New type of pycnostad in the western subtropical-subarctic transition region of the North Pacific: Transition Region Mode Water

Hiroko Saito, Toshio Suga, Kimio Hanawa, Tomowo Watanabe

Research output: Contribution to journalArticlepeer-review

30 Citations (Scopus)

Abstract

A new type of pycnostad has been identified in the western subtropical-subarctic transition region of the North Pacific, based on the intensive hydrographic survey carried out in July, 2002. The potential density, temperature and salinity of the pycnostad were found to be 26.5-26.7 σθ, 5°-7°C and 33.5-33.9 psu respectively. The pycnostad is denser, colder and fresher than those of the North Pacific Central Mode Water and different from those of other known mode waters in the North Pacific. The thickness of the pycnostad is comparable to that of other mode waters, spreading over an area of at least 650 × 500 km around 43°N and 160°E in the western transition region. Hence, we refer to the pycnostad as Transition Region Mode Water (TRMW). Oxygen data, geostrophic current speed and climatology of mixed layer depth in the winter suggest that the TRMW is formed regularly in the deep winter mixed layer near the region where it was observed. Analysis of surface heat flux also supports the idea and suggests that there is significant interannual variability in the property of the TRMW. The TRMW is consistently distributed between the Subarctic Boundary and the Subarctic Front. It is also characterized by a wide T-S range with similar density, which is the characteristic of such a transition region between subtropical and subarctic water masses, which forms a density-compensating temperature and salinity front. The frontal nature also tends to cause isopycnal intrusions within the pycnostad of the TRMW.

Original languageEnglish
Pages (from-to)589-600
Number of pages12
JournalJournal of Oceanography
Volume63
Issue number4
DOIs
Publication statusPublished - 2007 Dec 1

Keywords

  • Isopycnal intrusion
  • Kuroshio Bifurcation front
  • Mixed layer
  • Mode water
  • Pycnostad
  • Subarctic front
  • Transition region

ASJC Scopus subject areas

  • Oceanography

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