Observed weakening of the Kuroshio driven by the East Asian winter monsoon under ongoing climate warming

Abstract

Western boundary currents are generally thought to respond to global warming through basin-scale wind forcing and ocean stratification, yet the role of local winds remains unclear. Here, we investigate changes in the Kuroshio under ongoing climate warming using satellite altimetry and high-resolution reanalysis data. We find that the Kuroshio surface velocity weakened significantly in autumn–winter during 1993–2022, by 10 ± 4% of its climatological mean, whereas no coherent trend is detected in spring–summer. A trend in local wind stress opposing the mean Kuroshio flow—possibly linked to the response of the East Asian winter monsoon to a tropical La Niña–like trend—can account for more than half of the upper-layer Kuroshio weakening, primarily through nonlinear Ekman pumping. Remote wind forcing also weakens the Kuroshio but cannot explain the pronounced seasonal dependence of the trend. These results suggest that the Kuroshio responds to global warming through a local wind-driven process in addition to basin-scale gyre adjustment.