Physical Mechanisms of Sediment Trapping and Deposition on Spatially Confined Mud Depocenters in High-Energy Shelf Seas

Abstract

Mud depocenters in shelf seas serve as a key element in the source-to-sink system of sediment transport on the Earth surface. Despite their undoubtful importance, physical mechanisms for formation, sediment budgeting, and cycling of localized depocenters in high-energy environments remain largely unknown. This study aims to fill the knowledge gap by focusing on sediment dynamics related to a localized mud depocenter in the southern North Sea. By combining field observation with 3-dimensional numerical simulations, we analyzed hydrodynamics and sediment dynamics over a 3-year period. Our results indicate a persistent transport of fine-grained sediments toward the depocenter and subsequent trapping resulting in accumulation, with distinct seasonal and spatial variations in the net depositional rate. The interaction of wind-driven coastal circulation with two distinct frontal systems—a salinity front and a tidal mixing front—emerges as a key mechanism of sediment dynamics. While the salinity front remains persistently over the depocenter, promoting sediment deposition year-round, the tidal mixing front appears primarily in summer, limiting sediment deposition. Sediment flows from offshore and along the coast provide major supply to the depocenter, while contemporary riverine sediment outflows contribute only marginally. Southwesterly winds enhance erosion and northerly winds promote deposition in the depocenter. Additionally, short-term extreme events significantly contribute to annual net sedimentation. Our work highlights the critical importance of frontal systems and extreme events for mud depocenter development in high-energy shelf seas.