Aggregation processes in the benthic boundary layer at the Celtic Sea continental margin

Small particle scavenging rates in the benthic boundary layer (BBL) are calculated for the interaction between measured large particles and single particles at five stations (204, 667, 1445, 2285, 3660 m) at the Celtic Sea continental margin. In summer particle scavenging of small particles ⩽10 μm at the study site takes place under typical flow conditions of u∗>0.2 cm s−1. Scavenging of 10 μm particles can take place only at high particle concentrations, which result from sediment erosion. It is expected that the BBL aggregates found in the Celtic Sea at the mid- and lower-slope areas originate in sediment resuspension events. During these times of enhanced flow conditions, aggregates are formed and compacted by shear, which accounts for the fact that they do not disaggregate when they enter the viscous sublayer. Total clearance of bottom nepheloid layers occurs only during times of transport of large aggregates >1000 μm after the arrival of phytodetrital aggregates on the sea floor with number concentrations >200 dm−3 and flow conditions with u∗>1 cm s−1.