Subduction of North Pacific central mode water associated with subsurface mesoscale eddy

During a shipboard high-density hydrographic survey carried out in the western North Pacific in fall 2008, we observed an anticyclonic eddy with a thickness of 150 dbar and a diameter of 40 km near 500 dbar depth at 27.5°N, 145°E. This subsurface mesoscale eddy contains the North Pacific central mode water (CMW), which has anomalously low potential vorticity and high dissolved oxygen compared to the climatological CMW properties in the same region. Profiling float measurements detect similar CMW patches near and south of the Kuroshio Extension as well as southward CMW migratión within the CMW formation region north of the Kuroshio Extension. These observed facts suggest that CMW is subducted into the permanent pycnocline not only through large-scale eastward advection near the northern edge of the subtropical gyre but also through southward cross-frontal advection associated with the formation and migration of subsurface mesoscale eddies.