Some Implications of Ekman Layer Dynamics for Cross-Shelf Exchange in the Amundsen Sea

A. K. Wåhlin Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden

Search for other papers by A. K. Wåhlin in
Current site
Google Scholar
PubMed
Close
,
R. D. Muench Earth and Space Research, Seattle

Search for other papers by R. D. Muench in
Current site
Google Scholar
PubMed
Close
,
L. Arneborg Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden

Search for other papers by L. Arneborg in
Current site
Google Scholar
PubMed
Close
,
G. Björk Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden

Search for other papers by G. Björk in
Current site
Google Scholar
PubMed
Close
,
H. K. Ha Korea Polar Research Institute, Incheon, South Korea

Search for other papers by H. K. Ha in
Current site
Google Scholar
PubMed
Close
,
S. H. Lee Korea Polar Research Institute, Incheon, South Korea

Search for other papers by S. H. Lee in
Current site
Google Scholar
PubMed
Close
, and
H. Alsén Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden

Search for other papers by H. Alsén in
Current site
Google Scholar
PubMed
Close
Restricted access

We are aware of a technical issue preventing figures and tables from showing in some newly published articles in the full-text HTML view.
While we are resolving the problem, please use the online PDF version of these articles to view figures and tables.

Abstract

The exchange of warm, salty seawater across the continental shelves off West Antarctica leads to subsurface glacial melting at the interface between the ocean and the West Antarctic Ice Sheet. One mechanism that contributes to the cross-shelf transport is Ekman transport induced by along-slope currents over the slope and shelf break. An investigation of this process is applied to the Amundsen Sea shelfbreak region, using recently acquired and historical field data to guide the analyses. Along-slope currents were observed at transects across the eastern and western reaches of the Amundsen slope. Currents in the east flowed eastward, and currents farther west flowed westward. Under the eastward-flowing currents, hydrographic isolines sloped upward paralleling the seabed. In this layer, declining buoyancy forces rather than friction were bringing the velocity to zero at the seabed. The basin water in the eastern part of the shelf was dominated by water originating from 800–1000-m depth off shelf, suggesting that transport of such water across the shelf frequently occurs. The authors show that arrested Ekman layers mechanism can supply deep water to the shelf break in the eastern section, where it has access to the shelf. Because no unmodified off-shelf water was found on the shelf in the western part, bottom layer Ekman transport does not appear a likely mechanism for delivery of warm deep water to the western shelf area. Warming of the warm bottom water was most pronounced on the western shelf, where the deep-water temperature increased by 0.6°C during the past decade.

Corresponding author address: A. K. Wåhlin, Department of Earth Sciences, University of Gothenburg, Box 460, Gothenburg 401 30, Sweden. E-mail: awahlin@gu.se

Abstract

The exchange of warm, salty seawater across the continental shelves off West Antarctica leads to subsurface glacial melting at the interface between the ocean and the West Antarctic Ice Sheet. One mechanism that contributes to the cross-shelf transport is Ekman transport induced by along-slope currents over the slope and shelf break. An investigation of this process is applied to the Amundsen Sea shelfbreak region, using recently acquired and historical field data to guide the analyses. Along-slope currents were observed at transects across the eastern and western reaches of the Amundsen slope. Currents in the east flowed eastward, and currents farther west flowed westward. Under the eastward-flowing currents, hydrographic isolines sloped upward paralleling the seabed. In this layer, declining buoyancy forces rather than friction were bringing the velocity to zero at the seabed. The basin water in the eastern part of the shelf was dominated by water originating from 800–1000-m depth off shelf, suggesting that transport of such water across the shelf frequently occurs. The authors show that arrested Ekman layers mechanism can supply deep water to the shelf break in the eastern section, where it has access to the shelf. Because no unmodified off-shelf water was found on the shelf in the western part, bottom layer Ekman transport does not appear a likely mechanism for delivery of warm deep water to the western shelf area. Warming of the warm bottom water was most pronounced on the western shelf, where the deep-water temperature increased by 0.6°C during the past decade.

Corresponding author address: A. K. Wåhlin, Department of Earth Sciences, University of Gothenburg, Box 460, Gothenburg 401 30, Sweden. E-mail: awahlin@gu.se
Save
  • Allen, S., and X. D. de Madron, 2009: A review of the role of submarine canyons in deep-ocean exchange with the shelf. Ocean Sci., 5, 607620.

