The near-bottom turbulence induced resuspension of seabed material in deep sea

Abstract

Marine seabed material resuspension holds significant importance across various fields, from ocean engineering to environmental science. However, it has been seldom explored in deep-sea environments. In this study, we conducted an in-situ field observation using a lander at the toe of Shenhu Canyon (1405 m). A sediment resuspension event and down-slope current were simultaneously recorded. The suspended particulate concentration synchronously varied with current velocity. Despite the occurrence of resuspension, the velocity and near-bed shear stress were below their critical values. This phenomenon was attributed to the resuspension of loose aggregates, which required a low current velocity exceeding 0.1 m/s and small near-bed shear stress. Sweep was identified as the primary contributor to resuspension, followed by ejection, while the contributions of down-deceleration and up-acceleration were negligible. An intriguing observation was the bimodal characteristic of both near-bed shear stress and sweep. At the highest suspended particulate concentration, both parameters decreased to small values. Additionally, the amplitude of acoustic backscatter increased with distance from the seabed in the near-bed vertical profile. This can be explained by the slow settling of the resuspended loose aggregates, shedding light on the formation of giant bottom nepheloid layers in the South China Sea.