Internal solitary waves induced deep-water nepheloid layers and seafloor geomorphic changes on the continental slope of the northern South China Sea

Internal solitary waves (ISWs) can cause strong seafloor sediment resuspension and induce nepheloid layers in both shallow and deep-water environments. However, the roles of ISWs in the >1000 m deep sea sediment resuspension and seafloor geomorphic changes are still unclear. To answer the above question, in the Dongsha area of the northern South China Sea, we measured suspended particulate matter along with a section covering the entire continental slope between 300 and 2000 m water depths, together with high-resolution multibeam bathymetric data for examining geomorphic changes. The results indicate that, on the upper slope with water depth<700 m, seafloor sediments were heavily disturbed and resuspended. We find that ISWs could suspend seabed sediments and shape a bedform at water depths less than or similar to 1000 m. The maximum water depth of sediment resuspension by ISWs measured is found as deep as 1500 m. The distribution pattern of the seafloor surface sediments on the east of the Dongsha continental slope (fine and silty sand in<700 m water depth, clayey silt between 700 and 1500 m, and silty clay > 1500 m) also indicates that they are mainly controlled and impacted by ISWs. The wave refraction theory could be applied to the upper slope, but sediment resuspension is related to the seabed topography on the lower slope. Our study shows that the suspension and transport of sediments induced by episodic ISWs on the Dongsha slope of the northern South China Sea could shape the bedform and affect the sedimentary seabed geomorphology. This research will help explain the impacts of the ISWs on the deep-water sediment resuspension and seafloor geopmorphic changes along with the continental slope in the margin sea. Published under license by AIP Publishing.

Automated summary

The study reveals that internal solitary waves (ISWs) in deep sea (>1000 m) can cause sediment resuspension and seafloor geomorphic changes, with a maximum resuspension depth of 1500 m. ISWs have a greater impact on water depths less than or similar to 1000 m, shaping the seabed and controlling sediment distribution patterns on the Dongsha continental slope.