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 dataset combines the measurements from the pilot EMSO ERIC sub-surface mooring deployment from October 2018 to May 2019 and April 2020 to June 2021 into a non-continuous time-series. Subsequent mooring retrieval/deployment activities have taken place on an annual basis in June 2021, April 2022 and May 2023 have provided continuous coverage. Combining the data from these mooring deployments builds long-term time series data to monitor ocean climate which is vital in understanding the likely impact of future ocean climate scenarios on key marine sectors as well as understanding possible impacts on North East Atlantic Ocean ecosystems. Water masses have recognisable properties of temperature, salinity, oxygen and nutrients, unless they are modified significantly by mixing with other water masses. Several different water mass types are found in the south Rockall Trough, such as Labrador Sea Water, which travels from the western Atlantic, Mediterranean Overflow Water and Subarctic Intermediate Water. Deployment of subsequent moorings and CTD sensors help provide a time series of data that can reveal information about seasonal variations in the water and ocean circulation as well as advancing our understanding of key environmental processes in the North Eastern Atlantic Ocean. These mooring deployments complement an annual Marine Institute oceanographic survey to the South Rockall Trough taking place since 2004. This site was recognised as an official EMSO Regional Facility from September 2023. Combining the data from these mooring deployments builds long-term time series data to monitor ocean climate which is vital in understanding the likely impact of future ocean climate scenarios on key marine sectors as well as understanding possible impacts on ecosystem in the North East Atlantic Ocean. Water masses have recognisable properties of temperature, salinity, oxygen and nutrients, unless they have been modified significantly by mixing with other water masses. Several different water masses are found in the south Rockall Trough, such as Labrador Sea Water, which travels from the western Atlantic, Mediterranean Overflow Water and SubArctic Intermediate Water.Deployment of the subsequent moorings and CTD sensors help provide a time series of data that can reveal information about seasonal variations in the water and ocean circulation as well as advancing our understanding of key environmental processes in the North Eastern Atlantic Ocean. These mooring deployments complement an annual Marine Institute oceanographic survey to the South Rockall Trough taking place since 2004.