Journal of Oceanography

, Volume 60, Issue 2, pp 453–462 | Cite as

Formation Process of North Pacific Intermediate Water Revealed by Profiling Floats Set to Drift on 26.7 σθ Isopycnal Surface

  • Yugo Shimizu
  • Takanori Iwao
  • Ichiro Yasuda
  • Shin-Ichi Ito
  • Tomowo Watanabe
  • Kazuyuki Uehara
  • Nobuyuki Shikama
  • Toshiya Nakano

Abstract

Six newly developed floats, which were set to drift on the 26.7 σθ isopycnal surface and to profile temperature, salinity and pressure above 1000 dbar once a week, were deployed in the Oyashio and Kuroshio Extension (KE) in order to examine the circulation, formation site and time scale of newly formed North Pacific Intermediate Water (NPIW). The floats were deployed in February or May 2001, and the data from their deployments to December 2002 are analyzed here. Four of the six floats were deployed near the KE axis at around the first meander crest, and they moved eastward to 157°E–176°W at latitudes of 30°N–45°N. The other two floats deployed in the Oyashio water with low-potential vorticity near the south coast of Hokkaido moved southward to reach the KE front and then moved eastward to the same region as the first four floats. The temperature and salinity at 26.7 σθ measured by the profiling floats indicate that the source waters of NPIW, Oyashio and Kuroshio waters are drastically mixed and modified in the mixed water region west of 160°E. The floats were separated into the three paths east of 160°E between the Kuroshio Extension front and the north of Water-Mass front (nearly subarctic front). New NPIW is judged to be formed along these three paths since the vertical profiles of temperature and salinity are quite smooth, having a salinity minimum at about 26.7σθ along each path. Kuroshio-Oyashio isopycnal mixing ratios of the new NPIW are 7:3, 6:4 and 5:5 at 26.7σθ along the southern, middle and northern paths, respectively. Potential vorticity converges to about 14–15 × 10−11 m−1s−1 along these paths. The time scale of new NPIW formation is estimated to be 1–1.5 years from the merger of Oyashio and Kuroshio waters to the formation of the new NPIW.

North Pacific Intermediate Water Kuroshio Oyashio profiling float 

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Copyright information

© The Oceanographic Society of Japan 2004

Authors and Affiliations

  • Yugo Shimizu
    • 1
  • Takanori Iwao
    • 2
  • Ichiro Yasuda
    • 3
  • Shin-Ichi Ito
    • 1
  • Tomowo Watanabe
    • 4
  • Kazuyuki Uehara
    • 5
  • Nobuyuki Shikama
    • 6
  • Toshiya Nakano
    • 7
  1. 1.Tohoku National Fisheries Research InstituteMiyagiJapan
  2. 2.Hakodate Marine ObservatoryHokkaidoJapan
  3. 3.Department of Earth and Planetary Science, Graduate School of ScienceUniversity of TokyoTokyoJapan
  4. 4.National Research Institute of Fisheries ScienceKanagawaJapan
  5. 5.National Research Institute of Far Seas FisheriesShizuokaJapan
  6. 6.Frontier Observational Research System for Global ChangeKanagawaJapan
  7. 7.Meteorological Research InstituteIbarakiJapan

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