Heton Shedding from Submarine-Canyon Plumes in an Arctic Boundary Current System: Sensitivity to the Undercurrent

Shenn-Yu Chao Horn Point Laboratory, University of Maryland Center for Environmental Science, Cambridge, Maryland

Search for other papers by Shenn-Yu Chao in
Current site
Google Scholar
PubMed
Close
and
Ping-Tung Shaw Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina

Search for other papers by Ping-Tung Shaw in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

The lateral injection of dense outflow into an Arctic baroclinic current though a submarine canyon is examined using a three-dimensional nonhydrostatic numerical model. The oceanographic setting in this model retains essential features of the active outflow region from the Chukchi shelf to the Beaufort Sea. The coastal ocean mainly consists of a continental shelf and slope region indented by a submarine canyon. The ocean surface is partially frictional to account for the ice-exerted friction. A boundary current is bounded to the left by the continental slope and, in the most interesting cases, is bounded below by a reverse undercurrent. Dense water is released from the upper canyon and produces a sinking plume that follows the canyon axis seaward. As it approaches the maximum sinking depth, the subsurface plume moves out of the canyon and turns to the right to become a right-bounded undercurrent over the continental slope. The right turn generates anticyclonic vorticity. The sinking motion also induces a surface cyclone trapped over the canyon. If the centers of the top cyclone and subsurface anticyclone are sufficiently separated horizontally, the pair can form a self-propagating heton moving seaward from the canyon. Thus the heton shedding is an efficient way to produce halocline anticyclones that are known to populate the Beaufort Sea. Shedding is most active for fast release of dense water and if the maximum sinking depth is in the lower halocline. Heton shedding can occur in the absence of a boundary current. A unidirectional boundary current enhances heton shedding. An undercurrent provides background negative vorticity to the subsurface anticyclone and moves the anticyclone in the direction favorable for the seaward heton propagation. In consequence, the addition of an undercurrent facilitates much more efficient heton shedding.

Corresponding author address: Shenn-Yu Chao, Center for Environmental Science Horn Point Laboratory, University of Maryland, Cambridge, MD 21613-0775. Email: chao@hpl.umces.edu

Abstract

The lateral injection of dense outflow into an Arctic baroclinic current though a submarine canyon is examined using a three-dimensional nonhydrostatic numerical model. The oceanographic setting in this model retains essential features of the active outflow region from the Chukchi shelf to the Beaufort Sea. The coastal ocean mainly consists of a continental shelf and slope region indented by a submarine canyon. The ocean surface is partially frictional to account for the ice-exerted friction. A boundary current is bounded to the left by the continental slope and, in the most interesting cases, is bounded below by a reverse undercurrent. Dense water is released from the upper canyon and produces a sinking plume that follows the canyon axis seaward. As it approaches the maximum sinking depth, the subsurface plume moves out of the canyon and turns to the right to become a right-bounded undercurrent over the continental slope. The right turn generates anticyclonic vorticity. The sinking motion also induces a surface cyclone trapped over the canyon. If the centers of the top cyclone and subsurface anticyclone are sufficiently separated horizontally, the pair can form a self-propagating heton moving seaward from the canyon. Thus the heton shedding is an efficient way to produce halocline anticyclones that are known to populate the Beaufort Sea. Shedding is most active for fast release of dense water and if the maximum sinking depth is in the lower halocline. Heton shedding can occur in the absence of a boundary current. A unidirectional boundary current enhances heton shedding. An undercurrent provides background negative vorticity to the subsurface anticyclone and moves the anticyclone in the direction favorable for the seaward heton propagation. In consequence, the addition of an undercurrent facilitates much more efficient heton shedding.

Corresponding author address: Shenn-Yu Chao, Center for Environmental Science Horn Point Laboratory, University of Maryland, Cambridge, MD 21613-0775. Email: chao@hpl.umces.edu

Save
  • Aagaard, K., 1984: The Beaufort undercurrent. The Alaskan Beaufort Sea, Ecosystems and Environments, P. W. Barnes et al., Eds., Academic Press, 47–71.

    • Search Google Scholar
    • Export Citation
  • Aagaard, K., L. K. Coachman, and E. C. Carmack, 1981: On the halocline of the Arctic Ocean. Deep-Sea Res., 28 , 529545.

  • Cavalieri, D. J., and S. Martin, 1994: The contribution of Alaskan, Siberian, and Canadian coastal polynyas to the cold halocline layer of the Arctic Ocean. J. Geophys. Res., 99 , 1834318362.

    • Search Google Scholar
    • Export Citation
  • Chao, S-Y., 1998: Hyperpycnal and buoyant plumes from a sediment-laden river. J. Geophys. Res., 103 , 30673081.

  • Chao, S-Y., and P-T. Shaw, 2000: Slope-enhanced fission of salty hetons under sea ice. J. Phys. Oceanogr., 30 , 28662882.

  • Chao, S-Y., and P-T. Shaw, 2003: A numerical study of dense outflow and halocline anticyclones in an Arctic baroclinic current. J. Geophys. Res., in press.

    • Search Google Scholar
    • Export Citation
  • Chapman, D. C., and G. Gawarkiewicz, 1995: Offshore transport of dense shelf water in the presence of a submarine-canyon. J. Geophys. Res., 100 , 1337313387.

