Journal of Oceanography

, Volume 70, Issue 3, pp 211–223 | Cite as

Regeneration of a warm anticyclonic ring by cold water masses within the western subarctic gyre of the North Pacific

  • Sachihiko Itoh
  • Ichiro Yasuda
  • Hiromichi Ueno
  • Toshio Suga
  • Shigeho Kakehi
Original Article

Abstract

Regeneration of a warm anticyclonic ring as a result of interaction with cold water masses was observed within the western subarctic gyre of the North Pacific. Satellite, profiling float, and shipboard observations revealed that a warm-core ring originated from the Kuroshio Extension, propagating northeastwards, entrained cold and fresh water masses from the coastal area of Hokkaido, which are typically recognized within the ring as water that is colder than 2.5 °C. The potential temperature and planetary contribution of potential vorticity of the cold water in the coastal area of Hokkaido were <2 °C and 15 × 10−11 m−1s−1, respectively, suggesting that it originated from the Sea of Okhotsk. After the intrusion, the warm core of the ring cooled, freshened, and contracted, while the outer and lower parts became occupied by the cold and fresh water; however, even after the cooling, the positive surface elevation and downward depression of the main pycnocline, typical of an anticyclonic ring, were still evident. The ring continued to propagate northeastwards, with the main part of its structure occupied by the cold water, but changed its direction of travel from northwest to west-southwest 8 months after the cold-water event, and was finally absorbed into another warm-core ring. It is suggested that these anticyclonic rings, which transported and mixed warm and cold water masses, play important roles in the cross-gyre exchange of subtropical and subarctic waters in the North Pacific.

Keywords

Anticyclonic ring Regeneration Warm core Cold core Kuroshio Sea of Okhotsk Cross-gyre exchange Profiling float 

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Copyright information

© The Oceanographic Society of Japan and Springer Japan 2014

Authors and Affiliations

  • Sachihiko Itoh
    • 1
  • Ichiro Yasuda
    • 1
  • Hiromichi Ueno
    • 2
  • Toshio Suga
    • 3
    • 4
  • Shigeho Kakehi
    • 5
  1. 1.Atmosphere and Ocean Research InstituteThe University of TokyoKashiwaJapan
  2. 2.Faculty of Fisheries ScienceHokkaido UniversitySapporoJapan
  3. 3.Department of Geophysics, Graduate School of ScienceTohoku UniversitySendaiJapan
  4. 4.Japan Agency for Marine-Earth Science and TechnologyYokosukaJapan
  5. 5.Tohoku National Fisheries Research Institute, Fisheries Research AgencyShiogamaJapan

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