Internal wave-induced sediment wave formation on continental margins: Insights from the South China Sea

Accurately identifying the types and formation mechanisms of seafloor bedforms is crucial for understanding sediment transport and deposition on continental margins, and assessing seafloor stability for marine geohazard evaluation. This study, using high-resolution bathymetric, 2-D/3-D seismic and sediment core data, investigates sediment waves at the heads of the Shenhu Canyon System in the northern South China Sea. These sediment waves have wavelengths up to 1.4 km and heights reaching 50 m, exhibiting continuous internal reflections and an upslope migration trend. Sediment samples reveal that these waves are predominantly composed of silt (73.21%−88.45%). Our findings suggest that internal waves, particularly those at diurnal frequencies, are the primary driver for the formation of these sediment waves. In critical and near-critical areas, the interaction of internal waves with the seafloor induces strong energy dissipation, which enhances bottom mixing and facilitates sediment resuspension and transport, leading to the formation of sediment waves. The variation in sediment wave scale is linked to differences in internal wave conditions, energy, and slope morphology. In the northeastern canyon heads (C11−C19), near-critical/critical conditions of diurnal internal waves, higher initial internal wave energy, and longer slopes enhance sediment resuspension, forming larger sediment waves. Conversely, reflective conditions, lower wave energy, and shorter slopes in the central (C8−C10) and southwestern (C1−C7) canyon heads limit sediment resuspension and transport, resulting in smaller or no sediment waves. These results provide new insights into sediment wave formation adjacent to submarine canyon heads, highlighting the significant role of internal waves in shaping continental margin geomorphology.