    • Search Google Scholar
    • Export Citation
  • Beardsley, R. C., R. Limeburner, and W. B. Owens, 2004: Drifter measurements of surface currents near Marguerite Bay on the western Antarctic Peninsula shelf during austral summer and fall, 2001 and 2002. Deep-Sea Res. II, 51, 19471964, doi:10.1016/j.dsr2.2004.07.031.

    • Search Google Scholar
    • Export Citation
  • Bindoff, N. L., M. A. Rosenberg, and M. J. Warner, 2000: On the circulation and water masses over the Antarctic continental slope and rise between 80 and 150°E. Deep-Sea Res. II, 47, 22992326.

    • Search Google Scholar
    • Export Citation
  • Boyer, T. P., and Coauthors, 2006: World Ocean Database 2005. NOAA Atlas NESDIS 60, 190 pp.

  • Cossu, R., M. G. Wells, and A. K. Wåhlin, 2010: Influence of the Coriolis force on the velocity structure of gravity currents in straight submarine channel systems. J. Geophys. Res., 115, C11016, doi:10.1029/2010JC006208.

    • Search Google Scholar
    • Export Citation
  • Dinniman, M. S., and J. M. Klinck, 2004: A model study of circulation and cross-shelf exchange on the west Antarctic Peninsula continental shelf. Deep-Sea Res. II, 51, 20032022, doi:10.1016/j.dsr2.2004.07.030.

    • Search Google Scholar
    • Export Citation
  • Foldvik, A., and Coauthors, 2004: Ice shelf water overflow and bottom water formation in the southern Weddell Sea. J. Geophys. Res., 109, C02015, doi:10.1029/2003JC002008.

    • Search Google Scholar
    • Export Citation
  • Gade, H., 1979: Melting of ice in sea water: A primitive model with application to the antarctic ice shelf and icebergs. J. Phys. Oceanogr., 9, 189198.

    • Search Google Scholar
    • Export Citation
  • Garrett, C., P. MacCready, and P. Rhines, 1993: Boundary mixing and arrested Ekman layers: Rotating stratified flow near a sloping boundary. Annu. Rev. Fluid Mech., 25, 291323, doi:10.1146/annurev.fl.25.010193.001451.

    • Search Google Scholar
    • Export Citation
  • Gordon, A. L., E. Zambianchi, A. Orsi, M. Visbeck, C. Giulivi, T. Whitworth III, and G. Spezie, 2004: Energetic plumes over the western Ross Sea continental slope. Geophys. Res. Lett., 31, L21302, doi:10.1029/2004GL020785.

    • Search Google Scholar
    • Export Citation
  • Gordon, A. L., A. H. Orsi, R. Muench, B. A. Huber, E. Zambianchi, and M. Visbeck, 2009: Western Ross Sea continental slope gravity currents. Deep-Sea Res. II, 56, 796817.

    • Search Google Scholar
    • Export Citation
  • Hofmann, E. E., P. H. Wiebe, D. P. Costa, and J. J. Torres, 2004: An overview of the Southern Ocean Global Ocean Ecosystems Dynamics program. Deep-Sea Res. II, 51, 19211924, doi:10.1016/j.dsr2.2004.08.007.

    • Search Google Scholar
    • Export Citation
  • Jackett, D. R., and T. R. McDougall, 1997: A Neutral Density Variable for the World’s Oceans. J. Phys. Oceanogr., 27, 237263.

  • Jacobs, S., A. Jenkins, C. Giulivi, and P. Dutrieux, 2011: Stronger ocean circulation and increased melting under Pine Island Glacier ice shelf. Nat. Geosci., 4, 519523.

    • Search Google Scholar
    • Export Citation
  • Jenkins, A., P. Dutrieux, S. S. Jacobs, S. D. McPhail, J. R. Perrett, A. T. Webb, and D. White, 2010: Observations beneath Pine Island Glacier in West Antarctica and implications for its retreat. Nat. Geosci., 3, 468472, doi:10.1038/ngeo890.

