Development, migration and evolution of submarine sandwaves in the Dongsha Atoll of the South China Sea under the influence of internal waves

Submarine sandwaves are common undulating sandy landforms in estuaries, bays, continental shelf, and continental slope regions. Due to the fact that their morphological development characteristics can reflect the regional hydrodynamic environment, they have attracted extensive attention from scholars. Under the action of marine hydrodynamic forces, submarine sandwaves could migrate, which is likely to cause hazards such as the suspension and burial of submarine pipelines, the silting of nearshore channels, and the overturning of offshore oil and gas platforms. Therefore, the study on submarine sandwaves is of great theoretical significance and engineering value. Based on the field observation work carried out in the sandwave area in the northeast of the Dongsha Atoll in the South China Sea in 2020 and 2022, the morphological development characteristics, migration and evolution processes, and dynamic sources of the sandwaves in this area were analyzed. Results indicate that the observed sandwaves developed at 700～830 m water depth with wave length of 140～400 m and wave height of 1.4～16.5 m, could be classified as giant sandwaves. By the calculation with the Shields parameter, we found that both the distribution direction of the crest lines and the migration direction of the sandwaves in the study area were mainly influenced by the regional internal tide. Under the influence of the internal tide, the crest lines of the sandwaves were distributed along the NNE-SSW direction and migrate towards the NWW direction at speed of 10 m/a. These findings enriched our understanding of the development characteristics of deep-sea sandwaves in the Dongsha Atoll of the South China Sea, provided a new perspective on the influence of internal waves on the migration and evolution of deep-sea sandwaves, and contributed to more systematic research on deep-sea sandwaves.