A Basinwide Estimate of Vertical Mixing in the Upper Pycnocline: Spreading of Bomb Tritium in the North Pacific Ocean

Dan E. Kelley Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada

Search for other papers by Dan E. Kelley in
Current site
Google Scholar
PubMed
Close
and
Kim A. Van Scoy Department of Atmospheric and Oceanic Science, University of Wisconsin—Madison, Madison, Wisconsin

Search for other papers by Kim A. Van Scoy in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

The vertical diffusivity KV in the upper half-kilometer of the North Pacific subtropical pycnocline is estimated from observations of the spreading rate of anthropogenic tritium. The calculation is based on approximately 300 ocean tritium profiles made since tritium was introduced to the atmosphere via bomb testing in the 1960s. The data coverage does not permit detailed mapping of tritium penetration, especially in the sparsely sampled western Pacific. For this reason, and to minimize advective effects, the spreading rate is averaged within the closed streamlines of the subtropical gyre spanning ∼5°N to ∼40°N. The result, KV = (1.5 ± 0.7) × 10−5 m2 s−1, is consistent with inferences from microstructure and purposefully released tracer measurements in the North Atlantic, confirming that the spatially averaged rate of mixing in the upper pycnocline is substantially lower than the canonical Munk estimate for the lower pycnocline.

Corresponding author address: Dan Kelley, Dept. of Oceanography, Dalhousie University, Halifax, NS B3H 4J1, Canada.

Abstract

The vertical diffusivity KV in the upper half-kilometer of the North Pacific subtropical pycnocline is estimated from observations of the spreading rate of anthropogenic tritium. The calculation is based on approximately 300 ocean tritium profiles made since tritium was introduced to the atmosphere via bomb testing in the 1960s. The data coverage does not permit detailed mapping of tritium penetration, especially in the sparsely sampled western Pacific. For this reason, and to minimize advective effects, the spreading rate is averaged within the closed streamlines of the subtropical gyre spanning ∼5°N to ∼40°N. The result, KV = (1.5 ± 0.7) × 10−5 m2 s−1, is consistent with inferences from microstructure and purposefully released tracer measurements in the North Atlantic, confirming that the spatially averaged rate of mixing in the upper pycnocline is substantially lower than the canonical Munk estimate for the lower pycnocline.

Corresponding author address: Dan Kelley, Dept. of Oceanography, Dalhousie University, Halifax, NS B3H 4J1, Canada.

Save
  • Abramowitz, M., and I. A. Stegun, 1972: Handbook of Mathematical Functions, Dover, 1046 pp.

  • Barnes, S. L., 1994: Application of Barnes objective analysis scheme. Part I: Effects of undersampling, wave position, and station randomness. J. Atmos. Oceanic Technol.,11, 109–116.

  • Bryan, F., 1987: Parameter sensitivity of primitive equation ocean general circulation models. J. Phys. Oceanogr.,17, 970–985.

  • Carslaw, H. S., 1921: Introduction to the Mathematical Theory of the Conduction of Heat in Solids. Macmillan. 268 pp.

  • Daley, R., 1991: Atmospheric Data Analysis. Cambridge Press, 457 pp.

  • Dreisigacker, E., and W. Roether, 1978: Tritium and 90Sr in North Atlantic surface water. Earth Planet. Sci.,38, 301–312.

  • Fine, R. A., J. L. Reid, and H. G. Östlund, 1981: Circulation of tritium in the Pacific Ocean. J. Phys. Oceanogr.,11, 3–14.

  • Giletti, B. J., F. Bazan, and J. L. Kulp, 1958: The geochemistry of tritium. Eos, Trans. Amer. Geophys. Union,39, 807–817.

  • Gill, A. E., 1982: Atmosphere–Ocean Dynamics. Academic Press, 662 pp.

  • Hamilton, J. M., N. S. Oakey, and D. E. Kelley, 1993: Salt-finger signatures in microstructure measurements. J. Geophys. Res.,98, 2453–2460.

  • Jenkins, W. J., 1980: Tritium and 3He in the Sargasso Sea. J. Mar. Res.,38, 533–569.

  • ——, 1988: The use of anthropogenic tritium and helium-3 to study subtropical gyre ventilation and circulation. Philos. Trans. Roy. Soc. London A,325, 43–61.

  • Killworth, P. D., and J. M. Smith, 1984: A one-and-a-half dimensional model for the arctic halocline. Deep-Sea Res.,31, 271–293.

