Mass fluxes of particulate matter were studied in two large seawater flumes under three different flow conditions of 4.1, 6.3 and 11.1 cm s-1 free-stream velocities (42,65 and 125% of critical shear velocity). These experiments were carried out with original and sieved (control) sediments from a 200-m depth station, mainly inhabited by the surface deposit feeders Spiophanes krøyeri and Abra nitida. We simulated a situation with and one without phytodetritus suspended in the water column and studied the feeding behaviour of the two surface deposit feeders Spiophanes krøyeri and Sipunculus sp. Depositional fluxes of particulate organic carbon and chlorophyll equivalents were highest during periods of mid-flow conditions (6.3 cm s-1) when surface deposit feeders switched to suspension feeding. The observed sedimentation of 4 to 39 mg POC m-2 d-1 was in the same order of magnitude as reported for lateral depositional fluxes at the Barents Sea continental margin. Total suspended matter was reduced during subcritical flow conditions (4.1 and 6.3 cm S-1) when no phytodetritus was suspended in the water. Bioresuspension of total particulate matter occurred during chlorophyll transport. Even under supercritical flow conditions with sediment erosion (11.1 cm s-1, 125% of critical shear velocity) as reported for mid-slope areas, the reduction of phytodetritus and POC from the benthic boundary layer was 50% and 60% higher in original sediments with macrofauna than in control sediments of similar bottom roughness without macrofauna.
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