Numerical investigation of deep water circulation in the Faroese Channels

The overflow of dense water from the Nordic Seas through the Faroese Channels is investigated numerically using the Massachusetts Institute of Technology General Circulation Model. The model is forced by the removal of a barrier that separates different water masses in the bottom layer of the Faroe–Shetland Channel at the north-eastern boundary. An analysis of the output reveals that during its adjustment in the rotating channel the propagating flow is unstable and forms cyclonic and anti-cyclonic eddies in the Faroese Channels. The life-time of the cyclonic eddy is about 10 days, but an anti-cyclonic eddy that is formed upstream of the sill crest of the Faroe Bank Channel has a longer life-time. However, after 50 days it eventually loses its structure below 400 m due to the decay of a counter-rotating current. In the upper 400 m layer this anti-cyclonic eddy remains persistent for longer. Observational evidence of the eddy is confirmed by the tracks of experimental drifters released in the area and by the temperature and salinity fields observed in the Faroese Channels.The pinching of isotherms along the Wyville Thomson Ridge results in the concentration of cold water on the southern side of the Faroese Channels that overflows into the Rockall Trough. The model results demonstrate that the main part of the cold water outflows through the Faroe Bank Channel, rather than across the Wyville Thompson Ridge, due to Earth rotation. The apparent similarity of modelled temperature, salinity and velocity sections to recent measurements in this area adds confidence to these results.

► Deep water circulation in the Faroese Channels is characterised by the formation of cyclonic and anti-cyclonic eddies,
► The eddies appear due to the joint effect of the Earth rotation and complicated bottom topography,
► Evidence of eddies is confirmed by in situ observations,
► The pinching of isotherms along the Wyville Thomson Ridge results in concentration of cold water on the southern side of the Faroese Channels,
► The accumulated cold water overflows into the Rockall Trough.