Stokes Drift Drives the Intensification of Nearshore Submesoscale Fronts in the Northern South China Sea

Submesoscale processes in marginal seas are central to the ocean’s energy cascade, mixed-layer dynamics, and biogeochemical exchanges and are typically driven by complex mechanisms influenced by local background currents as well as external forcings such as winds, tides, and topography. Among these drivers, however, the role of surface gravity waves has received comparatively little attention. In this study, we investigate the influence of surface waves on nearshore submesoscale processes in the northern South China Sea using high-resolution nested simulations with the Coastal and Regional Ocean COmmunity model (CROCO). The model implements the Eulerian wave-averaged current equations based on the vortex-force formalism, accounting for wave-induced effects. Our results reveal that onshore Stokes drift induces an onshore transport of water masses, thereby raising the nearshore sea level and intensifying nearshore currents. The strengthened currents, in turn, enhance convergence- and strain-induced frontogenesis, leading to the intensification of nearshore submesoscale fronts. These findings elucidate a specific mechanistic link between wave-induced sea-level changes and submesoscale dynamics, contributing to a better understanding of the role of surface waves in shaping coastal circulation.