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Hydrographic data from the 145°E, 165°E and other sections in May/June 1993 made by R/V Hakuho-Maru is used to examine North Pacific Subtropical Mode Water (NPSTMW) with respect to its spatial structure and related flow fields. Prominently thick NPSTMW is distributed in both the Kuroshio Extension and the recirculation regions and bounded on the south by the Subtropical Front. The NPSTMW cores are clearly defined by the vertical minima of potential vorticity and divided into three groups by means of apparent oxygen utilization (AOU). The cores with low AOU and with high AOU represent the new NPSTMW formed in the winter of 1993 and the old NPSTMW formed in the winter of 1992, respectively, according to the AOU climatology in the previous work. The cores of the other group have middle AOU values and thus possibly represent the new NPSTMW influenced by vigorous mixing. An anticyclonic eddy with a lateral scale of about 300 km centered around 28°N and 145°E is found. The eddy contains thick NPSTMW, at least, part of which is new. Time series of subsurface temperature and current velocities recorded by the surface mooring system deployed during the same cruise indicate that the eddy migrates westward along the recirculation pattern with trapping the thick NPSTMW. This might be an important mechanism of redistribution of NPSTMW in the recirculation region.
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