Editorial Type:
Article
Article Type:
Research Article

The Influence of Diapycnal Mixing on Quasi-Steady Overturning States in the Indian Ocean

Matthew D. Palmer National Oceanography Centre, Southampton, Southampton, and Hadley Centre for Climate Prediction and Research, Exeter, United Kingdom

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Alberto C. Naveira Garabato National Oceanography Centre, Southampton, Southampton, United Kingdom

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John D. Stark Hadley Centre for Climate Prediction and Research, Exeter, United Kingdom

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Joël J-M. Hirschi National Oceanography Centre, Southampton, Southampton, United Kingdom

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Jochem Marotzke Max Planck Institute for Meteorology, Hamburg, Germany

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Print Publication:
01 Sep 2007
DOI:
https://doi.org/10.1175/JPO3117.1
Page(s):
2290–2304
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Abstract

A regional general circulation model (GCM) of the Indian Ocean is used to investigate the influence of prescribed diapycnal diffusivity (Kd) on quasi-steady states of the meridional overturning circulation (MOC). The model has open boundaries at 35°S and 123°E where velocity, temperature, and salinity are prescribed at each time step. The results suggest that quasi-steady overturning states in the Indian Ocean are reached on centennial time scales. The size and structure of the MOC are controlled by the distribution of Kd and the southern boundary conditions. The distribution of Kd required to support an overturning circulation in the model interior of a magnitude equal to that prescribed at the southern boundary is estimated using a 1D advection–diffusion balance in isopycnal layers. Implementing this approach, 70%–90% of the prescribed deep inflow can be supported in quasi-steady state. Thus one is able to address the systematic discrepancy between past estimates of the deep MOC based on hydrographic sections and those based on GCM results. However, the Kd values required to support a substantial MOC in the model are much larger than current observation-based estimates, particularly for the upper 3000 m. The two estimates of the flow field near 32°S used to force the southern boundary imply a highly nonuniform distribution of Kd, as do recent estimates of Kd based on hydrographic observations. This work highlights the need to improve and implement realistic estimates of (nonuniform) Kd in ocean and coupled ocean–atmosphere GCMs when investigating quasi-equilibrium model states.

Corresponding author address: Matthew Palmer, Hadley Centre for Climate Prediction and Research, Met Office, FitzRoy Road, Exeter, Devon EX1 3PB, United Kingdom. Email: matthew.palmer@metoffice.gov.uk

Abstract

A regional general circulation model (GCM) of the Indian Ocean is used to investigate the influence of prescribed diapycnal diffusivity (Kd) on quasi-steady states of the meridional overturning circulation (MOC). The model has open boundaries at 35°S and 123°E where velocity, temperature, and salinity are prescribed at each time step. The results suggest that quasi-steady overturning states in the Indian Ocean are reached on centennial time scales. The size and structure of the MOC are controlled by the distribution of Kd and the southern boundary conditions. The distribution of Kd required to support an overturning circulation in the model interior of a magnitude equal to that prescribed at the southern boundary is estimated using a 1D advection–diffusion balance in isopycnal layers. Implementing this approach, 70%–90% of the prescribed deep inflow can be supported in quasi-steady state. Thus one is able to address the systematic discrepancy between past estimates of the deep MOC based on hydrographic sections and those based on GCM results. However, the Kd values required to support a substantial MOC in the model are much larger than current observation-based estimates, particularly for the upper 3000 m. The two estimates of the flow field near 32°S used to force the southern boundary imply a highly nonuniform distribution of Kd, as do recent estimates of Kd based on hydrographic observations. This work highlights the need to improve and implement realistic estimates of (nonuniform) Kd in ocean and coupled ocean–atmosphere GCMs when investigating quasi-equilibrium model states.

Corresponding author address: Matthew Palmer, Hadley Centre for Climate Prediction and Research, Met Office, FitzRoy Road, Exeter, Devon EX1 3PB, United Kingdom. Email: matthew.palmer@metoffice.gov.uk

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  • Armi, L., 1978: Some evidence for boundary mixing in the deep ocean. J. Geophys. Res., 83 , 1971–1979.

  • Bryden, H. L., 2003: RRS Charles Darwin Cruise 139, 01 Mar–15 April 2002, Trans-Indian hydrographic section across 32S. Southampton Oceanography Centre Cruise Rep. 45, 122 pp.

  • Bryden, H. L., and L. M. Beal, 2001: Role of the Agulhas Current in Indian Ocean circulation and associated heat and freshwater fluxes. Deep-Sea Res. I, 48 , 1821–1845.

