Journal of Oceanography

, Volume 67, Issue 3, pp 281–293 | Cite as

Evolution and decay of a warm-core ring within the western subarctic gyre of the North Pacific, as observed by profiling floats

  • Sachihiko Itoh
  • Yugo Shimizu
  • Shin-ichi Ito
  • Ichiro Yasuda
Original Article


This study investigated temporal variations in the vertical structure and water properties of a warm-core ring that migrated into the western subarctic gyre of the North Pacific, based on analyses of temperature and salinity data derived from two profiling floats, together with shipboard and satellite observation data. The floats were initially deployed into cold and fresh Oyashio water in September 2003, and were entrained into a warm-core ring in October 2003, remaining within the ring until detrainment in December 2004. Drastic cooling and freshening of the upper core water of the ring were observed during the above entrainment of the floats with cold and fresh water into the ring, whereas moderate variations in structure and water properties were observed during a quasi-isolated phase from November 2003 to November 2004 when the ring did not experience major interactions with ambient hydrographic features. The upper part of the core water (upper core), with relatively warm/saline water above 26.6 σ θ , was under the influence of the atmosphere in winter via the formation of a deep mixed layer exceeding 300 dB, and had a prominent pycnostad below the seasonal pycnocline from spring to autumn. In contrast, the lower core, with relatively cold and fresh water below 26.6 σ θ , was not ventilated throughout the observation period. Isopycnal surfaces showed a shoaling trend of about 50 dB/year during the quasi-isolated phase, suggesting viscous decay over a timescale of several years. Markedly cold and thick water was also frequently observed within the ring, indicating the intrusion of water from the Sea of Okhotsk.


Anticyclonic Eddy Kuroshio Extension Lower Core Isopycnal Surface Core Water 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



We would like to thank to the captain, officers, crew and scientists onboard the R/V Wakataka-maru for their efforts in deploying the floats and in undertaking hydrographic observations. This study was financially supported by the Japanese Ministry of Education, Culture, Sports, Science and Technology (KAKENHI, Grand-in-Aid for Young Scientists (B), 21740340; KAKENHI, Grant-in-Aid for Young Scientists (A), 19684016).


