Short-circuiting of the overturning circulation in the Antarctic Circumpolar Current

Abstract

The oceanic overturning circulation has a central role in the Earth’s climate system and in biogeochemical cycling1,2, as it transports heat, carbon and nutrients around the globe and regulates their storage in the deep ocean. Mixing processes in the Antarctic Circumpolar Current are key to this circulation, because they control the rate at which water sinking at high latitudes returns to the surface in the Southern Ocean3,4,5,6,7,8. Yet estimates of the rates of these processes and of the upwelling that they induce are poorly constrained by observations. Here we take advantage of a natural tracer-release experiment—an injection of mantle helium from hydrothermal vents into the Circumpolar Current near Drake Passage9—to measure the rates of mixing and upwelling in the current’s intermediate layers over a sector that spans nearly one-tenth of its circumpolar path. Dispersion of the tracer reveals rapid upwelling along density surfaces and intense mixing across density surfaces, both occurring at rates that are an order of magnitude greater than rates implicit in models of the average Southern Ocean overturning4,5,6,7,8. These findings support the view that deep-water pathways along and across density surfaces intensify and intertwine as the Antarctic Circumpolar Current flows over complex ocean-floor topography, giving rise to a short circuit of the overturning circulation in these regions.

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Figure 1: Large-scale distribution of primordial 3 He in the deep Southeast Pacific and Southwest Atlantic.
Figure 2: Downstream evolution of the primordial 3 He distribution in density coordinates.
Figure 3: Distribution of primordial 3 He and streamfunction along the Scotia Sea rim.

References

  1. 1

    Rahmstorf, S. Ocean circulation and climate during the past 120,000 years. Nature 419, 207–214 (2002)

    ADS  CAS  Article  Google Scholar 

  2. 2

    Sarmiento, J. L., Gruber, N., Brzezinski, M. & Dunne, J. P. High-latitude controls of thermocline nutrients and low latitude biological productivity. Nature 427, 56–60 (2004)

    ADS  CAS  Article  Google Scholar 

  3. 3

    Marshall, D. Subduction of water masses in an eddying ocean. J. Mar. Res. 55, 201–222 (1997)

    Article  Google Scholar 

  4. 4

    Gnanadesikan, A. A simple predictive model for the structure of the oceanic pycnocline. Science 283, 2077–2079 (1999)

    ADS  CAS  Article  Google Scholar 

  5. 5

    Speer, K., Rintoul, S. R. & Sloyan, B. The diabatic Deacon cell. J. Phys. Oceanogr. 30, 3212–3222 (2000)

    ADS  MathSciNet  Article  Google Scholar 

  6. 6

    Marshall, J. & Radko, T. Residual-mean solutions for the Antarctic Circumpolar Current and its associated overturning circulation. J. Phys. Oceanogr. 33, 2341–2354 (2003)

    ADS  Article  Google Scholar 

  7. 7

    Bryden, H. L. & Cunningham, S. A. How wind forcing and air–sea heat exchange determine the meridional temperature gradient and stratification for the Antarctic Circumpolar Current. J. Geophys. Res. 108 3275 doi: 1029/2001/JC001296 (2003)

    ADS  Article  Google Scholar 

  8. 8

    Olbers, D. & Visbeck, M. A model of the zonally averaged stratification and overturning in the Southern Ocean. J. Phys. Oceanogr. 35, 1190–1205 (2005)

    ADS  Article  Google Scholar 

  9. 9

    Well, R., Roether, W. & Stevens, D. P. An additional deep-water mass in Drake Passage as revealed by 3He data. Deep-Sea Res. I 50, 1079–1098 (2003)

    CAS  Article  Google Scholar 

  10. 10

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

    ADS  MathSciNet  Article  Google Scholar 

  11. 11

    Toggweiler, J. R. & Samuels, B. On the ocean’s large-scale circulation near the limit of no vertical mixing. J. Phys. Oceanogr. 28, 1832–1852 (1998)

    ADS  Article  Google Scholar 

  12. 12

    Webb, D. J. & Suginohara, N. Vertical mixing in the ocean. Nature 409, 37 (2001)

    ADS  CAS  Article  Google Scholar 

  13. 13

    Naveira Garabato, A. C., Polzin, K. L., King, B. A., Heywood, K. J. & Visbeck, M. Widespread intense turbulent mixing in the Southern Ocean. Science 303, 210–213 (2004)

    ADS  CAS  Article  Google Scholar 

  14. 14

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

    ADS  Article  Google Scholar 

  15. 15

    Ledwell, J. R., Watson, A. J. & Law, C. S. Mixing of a tracer in the pycnocline. J. Geophys. Res. 103, 21499–21529 (1998)

