The 14 day Celtic Explorer CE21003 cruise took place in March 2021 to collect high quality oceanographic data to contribute to the Atlantic Ocean Observing System. Physical Oceanography: During the CE21003 cruise, full water column CTD (Conductivity, Temperature, Depth) casts were carried out. The Seabird 911 CTD profiles obtained measurements from ~ 2 m subsurface to ~10 m above the seabed with a CTD Rosette sampling system (24 X 10 L Niskin bottles) in the deep water South Rockall Trough ocean climate section and an extended part. Chemical Oceanography: Samples at targeted discrete depths were also collected to measure 1. Dissolved Oxygen , 2. Dissolved Inorganic Carbon/Total Alkalinity (DIC/TA) to constrain and describe the carbonate system, 3. Dissolved Inorganic nutrient samples: phosphate, total oxidised nitrogen, nitrite, silicate 4. Salinity sample analyses was carried out samples or analysed post-cruise?? Other cruise data collections include vessel underway data - temperature, salinity (calculated), DO and relative fluorescence in real-time using the CE CTD, DO, fluorometer underway system). The partial pressure of carbon dioxide (pCO2) data in real-time using the CE Global Oceanics underway system. Water column current velocity data with a hull mounted Ship Acoustic Doppler Current Profiler (SADCP). 2 ARGO floats were also deployed in the North East Atlantic Ocean subject to contribute to the EuroARGO programme [1 X ARGO floats to measure temperature, salinity and currents (lagrangian), and the other to measure temperature, salinity, DO and currents (lagrangian)]. Light and bio-optical variable data were also recorded using Trios RAMSES hyperspectral radiometers (in-air). The Ocean Climate cruise facilitates long-term monitoring of the deep-water environment to the west of Ireland. Oceanographic data collected contributes to the Atlantic Ocean Observing System and survey results are included in Ireland’s national report submitted each year to the International Council for the Exploration of the Sea (ICES) Working Group on Oceanic Hydrography (WGOH). Each year, the survey data is submitted to the ICES Data Centre through the ICES Working Group on Oceanic Hydrography (WGOH). This working group produces an annual ICES Report on Ocean Climate (IROC), which summarises oceanic variability from year to year in the ICES region. Multidisciplinary information collected on the survey can support future reporting Marine Strategy Framework Directive (2008/56/EC), OSPAR Coordinated Environmental Monitoring Programme, Irish Climate Change assessments (e.g., Nolan et al. 2009) and national research efforts (e.g., MI funded A4 project) that focuses on temporal dynamics of environmental variables in offshore deep territorial waters.