Submarine Trenches and Wave-Wave Interactions Enhance the Sediment Resuspension Induced by Internal Solitary Waves

Internal solitary waves (ISWs) are nonlinear fluctuations in nature that could cause significant interactions between seawater and the seabed. ISWs have been proven to be an adequate cause of sediment resuspension in shallow and deep-sea environments. In the South China Sea, ISWs have the largest amplitude globally and directly interact with the seabed near the Dongsha slope in the northern South China Sea. We analyzed the water profile and high-resolution multibeam bathymetric data near the Dongsha slope and revealed that submarine trenches have a significant impact on the sediment resuspension by ISWs. Moreover, ISWs in the zone of the wave-wave interaction enhanced sediment mixing and resuspension. The concentration of the suspended particulate matter inside submarine trenches was significantly higher than that outside them. The concentration of the suspended particulate matter near the bottoms of trenches could be double that outside them and formed a vast bottom nepheloid layer. Trenches could increase the concentration of the suspended particulate matter in the entire water column, and a water column with a high concentration of the suspended particulate matter was formed above the trench. ISWs in the wave-wave interaction zone near Dongsha could induce twice the concentration of the bottom nepheloid layer than those in other areas. The sediment resuspension caused by ISWs is a widespread occurrence all around the world. The findings of this study can offer new insights into the influence of submarine trench and wave-wave interaction on sediment resuspension and help in geohazard assessment.