• Argo, 2014: Argo floats data and metadata from Global Data Assembly Centre (Argo GDAC)—Snapshot of Argo GDAC of December, 8th 2014. SEANOE, accessed 11 December 2014, doi:10.17882/42182.

  • Balmaseda, M. A., , Mogensen K. , , and Weaver A. T. , 2013: Evaluation of the ECMWF ocean reanalysis system ORAS4. Quart. J. Roy. Meteor. Soc., 139, 11321161, doi:10.1002/qj.2063.

    • Search Google Scholar
    • Export Citation
  • Bilmes, J. A., 1998: A gentle tutorial of the EM algorithm and its application to parameter estimation for Gaussian mixture and hidden Markov models. International Computer Science Institute Tech. Rep. TR-97-021, 126 pp.

  • Brambilla, E., , and Talley L. D. , 2008: Subpolar Mode Water in the northeastern Atlantic: 1. Averaged properties and mean circulation. J. Geophys. Res., 113, C04025, doi:10.1029/2006JC004062.

    • Search Google Scholar
    • Export Citation
  • Capotondi, A., , Alexander M. A. , , Bond N. A. , , Curchitser E. N. , , and Scott J. D. , 2012: Enhanced upper ocean stratification with climate change in the CMIP3 models. J. Geophys. Res., 117, C04031, doi:10.1029/2011JC007409.

    • Search Google Scholar
    • Export Citation
  • Carval, T., and et al. , 2012: Argo user’s manual. Version 2.4, Argo Reference ar-um-02-01, Ifremer Reference cor-do/dti-mut/02-084, 85 pp.

  • Cessi, P., 2007: Regimes of thermocline scaling: The interaction of wind stress and surface buoyancy. J. Phys. Oceanogr., 37, 20092021, doi:10.1175/JPO3103.1.

    • Search Google Scholar
    • Export Citation
  • Daniault, N., , Mazé J. , , and Arhan M. , 1994: Circulation and mixing of Mediterranean water west of the Iberian Peninsula. Deep-Sea Res. I, 41, 16851714, doi:10.1016/0967-0637(94)90068-X.

    • Search Google Scholar
    • Export Citation
  • De Boyer Montégut, C., , Madec G. , , Fischer A. S. , , Lazar A. , , and Iudicone D. , 2004: Mixed layer depth over the global ocean: An examination of profile data and a profile-based climatology. J. Geophys. Res., 109, C12003, doi:10.1029/2004JC002378.

    • Search Google Scholar
    • Export Citation
  • Donguy, J. R., 1987: Recent advances in the knowledge of the climatic variations in the tropical Pacific Ocean. Prog. Oceanogr., 19, 4985, doi:10.1016/0079-6611(87)90003-6.

    • Search Google Scholar
    • Export Citation
  • Feucher, C., , Maze G. , , and Mercier H. , 2016: 2000–2014 climatology of the North Atlantic permanent pycnocline properties. SEANOE, accessed 3 June 2016, doi:10.17882/42386.

  • Fiedler, P. C., 2010: Comparison of objective descriptions of the thermocline. Limnol. Oceanogr. Methods, 8, 313325, doi:10.4319/lom.2010.8.313.

    • Search Google Scholar
    • Export Citation
  • Fiedler, P. C., , Mendelssohn R. , , Palacios D. M. , , and Bograd S. J. , 2013: Pycnocline variations in the eastern tropical and North Pacific, 1958–2008. J. Climate, 26, 583599, doi:10.1175/JCLI-D-11-00728.1.

    • Search Google Scholar
    • Export Citation
  • Fofonoff, N. P., , and Millard R. C. Jr., 1983: Algorithms for computation of fundamental properties of seawater. UNESCO Technical Papers in Marine Science 44, 54 pp.

  • Forget, G., , Maze G. , , Buckley M. , , and Marshall J. , 2011: Estimated seasonal cycle of North Atlantic Eighteen Degree Water volume. J. Phys. Oceanogr., 41, 269286, doi:10.1175/2010JPO4257.1.

    • Search Google Scholar
    • Export Citation
  • Fučkar, N.-S., 2010: Adaptive scaling model of the main pycnocline and the associated overturning circulation. Ph.D. thesis, Princeton University, 251 pp.

  • García-Ibáñez, M. I., , Pardo P. C. , , Carracedo L. I. , , Mercier H. , , Lherminier P. , , Ríos A. F. , , and Pérez F. F. , 2015: Structure, transports and transformations of the water masses in the Atlantic Subpolar Gyre. Prog. Oceanogr., 135, 1836, doi:10.1016/j.pocean.2015.03.009.

