Spurious diapycnal mixing associated with advection in a z-coordinate ocean model. Mon. Wea. Rev., 128 , 538564.

    • Search Google Scholar
    • Export Citation
  • Hallberg, R., , and A. Gnanadesikan, 2006: The role of eddies in determining the structure and response of the wind-driven Southern Hemisphere overturning: Results from the Modeling Eddies in the Southern Ocean (MESO) project. J. Phys. Oceanogr., 36 , 22322252.

    • Search Google Scholar
    • Export Citation
  • Henning, C. C., , and G. K. Vallis, 2005: The effects of mesoscale eddies on the stratification and transport of an ocean with a circumpolar channel. J. Phys. Oceanogr., 35 , 880896.

    • Search Google Scholar
    • Export Citation
  • Jackett, D. R., , and T. J. McDougall, 1997: A neutral density variable for the world’s oceans. J. Phys. Oceanogr., 27 , 237263.

  • Johnson, G. C., , and H. L. Bryden, 1989: On the size of the Antarctic Circumpolar Current. Deep-Sea Res., 36 , 3953.

  • Johnson, H. L., , D. P. Marshall, , and D. A. J. Sproson, 2007: Reconciling theories of a mechanically driven meridional overturning circulation with thermohaline forcing and multiple equilibria. Climate Dyn., 29 , 821836. doi:10.1007/s00382-007-0262-9.

    • Search Google Scholar
    • Export Citation
  • Karsten, R. H., , H. Jones, , and J. Marshall, 2002: The role of eddy transfer in setting the stratification and transport of a circumpolar current. J. Phys. Oceanogr., 32 , 3954.

    • Search Google Scholar
    • Export Citation
  • Klinger, B. A., , S. Drijfhout, , J. Marotzke, , and J. R. Scott, 2003: Sensitivity of basinwide meridional overturning to diapycnal diffusion and remote wind forcing in an idealized Atlantic–Southern Ocean geometry. J. Phys. Oceanogr., 33 , 249266.

    • Search Google Scholar
    • Export Citation
  • Kunze, E., , E. Firing, , J. M. Hummon, , T. K. Chereskin, , and A. M. Thurnherr, 2006: Global abyssal mixing inferred from lowered ADCP shear and CTD strain profiles. J. Phys. Oceanogr., 36 , 15531576.

    • Search Google Scholar
    • Export Citation
  • Ledwell, J. R., , E. T. Montgomery, , K. L. Polzin, , L. C. St. Laurent, , R. W. Schmitt, , and J. M. Toole, 2000: Evidence for enhanced mixing over rough topography in the abyssal ocean. Nature, 403 , 179182.

    • Search Google Scholar
    • Export Citation
  • Locarnini, R. A., , A. V. Mishonov, , J. I. Antonov, , T. P. Boyer, , and H. E. Garcia, 2006: Temperature. Vol. 1, World Ocean Atlas 2005, NOAA Atlas NESDIS 61, 182 pp.

    • Search Google Scholar
    • Export Citation
  • Luyten, J., , J. Pedlosky, , and H. Stommel, 1983: The ventilated thermocline. J. Phys. Oceanogr., 13 , 292309.

  • Marshall, J., , and T. Radko, 2003: Residual-mean solutions for the Antarctic Circumpolar Current and its associated overturning circulation. J. Phys. Oceanogr., 33 , 23412354.

    • Search Google Scholar
    • Export Citation
  • Marshall, J., , and T. Radko, 2006: A model of the upper branch of the meridional overturning of the Southern Ocean. Prog. Oceanogr., 70 , 331345.

    • Search Google Scholar
    • Export Citation
  • Marshall, J., , A. Adcroft, , C. Hill, , L. Perelman, , and C. Heisey, 1997a: A finite-volume, incompressible Navier Stokes model for studies of the ocean on parallel computers. J. Geophys. Res., 102 , 57535766.

    • Search Google Scholar
    • Export Citation
  • Marshall, J., , C. Hill, , L. Perelman, , and A. Adcroft, 1997b: Hydrostatic, quasi-hydrostatic, and nonhydrostatic ocean modeling. J. Geophys. Res., 102 , 57335752.