  1. Favorite F et al (1976) Oceanography of the Subarctic Pacific region, 1960–1971. Bull Int North Pac Fish Comm 33:1–187Google Scholar
  2. Flierl GR (1981) Particle motions in large-amplitude wave fields. Geophys Astro Fluid 18:39–74CrossRefGoogle Scholar
  3. Flierl GR, Mied RP (1985) Frictionally induced circulations and spin down of a warm-core ring. J Geophys Res 90:8917–8927CrossRefGoogle Scholar
  4. FRA (2003) A-line data homepage. Fisheries Research Agency of Japan. Accessed 28 June 2010
  5. Hata K (1974) Behavior of a warm eddy detached from the Kuroshio (in Japanese with English abstract). J Meteor Res 26:295–321Google Scholar
  6. Itoh S, Sugimoto T (2001) Numerical experiments on the movement of a warm-core ring with the bottom slope of a western boundary. J Geophys Res 106:26851–26862CrossRefGoogle Scholar
  7. Itoh S, Yasuda I (2010a) Characteristics of mesoscale eddies in the Kuroshio-Oyashio Extension region detected from the distribution of the sea surface height anomaly. J Phys Oceanogr 40:1018–1034CrossRefGoogle Scholar
  8. Itoh S, Yasuda I (2010b) Water mass structures of warm and cold anticyclonic eddies in the western boundary region of the subarctic North Pacific. J Phys Oceanogr 40:2624–2642CrossRefGoogle Scholar
  9. JMA (2004) Oceanographic and marine meteorological observations by research vessels. Japan Meteorological Agency, TokyoGoogle Scholar
  10. Katsumata K et al (2004) Water exchange and tidal currents through the Bussol’ Strait revealed by direct current measurements. J Geophys Res 109:1–11CrossRefGoogle Scholar
  11. Kawai H (1969) Statistical estimation of isotherms indicative of Kuroshio Axis. Deep-Sea Res 16:109–115Google Scholar
  12. Kawai Y et al (2006) Satellite-based high-resolution global optimum interpolation sea surface temperature data. J Geophys Res 111. doi: 10.1029/2005JC003313
  13. Masujima M, Yasuda I (2009) Distribution and Modification of North Pacific Intermediate Water around the Subarctic Frontal Zone East of 150 degrees E. J Phys Oceanogr 39:1462–1474CrossRefGoogle Scholar
  14. Masuzawa J (1969) Subtropical Mode Water. Deep-Sea Res 16:463–472Google Scholar
  15. Nof D, Dewar WK (1994) Alignment of lenses—laboratory and numerical experiments. Deep-Sea Res Pt I 41:1207–1229CrossRefGoogle Scholar
  16. Ohno Y et al (2004) The mixed layer depth in the North Pacific as detected by the Argo floats. Geophys Res Lett 31. doi: 10.1029/2004GL019576
  17. Oka E (2009) Seasonal and interannual variation of North Pacific Subtropical Mode Water in 2003–2006. J Oceanogr 65:151–164CrossRefGoogle Scholar
  18. Oka E, Suga T (2005) Differential formation and circulation of North Pacific Central Mode Water. J Phys Oceanogr 35:1997–2011CrossRefGoogle Scholar
  19. Oka E et al (2011) Formation and subduction of Central Mode Water based on profiling float data. J Phys Oceanogr 41:113–129CrossRefGoogle Scholar
  20. Polvani LM (1991) Two-layer geostrophic vortex dynamics. Part 2. Alignment and two-layer V-states. J Fluid Mech 225:241–270CrossRefGoogle Scholar
  21. Qiu B et al (2006) Observations of the subtropical mode water evolution from the Kuroshio Extension System Study. J Phys Oceanogr 36:457–473CrossRefGoogle Scholar
  22. Rio MH, Hernandez F (2004) A mean dynamic topography computed over the world ocean from altimetry, in situ measurements, and a geoid model. J Geophys Res 109. doi: 10.1029/2003JC002226, 2004
  23. Saito H et al (2007) New type of pycnostad in the western subtropical-subarctic transition region of the North Pacific: transition region mode water. J Oceanogr 63:589–600CrossRefGoogle Scholar
  24. Shimizu Y et al (2009) Transport of subarctic large copepods from the Oyashio area to the mixed water region by the coastal Oyashio intrusion. Fish Oceanogr 18:312–327CrossRefGoogle Scholar
  25. Tomosada A (1986) Generation and decay of Kuroshio Warm-Core Rings. Deep-Sea Res 33:1475–1486CrossRefGoogle Scholar
  26. Uchimoto K et al (2007) Anticyclonic eddy caused by the soya warm current in an Okhotsk OGCM. J Oceanogr 63:379–391CrossRefGoogle Scholar
  27. Yasuda I et al (1992) Evolution of a Kuroshio Warm-Core Ring—variability of the hydrographic structure. Deep-Sea Res 39:S131–S161Google Scholar
  28. Yasuda IY et al (2000) Cold-core anticyclonic eddies south of the Bussol’ Strait in the northwestern subarctic Pacific. J Phys Oceanogr 30:1137–1157CrossRefGoogle Scholar
  29. Yoshida T, Hoshimoto M (2006) Heat content change in the surface isothermal layer of a warm core ring in the sea east of Japan. J Oceanogr 62:283–287CrossRefGoogle Scholar

Copyright information

© The Oceanographic Society of Japan and Springer 2011

Authors and Affiliations

  • Sachihiko Itoh
    • 1
  • Yugo Shimizu
    • 2
  • Shin-ichi Ito
    • 2
  • Ichiro Yasuda
    • 1
  1. 1.Atmosphere and Ocean Research InstituteThe University of TokyoKashiwaJapan
  2. 2.Tohoku National Fisheries Research InstituteFisheries Research AgencyShiogamaJapan

Personalised recommendations