  • Koch, S. E., M. DesJardins, and P. J. Kocin, 1983: An interactive Barnes objective map analysis scheme for use with satellite and conventional data. J. Climate Appl. Meteor.,22, 1487–1503.

  • Kunze, E. L., and T. B. Sanford, 1996: Abyssal mixing: Where it is not. J. Phys. Oceanogr.,26, 2286–2296.

  • Ledwell, J. R., A. J. Watson, and C. S. Law, 1993: Evidence for slow mixing across the pycnocline from an open ocean tracer release experiment. Nature,364, 701–703.

  • ——, ——, and ——, 1994: Tracer dispersion during the North Atlantic Tracer Release Experiment (NATRE). Eos, Trans. Amer. Geophys. Union,75, 121.

  • Levitus, S., 1988: Ekman volume fluxes for the world ocean and individual ocean basins. J. Phys. Oceanogr.,18, 271–279.

  • ——, and T. P. Boyer, 1994: World Ocean Atlas 1994. NOAA Atlas NESDIS 4, U.S. Dept. of Commerce, 117 pp.

  • Liu, Z., and J. Pedlosky, 1994: Thermocline forced by annual and decadal surface temperature variation. J. Phys. Oceanogr.,24, 587–608.

  • Luyten, J. R., J. Pedlosky, and H. Stommel, 1983: The ventilated thermocline. J. Phys. Oceanogr.,13, 292–309.

  • Marshall, D., and J. Marshall, 1995: On the thermodynamics of subduction. J. Phys. Oceanogr.,25, 138–151.

  • McCartney, M. S., 1982: The subtropical recirculation of mode waters. Deep-Sea Res.,40, 427–464.

  • McDougall, T. J., and B. R. Ruddick, 1992: The use of ocean microstructure to quantify both turbulent mixing and salt-fingering. Deep-Sea Res.,39, 1931–1952.

  • Michel, R. L., 1974: Uptake of bomb-produced tritium by the Pacific Ocean. Ph.D. thesis, University of California, San Diego, 222 pp. [Available from UMI Dissertation Service, 300 N. Zeeb Rd., P.O. Box 1346, Ann Arbor, MI 48106-1346.].

  • ——, and H. E. Suess, 1975: Bomb tritium in the Pacific Ocean. J. Geophys. Res.,80, 4139–4152.

  • Miyake, Y., T. Shimada, Y. Sugimura, K. Shigehara, and K. Saruhasi, 1975: Distribution of Tritium in the Pacific Ocean. Rec. Oceanogr. Works Japan,13, 17–31.

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

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

  • Musgrave, D. L., 1990: Numerical studies of tritium and helium-3 in the thermocline. J. Phys. Oceanogr.,20, 344–373.

  • Osborn, T. R., and C. S. Cox, 1972: Oceanic finestructure. Geophys. Fluid Dyn.,3, 321–345.

  • Östlund, H. G., 1984: TTO/North Pacific study, Discoverer 1982—Tritium results: Data release 84-10. University of Miami Tritium Laboratory, Miami, FL.

  • ——, 1985a: Niiler cruise 1983 R/V Thomas Thompson 173 tritium samples: Data release 85-44 (amended in 86-22). University of Miami Tritium Laboratory, Miami, FL.

  • ——, 1985b: TTO/North Pacific study, Discoverer 1983—Tritium results: Data release 85-37. University of Miami Tritium Laboratory, Miami, FL.

  • ——, 1985c: Ocean station Papa tritium results 1979–1982: Data release 85-06. University of Miami Tritium Laboratory, Miami, FL.

  • ——, 1986: Ocean Station Papa summer 1985 tritium and radiocarbon results: Data release 86-24. University of Miami Tritium Laboratory, Miami, FL.

  • ——, 1987a: TPS47-transpacific cruise 1985 tritium results: Data release 87-33. University of Miami Tritium Laboratory, Miami, FL.

  • ——, 1987b: TPS24-transpacific cruise 1985 tritium results: Data release 87-35. University of Miami Tritium Laboratory, Miami, FL.

  • ——, 1987c: Marathon II North Pacific cruise R/V Thomas Thompson 1984 tritium results: Data release 87-20. University of Miami Tritium Laboratory, Miami, FL.

