Generation of high-energy flow events in a deep depositional area – The Norwegian Trench

In the Norwegian Trench, a deep region in the North Sea in front of the Norwegian coast, there are indications that resuspension events take place, but knowledge about the forcing of the deep currents is limited. Deep flows in this area are driven by diverse processes, showing influences of surface forcing, interactions with the North Atlantic across the continental shelf slope, and canyon dynamics. Here we present unique insights from a one-year time series of high-resolution, near-bed current velocities collected with two moored ADCPs in the Norwegian Trench. At a depth of 300 metres, the tidal contribution is highly variable because of the Spring-Neap tidal cycle and primarily visible in alongshore-directed velocities and pressure data. However, the largest velocities are not induced by periodic forcing, but are presumably generated by inflow of warmer Atlantic water (AW) into the trench and the canyons response to storm events. Both, AW inflow and storm events are detected during winter time. During storm events, current speeds can exceed 0.5 m/s. These velocities are high enough to lift the sediment up to at least 20 metres above the bed. Once resuspended, the sediment can stay over several days or even weeks in the water column and be transported by deep currents. These preliminary results indicate that the influence of storms on the near-bed flows in the Norwegian Trench is much larger than previously expected.