    • Search Google Scholar
    • Export Citation

  • Bryden, H. L., and A. J. G. Nurser, 2003: Effects of strait mixing on ocean stratification. J. Phys. Oceanogr., 33 , 1870–1872.

  • Danabasoglu, G., J. C. McWilliams, and P. R. Gent, 1994: The role of mesoscale tracer transports in the global ocean circulation. Science, 264 , 1123–1126.

    • Search Google Scholar
    • Export Citation

  • Ferron, B., and J. Marotzke, 2003: Impact of 4D-variational assimilation of WOCE hydrography on the meridional circulation of the Indian Ocean. Deep-Sea Res. II, 50 , 2005–2021.

    • Search Google Scholar
    • Export Citation

  • Ganachaud, A., 2003: Large-scale mass transports, water mass formation, and diffusivities estimated from World Ocean Circulation Experiment (WOCE) hydrographic data. J. Geophys. Res., 108 .3213, doi:10.1029/2002JC001565.

    • Search Google Scholar
    • Export Citation

  • Ganachaud, U., C. Wunsch, J. Marotzke, and J. Toole, 2000: Meridional overturning and large-scale circulation of the Indian Ocean. J. Geophys. Res., 105 , 26117–26134.

    • Search Google Scholar
    • Export Citation

  • Garternicht, U., and F. Schott, 1997: Heat fluxes of the Indian Ocean from a global eddy-resolving model. J. Geophys. Res., 102 , 21147–21159.

    • Search Google Scholar
    • Export Citation

  • Gent, P. R., and J. C. McWilliams, 1990: Isopycnal mixing in ocean circulation models. J. Phys. Oceanogr., 20 , 150–155.

  • Gouretski, V. V., and K. P. Koltermann, 2004: WOCE global hydrographic climatology. Berichte des Bundesamtes für Seeschifffahrt und Hydrographie Tech. Rep. 35/2004, 55 pp.

  • Griffies, S. M., A. Gnanadesikan, R. C. Pacanowski, V. D. Larichev, J. K. Dukowicz, and R. D. Smith, 1998: Isoneutral diffusion in a z-coordinate ocean model. J. Phys. Oceanogr., 28 , 805–830.

    • Search Google Scholar
    • Export Citation

  • Hasumi, H., and N. Suginohara, 1999: Effects of locally enhanced vertical diffusivity over rough bathymetry on the world ocean circulation. J. Geophys. Res., 104 , 23367–23374.

    • Search Google Scholar
    • Export Citation

  • Huang, R. X., 1999: Mixing and energetics of the oceanic thermohaline circulation. J. Phys. Oceanogr., 29 , 727–746.

  • Johnson, G. C., D. L. Musgrave, B. A. Warren, A. Ffield, and D. B. Olson, 1998: Flow of bottom and deep water in the Amirante Passage and Mascarene Basin. J. Geophys. Res., 103 , 30973–30984.

    • Search Google Scholar
    • Export Citation

  • Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-Year Reanalysis Project. Bull. Amer. Meteor. Soc., 77 , 437–471.

  • Kunze, E., E. Firing, J. M. Hummon, T. K. Chereskin, and A. Thurnherr, 2006: Global abyssal mixing inferred from lowered ADCP shear and CTD strain profiles. J. Phys. Oceanogr., 36 , 1553–1576.

    • 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 , 179–182.

    • Search Google Scholar
    • Export Citation

  • Lee, T., and J. Marotzke, 1997: Inferring meridional mass and heat transports of the Indian Ocean by fitting a general circulation model to climatological data. J. Geophys. Res., 102 , 10585–10602.

    • Search Google Scholar
    • Export Citation

  • Lee, T., and J. Marotzke, 1998: Seasonal cycles of meridional overturning and heat transport of the Indian Ocean. J. Phys. Oceanogr., 28 , 923–943.

    • Search Google Scholar
    • Export Citation

  • Levitus, S., and T. P. Boyer, 1994: Temperature. Vol. 4, World Ocean Atlas 1994, NOAA Atlas NESDIS 4, 117 pp.

  • Levitus, S., R. Burgett, and T. P. Boyer, 1994: Salinity. Vol. 3, World Ocean Atlas 1994, NOAA Atlas NESDIS 3, 99 pp.

  • Mantyla, A. W., and J. L. Reid, 1995: On the origins of deep and bottom waters of the Indian Ocean. J. Geophys. Res., 100 , 2417–2439.

  • 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 , 5753–5766.

    • 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 , 5733–5752.

