Sediment erosion thresholds and characteristics of resuspended aggregates on the western European continental margin

Sediment erosion thresholds and characteristics of resuspended aggregates were experimentally determined on cores from the western European continental margin with a ship-borne erosion chamber augmented by image analysis. Bottom sediments (212–4940 m water depth) had a thin surface layer that was resuspended as aggregates (median diameter 125–2403 μm) under critical shear velocities (u∗c) of 0.4–1.2 cm s−1. For the underlying sediments, eroded as primary particles, u∗c increased with water depth from 0.7 cm s−1 (sandy shelf sediments) to 2.1 cm s−1 (lower slope sediments). A two-layer concept of the sediment interface is discussed which distinguishes between an underlying sediment layer, bound by both physico-chemical and biological adhesion, and a more easily resuspendable surface aggregate layer. The surface layer consists mainly of aggregates in the 140–450 μm size range and is resuspended at mean thresholds u∗c of 0.8–0.9 cm s−1. These aggregates can subsequently be transported in tide-related resuspension–deposition loops over long distances.