The Role of Long-Term Hydrodynamic Evolution in the Accumulation and Preservation of Organic Carbon-Rich Shelf Sea Deposits

Understanding and mapping seabed sediment distribution in shelf seas is essential for effective coastal management, offshore developments, and for blue carbon stock assessments and conservation. Fine-grained marine sediments, particularly muds, play a key role in long-term organic carbon sequestration, so knowledge of the spatial extent of these carbon-rich deposits is important. Here, we consider how changes in shelf sea tidal dynamics since the Last Glacial Maximum have influenced the development of three mud depocenters in the northwest European shelf seas: the Fladen Ground, the Celtic Deep, and the Western Irish Sea Mud Belt. Using a new high-resolution paleotidal model, we demonstrate how the evolution of simulated tidal parameters, including bed shear stress and bottom boundary layer thickness, differ across these sites. Geological data support our findings, indicating that long-term mud sedimentation continues to the present in the Celtic Deep and Western Irish Sea Mud Belt, while in the Fladen Ground, accumulation cannot be fully explained by contemporary hydrodynamics. In the latter, mud deposition is relict, deposited during quiescent tidal conditions between 17,000 and 5,000 years ago. We suggest that simulating paleoceanographic conditions can contribute to understanding first-order sediment dynamics over large spatial and temporal scales, a key input for predictive mapping and regional blue carbon inventories. This approach is a valuable first step in data-poor regions to identify potential fine sediment deposits. By illustrating the temporal evolution of organic carbon-rich deposits, we provide a broader context for managing organic carbon storage in shelf sea sedimentary environments.