Spreading of Denmark Strait Overflow Water in the Western Subpolar North Atlantic: Insights from Eddy-Resolving Simulations with a Passive Tracer

Xiaobiao Xu Center for Ocean–Atmospheric Prediction Studies/Florida State University, Tallahassee, Florida

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Peter B. Rhines University of Washington, Seattle, Washington

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Eric P. Chassignet Center for Ocean–Atmospheric Prediction Studies/Florida State University, Tallahassee, Florida

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William J. Schmitz Jr. Woods Hole Oceanographic Institute, Woods Hole, Massachusetts

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Abstract

The oceanic deep circulation is shared between concentrated deep western boundary currents (DWBCs) and broader interior pathways, a process that is sensitive to seafloor topography. This study investigates the spreading and deepening of Denmark Strait overflow water (DSOW) in the western subpolar North Atlantic using two ° eddy-resolving Atlantic simulations, including a passive tracer injected into the DSOW. The deepest layers of DSOW transit from a narrow DWBC in the southern Irminger Sea into widespread westward flow across the central Labrador Sea, which remerges along the Labrador coast. This abyssal circulation, in contrast to the upper levels of overflow water that remain as a boundary current, blankets the deep Labrador Sea with DSOW. Farther downstream after being steered around the abrupt topography of Orphan Knoll, DSOW again leaves the boundary, forming cyclonic recirculation cells in the deep Newfoundland basin. The deep recirculation, mostly driven by the meandering pathway of the upper North Atlantic Current, leads to accumulation of tracer offshore of Orphan Knoll, precisely where a local maximum of chlorofluorocarbon (CFC) inventory is observed. At Flemish Cap, eddy fluxes carry ~20% of the tracer transport from the boundary current into the interior. Potential vorticity is conserved as the flow of DSOW broadens at the transition from steep to less steep continental rise into the Labrador Sea, while around the abrupt topography of Orphan Knoll, potential vorticity is not conserved and the DSOW deepens significantly.

Corresponding author address: X. Xu, COAPS/Florida State University, 2000 Levy Avenue, Building A, Tallahassee, FL 32306. E-mail: xxu@coaps.fsu.edu

Abstract

The oceanic deep circulation is shared between concentrated deep western boundary currents (DWBCs) and broader interior pathways, a process that is sensitive to seafloor topography. This study investigates the spreading and deepening of Denmark Strait overflow water (DSOW) in the western subpolar North Atlantic using two ° eddy-resolving Atlantic simulations, including a passive tracer injected into the DSOW. The deepest layers of DSOW transit from a narrow DWBC in the southern Irminger Sea into widespread westward flow across the central Labrador Sea, which remerges along the Labrador coast. This abyssal circulation, in contrast to the upper levels of overflow water that remain as a boundary current, blankets the deep Labrador Sea with DSOW. Farther downstream after being steered around the abrupt topography of Orphan Knoll, DSOW again leaves the boundary, forming cyclonic recirculation cells in the deep Newfoundland basin. The deep recirculation, mostly driven by the meandering pathway of the upper North Atlantic Current, leads to accumulation of tracer offshore of Orphan Knoll, precisely where a local maximum of chlorofluorocarbon (CFC) inventory is observed. At Flemish Cap, eddy fluxes carry ~20% of the tracer transport from the boundary current into the interior. Potential vorticity is conserved as the flow of DSOW broadens at the transition from steep to less steep continental rise into the Labrador Sea, while around the abrupt topography of Orphan Knoll, potential vorticity is not conserved and the DSOW deepens significantly.

Corresponding author address: X. Xu, COAPS/Florida State University, 2000 Levy Avenue, Building A, Tallahassee, FL 32306. E-mail: xxu@coaps.fsu.edu
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  • Armi, L., and R. Williams, 1991: The deep western boundary undercurrent off the Newfoundland Ridge. Deep-Sea Res. I, 38, 371391, doi:10.1016/0198-0149(91)90074-P.

    • Search Google Scholar
    • Export Citation
  • Bacon, S., and P. M. Saunders, 2010: The deep western boundary current at Cape Farewell: Results from a moored current meter array. J. Phys. Oceanogr., 40, 815829, doi:10.1175/2009JPO4091.1.

    • Search Google Scholar
    • Export Citation
  • Biastoch, A., C. W. Böning, J. Getzlaff, J.-M. Molines, and G. Madec, 2008: Causes of interannual–decadal variability in the meridional overturning circulation of the midlatitude North Atlantic Ocean. J. Climate, 21, 65996615, doi:10.1175/2008JCLI2404.1.

