This dataset contains raw water temperature, conductivity (derived salinity) and pressure data from CTD instruments from a succession of deep water moorings deployed at a site (15.52 degrees West, 52.999 degrees North) in the South Rockall Trough close to the M6 met-ocean buoy. The sub-surface moorings consisted of an array of 10 Sea-Bird SBE 37 CTD sensors at a series of fixed depths below the surface (500m, 625m, 750m, 1000m, 1250m, 1500m, 1750m, 2000m, 2500m, 3000m). The CTD sensors were fully calibrated by Sea-Bird in Germany both pre and post deployment. Additional sensors on the mooring include ADCP sensors to measure ocean currents and direction. This datasets combines the measurements from a pilot sub-surface mooring was deployed in October 2018 and retrieved in May 2019 by the Marine Institute and second deployment was made in April 2020 into a broken time-series. At present there are no operational funds to maintain a continuous series of moorings at the South Rockall Trough location but when logistics and infrastructure are available future deployments may take place.