Glider observation of an eastward moving anticyclonic eddy in the western North Pacific

Direct observation of an anticyclonic eddy off the south coast of Japan by an underwater glider (TWR Slocum G2 glider) was conducted in the spring of 2019. The glider is equipped with CTD, Rinko II (dissolved oxygen), and FLbbCD (Chl.a, backscattering, and CDOM) sensors. Satellite sea level observations show the eddy was accompanied by a cyclonic eddy to the north to form a dipole pair of eddies travelling eastward for a month or more. This is in contrast to almost all of the ordinal monopolar eddies in this area travelling westward at a speed close to the long baroclinic Rossby wave. The glider has approached the center of the eddy twice, while the eddy was moving eastward. It is clear from the glider data that the eddy contains thick oxygen-rich water masses at around 250m and 650m depths which correspond to the Subtropical Mode Water (STMW) and Central Mode Water (CMW) of the western North Pacific, respectively. The dense (26.3–26.4 kgm^-3) and oxygen-rich (saturation rate > 90%) feature of the observed CMW suggests it may be subducted through southward cross-frontal advection across the Kuroshio Extension front (Oka et al., 2009). The formation and migration of the anticyclonic eddy and/or the dipole pair of eddies may have significant effects on the formation and redistribution of these water masses in this area.