    • Search Google Scholar
    • Export Citation
  • Bleck, R., 2002: An oceanic general circulation model framed in hybrid isopycnic-Cartesian coordinates. Ocean Modell., 4, 5588, doi:10.1016/S1463-5003(01)00012-9.

    • Search Google Scholar
    • Export Citation
  • Böning, C. W., M. Scheinert, J. Dengg, A. Biastoch, and A. Funk, 2006: Decadal variability of subpolar gyre transport and its reverberation in the North Atlantic overturning. Geophys. Res. Lett., 33, L21S01, doi:10.1029/2006GL026906.

    • Search Google Scholar
    • Export Citation
  • Bower, A. S., M. S. Lozier, S. F. Gary, and C. W. Böning, 2009: Interior pathways of the North Atlantic meridional overturning circulation. Nature, 459, 243247, doi:10.1038/nature07979.

    • Search Google Scholar
    • Export Citation
  • Bower, A. S., M. S. Lozier, and S. F. Gary, 2011: Export of Labrador Sea Water from the subpolar North Atlantic: A Lagrangian perspective. Deep-Sea Res. II, 58, 17981818, doi:10.1016/j.dsr2.2010.10.060.

    • Search Google Scholar
    • Export Citation
  • Bryden, H. L., W. E. Johns, and P. M. Saunders, 2005: Deep western boundary current east of Abaco: Mean structure and transport. J. Mar. Res., 63, 3557, doi:10.1357/0022240053693806.

    • Search Google Scholar
    • Export Citation
  • Carnes, M. R., 2009: Description and evaluation of GDEM-V 3.0. Naval Research Laboratory Tech. Rep. NRL/MR/7330–09-9165, 21 pp. [Available online at http://www7320.nrlssc.navy.mil/pubs/2009/carnes-2009.pdf.]

  • Chassignet, E. P., L. T. Smith, G. R. Halliwell, and R. Bleck, 2003: North Atlantic simulations with the Hybrid Coordinate Ocean Model (HYCOM): Impact of the vertical coordinate choice, reference pressure, and thermobaricity. J. Phys. Oceanogr., 33, 25042526, doi:10.1175/1520-0485(2003)033<2504:NASWTH>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Clarke, R. A., H. W. Hill, R. F. Reiniger, and B. A. Warren, 1980: Current system south and east of the Grand Banks of Newfoundland. J. Phys. Oceanogr., 10, 2565, doi:10.1175/1520-0485(1980)010<0025:CSSAEO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Clarke, R. A., R. M. Hendry, and I. Yashayaev, 1998: A western boundary current meter array in the North Atlantic near 42°N. International WOCE Newsletter, No. 33, WOCE International Project Office, Southampton, United Kingdom, 33–34. [Available online at http://www.nodc.noaa.gov/woce/wdiu/wocedocs/newsltr/news33/news33.pdf.]

    • Search Google Scholar
    • Export Citation
  • Dickson, R. R., and J. Brown, 1994: The production of North Atlantic Deep Water: Source, rates, and pathways. J. Geophys. Res., 99, 12 31912 341, doi:10.1029/94JC00530.

    • Search Google Scholar
    • Export Citation
  • Dickson, R. R., I. Yashayaev, J. Meincke, B. Turrell, S. Dye, and J. Holfort, 2002: Rapid freshening of the deep North Atlantic over the past four decades. Nature, 416, 832837, doi:10.1038/416832a.

    • Search Google Scholar
    • Export Citation
  • Dickson, R. R., and Coauthors, 2008: The overflow flux west of Iceland: Variability, origins, and forcing. Arctic–Subarctic Ocean Fluxes: Defining the Role of the Northern Seas in Climate, R. R. Dickson, J. Meincke, and P. B. Rhines, Eds., Springer, 443–474, doi:10.1007/978-1-4020-6774-7_20.

  • Fischer, J., F. A. Schott, and M. Dengler, 2004: Boundary circulation at the exit of the Labrador Sea. J. Phys. Oceanogr., 34, 15481570, doi:10.1175/1520-0485(2004)034<1548:BCATEO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Fischer, J., M. Visbeck, R. Zantopp, and N. Nunes, 2010: Interannual to decadal variability of outflow from the Labrador Sea. Geophys. Res. Lett., 37, L24610, doi:10.1029/2010GL045321.

