Differential Formation and Circulation of North Pacific Central Mode Water

Eitarou Oka Institute of Observational Research for Global Change, JAMSTEC, Yokosuka, Japan

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Toshio Suga Institute of Observational Research for Global Change, JAMSTEC, Yokosuka, and Department of Geophysics, Graduate School of Science, Tohoku University, Sendai, Japan

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Abstract

A repeat hydrographic section along 165°E was analyzed to verify a westward extension of the formation region of the North Pacific Ocean Central Mode Water (CMW) suggested by previous synoptic observations, and to investigate the relation between the formation region and thermohaline fronts. The CMW formation region extends at least as far west as 155°E, much farther than recognized in a previous study based on climatology. It is located in two interfrontal regions between the Kuroshio Extension front and the Kuroshio Bifurcation front (KBF), and between the KBF and the subarctic front, where two types of CMW—namely, the lighter variety with potential density of 25.8–26.2 kg m−3 and the denser one of 26.3–26.4 kg m−3—are formed. How this differential formation of CMW is reflected in its gyrewide distribution was examined using one-time sections of the World Ocean Circulation Experiment (WOCE) Hydrographic Program in the North Pacific. The main circulation paths of the two types of CMW diverge east of the date line; the lighter variety is located in the inner part of the eastern subtropical gyre, and the denser variety is located in the outer part. These results demonstrate that the frontal structure around the northern boundary of the subtropical gyre, particularly the existence of KBF, is essential in determining the properties and the gyrewide distribution of CMW.

Corresponding author address: Dr. Eitarou Oka, Institute of Observational Research for Global Change, JAMSTEC, 2-15 Natsushima-Cho, Yokosuka, Kanagawa 237-0061, Japan. Email: okae@jamstec.go.jp

Abstract

A repeat hydrographic section along 165°E was analyzed to verify a westward extension of the formation region of the North Pacific Ocean Central Mode Water (CMW) suggested by previous synoptic observations, and to investigate the relation between the formation region and thermohaline fronts. The CMW formation region extends at least as far west as 155°E, much farther than recognized in a previous study based on climatology. It is located in two interfrontal regions between the Kuroshio Extension front and the Kuroshio Bifurcation front (KBF), and between the KBF and the subarctic front, where two types of CMW—namely, the lighter variety with potential density of 25.8–26.2 kg m−3 and the denser one of 26.3–26.4 kg m−3—are formed. How this differential formation of CMW is reflected in its gyrewide distribution was examined using one-time sections of the World Ocean Circulation Experiment (WOCE) Hydrographic Program in the North Pacific. The main circulation paths of the two types of CMW diverge east of the date line; the lighter variety is located in the inner part of the eastern subtropical gyre, and the denser variety is located in the outer part. These results demonstrate that the frontal structure around the northern boundary of the subtropical gyre, particularly the existence of KBF, is essential in determining the properties and the gyrewide distribution of CMW.

Corresponding author address: Dr. Eitarou Oka, Institute of Observational Research for Global Change, JAMSTEC, 2-15 Natsushima-Cho, Yokosuka, Kanagawa 237-0061, Japan. Email: okae@jamstec.go.jp

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  • Akima, H., 1970: A new method of interpolation and smooth curve fitting based on local procedures. J. Assoc. Comput. Meth., 17 , 589603.

    • Search Google Scholar
    • Export Citation
  • Aoki, Y., T. Suga, and K. Hanawa, 2002: Subsurface subtropical fronts of the North Pacific as inherent boundaries in the ventilated thermocline. J. Phys. Oceanogr., 32 , 22992311.

    • Search Google Scholar
    • Export Citation
  • Argo Science Team, 2001: Argo: The global array of profiling floats. Observing the Oceans in the 21st Century, C. J. Koblinsky and N. R. Smith, Eds., GODAE Project Office, Bureau of Meteorology, 248–258.

    • Search Google Scholar
    • Export Citation
  • Hanawa, K., and J. Kamada, 2001: Variability of core layer temperature (CLT) of the North Pacific Subtropical Mode Water. Geophys. Res. Lett., 28 , 22292232.

    • Search Google Scholar
    • Export Citation
  • JMA, 1997: Data report of oceanographic observations. No. 87, CD-ROM.

  • JMA, 1998: Data report of oceanographic observations. No. 88, CD-ROM.

  • JMA, 1999: Data report of oceanographic observations. No. 89, CD-ROM.

  • JMA, 2001: Data report of oceanographic observations. No. 91, CD-ROM.

  • JMA, 2002: Data report of oceanographic and marine meteorological observations. No. 92, CD-ROM.

  • JMA, 2003: Data report of oceanographic and marine meteorological observations. No. 93, CD-ROM.

  • Kawabe, M., and K. Taira, 1998: Water masses and properties at 165°E in the western Pacific. J. Geophys. Res., 103 , 1294112958.

  • Kubokawa, A., and T. Inui, 1999: Subtropical countercurrent in an idealized ocean GCM. J. Phys. Oceanogr., 29 , 13031313.

  • Levine, E. R., and W. B. White, 1983: Bathymetric influences upon the character of North Pacific fronts, 1976–1980. J. Geophys. Res., 88 , 96179625.

