Spatiotemporal sediment dynamics within the Belgica Mound Drift during the last deglaciation, offshore Ireland

The Belgica Mound Drift, located in the Porcupine Seabight offshore west Ireland, is a small (~30 km²) contourite drift situated between the Irish Shelf to the east and cold-water coral mounds to the west. These contourite deposits are shaped by the dynamic interaction of the Mediterranean Outflow Water and the complex seabed topography. Despite significant advances in marine research, identifying and characterising contourites within the sedimentary record remains poorly understood. The relatively small size of the Belgica Mound Drift presents a unique opportunity to examine spatial and temporal sedimentological variability within a contourite drift. During the 2023-13 RV Belgica campaign, new sediment 3 m long cores were collected from the crest and the flanks of the drift, estimated to cover the last deglaciation. The cores were used for sedimentological and compositional analysis. The results of the medical CT scans and line-scan imaging, reveal that the cores from both locations exhibit similar sedimentary characteristics. Sedimentological analyses, including grain size, and magnetic susceptibility measurements (MS), coupled with compositional analysis via Itrax XRF scanning, suggest that the cores can be subdivided into two primary units. The top layer of unimodal fine sand has a mean grain size of 185 µm and relatively low MS values. The bottom part of the cores consists of bimodal sandy silt to silt with a mean grain size of 15 µm and relatively high MS. Additionally, the lower unit is heavily bioturbated, obscuring many primary sedimentary structures. The two distinct sedimentary layers indicate a clear change in depositional settings and the current regime of the Mediterranean Outflow Water in the Porcupine Seabight during the last deglaciation.