    ADS  Article  Google Scholar 

  16. 16

    Gille, S. T. Float observations of the Southern Ocean: Part 2. Eddy fluxes. J. Phys. Oceanogr. 33, 1182–1196 (2003)

    ADS  Article  Google Scholar 

  17. 17

    Stammer, D. On eddy characteristics, eddy transports, and mean flow properties. J. Phys. Oceanogr. 28, 727–739 (1998)

    ADS  Article  Google Scholar 

  18. 18

    Ferreira, D., Marshall, J. & Heimbach, P. Estimating eddy stresses by fitting dynamics to observations using a residual-mean ocean circulation model and its adjoint. J. Phys. Oceanogr. 35, 1891–1910 (2005)

    ADS  Article  Google Scholar 

  19. 19

    Olbers, D., Borowski, D., Völker, C. & Wolff, J.-O. The dynamical balance, transport and circulation of the Antarctic Circumpolar Current. Antarct. Sci. 16, 439–470 (2004)

    ADS  Article  Google Scholar 

  20. 20

    MacCready, P. & Rhines, P. B. Meridional transport across a zonal channel: Topographic localization. J. Phys. Oceanogr. 31, 1427–1439 (2001)

    ADS  Article  Google Scholar 

  21. 21

    Lee, M.-M. & Coward, A. C. Eddy mass transport in an eddy-permitting global ocean model. Ocean Model. 5, 249–266 (2003)

    ADS  Article  Google Scholar 

  22. 22

    Hallberg, R. & Gnanadesikan, A. The role of eddies in determining the structure and response of the wind-driven Southern Hemisphere overturning: Results from the MESO project. J. Phys. Oceanogr. 36, 2232–2252 (2006)

    ADS  Article  Google Scholar 

  23. 23

    Aguilar, D. A. & Sutherland, B. R. Internal wave generation from rough topography. Phys. Fluids 18 doi: 10.1063/1.2214538 (2006)

  24. 24

    Polzin, K. L. Subinertial finestructure on the continental slope / rise transition. J. Phys. Oceanogr. (submitted).

  25. 25

    Sanson, L. Z. & van Heijst, G. J. F. Ekman effects in a rotating flow over bottom topography. J. Fluid Mech. 471, 239–255 (2002)

    ADS  MathSciNet  Article  Google Scholar 

  26. 26

    Wilson, C. & Williams, R. G. When are eddy tracer fluxes directed down gradient? J. Phys. Oceanogr. 36, 189–201 (2006)

    ADS  Article  Google Scholar 

  27. 27

    Wunsch, C. The work done by the wind on the oceanic general circulation. J. Phys. Oceanogr. 28, 2332–2340 (1998)

    ADS  Article  Google Scholar 

  28. 28

    Scott, R. B. & Wang, F. Direct evidence of an oceanic inverse kinetic energy cascade from satellite altimetry. J. Phys. Oceanogr. 35, 1650–1666 (2005)

    ADS  Article  Google Scholar 

  29. 29

    Tandon, A. & Garrett, C. On a recent parameterization of mesoscale eddies. J. Phys. Oceanogr. 26, 406–411 (1996)

    ADS  Article  Google Scholar 

  30. 30

    Ledwell, J. R., Watson, A. J. & Law, C. S. Evidence for slow mixing across the pycnocline from an open-ocean tracer release experiment. Nature 364, 702–703 (1993)

    ADS  Article  Google Scholar 

  31. 31

    Jackett, D. R. & McDougall, T. J. A neutral density variable for the world's oceans. J. Phys. Oceanogr. 27, 237–263 (1997)

    ADS  Article  Google Scholar 

  32. 32

    Naveira Garabato, A. C., Stevens, D. P. & Heywood, K. J. Water mass conversion, fluxes and mixing in the Scotia Sea diagnosed by an inverse model. J. Phys. Oceanogr. 33, 2565–2587 (2003)

    ADS  Article  Google Scholar 

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Acknowledgements

A NERC Advanced Research Fellowship supported A.C.N.G. during the analysis and writing of this Letter. We gratefully acknowledge feedback from J. Ledwell and K. Polzin.

Author Contributions A.C.N.G. designed and conducted the analysis and wrote the letter. D.P.S. and A.J.W. discussed aspects of the methodology and results, and helped with the writing. W.R. provided many of the 3He data and advised on their use.

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Correspondence to Alberto C. Naveira Garabato.

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This file contains Supplementary Notes containing a detailed description of the methodology, derivation of equations, and error analysis, Supplementary Figure 1 with Legend and additional references. (PDF 278 kb)

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Garabato, A., Stevens, D., Watson, A. et al. Short-circuiting of the overturning circulation in the Antarctic Circumpolar Current. Nature 447, 194–197 (2007). https://doi.org/10.1038/nature05832

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