    • Search Google Scholar
    • Export Citation
  • McIntosh, P. C., , and T. J. McDougall, 1996: Isopycnal averaging and the residual mean circulation. J. Phys. Oceanogr., 26 , 16551660.

  • Munk, W. H., 1966: Abyssal recipes. Deep-Sea Res., 13 , 707730.

  • Munk, W. H., , and C. Wunsch, 1998: Abyssal recipes II: Energetics of tidal and wind mixing. Deep Sea Res. I, 45 , 19772010.

  • Naviera Garabato, A. C., , K. L. Polzin, , B. A. King, , K. J. Heywood, , and M. Visbeck, 2004: Widespread intense turbulent mixing in the Southern Ocean. Science, 303 , 210213. doi:10.1126/science.1090929.

    • Search Google Scholar
    • Export Citation
  • Olbers, D., , and M. Visbeck, 2005: A model of the zonally averaged stratification and overturning in the Southern Ocean. J. Phys. Oceanogr., 35 , 11901205.

    • Search Google Scholar
    • Export Citation
  • Polzin, K. L., , J. M. Toole, , J. R. Ledwell, , and R. W. Schmitt, 1997: Spatial variability of turbulent mixing in the abyssal ocean. Science, 276 , 9396. doi:10.1126/science.276.5309.93.

    • Search Google Scholar
    • Export Citation
  • Rhines, P. B., , and W. R. Young, 1982a: A theory of wind-driven ocean circulation. I. Mid-ocean gyres. J. Mar. Res., 40 , 559596.

  • Rhines, P. B., , and W. R. Young, 1982b: Homogenization of potential vorticity in planetary gyres. J. Fluid Mech., 122 , 347367.

  • Salmon, R., 1990: The thermocline as an “internal boundary layer”. J. Mar. Res., 48 , 437469.

  • Samelson, R. M., 1999: Geostrophic circulation in a rectangular basin with a circumpolar connection. J. Phys. Oceanogr., 29 , 31753184.

    • Search Google Scholar
    • Export Citation
  • Samelson, R. M., 2004: Simple mechanistic models of middepth meridional overturning. J. Phys. Oceanogr., 34 , 20962103.

  • Samelson, R. M., 2009: A simple dynamical model of the warm-water branch of the middepth meridional overturning cell. J. Phys. Oceanogr., 39 , 12161230.

    • Search Google Scholar
    • Export Citation
  • Samelson, R. M., , and G. K. Vallis, 1997: Large-scale circulation with small diapycnal diffusion: The two-thermocline limit. J. Mar. Res., 55 , 223275.

    • Search Google Scholar
    • Export Citation
  • Schneider, T., 2005: Zonal momentum balance, potential vorticity dynamics, and mass fluxes on near-surface isentropes. J. Atmos. Sci., 62 , 18841900.

    • Search Google Scholar
    • Export Citation
  • Spence, P., , O. A. Saenko, , M. Eby, , and A. J. Weaver, 2009: The Southern Ocean overturning: Parameterized versus permitted eddies. J. Phys. Oceanogr., 39 , 16341651.

    • Search Google Scholar
    • Export Citation
  • Stommel, H., , and A. B. Arons, 1959: On the abyssal circulation of the world ocean—I. Stationary planetary flow patterns on a sphere. Deep-Sea Res., 6 , 140154.

    • Search Google Scholar
    • Export Citation
  • Toggweiler, J. R., , and B. Samuels, 1993: Is the magnitude of the deep outflow from the Atlantic Ocean actually governed by Southern Hemisphere winds? The Global Carbon Cycle, M. Heimann, Ed., NATO ASI Series, Vol. 15, Springer, 333–366.

    • Search Google Scholar
    • Export Citation
  • Toggweiler, J. R., , and B. Samuels, 1995: Effect of Drake Passage on the global thermohaline circulation. Deep-Sea Res. I, 42 , 477500.

    • Search Google Scholar
    • Export Citation
  • Toggweiler, J. R., , and B. Samuels, 1998: On the ocean’s large-scale circulation near the limit of no vertical mixing. J. Phys. Oceanogr., 28 , 18321852.

    • Search Google Scholar
    • Export Citation
  • Vallis, G. K., 2000: Large-scale circulation and production of stratification: Effects of wind, geometry, and diffusion. J. Phys. Oceanogr., 30 , 933954.

