Abstract The slope current in the northwest South China Sea (SCS) plays a vital role in regulating mass and nutrient exchange between the coastal region and the open ocean. Over the past three decades, this current has exhibited a significant increasing trend, indicating a much stronger marginal sea‐open ocean interaction. Using observational data, we show that the intensified anticyclonic warm eddy shedding from the Luzon Strait propagates along the continental slope, leading to a stronger slope current. During 1993–2022, a reduction in Subtropical Mode Water was accompanied by decreases in sea surface height (SSH) and Kuroshio transport in the Luzon Strait, as well as an enhanced looping pathway of the Kuroshio in the northern SCS. These conditions favor anticyclonic warm eddies (positive SSH anomaly) shedding from the northwestern Luzon Strait and propagating along the continental slope southwestward. At the same time, the accompanying cold eddies (negative SSH anomaly) propagate westward towards western SCS. The combined propagation of these dipole‐like eddies further strengthens the SSH gradient between the shelf and inner ocean in the SCS, thereby intensifying the slope current. Importantly, it is the increased mean strength of the anticyclonic eddies, rather than their number, that drives this long‐term current intensification. In contrast, neither local surface wind nor buoyancy forcing can account for the observed enhancement of the slope current, although wind forcing likely contributes to strengthening its southern segment. These findings highlight the crucial role of Kuroshio intrusion and eddy‐current interaction in regulating the long‐term variability of circulation in the SCS.
Wu et al. (2026) studied this question.