Wind-driven monthly variations in transport and the flow field in the Faroe–Shetland Channel

Abstract

The transport of water from the North Atlantic to the Nordic seas through the Faroe–Shetland Channel is analysed from a decade of conductivity, temperature and depth (CTD) and acoustic Doppler current profiler (ADCP) data. The long-term mean transport, integrated over the upper 500 m, is 3.5 } 0.1 Sv (1 Sv = 10 6 m 3 s ? 1 ), of which 2.1 Sv is barotropic flow and 1.4 Sv is baroclinic flow. Short-term variability leads to a standard deviation of ca. 2.2 Sv in 3-day averages of the ADCP-measured transport. The barotropic transport is located over the upper part of the slope region of the Shetland Shelf, but sometimes broadens over deeper water. There is a peak surface baroclinic transport above the foot of the slope, and a weak recirculation of Modified North Atlantic Water (MNAW), which enters from the north, on the Faroese side. In September, when isobars downwell on the eastern side, the strong transport (ca. 4 Sv) is barotropic and evenly distributed across the Shetland slope, and both recirculation of MNAW from the Faroe side and mesoscale activity are weak. In spring, the net transport is small (ca. 2.5 Sv), the MNAW recirculation is strong and mesoscale activity is relatively large. These seasonal variations appear to correlate with the local south-west wind stress, which may contribute to nearly half of the long-term transport in the channel.