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

Abstract

AbstractNorth 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.