    • Search Google Scholar
    • Export Citation
  • Vallis, G. K., 2006: Atmospheric and Oceanic Fluid Dynamics: Fundamentals and Large-Scale Circulation. Cambridge University Press, 745 pp.

    • Search Google Scholar
    • Export Citation
  • Wolfe, C. L., , and P. Cessi, 2009: Overturning in an eddy-resolving model: The effect of the pole-to-pole temperature gradient. J. Phys. Oceanogr., 39 , 125142.

    • Search Google Scholar
    • Export Citation
  • Wolfe, C. L., , P. Cessi, , J. L. McClean, , and M. E. Maltrud, 2008: Vertical heat flux in eddying ocean models. Geophys. Res. Lett., 35 , L23605. doi:10.1029/2008GL036138.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 62 62 13
PDF Downloads 50 50 11

What Sets the Strength of the Middepth Stratification and Overturning Circulation in Eddying Ocean Models?

View More View Less
  • 1 Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California
© Get Permissions
Restricted access

Abstract

The processes maintaining stratification in the oceanic middepth (between approximately 1000 and 3000 m) are explored using an eddy-resolving general circulation model composed of a two-hemisphere, semienclosed basin with a zonal reentrant channel in the southernmost eighth of the domain. The middepth region lies below the wind-driven main thermocline but above the diffusively driven abyssal ocean. Here, it is argued that middepth stratification is determined primarily in the model’s Antarctic Circumpolar Current. Competition between mean and eddy overturning in the channel leads to steeper isotherms and thus deeper stratification throughout the basin than would exist without the channel. Isotherms that outcrop only in the channel are nearly horizontal in the semienclosed portion of the domain, whereas isotherms that also outcrop in the Northern Hemisphere deviate from horizontal and are accompanied by geostrophically balanced meridional transport. A northern source of deep water (water with temperatures in the range of those in the channel) leads to the formation of a thick middepth thermostad. Changes in wind forcing over the channel influence the stratification throughout the domain. Since the middepth stratification is controlled by adiabatic dynamics in the channel, it becomes independent of the interior diffusivity κ as κ → 0. The meridional overturning circulation (MOC), as diagnosed by the mean meridional volume transport, also shows a tendency to become independent of κ as κ → 0, whereas the MOC diagnosed by water mass transport shows a continuing dependence on κ as κ → 0. A nonlocal scaling for MOC is developed that relates the strength of the northern MOC to the depth of isotherms in the southern channel. The results of this paper compare favorably to observations of large-scale neutral density in the World Ocean.

Corresponding author address: Christopher L. Wolfe, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0213. Email: clwolfe@ucsd.edu

Abstract

The processes maintaining stratification in the oceanic middepth (between approximately 1000 and 3000 m) are explored using an eddy-resolving general circulation model composed of a two-hemisphere, semienclosed basin with a zonal reentrant channel in the southernmost eighth of the domain. The middepth region lies below the wind-driven main thermocline but above the diffusively driven abyssal ocean. Here, it is argued that middepth stratification is determined primarily in the model’s Antarctic Circumpolar Current. Competition between mean and eddy overturning in the channel leads to steeper isotherms and thus deeper stratification throughout the basin than would exist without the channel. Isotherms that outcrop only in the channel are nearly horizontal in the semienclosed portion of the domain, whereas isotherms that also outcrop in the Northern Hemisphere deviate from horizontal and are accompanied by geostrophically balanced meridional transport. A northern source of deep water (water with temperatures in the range of those in the channel) leads to the formation of a thick middepth thermostad. Changes in wind forcing over the channel influence the stratification throughout the domain. Since the middepth stratification is controlled by adiabatic dynamics in the channel, it becomes independent of the interior diffusivity κ as κ → 0. The meridional overturning circulation (MOC), as diagnosed by the mean meridional volume transport, also shows a tendency to become independent of κ as κ → 0, whereas the MOC diagnosed by water mass transport shows a continuing dependence on κ as κ → 0. A nonlocal scaling for MOC is developed that relates the strength of the northern MOC to the depth of isotherms in the southern channel. The results of this paper compare favorably to observations of large-scale neutral density in the World Ocean.

Corresponding author address: Christopher L. Wolfe, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0213. Email: clwolfe@ucsd.edu

Save