Norwegian Sea overflow through the Faroe–Shetland gateway as documented by its bedforms

Abstract

We have used seabed information from three deep-tow side-scan sonar surveys in order to trace the high-energy current core of Norwegian Sea Overflow Water (NSOW) from the Faroe–Shetland Channel (FSC) through the Faroe Bank Channel (FBC) towards the southern flank of the Iceland–Faroe Ridge. A hierarchy of bedform types was used for estimating maximum mean near-bottom current speed, which has been compared with results from current meter measurements. We conclude that in the FSC maximum mean NSOW near-bottom flow speed at some sites may occasionally approach or even exceed 1.0 m/s. Both seabed data and oceanographic information indicate that the current core is concentrated along the Faroes slope at the 500–600-m depth stratum. With a change of the large-scale channel topography towards the southern extremity of the Faroe Plateau, where the FSC turns west towards the FBC, the slope current core gradually descends towards basin depth. Along the Wyville–Thomson Ridge (1100–1200 m water depth) maximum mean NSOW near-bottom current speed decreases slightly towards the west as the high-speed current core runs upslope the ridge. At the entrance to the narrow channel between Faroe Bank and the Faroe Plateau funnelling results in a renewed current acceleration at basin depth. Seabed evidence shows that further west in the FBC the NSOW high-speed current core is detached from the channel floor over larger areas. From the FBC outlet most of the overflow waters continue as a high-energy contour current concentrated along the southern flank of the Iceland–Faroe Ridge between 600 and 1000 m water depth.