Abstract The western marginal sea of the northwest Pacific has warmed rapidly in recent decades, yet the mechanisms of its recent reorganization remain unclear. Using 1990–2024 observations, we identify a winter sea-surface-temperature (SST) regime shift around 2015, supported by non-parametric change-point tests and the persistence of positive anomalies thereafter. Before 2015, SST variability reflected a balance between atmospheric forcing and East Korea Warm Current (EKWC) transport; afterward, oceanic processes EKWC intensification and a northward Kuroshio displacement—became dominant, concurrent with a meridional reorganization of the Aleutian Low. Despite stable chlorophyll-a, phytoplankton size structure shifted toward pico-dominance at the expense of nano-classes, consistent with enhanced stratification and altered nutrient pathways. These results show that teleconnection-driven boundary-current variability now governs both physical and biological states in this marginal sea, highlighting its role as a sentinel of basin-scale Pacific decadal variability and its relevance for inter-basin climate linkages and decadal prediction.
Jung et al. (Wed,) studied this question.