Effects of Eddies on the Formation and Subduction of North Pacific Subtropical Mode Water Based on Argo Observations

North Pacific subtropical mode water (NPSTMW) is formed in the winter deep mixed layer (ML), due to ocean-to-atmosphere interactions, south of the Kuroshio Extension (KE), one of the most energetic eddy activity regions. The large-scale effects of eddies on the formation and subduction of NPSTMW are investigated on updated Argo observations via kinematic and thermodynamic parameterization approaches. The climatological annual mean eddy-induced subduction of NPSTMW can reach 4.51 Sv, which accounts for nearly 56% of the total subduction. The local enhancement of the eddy-induced subduction rate can reach 90 m yr-1 in the high eddy kinetic energy (EKE) zone. Moreover, the spatial distributions of the large eddy-induced subduction are mostly generated in a zone of steep isopycnals near the KE front area via the parameterization. The diagnosis of the thermodynamic relationship indicates that the eddy-induced buoyancy flux broadens the area of ocean surface buoyancy loss and then fosters the formation of NPSTMW in winter. The eddy-induced buoyancy loss due to diapycnal mixing is likely to occur in the relatively steep isopycnals near the KE region, which accounts for 21.2% of the net NPSTMW formation. The contribution of eddy-induced subduction has the same order as that of lateral induction in each year. The eddy-induced subduction and lateral induction show similar interannual variations related to the KE variable state. North Pacific subtropical mode water (NPSTMW) is formed due to ocean-to-atmosphere heat release in the region south of the Kuroshio Extension (KE), where eddy activities are energetic. Hence NPSTMW is the memory of atmospheric conditions in winter and is key to understanding interannual-to-interdecadal climate variability. Meanwhile, eddies are also an important factor that affects the formation of NPSTMW. Eddies have made important contribution of approximately 56% to the NPSTMW that enters the ocean interior. Furthermore, eddies modulate the interannual variability of NPSTMW in the corresponding years due to the variable KE path. In a period of the stable (unstable) KE path, the NPSTMW volume was increased (decreased) and partially affected by the activities of eddies. Our results provide a potential quantitative assessment for the effects of the interannual variations in eddies on the formation of NPSTMW and are important for the biogeochemical processes in the Northwestern Pacific Ocean. The contributions of eddies to the total formation and subduction of NPSTMW are 21.2% and 56%, respectivelyThe eddy-induced buoyancy loss broadens the region of air-sea buoyancy loss near the KEEddy-induced subduction and lateral induction have similar interannual variations related to the KE variable state