Journal of Oceanography

, Volume 52, Issue 2, pp 171–188 | Cite as

A pycnostad on the bottom of the ventilated portion in the central subtropical North Pacific: Its distribution and formation

  • Hirohiko Nakamura


A water mass characterized by the pycnostad on the bottom of the ventilated portion in the central subtropical North Pacific is described through the comparison with the Subtropical Mode Wate (STMW). In this paper, this water mass is called the North Pacific Central Mode Water (CMW), because of its vertical homogeneity. The distribution of CMW is examined based on the climatological maps of annual mean potential vorticity. On the other hand, its formation area is examined based on the climatological winter temperature data set and the STD sections across the Kuroshio Extension in early spring of individual years. The main results are summarized as follows: 1) STMW is formed in the deep winter mixed layer south of the main path of the Kuroshio Extension (termed 12°C Front in this paper). On the other hand, CMW is formed in the deep winter mixed layer in the east-west band surrounded by a branch of the Kuroshio Extension (termed 9°C Front in this paper) and the boundary of two water masses representing the subtropical and subpolar gyres. 2) The winter mixed layer between the 12°C Front and the 9°C Front is shallower than that in the CMW and STMW formation areas. 3) These geographical features of the winter mixed layer depths near the subarcticsubtropical transition zone result in two pycnostads (STMW and CMW) in the main thermocline of the subtropical North Pacific through the advection caused by the subtropical gyre.


Potential Vorticity Mixed Layer Depth Pacific Central Subtropical Gyre Kuroshio Extension 
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  1. Hanawa, K. (1987): Interannual variations in the winter-time outcrop area of Subtropical Mode Water in the western North Pacific Ocean.Atmosphere-Ocean,25, 358–374.Google Scholar
  2. Hanawa, K. and I. Hoshino (1988): Temperature structure and mixed layer over the Izu Ridge.J. Mar. Res.,46, 683–700.Google Scholar
  3. Kawai, H. (1972): Hydrography of the Kuroshio Extension. p. 235–352.Kuroshio, It's Physical Aspects, ed. by H. Stommel and K. Yoshida, University of Tokyo Press.Google Scholar
  4. Keffer, T. (1985): The ventilation of the world's oceans: Maps of the potential vorticity field.J. Phys. Oceanogr.,15, 509–523.CrossRefGoogle Scholar
  5. Levitus, S. (1982): Climatological atlas of the world ocean. NOAA Prof. Paper 13, 173 pp.Google Scholar
  6. Luyten, J. R., J. Pedlosky and H. Stommel (1983): The ventilated thermocline.J. Phys. Oceanogr.,13, 282–309.CrossRefGoogle Scholar
  7. Marshall, J. C., A. J. G. Nurser and R. G. Williams (1993): Inferring the subduction rate and period over the North Atlantic.J. Phys. Oceanogr.,23, 1315–1329.CrossRefGoogle Scholar
  8. Masuzawa, J. (1969): Subtropical mode water.Deep-Sea Res.,16, 463–472.Google Scholar
  9. Masuzawa, J. (1972): Water characteristics of the North Pacific central region. p. 95–127.Kuroshio, It's Physical Aspects, ed. by H. Stommel and K. Yoshida, University of Tokyo Press.Google Scholar
  10. McCartney, M. S. (1982): The subtropical recirculation of Mode Waters.J. Mar. Res.,40 (suppl.), 427–464.Google Scholar
  11. McCartney, M. S. and L. D. Talley (1982): The subpolar mode water of the North Atlantic.J. Phys. Oceanogr.,12, 1169–1188.CrossRefGoogle Scholar
  12. McDowell, S., P. Rhines and T. Keffer (1982): North Atlantic potential vorticity and its relation to the general circulation.J. Phys. Oceanogr.,12, 1417–1436.CrossRefGoogle Scholar
  13. Mizuno, K. and W. B. White (1983): Annual and interannual variability in the Kuroshio current system.J. Phys. Oceanogr.,13, 1847–1867.CrossRefGoogle Scholar
  14. Rhines, P. B. and W. R. Young (1982): A theory of wind-driven circulation of the world ocean 1. Mid-ocean gyres.J. Mar. Res.,40, (suppl.), 559–596.Google Scholar
  15. Roden, G. I. (1970): Aspects of the mid-Pacific transition zone.J. Geophys. Res.,75, 1097–1109.Google Scholar
  16. Roden, G. I. (1972): Temperature and salinity fronts at the boundary of the subarctic-subtropical transition zone in the western Pacific.J. Geophys. Res.,77, 7175–7187.Google Scholar
  17. 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, 543–566.Google Scholar
  18. Suga, T. and K. Hanawa (1995a): The Subtropical mode water circulation in the North Pacific.J. Phys. Oceanogr.,25, 958–970.CrossRefGoogle Scholar
  19. Suga, T. and K. Hanawa (1995b): Interannual variations of North Pacific Subtropical Mode Water in the 137°E section.J. Phys. Oceanogr.,25, 1012–1017.CrossRefGoogle Scholar
  20. Suga, T., K. Hanawa and Y. Toba (1989): Subtropical Mode Water in the 137°E section.J. Phys. Oceanogr.,19, 1605–1618.CrossRefGoogle Scholar
  21. Suga, T., Y. Takei and K. Hanawa (1995): Thermostad distribution in the North Pacific subtropical gyre: The Subtropical Mode Water and the Central Mode Water.J. Phys. Oceanogr (to be submitted).Google Scholar
  22. Talley, L. D. (1988): Potential vorticity distribution in the North Pacific.J. Phys. Oceanogr.,18, 89–106.CrossRefGoogle Scholar
  23. Worthington, L. V. (1959): The 18° Water in the Sargasso Sea.Deep-Sea Res.,5, 297–305.CrossRefGoogle Scholar
  24. Yasuda, I., K. Okuda and M. Hirai (1992): Evolution of a Kuroshio warm-core ring—variability of the hydrographic structure.Deep-Sea Res.,39, (suppl.), 131–161.Google Scholar
  25. Yuan, X. and L. D. Talley (1992): Shallow salinity minima in the North Pacific.J. Phys. Oceanogr.,22, 1302–1316.CrossRefGoogle Scholar
  26. Zhang, R. C. and K. Hanawa (1993): Features of the Water-Mass Front in the northwestern North Pacific.J. Geophys. Res.,98, 967–975.Google Scholar

Copyright information

© Oceanographic Society of Japan 1996

Authors and Affiliations

  • Hirohiko Nakamura
    • 1
  1. 1.Division of Earth and Planetary Science, Graduate school of ScienceHokkaido UniversitySapporoJapan

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