    • Search Google Scholar
    • Export Citation
  • Klinck, J. M., and M. S. Dinniman, 2010: Exchange across the shelf break at high southern latitudes. Ocean Sci., 6, 513524, doi:10.5194/os-6-513-2010.

    • Search Google Scholar
    • Export Citation
  • Klinck, J. M., E. E. Hofmann, R. C. Beardsley, B. Salihoglu, and S. Howard, 2004: Water-mass properties and circulation on the west Antarctic Peninsula continental shelf in austral fall and winter 2001. Deep-Sea Res. II, 51, 19251946, doi:10.1016/j.dsr2.2004.08.001.

    • Search Google Scholar
    • Export Citation
  • MacCready, P., and P. B. Rhines, 1991: Buoyant inhibition of Ekman transport on a slope and its effect on stratified spin-up. J. Fluid Mech., 223, 631666.

    • Search Google Scholar
    • Export Citation
  • MacCready, P., and P. B. Rhines, 1993: Slippery bottom boundary layers on a slope. J. Phys. Oceanogr., 23, 522.

  • Orsi, A., and C. Wiederwohl, 2009: A recount of Ross Sea Waters. Deep-Sea Res. II, 56 (13–14), 778795.

  • Orsi, A., T. Whitworth, and W. Nowlin, 1995: On the meridional extent and fronts of the Antarctic Circumpolar Current. Deep-Sea Res. I, 42, 641673.

    • Search Google Scholar
    • Export Citation
  • Padman, L., H. A. Fricker, R. Coleman, S. Howard, and S. Erofeeva, 2002: A new tide model for the Antarctic ice shelves and seas. Ann. Glaciol., 34, 247254.

    • Search Google Scholar
    • Export Citation
  • Rignot, E., 1998: Fast recession of a West Antarctic glacier. Science, 281, 549551.

  • Rignot, E., and S. Jacobs, 2002: Rapid bottom melting widespread near Antarctic ice sheet grounding lines. Science, 296, 20202023.

  • Shepherd, A., D. Wingham, and E. Rignot, 2004: Warm ocean is eroding West Antarctic Ice Sheet. Geophys. Res. Lett., 31, L23402, doi:10.1029/2004GL021106.

    • Search Google Scholar
    • Export Citation
  • Thoma, M., A. Jenkins, D. Holland, and S. Jacobs, 2008: Modelling Circumpolar Deep Water intrusions on the Amundsen Sea continental shelf, Antarctica. Geophys. Res. Lett., 35, L18602, doi:10.1029/2008GL034939.

    • Search Google Scholar
    • Export Citation
  • Timmermann, R., and Coauthors, 2010: A consistent dataset of Antarctic ice sheet topography, cavity geometry, and global bathymetry. Earth Syst. Sci. Data, 2, 261273, doi:10.5194/essd-2-261-2010.

    • Search Google Scholar
    • Export Citation
  • Trowbridge, J. H., and S. J. Lentz, 1991: Asymmetric behavior of an oceanic boundary layer above a sloping bottom. J. Phys. Oceanogr., 21, 11711185.

    • Search Google Scholar
    • Export Citation
  • Wåhlin, A. K., and G. Walin, 2001: Downward migration of dense bottom currents. Environ. Fluid Mech., 1, 257279.

  • Wåhlin, A. K., X. Yuan, G. Björk, and C. Nohr, 2010: Inflow of warm Circumpolar Deep Water in the central Amundsen shelf. J. Phys. Oceanogr., 40, 14271434.

    • Search Google Scholar
    • Export Citation
  • Walker, D. P., M. A. Brandon, A. Jenkins, J. T. Allen, J. A. Dowdeswell, and J. Evans, 2007: Oceanic heat transport onto the Amundsen Sea shelf through a submarine glacial trough. Geophys. Res. Lett., 34, L02602, doi:10.1029/2006GL028154.

    • Search Google Scholar
    • Export Citation
  • Whitworth, T., III, A. H. Orsi, S.-J. Kim, and W. D. Nowlin Jr., 1998. Water masses and mixing near the Antarctic Slope Front. Ocean, Ice, and Atmosphere: Interactions at the Antarctic Continental Margin, S. S. Jacobs and R. F. Weiss, Eds., Antarctic Research Series, Amer. Geophys. Union, 1–27.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 1462 678 166
PDF Downloads 731 141 12