Warming structure of the Kuroshio in the East China Sea since 1970

Abstract The Kuroshio Current (KC) has witnessed rapid surface warming during the past half-century, impacting the marine ecosystems in surrounding regions. However, the vertical structure of the warming KC remains unclear. This study utilizes historical hydrographic observational data and ocean model experiments to investigate temperature changes of the KC in the East China Sea since 1970. The KC at the Pollution Nagasaki (PN) section has shown rapid warming in the upper 350 m and insignificant warming or cooling trends in the subsurface layer of 350–800 m. Our diagnosis suggests that the rapid upper-layer warming results from the downward displacement of isopycnal surfaces, whereas the subsurface cooling arises from lateral advection along isopycnal surfaces. In addition to surface heating, surface wind changes over the subtropical North Pacific-induced by the phase shift of the Pacific Decadal Oscillation (PDO)-also enhance the upper-layer warming of the KC by driving downwelling Rossby waves. The subsurface cooling reflects property changes of the North Pacific Intermediate Water (NPIW) which can be traced to buoyancy fluxes in the subpolar northwestern Pacific. By linking the regional changes observed in the ECS to basin-scale processes over the North Pacific, this work contributes to the understanding of the response of the KC to climate change.