Quantifying the overflow across the Wyville Thomson Ridge into the Rockall Trough

Abstract

The overflow of cold water across the Wyville Thomson Ridge transports part of the return flow of the North Atlantic Meridional Overturning Circulation into the Rockall Trough. It is captured in a narrow westward flowing gully (the Ellett gully) that constrains lateral spreading. The mean total transport (including entrained North Atlantic Water) from several current meter deployments located in the gully since 2003 was between 0.8 and 0.9 Sv, and that of undiluted 0 °C Faroe-Shetland Channel Bottom Water (FSCBW) >0.2 Sv. A significant part of the overflow appears to be channelled through a newly discovered canyon that leads southward down the southern flank of the Faroe Bank into the Ellett gully. There is a suggestion that the transport has a seasonal signal with larger flows in the summer. The total transport is significantly larger than is sometimes assumed, and the transport of FSCBW into the northeastern North Atlantic is about one-third that of Mediterranean Water into the sub-tropical North Atlantic. The overflow can be expected to have an impact on circulation in the Rockall Trough.