Transports and pathways of overflow water in the Rockall Trough

- Flow pathway deep overflow around northern and western boundary.
- Transport time Wyville Thomson Ridge to central trough <50 days.
- >15% Norwegian Sea Deep Water seen one quarter of time.
- Transport modified WTOW (>27.65 kg m−3) at 57.5°N −0.3±0.04 Sv.
- No trend in transport over past 40 years.

Water mass analysis reveals a persistent core of deep overflow water within the Rockall Trough which hugs the northern and western boundaries of the basin. Mean speeds within this overflow are 10-15 cm s−1 giving a transport time from the Wyville Thomson Ridge to the central basin of <50 days. Analysis of the 40-year Extended Ellett Line record shows proportions of Norwegian Sea Deep Water associated with the deep core exceed 15% around one quarter of the time. We present the first transport estimates for overflow water in the Rockall Trough. This flux is for overflow water modified by mixing with a density greater than 27.65 kg m−3. Mean values calculated both from a newly deployed mooring array (OSNAP project) and indirectly from the Extended Ellett Line time-series are −0.3±0.04 Sv. Although the flux is highly variable there is no long term trend. As some overflow appears to exit into the Iceland Basin via channels between the northern banks, we suggest that the volume transport will likely increase as the flow pathway is traced back around the boundary of the Rockall Trough towards the Wyville Thomson Ridge.