Water masses and properties at 165°E in the western Pacific

Full-depth conductivity-temperature-depth-oxygen profiler (CTDO2,) data at 165 degrees E in 5 degrees S-40 degrees N in summer 1991 (World Ocean Circulation Experiment (WOCE) Hydrographic Program P13C) and 27 degrees-48 degrees N in spring 1993 (P13J) are analyzed. Distributions of salinity and temperature are characterized by the fronts associated with ocean currents, such as the Kuroshio Extension front at 34 degrees-35 degrees N, the Kuroshio Bifurcation front at 38 degrees-40 degrees N, the subarctic front at 40 degrees-42 degrees N, other salinity fronts in the tropical waters, and some oxygen fronts. Dissolved oxygen increases upward sharply, called oxycline, just above the intermediate oxygen minimum layer. The processes of water-mass extension are clarified mainly from oxygen and potential vorticity (PV). The North Pacific Tropical Water (NPTW) forms at the sea surface in 18 degrees-31 degrees N from winter to summer, and the winter-formed NPTW of 23.0-25.0 sigma(theta), (where a, is potential density) extends to 12 degrees N by the subtropical ocean gyre, so that it occupies a layer of 23.0-25.0 sigma(theta), in 12 degrees-31 degrees N. The Subtropical Mode Water (STMW) forms at the surface in 29 degrees-34 degrees N in winter and extends to 25 degrees N by the ocean circulation; it occupies a layer around 25.4 sigma(theta), between the main and seasonal pycnoclines in 25 degrees-34 degrees N. The North Pacific Intermediate Water (NPIW) extends to 34 degrees-38 degrees N on 26.83 sigma(theta), by the Kuroshio Extension and its northern branch and extends to 27 degrees-33 degrees N on 26.77 sigma(theta), and to 15 degrees-22 degrees N on 26.61 sigma(theta), by westward currents; it occupies 15 degrees-38 degrees N in the intermediate subtropical gyre. The NPIW is located in the oxycline with similar PV to the STMW. The boundary of the subtropical and tropical gyres is concluded to be around 12 degrees N (14 degrees-16 degrees N) in a surface (intermediate) layer <25.0 sigma(theta), (>26.0 sigma(theta)). Bottom waters are also examined.