    • Search Google Scholar
    • Export Citation
  • Gnanadesikan, A., 1999: A simple predictive model for the structure of the oceanic pycnocline. Science, 283, 20772079, doi:10.1126/science.283.5410.2077.

    • Search Google Scholar
    • Export Citation
  • Gnanadesikan, A., , de Boer A. M. , , and Mignone B. K. , 2007: A simple theory of the pycnocline and overturning revisited. Ocean Circulation: Mechanisms and Impacts—Past and Future Changes of Meridional Overturning, Geophys. Monogr., Vol. 173, Amer. Geophys. Union, 19–32, doi:10.1029/173GM04.

  • Hanawa, K., , and Talley L. D. , 2001: Mode waters. Ocean Circulation and Climate: Observing and Modelling the Global Ocean, G. Siedler, J. Church, and W. J. Gould, Eds., International Geophysics Series, Vol. 77, Academic Press, 373–386.

  • Hauser, T., , Demirov E. , , Zhu J. , , and Yashayaev I. , 2015: North Atlantic atmospheric and ocean inter-annual variability over the past fifty years—Dominant patterns and decadal shifts. Prog. Oceanogr., 132, 197219, doi:10.1016/j.pocean.2014.10.008.

    • Search Google Scholar
    • Export Citation
  • IPCC, 2013: Climate Change 2013: The Physical Science Basis. Cambridge University Press, 1535 pp., doi:10.1017/CBO9781107415324.

  • Iselin, C., 1939: The influence of vertical and lateral turbulence on the characteristics of the waters at mid-depths. Eos, Trans. Amer. Geophys. Union, 20, 414417, doi:10.1029/TR020i003p00414.

    • Search Google Scholar
    • Export Citation
  • Jackett, D. R., , and Mcdougall T. J. , 1995: Minimal adjustment of hydrographic profiles to achieve static stability. J. Atmos. Oceanic Technol., 12, 381389, doi:10.1175/1520-0426(1995)012<0381:MAOHPT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Kessler, W. S., 1990: Observations of long Rossby waves in the northern tropical Pacific. J. Geophys. Res., 95, 51835217, doi:10.1029/JC095iC04p05183.

    • Search Google Scholar
    • Export Citation
  • Kessler, W. S., , McPhaden M. J. , , and Weickmann K. M. , 1995: Forcing of intraseasonal Kelvin waves in the equatorial Pacific. J. Geophys. Res., 100, 10 61310 631, doi:10.1029/95JC00382.

    • Search Google Scholar
    • Export Citation
  • Klein, B., , and Siedler G. , 1989: On the origin of the Azores Current. J. Geophys. Res., 94, 61596168, doi:10.1029/JC094iC05p06159.

  • Levitus, S., and et al. , 2012: World ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010. Geophys. Res. Lett., 39, L10603, doi:10.1029/2012GL051106.

    • Search Google Scholar
    • Export Citation
  • Li, Y., , and Wang F. , 2013: Thermohaline intrusions in the thermocline of the western tropical Pacific Ocean. Acta Oceanol. Sin., 32, 4756, doi:10.1007/s13131-013-0331-3.

    • Search Google Scholar
    • Export Citation
  • Luyten, J. R., , Pedlovsky J. , , and Stommel H. , 1983: The ventilated thermocline. J. Phys. Oceanogr., 13, 292309, doi:10.1175/1520-0485(1983)013<0292:TVT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Mann, C. R., 1967: The termination of the Gulf Stream and the beginning of the North Atlantic Current. Deep-Sea Res. Oceanogr. Abstr., 14, 337359, doi:10.1016/0011-7471(67)90077-0.

    • Search Google Scholar
    • Export Citation
  • Matear, R. J., , and Hirst A. C. , 2003: Long-term changes in dissolved oxygen concentrations in the ocean caused by protracted global warming. Global Biogeochem. Cycles, 17, 1125, doi:10.1029/2002GB001997.

    • Search Google Scholar
    • Export Citation
  • Maze, G., , and Marshall J. , 2011: Diagnosing the observed seasonal cycle of Atlantic subtropical mode water using potential vorticity and its attendant theorems. J. Phys. Oceanogr., 41, 19861999, doi:10.1175/2011JPO4576.1.

    • Search Google Scholar
    • Export Citation
  • McPhaden, M. J., 1985: Fine-structure variability observed in CTD measurements from the central equatorial Pacific. J. Geophys. Res., 90, 11 72611 740, doi:10.1029/JC090iC06p11726.