    • Search Google Scholar
    • Export Citation
  • Gary, S. F., M. Susan Lozier, C. W. Böning, and A. Biastoch, 2011: Deciphering the pathways for the deep limb of the meridional overturning circulation. Deep-Sea Res. II, 58, 17811797, doi:10.1016/j.dsr2.2010.10.059.

    • Search Google Scholar
    • Export Citation
  • Girton, J. B., and T. B. Sanford, 2003: Descent and modification of the overflow plume in the Denmark Strait. J. Phys. Oceanogr., 33, 13511363, doi:10.1175/1520-0485(2003)033<1351:DAMOTO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Hall, M. M., D. J. Torres, and I. Yashayaev, 2013: Absolute velocity along the AR7W section in the Labrador Sea. Deep-Sea Res. I, 72, 7287, doi:10.1016/j.dsr.2012.11.005.

    • Search Google Scholar
    • Export Citation
  • Holland, W. R., and P. B. Rhines, 1980: An example of eddy-induced ocean circulation. J. Phys. Oceanogr., 10, 10101031, doi:10.1175/1520-0485(1980)010<1010:AEOEIO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Jenkins, W. J., and P. B. Rhines, 1980: Tritium in the deep North Atlantic Ocean. Nature, 286, 877880, doi:10.1038/286877a0.

  • Jochumsen, K., D. Quadfasel, H. Valdimarsson, and S. Jónsson, 2012: Variability of the Denmark Strait overflow: Moored time series from 1996–2011. J. Geophys. Res., 117, C12003, doi:10.1029/2012JC008244.

    • Search Google Scholar
    • Export Citation
  • Johns, W. E., L. M. Beal, M. O. Baringer, J. R. Molina, S. A. Cunningham, T. Kanzow, and D. Rayner, 2008: Variability of shallow and deep western boundary currents off the Bahamas during 2004–05: Results from the 26°N RAPID–MOC array. J. Phys. Oceanogr., 38, 605623, doi:10.1175/2007JPO3791.1.

    • Search Google Scholar
    • Export Citation
  • Kanzow, T., and W. Zenk, 2014: Structure and transport of the Iceland Scotland Overflow plume along the Reykjanes Ridge in the Iceland basin. Deep-Sea Res. I, 86, 8293, doi:10.1016/j.dsr.2013.11.003.

    • Search Google Scholar
    • Export Citation
  • Klaucke, I., and R. Hesse, 1996: Fluvial features in the deep-sea: New insights from the glacigenic submarine drainage system of the Northwest Atlantic Mid-Ocean Channel in the Labrador Sea. Sediment. Geol., 106, 223234, doi:10.1016/S0037-0738(96)00008-5.

    • Search Google Scholar
    • Export Citation
  • Large, W. G., J. C. McWilliams, and S. C. Doney, 1994: Ocean vertical mixing: A review and a model with a nonlocal boundary layer parameterization. Rev. Geophys., 32, 363403, doi:10.1029/94RG01872.

    • Search Google Scholar
    • Export Citation
  • Lazier, J. R. N., 1994: Observations in the northwest corner of the North Atlantic Current. J. Phys. Oceanogr., 24, 14491463, doi:10.1175/1520-0485(1994)024<1449:OITNCO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Lazier, J. R. N., R. Hendry, A. Clarke, I. Yashayaev, and P. Rhines, 2002: Convection and restratification in the Labrador Sea, 1990–2000. Deep-Sea Res. I, 49, 18191835, doi:10.1016/S0967-0637(02)00064-X.

    • Search Google Scholar
    • Export Citation
  • LeBel, D. A., and Coauthors, 2008: The formation rate of North Atlantic Deep Water and Eighteen Degree Water calculated from CFC-11 inventories observed during WOCE. Deep-Sea Res. I, 55, 891910, doi:10.1016/j.dsr.2008.03.009.

    • Search Google Scholar
    • Export Citation
  • Lozier, M. S., S. F. Gary, and A. S. Bower, 2013: Simulated pathways of the overflow waters in the North Atlantic: Subpolar to subtropical export. Deep-Sea Res. II, 85, 147153, doi:10.1016/j.dsr2.2012.07.037.

    • Search Google Scholar
    • Export Citation
  • Mauritzen, C., 1996: Production of dense overflow waters feeding the North Atlantic across the Greenland-Scotland Ridge. Part 1: Evidence for a revised circulation scheme. Deep-Sea Res. I, 43, 769806, doi:10.1016/0967-0637(96)00037-4.

