Sedimentary environment of the Faroe-Shetland and Faroe Bank Channels, north-east Atlantic, and the use of bedforms as indicators of bottom current velocity in the deep ocean

In the northeast Atlantic, much of the deep cold water flow between the Norwegian Sea and the main North Atlantic basin passes through the Faroe-Shetland and Faroe Bank Channels, generating strong persistent bottom currents capable of eroding and transporting sediment up to and including gravel. A large variety of sedimentary bedforms, including scours, furrows, comet marks, barchan dunes, sand sheets and sediment drifts, is documented using sidescan sonar images, seismic profiles, seabed photographs and sediment cores from the floor of the channel. Published information on current velocities associated with the various bedforms has been used to reconstruct the pattern of bottom currents acting on the channel floor. The results broadly reflect the current pattern predicted on the basis of regional oceanographic observations, but add considerable detail. The internal consistency of the results suggests that the methods used are robust, giving confidence in the fine detail of the observed bottom current structure. Bottom current velocities in the range 0\textperiodcentered3 to 1\textperiodcentered0 m s-1 are indicated by the range of observed bedforms, with the strongest currents associated with south-west transport of Norwegian Sea Deep Water (NSDW) at water depths of 800\textendash1200 m. The main NSDW flow forms a relatively narrow core that follows the base of the Faroes slope. This core follows the 90\textdegree change in trend of the Faroes slope at the junction between the Faroe-Shetland and Faroe Bank Channels. The strongest currents within the NSDW core are found over the shallowest sill in the Faroe-Shetland Channel and in the narrowest part of the channel immediately downstream of the sill, and are generated by topographic constriction of the flow. Eastward flow of deep water along the northern flank of the Wyville-Thomson ridge suggests a complex current pattern with some recirculation of deep water within the deep Faroe Bank Channel basin. The observations suggest that Coriolis force is the main agent controlling the westward deflection of the NSDW into the Faroe Bank Channel, contradicting a previous suggestion that this was controlled by the topography of the Wyville Thomson Ridge.