The Extended Ellett Line: Discoveries from 65 years of marine observations west of the UK

Shallow and deep branches of the Meridional Overturning Circulation pass through the Rockall Trough and Iceland Basin where measurements of salinity and temperature have been made for 65 years. There is a very small number of decadal-scale time series in the world ocean, so this long-term data collection represents an unusually rich resource for climate science. The early data sets of surface temperature and salinity collected by ocean weather ships provided a previously unseen picture of the annual cycle of these properties as well as multiyear variability. In 1975, regular, repeated sampling of the full-depth deep ocean began to reveal the variability of water masses and details of their circulation. Here, we describe the history of sampling in the region and the main scientific discoveries about ocean circulation and variability made using these data. Continuing sustained observing of temperature, salinity, nutrients, and carbon from ships will contribute to the international focus in the subpolar gyre over the next decade.