    • Search Google Scholar
    • Export Citation
  • Orre, S., J. N. Smith, V. Alfimov, and M. Bentsen, 2009: Simulating transport of 129I and idealized tracers in the North Atlantic Ocean. Environ. Fluid Mech., 10, 213233, doi:10.1007/s10652-009-9138-3.

    • Search Google Scholar
    • Export Citation
  • Pickart, R. S., and R. X. Huang, 1995: Structure of an inertial deep western boundary current. J. Mar. Res., 53, 739770, doi:10.1357/0022240953213007.

    • Search Google Scholar
    • Export Citation
  • Pickart, R. S., D. J. Torres, and R. A. Clarke, 2002: Hydrography of the Labrador Sea during active convection. J. Phys. Oceanogr., 32, 428457, doi:10.1175/1520-0485(2002)032<0428:HOTLSD>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Polzin, K. L., J. M. Toole, J. R. Ledwell, and R. W. Schmitt, 1997: Spatial variation of turbulent mixing in the abyssal ocean. Science, 276, 9396, doi:10.1126/science.276.5309.93.

    • Search Google Scholar
    • Export Citation
  • Price, J. F., and M. O. Baringer, 1994: Outflows and deep water production by marginal seas. Prog. Oceanogr., 33, 161200, doi:10.1016/0079-6611(94)90027-2.

    • Search Google Scholar
    • Export Citation
  • Rhein, M., and Coauthors, 2002: Labrador Sea Water: Pathways, CFC inventory, and formation rates. J. Phys. Oceanogr., 32, 648665, doi:10.1175/1520-0485(2002)032<0648:LSWPCI>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Rhein, M., D. Kieke, S. H. Kabus, A. Roessler, C. Mertens, R. Meissner, C. W. Böning, and I. Yashayaev, 2011: Deep water formation, the subpolar gyre, and the meridional overturning circulation in the subpolar North Atlantic. Deep-Sea Res. II, 58, 18191832, doi:10.1016/j.dsr2.2010.10.061.

    • Search Google Scholar
    • Export Citation
  • Rhines, P. B., and W. R. Holland, 1979: A theoretical discussion of eddy-driven mean flows. Dyn. Atmos. Oceans, 3, 289325, doi:10.1016/0377-0265(79)90015-0.

    • Search Google Scholar
    • Export Citation
  • Rio, M. H., S. Guinehut, and G. Larnicol, 2011: New CNES-CLS09 global mean dynamic topography computed from the combination of GRACE data, altimetry, and in situ measurements. J. Geophys. Res., 116, C07018, doi:10.1029/2010JC006505.

    • Search Google Scholar
    • Export Citation
  • Rosmond, T., J. Teixeira, M. Peng, T. Hogan, and R. Pauley, 2002: Navy Operational Global Atmospheric Prediction System (NOGAPS): Forcing for ocean models. Oceanography, 15, 99108, doi:10.5670/oceanog.2002.40.

    • Search Google Scholar
    • Export Citation
  • Ross, C. K., 1984: Temperature-salinity characteristics of the ‘overflow’ water in Denmark Strait during OVERFLOW ‘73’. Rapp. P. V. Reun. Cons. Int. Explor. Mer, 185, 111119.

    • Search Google Scholar
    • Export Citation
  • Rossby, T., 1996: The North Atlantic Current and surrounding waters: At the crossroads. Rev. Geophys., 34, 463481, doi:10.1029/96RG02214.

    • Search Google Scholar
    • Export Citation
  • Schott, F. A., L. Stramma, R. Zantopp, M. Dengler, J. Fischer, and M. Wibaux, 2004: Circulation and deep water export at the western exit of the subpolar North Atlantic. J. Phys. Oceanogr., 34, 817843, doi:10.1175/1520-0485(2004)034<0817:CADEAT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Schott, F. A., J. Fischer, M. Dengler, and R. Zantopp, 2006: Variability of the deep western boundary current east of the Grand Banks. Geophys. Res. Lett., 33, L21S07, doi:10.1029/2006GL026563.

    • Search Google Scholar
    • Export Citation
  • Smethie, W. M., Jr., and R. A. Fine, 2001: Rates of North Atlantic Deep Water formation calculated from chlorofluorocarbon inventories. Deep-Sea Res. I, 48, 189215, doi:10.1016/S0967-0637(00)00048-0.