    • Search Google Scholar
    • Export Citation

  • Munk, W., 1966: Abyssal recipes. Deep-Sea Res., 13 , 707–730.

  • Munk, W., and C. Wunsch, 1998: Abyssal recipes II: Energetics of tidal and wind mixing. Deep-Sea Res. I, 45 , 1977–2010.

  • Naveira 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 , 210–213.

    • Search Google Scholar
    • Export Citation

  • Naveira Garabato, A. C., H. L. Bryden, and E. L. McDonagh, 2005: Closing the overturning circulation of the Indian Ocean: The mixing perspective. Geophys. Res. Abstr., 7 .Abstract EGU05-A-05052.

    • 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 , 93–96.

    • Search Google Scholar
    • Export Citation

  • Redi, M. H., 1982: Oceanic isopycnal mixing by coordinate rotation. J. Phys. Oceanogr., 12 , 1154–1158.

  • Reid, J. L., 2003: On the total geostrophic circulation of the Indian Ocean: Flow patterns, tracers, and transports. Prog. Oceanogr., 56 , 137–186.

    • Search Google Scholar
    • Export Citation

  • Robbins, P. E., and J. M. Toole, 1997: The dissolved silica budget as a constraint on the meridional overturning circulation of the Indian Ocean. Deep-Sea Res. I, 44 , 879–906.

    • Search Google Scholar
    • Export Citation

  • Scott, J. R., and J. Marotzke, 2002: The location of diapycnal mixing and the meridional overturning circulation. J. Phys. Oceanogr., 32 , 3578–3595.

    • Search Google Scholar
    • Export Citation

  • Shi, W., J. M. Morrison, and H. L. Bryden, 2002: Water, heat and freshwater flux out of the northern Indian Ocean in September-October 1995. Deep-Sea Res. II, 49 , 1231–1252.

    • Search Google Scholar
    • Export Citation

  • Simmons, H. L., S. R. Jayne, L. C. St. Laurent, and A. J. Weaver, 2004: Tidally driven mixing in a numerical model of the ocean general circulation. Ocean Modell., 6 , 245–263.

    • Search Google Scholar
    • Export Citation

  • Sloyan, B. M., 2006: Antarctic bottom and lower circumpolar deep water circulation in the eastern Indian Ocean. J. Geophys. Res., 111 .C02006, doi:10.1029/2005JC003011.

    • Search Google Scholar
    • Export Citation

  • Sloyan, B. M., and S. R. Rintoul, 2001: The Southern Ocean limb of the global deep overturning circulation. J. Phys. Oceanogr., 31 , 143–173.

    • Search Google Scholar
    • Export Citation

  • Stammer, D., C. Wunsch, R. Giering, Q. Zhang, J. Marotzke, J. Marshall, and C. N. Hill, 1997: The global ocean circulation estimated from TOPEX/Poseidon altimetry and the MIT general circulation model. MIT Center for Global Change Science Rep. 49, Massachusetts Institute of Technology, Cambridge, MA, 40 pp.

  • Stammer, D., and Coauthors, 2003: Volume, heat, and freshwater transports of the global ocean circulation 1993–2000, estimated from a general circulation model constrained by World Ocean Circulation Experiment (WOCE) data. J. Geophys. Res., 108 .3007, doi:10.1029/2001JC001115.

    • Search Google Scholar
    • Export Citation

  • Thurnherr, A. M., L. C. St. Laurent, K. G. Speer, J. M. Toole, and J. R. Ledwell, 2005: Mixing associated with sills in a canyon on the midocean ridge flank. J. Phys. Oceanogr., 35 , 1370–1381.

    • Search Google Scholar
    • Export Citation

  • Toole, J. M., and B. A. Warren, 1993: A hydrographic section across the subtropical south Indian Ocean. Deep-Sea Res. I, 40 , 1973–2019.

    • Search Google Scholar
    • Export Citation

  • Warren, B. A., and G. C. Johnson, 2002: The overflows across the Ninetyeast Ridge. Deep-Sea Res. II, 49 , 1423–1439.

  • Wunsch, C., and R. Ferrari, 2004: Vertical mixing, energy, and the general circulation of the oceans. Annu. Rev. Fluid Mech., 36 , 281–314.

    • Search Google Scholar
    • Export Citation

  • Zhang, K. Q., and J. Marotzke, 1999: The importance of open-boundary estimation for an Indian Ocean GCM-data synthesis. J. Mar. Res., 57 , 305–334.

    • Search Google Scholar
    • Export Citation
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