    • Search Google Scholar
    • Export Citation
  • Mercier, H., and et al. , 2015: Variability of the meridional overturning circulation at the Greenland–Portugal OVIDE section from 1993 to 2010. Prog. Oceanogr., 132, 250261, doi:10.1016/j.pocean.2013.11.001.

    • Search Google Scholar
    • Export Citation
  • Paillet, J., , and Arhan M. , 1996: Shallow pycnoclines and mode water subduction in the eastern North Atlantic. J. Phys. Oceanogr., 26, 96114, doi:10.1175/1520-0485(1996)026<0096:SPAMWS>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Pedlosky, J., , and Young W. , 1983: Ventilation, potential-vorticity homogenization and the structure of the ocean circulation. J. Phys. Oceanogr., 13, 20202037, doi:10.1175/1520-0485(1983)013<2020:VPVHAT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Pérez, F. F., , Mercier H. , , Vázquez-Rodríguez M. , , Lherminier P. , , Velo A. , , Pardo P. C. , , Rosón G. , , and Ríos A. F. , 2013: Atlantic Ocean CO2 uptake reduced by weakening of the meridional overturning circulation. Nat. Geosci., 6, 146152, doi:10.1038/ngeo1680.

    • Search Google Scholar
    • Export Citation
  • Potter, R. A., , and Lozier M. S. , 2004: On the warming and salinification of the Mediterranean outflow waters in the North Atlantic. Geophys. Res. Lett., 31, L01202, doi:10.1029/2003GL018161.

    • Search Google Scholar
    • Export Citation
  • Radko, T., , and Marshall J. , 2004: Eddy-induced diapycnal fluxes and their role in the maintenance of the thermocline. J. Phys. Oceanogr., 34, 372383, doi:10.1175/1520-0485(2004)034<0372:EDFATR>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Reynolds, D., 2009: Gaussian mixture models. Encyclopedia of Biometrics, S. Z. Li and A. Jain, Eds., Springer, 659–663, doi:10.1007/978-0-387-73003-5_196.

  • Riser, S. C., and et al. , 2016: Fifteen years of ocean observations with the global Argo array. Nat. Climate Change, 6, 145153, doi:10.1038/nclimate2872.

    • Search Google Scholar
    • Export Citation
  • Salmon, R., 1990: The thermocline as an internal boundary layer. J. Mar. Res., 48, 437469, doi:10.1357/002224090784984650.

  • Samelson, R. M., , and Vallis G. K. , 1997: Large-scale circulation with small diapycnal diffusion: The two-thermocline limit. J. Mar. Res., 55, 223275, doi:10.1357/0022240973224382.

    • Search Google Scholar
    • Export Citation
  • Sarachik, E. S., , and Cane M. A. , 2010: The El Niño–Southern Oscillation Phenomenon. Cambridge University Press, 384 pp.

  • Schlitzer, R., 2000: Electronic atlas of WOCE hydrographic and tracer data now available. Eos, Trans. Amer. Geophys. Union, 81, 4545, doi:10.1029/00EO00028.

    • Search Google Scholar
    • Export Citation
  • Siedler, G., , Kuhl A. , , and Zenk W. , 1987: The Madeira Mode Water. J. Phys. Oceanogr., 17, 15611570, doi:10.1175/1520-0485(1987)017<1561:TMMW>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Sprintall, J., , and Cronin M. , 2001: Upper ocean vertical structure. Encyclopedia of Ocean Sciences, Academic Press, 3120–3128, doi:10.1006/rwos.2001.0149.

  • Talley, L. D., 1996: North Atlantic circulation and variability, reviewed for the CNLS conference. Physica D, 98, 625646, doi:10.1016/0167-2789(96)00123-6.

    • Search Google Scholar
    • Export Citation
  • Talley, L. D., , Pickard G. L. , , Emery W. J. , , and Swift J. H. , 2011: Atlantic Ocean. Descriptive Physical Oceanography: An Introduction, 6th ed. Academic Press, 245–301, doi:10.1016/B978-0-7506-4552-2.10009-5.

  • Vallis, G. K., 2006: Atmospheric and Oceanic Fluid Dynamics: Fundamentals and Large-Scale Circulation. Cambridge University Press, 769 pp.