    • Search Google Scholar
    • Export Citation
  • Smethie, W. M., Jr., R. A. Fine, A. Putzka, and E. P. Jones, 2000: Tracing the flow of North Atlantic Deep Water using chlorofluorocarbons. J. Geophys. Res., 105, 14 29714 323, doi:10.1029/1999JC900274.

    • Search Google Scholar
    • Export Citation
  • Smith, J. N., E. P. Jones, S. B. Moran, W. M. Smethie Jr., and W. E. Kieser, 2005: Iodine 129/CFC 11 transit times for Denmark Strait overflow water in the Labrador and Irminger Seas. J. Geophys. Res., 110, C05006, doi:10.1029/2004JC002516.

    • Search Google Scholar
    • Export Citation
  • Stommel, H., and A. B. Arons, 1972: On the abyssal circulation of the World Ocean—V. The influence of bottom slope on the broadening of inertial boundary currents. Deep-Sea Res. Oceanogr. Abstr., 19, 707718, doi:10.1016/0011-7471(72)90062-9.

    • Search Google Scholar
    • Export Citation
  • Toole, J. M., R. G. Curry, T. M. Joyce, M. McCartney, and B. Peña-Molino, 2011: Transport of the North Atlantic deep western boundary current about 39°N, 70°W: 2004–2008. Deep-Sea Res. II, 58, 17681780, doi:10.1016/j.dsr2.2010.10.058.

    • Search Google Scholar
    • Export Citation
  • Uppala, S. M., and Coauthors, 2005: The ERA-40 Re-Analysis. Quart. J. Roy. Meteor. Soc., 131, 29613012, doi:10.1256/qj.04.176.

  • Worthington, L. V., and W. R. Wright, 1970: North Atlantic Ocean Atlas of Potential Temperature and Salinity in the Deep Water including Temperature, Salinity and Oxygen Profiles from the Erika Dan Cruise of 1962. Vol. 2. Woods Hole Oceanographic Institution, 24 pp.

  • Xu, X., W. J. Schmitz Jr., H. E. Hurlburt, P. J. Hogan, and E. P. Chassignet, 2010: Transport of Nordic Seas overflow water into and within the Irminger Sea: An eddy-resolving simulation and observations. J. Geophys. Res., 115, C12048, doi:10.1029/2010JC006351.

    • Search Google Scholar
    • Export Citation
  • Xu, X., W. J. Schmitz Jr., H. E. Hurlburt, and P. J. Hogan, 2012: Mean Atlantic meridional overturning circulation across 26.5°N from eddy-resolving simulations compared to observations. J. Geophys. Res., 117, C03042, doi:10.1029/2011JC007586.

    • Search Google Scholar
    • Export Citation
  • Xu, X., H. E. Hurlburt, W. J. Schmitz Jr., R. J. Zantopp, J. Fischer, and P. J. Hogan, 2013: On the currents and transports connected with the Atlantic meridional overturning circulation in the subpolar North Atlantic. J. Geophys. Res. Oceans, 118, 502516, doi:10.1002/jgrc.20065.

    • Search Google Scholar
    • Export Citation
  • Xu, X., E. P. Chassignet, W. E. Johns, W. J. Schmitz Jr., and E. J. Metzger, 2014: Intraseasonal to interannual variability of the Atlantic meridional overturning circulation from eddy-resolving simulations and observations. J. Geophys. Res. Oceans, 119, 51405159, doi:10.1002/2014JC009994.

    • Search Google Scholar
    • Export Citation
  • Yashayaev, I., 2007: Hydrographic changes in the Labrador Sea, 1960–2005. Prog. Oceanogr., 73, 242276, doi:10.1016/j.pocean.2007.04.015.

    • Search Google Scholar
    • Export Citation
  • Yashayaev, I., and R. R. Dickson, 2008: Transformation and fate of overflow in the northern North Atlantic. Arctic-Subarctic Ocean Fluxes: Defining the Role of the Northern Seas in Climate, R. R. Dickson, J. Meincke, and P. B. Rhines, Eds., Springer, 505–526.

  • Yashayaev, I., M. Bersch, and H. M. van Aken, 2007: Spreading of the Labrador Sea Water to the Irminger and Iceland basins. Geophys. Res. Lett., 34, L10602, doi:10.1029/2006GL028999.

    • Search Google Scholar
    • Export Citation
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