UK oceanographers have been making repeated measurements on a short section across a deep ocean basin, the Rockall Trough, since 1975 (red line on the map). The section consists of a series of stations from the Scottish continental shelf to a tiny rocky outcrop called Rockall. The time series was established by David Ellett and was thus called the "Ellett Line". The Ellett line is one of a relatively small number of high quality physical time series in the North Atlantic Ocean and is very important for investigating oceanic climate variability. It is particularly relevant to the UK and north-west Europe because the warm water flowing through the Rockall Trough moderates the climate of the region, keeping winters warmer than expected for this latitude.
Since 1996 NOC and SAMS have been occupying an extended version of the Ellett Line that runs all the way to Iceland (red and green line on the map). The Extended Ellett line is important oceanographically because it completes the measurements of the warm salty water flowing into the Nordic Seas from the eastern North Atlantic. It also measures around half of the returning deep and cold current, the overflow water (the rest returns to the Atlantic via the Denmark Strait which is west of Iceland).