Vertical structure of currents in the vicinity of the Iceland-Scotland Ridge

An analysis of current profiles carried out on moored Acoustic Doppler Current Profiler data sets recorded during the Variability of Exchanges In the Northern Seas project is presented here for several locations in three sections in the vicinity of the Iceland-Scotland Ridge: (1) north of the Faroes, (2) in the Faroe-Bank Channel and (3) in the Faroe-Shetland Channel. Total currents have been decomposed into three components, namely the mean residual flow, tide and surge. The mean residual flow is found to be dominant. Results for the major tidal constituents (M-2, S-2, N-2, O-1 and K-I) are shown and discussed. It is found that the predominant tidal harmonic M-2 becomes steered through depth to align with the bottom topography. The mean residual flow is found to be generally larger than the surge, particularly in the Faroe-Bank Channel below 500 m depth where it is the dominant component. Here tidal rectification, i.e. the topographic rectification of tidal currents originating in nonlinearities that rectify the oscillatory tidal motion, is identified as the process enhancing the large mean residual currents found. From the current structure, two water masses are identified in the channel: the upper slowing moving inflow water and the colder outflow water characterised by a 3-6-day periodicity. In the Faroe-Shetland Channel the flow is characterised by large tidal currents, particularly in shallow waters. Instead, north of the Faroes none of the component was identified as dominant. The results show that the variability of the current components is strongly dependent upon topography and water depth.