The origins of the Extended Ellett Line

The success of the Marine Laboratory, Aberdeen, in maintaining a long-time series of physical observations in the Faroe-Shetland Channel, led J.B. Tait (Aberdeen) and A.J. Lee (Lowestoft Fisheries Laboratory, now CEFAS Lowestoft Laboratory) to propose in 1960 that research was needed upstream of the Channel in the then poorly known deep water to the west of Scotland. In response, the UK Hydrographic Office arranged for the surveying ship HMS Dalrympie to be made available to representatives from both Aberdeen and Lowestoft. G.C. Baxter and J.H.A. Martin worked water bottle sections across the Rockall Trough from Main Head to Rockall on ten cruises between August 1963 and November 1965. The same section was subsequently repeated several times by R/V Ernest Holt - one of the Lowestoft Fishery Laboratory research vessels.

In the late 1960s, the Scottish Marine Biological Association (SMBA, now the Scottish Association for Marine Science (SAMS)) opened its new laboratory at Oban, on the west coast of Scotland, which had been the point of departure for several oceanographic cruises during the previous century. SMBA proposed a programme of work in the adjacent deep waters, and the new research ship RRS Challenger which was being built for the laboratory by the Natural Environment Research Council (NERC) was lengthened on the stocks so that she could be used to undertake these studies. Once Challenger was ready for service, a full programme of physical oceanography was initiated, and between May 1975 to January 1996, a section from the shelf-edge west of South Uist to Rockall, crossing the Anton Dohrn Seamount, was regularly profiled with a CTD. This section traverses the narrowest part of the Rockall Trough, so its 20 stations could usually be completed within 40 hours - an important consideration in an area traversed by depressions on a roughly 5-day cycle throughout most of the year. Since January 1996 the section extended to Iceland has been surveyed approximately annually.

The time coverage of the observations in the Rockall Trough can be extended using the 45 years of observations of surface temperature and salinity made mostly by UK Ocean Weather Ships on passage through the area. In addition, between the early 1960s and the 1990s the Weather Ships have made regular observations of the water column while on station to the south and west of the Rockall Plateau.

(This text has been extracted from the IACMST Information Document Number 9, 2001.)