  • ——, 1990: WEPOCS 3, 1988 tritium results: Data release 90-25. University of Miami Tritium Laboratory, Miami, FL.

  • ——, 1991: SAGA-II cruise 1987 tritium results: Data release 91-05. University of Miami Tritium Laboratory, Miami, FL.

  • ——, and R. Brescher, 1982: GEOSECS tritium, Data report No. 12. University of Miami Tritium Laboratory, Miami, FL.

  • ——, and C. G. H. Rooth, 1990: The North Atlantic tritium and radiocarbon transients 1972–1983. J. Geophys. Res.,95, 20 147–20 165.

  • ——, C. Grall, and R. E. Brescher, 1986: Equatorial pacific tritium. Data report No. 15. University of Miami Tritium Laboratory, Miami, FL.

  • Polzin, K. L., J. M. Toole, and R. W. Schmitt, 1995: Finescale parameterizations of turbulent dissipation. J. Phys. Oceanogr.,25, 306–328.

  • Press, W. H., S. A. Teukolsky, W. T. Vetterling, and B. P. Flannery, 1995: Numerical Recipes in C, the Art of Scientific Computing. Cambridge University Press, 994 pp.

  • Richards, K. J., Y. Jia, and C. F. Rogers, 1995: Dispersion of tracers by ocean gyres. J. Phys. Oceanogr.,25, 873–887.

  • Roether, W., 1974: The tritium and carbon-14 profiles at the GEOSECS I (1969) and GOGO I (1971) North Pacific Stations. Earth Planet. Sci.,23, 108–115.

  • Rooth, C. G., and H. G. Östlund, 1972: Penetration of tritium into the Atlantic thermocline. Deep-Sea Res.,19, 481–492.

  • Ruddick, B., D. Walsh, and N. Oakey, 1997: Variations in apparent mixing efficiency in the North Atlantic Central Water. J. Phys. Oceanogr.,27, 2589–2605.

  • Suess, H. E., 1969: Tritium geophysics as an international research project. Science,163, 1405–1410.

  • Sundermeyer, M. A., and J. F. Price, 1998: Lateral mixing in the North Atlantic Tracer Release Experiment: Observations and numerical simulations of Lagrangian particles and passive tracer. J. Geophys. Res.,103, 21 481–21 497.

  • Talley, L. D., 1985: Ventilation of the subtropical North Pacific: The shallow salinity minimum. J. Phys. Oceanogr.,15, 633–649.

  • Toggweiler, J. R., K. Dixon, and K. Bryan, 1989: Simulations of radiocarbon in a coarse-resolution World Ocean model. Part II:Distributions of bomb-produced carbon 14. J. Geophys. Res.,95, 8232–8264.

  • Unterweger, M. P., B. M. Coursey, F. J. Schima, and W. B. Mann, 1980: Preparation and calibration of the 1978 National Bureau of Standards tritated-water standards. Int. J. Appl. Rad. Isotopes,31, 611–614.

  • Van Scoy, K. A., and E. R. M. Druffel, 1993: Ventilation and transport of thermocline and intermediate waters in the North Pacific during recent El Niños. J. Geophys. Res.,98, 18 083–18 088.

  • ——, R. A. Fine, and H. G. Östlund, 1991a: Two decades of mixing tritium into the North Pacific Ocean. Deep-Sea Res.,38, S191–S219.

  • ——, D. B. Olson, and R. A. Fine, 1991b: Ventilation of North Pacific intermediate water: The role of the Alaskan gyre. J. Geophys. Res.,96, 16 801–16 810.

  • Weiss, W., and W. Roether, 1980: The rates of tritium input to the world oceans. Earth Planet. Sci.,49, 435–446.

  • Woods, J. D., 1985: The physics of thermocline ventilation. Coupled Ocean–Atmosphere Models. J. C. J. Nihoul and B. M. Jamart, Eds. Elsevier, 543–590.

  • ——, and W. Barkmann, 1986: A Lagrangian mixed layer model of Atlantic 18°C water formation. Nature,319, 574–576.

  • Wright, D. G., and T. F. Stocker, 1991: A zonally averaged ocean model for the thermohaline circulation. Part I: Model development and flow dynamics. J. Phys. Oceanogr.,21, 1713–1724.

  • ——, and ——, 1992: Sensitivities of a zonally averaged global ocean circulation model. J. Geophys. Res.,97, 12 707–12 730.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 428 161 40
PDF Downloads 85 31 1