Interannual Variations of North Pacific Subtropical Mode Water in the 137°E Section

Examination of interannual variations of North Pacific subtropical mode water (STMW) in the 137°E repeat hydrographic section by Suga et al. is extended to seek a relation between changes in STMW renewal and the wintertime cooling. Time series of isopycnal potential vorticity (PV) and apparent oxygen utilization (AOU) demonstrate substantial interannual variations of STMW. It is suggested that the interannual variations are closely related to the changes both in the Kuroshio recirculation system and in the formation rate. For the non-large-meander period of the Kuroshio, during which renewed STMW is advected vigorously from east of the section, the monsoon index as an indicator of cooling in a given winter, and PV and AOU at an STMW isopycnal surface in the following summer show significant correlation, indicating a strong relation between the wintertime cooling and the STMW formation.