Past and present sediment transport of the north-west european continental shelf

Abstract

Advances in both seabed imaging capabilities and numerical models of shelf sea dynamics means new approaches are required to study those seas which surround us. Shelf sediment transport pathways are still principally derived from bedform and sediment indicators. A wealth of newly acquired data requires novel tools for extracting meaning in order to better understand shelf sediment dynamics. A new objective and quantitative method for extracting bedform dimensions has been developed and tested against synthetic and real data. New bedform analysis results have produced the largest global bedform measurements collection and extended the analysis range by an order of magnitude. To explore sediment transport at both tidal bank (< 10 km) andmshelf (> 10 km) scales, a new well-calibrated unstructured grid model of the European shelf has been developed, and model results using uniform and observation-derived bed roughness compared. Temporal changes in shelf sediment transport over both the recent past (100 years) and during the Holocene marine transgression (last 8 ka BP)are further explored. Marine and aeolian bedforms are compared through a range of statistical analyses and are shown to share the same morphology. Variability in medium to large marine bedforms (Ashley, 1990) is greater, and due to sensitivity to relatively larger changes in flow; larger bedforms are found to be more stable. Deviations from the derived global relationships are shown, through the palaeomodelling, to be due to relict bedforms. Variable bed roughness derived from the bedform observations and grain size has produced hydrodynamic results at least as good as those obtained from uniform roughness. Modern sediment transport on the shelf is found to be more complex in areas where traditional analyses cannot capture the temporal variability. The flexible nature of the model has meant subset bank modelling has benefitted from the well calibrated shelf model, and results have highlighted the differences in sediment transport regimes on the shelf. Sediment transport evolution during the Holocene transgression is shown to have been episodic, with quiescent periods followed by rapid changes. The quantitative analysis and modelling performed here has shown it is possible to take advantage of newly acquired data: the bedform analysis has confirmed the relationship between aeolian and marine bedforms and provided a tool for use in numerical modelling. The unstructured grid shelf model flexibility has produced both individual bank transport as well as pathways across the entire shelf.

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ORCID for Justin K. Dix: orcid.org/0000-0003-2905-5403

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