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

Abstract

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 < 0·3 to > 1·0 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 800–1200 m. The main NSDW flow forms a relatively narrow core that follows the base of the Faroes slope. This core follows the 90° 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.

Recovery of deep-water megafaunal assemblages from hydrocarbon drilling disturbance in the Faroe−Shetland Channel

“…Removal of cuttings at Laggan probably took place over time by lateral advection during high current events (velocities up to 1 m s −1 ; Masson et al 2004) and from vertical redistribution in the sediments from bioturbation by abundant infaunal deposit feeders (Total E & P UK pers. comm.).…”

Benthic Habitats Around Iceland Investigated During the IceAGE Expeditions

“…For example, the Faroe−Shetland Channel (Fig. 13) is shaped by very strong persistent bottom currents, which have been reported to reach and also exceed current velocities of 1 ms −1 (Hansen and Østerhus 2000;Masson et al 2004). Deep cold water flowing from the Norwegian (2004) in the southern part of the Faroe−Shetland Channel and is also well re− flected by the different types of sediments identified in the larger region by our analyses (Fig.…”

The economic importance of contourites

“…The examples from the Faeroe-Shetland Channel and the Gulf of Cadiz channels (Habgood et al 2003;Masson et al 2004;Akhmetzhanov et al 2007) and Campos Basin upper slope terrace (Viana & Faug~res 1998;Viana et al 2002b) are good illustrations of such flow oscillations and their related erosionaldepositional features. The erosional pavements, gravel patches, furrows-grooves-striations, sand ribbons, sand dunes, current ripples and finegrained sediment waves are subsequently deposited with a decrease in the current intensity.…”

“…An order of increasing current velocity as proposed by Masson et al (2004) includes finegrained sediment waves and mounded contourite deposits, contourite sand sheets, coarse-grained sediment waves, barchan-like dunes, sand ribbons, channels, comet or obstacle marks, furrows and erosional scours.…”

“…Strong, semi-permanent bottom currents flowing at >30 ___ 10 cm s -1 are required for developing sand waves, such as the abyssal dunes of foraminiferal sands on the Carnegie Ridge (Lonsdale & Malfait 1974), and the siliciclastic sand dunes of the Campos Basin upper slope (Viana 1998), the lower Mississippi Fan (Kenyon et al 2002), the Gulf of Cadiz (Habgood et al 2003) and the Faeroe-Shetland Channel (Wynn et al 2002;Masson et al 2004;Akhmetzhanov et al 2007). Two main situations are considered as favourable to the supply of coarse-grained sediments and the action of contour current.…”