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.
This is a preview of subscription content, access via your institution
Access options
Subscribe to this journal
Receive 51 print issues and online access
$199.00 per year
only $3.90 per issue
Buy this article
- Purchase on Springer Link
- Instant access to full article PDF
Prices may be subject to local taxes which are calculated during checkout
Similar content being viewed by others
References
Rooth, C. G. & Ostlund, H. G. Deep-Sea Res. 19, 481–492 (1972).
Jenkins, W. J. J. Mar. Res. 38, 533–569 (1980).
Moum, J. N. & Osborn, T. R. J. phys. Oceanogr. 16, 1250–1259 (1986).
Gregg, M. C. J. geophys. Res. 94, 9686–9698 (1989).
Lester, D. & Greenberg, L. A. Arch. Ind. Hyg. Occup. Med. 2, 348–349 (1950).
Ledwell, J. R. & Watson, A. J. J. geophys. Res. 96, 8695–8718 (1991).
Watson, A. J., Ledwell, J. R. & Sutherland, S. C. J. geophys. Res. 96, 8719–8725 (1991).
Wanninkhof, R., Ledwell, J. R. & Watson, A. J. J. geophys. Res. 96, 8733–8740 (1991).
Watson, A. J. & Liddicoat, M. I. Atmos. Environ. 19, 1477–1484 (1985).
Price, J., McKee, T., Valdes, J., Richardson, P. & Armi, L. Report. 86-31, Woods Hole Oceanographic Institution (Woods Hole, MA, 1986).
Armi, L. & Stommel, H. J. phys. Oceanogr. 13, 828–857 (1983).
Thiele, G. et al. J. phys. Oceanogr. 16, 814–826 (1986).
Oakey, N. S. IEEE J. Ocean. Engng 13, 124–128 (1988).
Duda, T. F., Cox, C. S. & Deaton, T. K. J. Atmos. Ocean Tech. 5, 16–33 (1988).
Garrett, C. Dyn. Atmos. Oceans 7, 265–277 (1983).
Haidvogel, D. B. & Keffer, T. Dynam. Atmos. Oceans 8, 1–40 (1984).
Young, W. R., Rhines, P. B. & Garrett, C. J. R. J. phys. Oceanogr. 12, 515–527 (1982).
Muller, P., Lien, R.-C. & Williams, R. J. phys. Oceanogr. 18, 401–416 (1988).
Montgomery, E., Schmitt, R. W., Toole, J. M. & Polzin, K. L. EOS 73, 321 (1992).
Hosom, D. S., Weller, R. A., Prada, K. E. & Trask, R. P. Proc. Mar. Tech. Soc. 1, 206–210 (1991).
Williams, A. J., Converse, C. H. & Nicholson, J. Am. Soc. mech. Engng, OED 12, 25–29 (1987).
Eppley, R. W. & Peterson, B. J. Nature 282, 677–680 (1979).
Jenkins, W. J. Nature 331, 521–523 (1988).
Vilareal, T. A., Altabet, M. A. & Culver-Rymsza, K. Nature 363, 709–712 (1993).
Welander, P. Tellus 11, 309–318 (1959).
Luyten, J. R., Pedlosky, J. & Stommel, H. J. phys. Oceanogr. 13, 292–309 (1983).
Huang, R. X. Rev. Geophys. suppl. 590–609 (1991).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
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
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1038/364701a0
This article is cited by
-
Uncertainties in the Arctic Ocean response to CO\(_2\): a process-based analysis
Climate Dynamics (2024)
-
Eddy diffusivity in stratified ocean: a case study in Bay of Bengal
Environmental Fluid Mechanics (2023)
-
Observation of physical oceanography at the Y3 seamount (Yap Arc) in winter 2014
Journal of Oceanology and Limnology (2022)
-
Nitrogen isotopic constraints on nutrient transport to the upper ocean
Nature Geoscience (2021)
-
Vertical turbulent nitrate flux from direct measurements in the western subarctic and subtropical gyres of the North Pacific
Journal of Oceanography (2021)
Comments
By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.