    • Search Google Scholar
    • Export Citation
  • Coachman, L. K., K. Aagaard, and R. B. Tripp, 1975: Bering Strait: The Regional Physical Oceanography. University of Washington Press, 172 pp.

    • Search Google Scholar
    • Export Citation
  • D'Asaro, E. A., 1988a: Generation of submesoscale vortices: A new mechanism. J. Geophys. Res., 93 , 66856693.

  • D'Asaro, E. A., 1988b: Observations of small eddies in the Beaufort Sea. J. Geophys. Res., 93 , 66696684.

  • Griffiths, R. W., and E. J. Hopfinger, 1986: Experiments with baroclinic vortex pairs in a rotating fluid. J. Fluid Mech, 173 , 501518.

    • Search Google Scholar
    • Export Citation
  • Hogg, N. G., and H. M. Stommel, 1985: The heton: An elementary interaction between discrete baroclinic geostrophic vortices and its implications concerning eddy heat-flow. Proc. Roy. Soc. London, A397. 120.

    • Search Google Scholar
    • Export Citation
  • Holland, W. R., 1978: The role of mesoscale eddies in the general circulation model of the ocean—Numerical experiments using a wind-driven quasi-geostrophic model. J. Phys. Oceanogr., 8 , 363392.

    • Search Google Scholar
    • Export Citation
  • Jiang, L., and R. W. Garwood Jr., 1998: Effects of topographic steering and ambient stratification on overflows on continental slopes: A model study. J. Geophys. Res., 103 , 54595476.

    • Search Google Scholar
    • Export Citation
  • Jones, H., and J. Marshall, 1993: Convection with rotation in a neutral ocean: A study of open-ocean convection. J. Phys. Oceanogr., 23 , 10091039.

    • Search Google Scholar
    • Export Citation
  • Kreiss, H-O., 1966: Proceedings of a Symposium at the University of Wisconsin, May 1966. D. Greenspan, Ed., John Wiley and Sons.

  • Legg, S., and J. Marshall, 1993: A heton model of the spreading phase of open-ocean deep convection. J. Phys. Oceanogr., 23 , 10401056.

    • Search Google Scholar
    • Export Citation
  • Manley, T. O., and K. Hunkins, 1985: Mesoscale eddies of the Arctic Ocean. J. Geophys. Res., 90 , 49114930.

  • Marshall, J., A. Adcroft, C. Hill, L. Perelmam, and C. Heisey, 1997: A finite-volume, incompressible Navier–Stokes model for studies of the ocean on parallel computers. J. Geophys. Res., 102 , 57535766.

    • Search Google Scholar
    • Export Citation
  • Muench, R. D., J. T. Gunn, T. E. Whitledge, P. Schlosser, and W. Smethie, 2000: An Arctic Ocean cold eddy. J. Geophys. Res., 105 , 2399724006.

    • Search Google Scholar
    • Export Citation
  • Newton, J. L., K. Aagaard, and L. K. Coachman, 1974: Baroclinic eddies in Arctic Ocean. Deep-Sea Res., 21 , 707719.

  • Orlanski, I., 1976: A simple boundary condition for unbounded hyperbolic flows. J. Comput. Phys., 21 , 251269.

  • Pacanowski, R. C., and S. G. H. Philander, 1981: Parameterization of vertical mixing in numerical models of tropical oceans. J. Phys. Oceanogr., 11 , 14431451.

    • Search Google Scholar
    • Export Citation
  • Pozrikidis, C., 1997: Introduction to Theoretical and Computational Fluid Dynamics. Oxford University Press, 675 pp.

  • Roach, A. T., K. Aagaard, C. H. Pease, S. A. Salo, T. Weingartner, V. Parlov, and M. Kulakov, 1995: Direct measurements of transports and water properties through the Bering Strait. J. Geophys. Res., 100 , 1844318457.

    • Search Google Scholar
    • Export Citation
  • Shaw, P-T., and S-Y. Chao, 2003: Effects of a baroclinic current on a sinking dense water plumes from a submarine canyon and heton shedding. Deep-Sea Res., 50A , 357370.

    • Search Google Scholar
    • Export Citation
  • Signorini, S. R., and D. J. Cavalieri, 2002: Modeling dense water production and salt transport from Alaskan coastal polynyas. J. Geophys. Res., 107 , 3136. doi:10.1029/2000JC000491.

    • Search Google Scholar
    • Export Citation
  • Spall, M. A., and D. C. Chapman, 1998: On the efficiency of baroclinic eddy heat transport across narrow fronts. J. Phys. Oceanogr., 28 , 22752287.

    • Search Google Scholar
    • Export Citation
  • Weingartner, T. J., D. J. Cavalieri, K. Aagaard, and Y. Sasaki, 1998: Circulation, dense water formation, and outflow on the northeast Chukchi shelf. J. Geophys. Res., 103 , 76477661.

    • Search Google Scholar
    • Export Citation
  • Woodgate, R., K. Aagaard, E. Carmack, and T. Weingartner, cited 2002: Circulation in the Beaufort Sea. [Available online at http://psc.apl.washington.edu/HLD/Beaufort/Beaufort.html.].

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 170 44 10
PDF Downloads 34 13 0