Mixed sedimentation of the North Sea Fan - insights on volumes of contourites, plumites and downslope deposits during a full glacial- interglacial cycle

Trough mouth fans are important depocenters for glacial sedimentation in high latitude margins,recording sedimentological processes and their relationship with paleoclimatic fluctuations onshort timescales - from decades to millennia. The volume of sediments accumulated in these fansvaries significantly depending on the phase of the glacial cycle, with higher values typically reachedduring early retreats. The input of large volumes during short time intervals can potentially triggersubmarine landslides and overpressure build-up, making the understanding of processes andproportions related to sedimentation in glaciated margins crucial, especially during periods ofglobal warming. In this study we use high-quality 3D seismic cubes (vertical resolution of 2 m andbin size of 6.25 x 18.75 m) to delimitate different types of deposits on an area over 14000 km2 onthe North Sea Trough Mouth Fan during a full glacial-interglacial cycle of the last glaciation(Weichselian). After mapping the corresponding top and base surfaces of each type of deposittheir volumes were calculated using the mean thickness of the beds multiplied by their extent. Thebase of the studied package comprises a contourite body deposited on top of the Tampen Slide,whose failure is estimated to have happened around 130 ka ago. Next we have a thick (> 400 m)mixed package of debris flows and meltwater turbidites, with its rapid deposition happeningduring approximately 4 ka (~23 to 19 ka). The package is then completed with plume settlingrelated to the full retreat of the ice stream. Although not completely interpreted due to limitationsof the dataset extent and remobilization of a part of the fan by the Storegga Slide in the northernpart, the last glacial cycle comprises a total of 7160 km3 of sediments, with more than half of it(4850 km3) originated from the downslope processes. The plumites and contourites comprisevolumes of 1105 km3 and 1205 km3. This accounts to a significant variability of the magnitude ofsediment volume coming into the sink per year, with the downslope deposits having over 100times more sediment input and the plumites 5 times more when compared to thecontourites. These results highlight the range of sediment volume that can be delivered in aglaciated margin depending on changes in processes and climatic fluctuations, which may also entail changes in the potential geohazards.