    • Search Google Scholar
    • Export Citation
  • Masuzawa, J., 1969: Subtropical Mode Water. Deep-Sea Res., 16 , 463472.

  • Masuzawa, J., 1972: Water characteristics of the North Pacific central region. Kuroshio—Its Physical Aspects, H. Stommel and K. Yoshida, Eds., University of Tokyo Press, 95–127.

    • Search Google Scholar
    • Export Citation
  • Mecking, S., and M. J. Warner, 2001: On the subsurface CFC maxima in the subtropical North Pacific thermocline and their relation to mode waters and oxygen maxima. J. Geophys. Res., 106 , 2217922198.

    • Search Google Scholar
    • Export Citation
  • Mizuno, K., and W. B. White, 1983: Annual and interannual variability in the Kuroshio Current System. J. Phys. Oceanogr., 13 , 18471867.

    • Search Google Scholar
    • Export Citation
  • Nakamura, H., 1996: A pycnostad on the bottom of the ventilated portion in the central subtropical North Pacific: Its distribution and formation. J. Oceanogr., 52 , 171188.

    • Search Google Scholar
    • Export Citation
  • Nitani, H., 1972: Beginning of the Kuroshio. Kuroshio—Its Physical Aspects, H. Stommel and K. Yoshida, Eds., University of Tokyo Press, 129–163.

    • Search Google Scholar
    • Export Citation
  • Oka, E., and T. Suga, 2003: Formation region of North Pacific Subtropical Mode Water in the late winter of 2003. Geophys. Res. Lett., 30 .2205, doi:10.1029/2003GL018581.

    • Search Google Scholar
    • Export Citation
  • Roden, G. I., 1970: Aspects of the mid-Pacific transition zone. J. Geophys. Res., 75 , 10971109.

  • Roden, G. I., 1972: Temperature and salinity fronts at the boundaries of the subarctic-subtropical transition zone in the western Pacific. J. Geophys. Res., 77 , 71757187.

    • Search Google Scholar
    • Export Citation
  • Sainz-Trapaga, S., G. J. Goni, and T. Sugimoto, 2001: Identification of the Kuroshio Extension, its bifurcation and northern branch from altimetry and hydrographic data during October 1992–August 1999: Spatial and temporal variability. Geophys. Res. Lett., 28 , 17591762.

    • Search Google Scholar
    • Export Citation
  • Suga, T., and K. Hanawa, 1990: The mixed layer climatology in the northwestern part of the North Pacific subtropical gyre and the formation area of Subtropical Mode Water. J. Mar. Res., 48 , 543566.

    • Search Google Scholar
    • Export Citation
  • Suga, T., K. Hanawa, and Y. Toba, 1989: Subtropical Mode Water in the 137°E section. J. Phys. Oceanogr., 19 , 16051618.

  • Suga, T., Y. Takei, and K. Hanawa, 1997: Thermostad distribution in the North Pacific subtropical gyre: The Central Mode Water and the Subtropical Mode Water. J. Phys. Oceanogr., 27 , 140152.

    • Search Google Scholar
    • Export Citation
  • Suga, T., K. Motoki, Y. Aoki, and A. M. Macdonald, 2004: The North Pacific climatology of winter mixed layer and mode waters. J. Phys. Oceanogr., 34 , 322.

    • Search Google Scholar
    • Export Citation
  • Trenberth, K. E., and J. W. Hurrell, 1994: Decadal ocean-atmosphere variations in the Pacific. Climate Dyn., 9 , 303319.

  • Tsujino, H., and T. Yasuda, 2004: Formation and circulation of mode waters of the North Pacific in a high-resolution GCM. J. Phys. Oceanogr., 34 , 399415.

    • Search Google Scholar
    • Export Citation
  • Uchida, H., and S. Imawaki, 2003: Eulerian mean surface velocity field derived by combining drifter and satellite altimeter data. Geophys. Res. Lett., 30 .1229, doi:10.1029/2002GL016445.

    • Search Google Scholar
    • Export Citation
  • Uda, M., and K. Hasunuma, 1969: The eastward subtropical countercurrent in the western North Pacific Ocean. J. Oceanogr. Soc. Japan, 25 , 201210.

    • Search Google Scholar
    • Export Citation
  • Xie, S-P., T. Kunitani, A. Kubokawa, M. Nonaka, and S. Hosoda, 2000: Interdecadal thermocline variability in the North Pacific for 1958–97: A GCM simulation. J. Phys. Oceanogr., 30 , 27982813.

    • Search Google Scholar
    • Export Citation
  • Yuan, X., and L. D. Talley, 1996: The subarctic frontal zone in the North Pacific: Characteristics of frontal structure from climatological data and synoptic surveys. J. Geophys. Res., 101 , 1649116508.

    • Search Google Scholar
    • Export Citation
  • Zhang, H-M., and N. G. Hogg, 1992: Circulation and water mass balance in the Brazil Basin. J. Mar. Res., 50 , 385420.

  • Zhang, R-X., and K. Hanawa, 1993: Features of the water-mass front in the northwestern North Pacific. J. Geophys. Res., 98 , 967975.

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