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Evidence for slow mixing across the pycnocline from an open-ocean tracer-release experiment

Abstract

THE distributions of heat, salt and trace substances in the ocean thermocline depend on mixing along and across surfaces of equal density (isopycnal and diapycnal mixing, respectively). Measurements of the invasion of anthropogenic tracers, such as bomb tritium and 3He (see, for example, refs 1 and 2), have indicated that isopycnal processes dominate diapycnal mixing, and turbulence measurements have suggested that diapycnal mixing is small3,4, but it has not been possible to measure accurately the diapycnal diffusivity. Here we report such a measurement, obtained from the vertical dispersal of a patch of the inert compound SF6 released in the open ocean. The diapycnal diffusivity, averaged over hundreds of kilometres and five months, was 0.11 ± 0.02 cm2 s−1, confirming previous estimates1–4. Such a low diffusivity can support only a rather small diapycnal flux of nitrate into the euphotic zone; it justifies the neglect of diapycnal mixing in dynamic models of the thermocline25–27, and implies that heat, salt and tracers must penetrate the thermocline mostly by transport along, rather than across, density surfaces.

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References

  1. Rooth, C. G. & Ostlund, H. G. Deep-Sea Res. 19, 481–492 (1972).

    Google Scholar 

  2. Jenkins, W. J. J. Mar. Res. 38, 533–569 (1980).

    CAS  Google Scholar 

  3. Moum, J. N. & Osborn, T. R. J. phys. Oceanogr. 16, 1250–1259 (1986).

    ADS  Article  Google Scholar 

  4. Gregg, M. C. J. geophys. Res. 94, 9686–9698 (1989).

    ADS  Article  Google Scholar 

  5. Lester, D. & Greenberg, L. A. Arch. Ind. Hyg. Occup. Med. 2, 348–349 (1950).

    CAS  PubMed  Google Scholar 

  6. Ledwell, J. R. & Watson, A. J. J. geophys. Res. 96, 8695–8718 (1991).

    ADS  Article  Google Scholar 

  7. Watson, A. J., Ledwell, J. R. & Sutherland, S. C. J. geophys. Res. 96, 8719–8725 (1991).

    ADS  Article  Google Scholar 

  8. Wanninkhof, R., Ledwell, J. R. & Watson, A. J. J. geophys. Res. 96, 8733–8740 (1991).

    ADS  Article  Google Scholar 

  9. Watson, A. J. & Liddicoat, M. I. Atmos. Environ. 19, 1477–1484 (1985).

    ADS  CAS  Article  Google Scholar 

  10. Price, J., McKee, T., Valdes, J., Richardson, P. & Armi, L. Report. 86-31, Woods Hole Oceanographic Institution (Woods Hole, MA, 1986).

  11. Armi, L. & Stommel, H. J. phys. Oceanogr. 13, 828–857 (1983).

    ADS  Article  Google Scholar 

  12. Thiele, G. et al. J. phys. Oceanogr. 16, 814–826 (1986).

    ADS  Article  Google Scholar 

  13. Oakey, N. S. IEEE J. Ocean. Engng 13, 124–128 (1988).

    ADS  Article  Google Scholar 

  14. Duda, T. F., Cox, C. S. & Deaton, T. K. J. Atmos. Ocean Tech. 5, 16–33 (1988).

    Article  Google Scholar 

  15. Garrett, C. Dyn. Atmos. Oceans 7, 265–277 (1983).

    ADS  Article  Google Scholar 

  16. Haidvogel, D. B. & Keffer, T. Dynam. Atmos. Oceans 8, 1–40 (1984).

    ADS  Article  Google Scholar 

  17. Young, W. R., Rhines, P. B. & Garrett, C. J. R. J. phys. Oceanogr. 12, 515–527 (1982).

    ADS  Article  Google Scholar 

  18. Muller, P., Lien, R.-C. & Williams, R. J. phys. Oceanogr. 18, 401–416 (1988).

    ADS  Article  Google Scholar 

  19. Montgomery, E., Schmitt, R. W., Toole, J. M. & Polzin, K. L. EOS 73, 321 (1992).

    Google Scholar 

  20. Hosom, D. S., Weller, R. A., Prada, K. E. & Trask, R. P. Proc. Mar. Tech. Soc. 1, 206–210 (1991).

    Google Scholar 

  21. Williams, A. J., Converse, C. H. & Nicholson, J. Am. Soc. mech. Engng, OED 12, 25–29 (1987).

    Google Scholar 

  22. Eppley, R. W. & Peterson, B. J. Nature 282, 677–680 (1979).

    ADS  Article  Google Scholar 

  23. Jenkins, W. J. Nature 331, 521–523 (1988).

    ADS  CAS  Article  Google Scholar 

  24. Vilareal, T. A., Altabet, M. A. & Culver-Rymsza, K. Nature 363, 709–712 (1993).

    ADS  Article  Google Scholar 

  25. Welander, P. Tellus 11, 309–318 (1959).

    ADS  Google Scholar 

  26. Luyten, J. R., Pedlosky, J. & Stommel, H. J. phys. Oceanogr. 13, 292–309 (1983).

    ADS  Article  Google Scholar 

  27. Huang, R. X. Rev. Geophys. suppl. 590–609 (1991).

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Ledwell, J., Watson, A. & Law, C. Evidence for slow mixing across the pycnocline from an open-ocean tracer-release experiment. Nature 364, 701–703 (1993). https://doi.org/10.1038/364701a0

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