Using the Regional Ocean Modeling System (ROMS) and the Lagrangian particle tracking model TRACMASS, we conducted a numerical simulation of the cross-shelf connectivity of surface waters over the northern South China Sea (NSCS) shelf. A systematic analysis was carried out on the connectivity characteristics between coastal, shelf, and open sea surface waters from 2007 to 2016.The results present the seasonal and interannual distribution characteristics of the surface connectivity, revealing that the distribution and variation of surface connectivity in most regions are modulated by local winds, but in certain areas, other processes dominate. Seasonally, the connectivity between coastal and shelf waters (across the 30-meter isobath) exhibits significant seasonal differences, closely related to the monsoon wind direction.The connectivity between the shelf and the open sea (across the 100-meter isobath) is predominantly onshore during winter and offshore during summer for most refions, except in the widened shelf areas, where other ageostrophic processes, instead of surface Ekman transport, seem to be more important.In the widened shelf areas, the main mechanisms of cross-100-meter isobath connectivity also differ between winter and summer. During winter, abundant submesoscale processes lead to stronger offshore connectivity, while during summer, the along-isobath jet near the 100-meter isobath acts as a barrier, hindering strong connectivity across the isobath. Additionally, we statistically identified the main pathways of connectivity between different regions during winter and summer. In some regions, connectivity shows strong interannual variability, mostly associated with interannual changes in wind patterns; however, the interannual variability of cross-30-meter isobath connectivity south of the Pearl River Estuary (PRE) is attributed to changes in coastal currents.

NSCS,Cross-shelf connectivity,Numerical model,Lagrangian,Transport,ROMS