  • Wang, B., , Wu R. , , and Lukas R. , 2000: Annual adjustment of the thermocline in the tropical Pacific Ocean. J. Climate, 13, 596616, doi:10.1175/1520-0442(2000)013<0596:AAOTTI>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Weaver, A., , and Courtier P. , 2001: Correlation modelling on the sphere using a generalized diffusion equation. Quart. J. Roy. Meteor. Soc., 127, 18151846, doi:10.1002/qj.49712757518.

    • Search Google Scholar
    • Export Citation
  • Worthington, L. V., 1959: The 18° water in the Sargasso Sea. Deep-Sea Res., 5, 297305, doi:10.1016/0146-6313(58)90026-1.

  • Yang, H., , and Wang F. , 2009: Revisiting the thermocline depth in the equatorial Pacific. J. Climate, 22, 38563863, doi:10.1175/2009JCLI2836.1.

    • Search Google Scholar
    • Export Citation
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Mean Structure of the North Atlantic Subtropical Permanent Pycnocline from In Situ Observations

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  • 1 Laboratoire d’Océanographie Physique et Spatiale, Ifremer, Plouzané, France
  • | 2 Laboratoire d’Océanographie Physique et Spatiale, CNRS, Plouzané, France
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Abstract

A new objective algorithm for the characterization of the permanent pycnocline (OAC-P) in subtropical gyres is proposed. OAC-P is based on a pragmatic analysis of vertical density gradient features to identify the permanent pycnocline: OAC-P identifies the permanent pycnocline as the stratified layer found below surface mode waters. OAC-P provides the permanent pycnocline depth, unequivocally associated with a local maximum in the stratification, and top and bottom thicknesses, associated with upward and downward decreases in stratification, respectively. OAC-P uses half Gaussian curves as asymmetric nonlinear analytical models of the stratification peak. It is the first time that an algorithm is proposed to characterize objectively the permanent pycnocline for a region where handling the stronger stratification peak of the seasonal pycnocline is complex. A guideline for how to implement the OAC-P is given, with application to the North Atlantic Ocean Argo data as an example. OAC-P provides a detailed description of the mean structure of the North Atlantic subtropical permanent pycnocline. OAC-P detects a permanent pycnocline throughout the subtropical gyre north of the North Equatorial Current. The large-scale description of the permanent pycnocline depth structure as a classic bowl shape is captured however with much more detail. New regional information is provided. In particular, (i) there is only one region—the southern recirculation gyre of the Gulf Stream extension—where the permanent pycnocline is along an isopycnal surface and (ii) vertical asymmetries clearly discriminate one region from another.

Publisher’s Note: This article was revised on 23 June 2016 to fix a typographical error in the corresponding author’s email address that was present when originally published.

Corresponding author address: Charlène Feucher, Laboratoire d’Océanographie Physique et Spatiale, Ifremer, CS 10070, 29280 Plouzané, France. E-mail: charlene.feucher@ifremer.fr

Abstract

A new objective algorithm for the characterization of the permanent pycnocline (OAC-P) in subtropical gyres is proposed. OAC-P is based on a pragmatic analysis of vertical density gradient features to identify the permanent pycnocline: OAC-P identifies the permanent pycnocline as the stratified layer found below surface mode waters. OAC-P provides the permanent pycnocline depth, unequivocally associated with a local maximum in the stratification, and top and bottom thicknesses, associated with upward and downward decreases in stratification, respectively. OAC-P uses half Gaussian curves as asymmetric nonlinear analytical models of the stratification peak. It is the first time that an algorithm is proposed to characterize objectively the permanent pycnocline for a region where handling the stronger stratification peak of the seasonal pycnocline is complex. A guideline for how to implement the OAC-P is given, with application to the North Atlantic Ocean Argo data as an example. OAC-P provides a detailed description of the mean structure of the North Atlantic subtropical permanent pycnocline. OAC-P detects a permanent pycnocline throughout the subtropical gyre north of the North Equatorial Current. The large-scale description of the permanent pycnocline depth structure as a classic bowl shape is captured however with much more detail. New regional information is provided. In particular, (i) there is only one region—the southern recirculation gyre of the Gulf Stream extension—where the permanent pycnocline is along an isopycnal surface and (ii) vertical asymmetries clearly discriminate one region from another.

Publisher’s Note: This article was revised on 23 June 2016 to fix a typographical error in the corresponding author’s email address that was present when originally published.

Corresponding author address: Charlène Feucher, Laboratoire d’Océanographie Physique et Spatiale, Ifremer, CS 10070, 29280 Plouzané, France. E-mail: charlene.feucher@ifremer.fr
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