The Mace Head buoy is a Sentinel Site located 2 km offshore from the Mace Head atmospheric research station in Connemara, County Galway. This dataset contains visually quality controlled data from the Sea-Bird SBE37 sensor deployed on the mooring to measure temperature, salinity and dissolved oxygen in the surface waters at the buoy's location. It also The mooring was initially installed in May 2018 under the INTERREG funded project COMPASS – Collaborative Oceanography and Monitoring for Protected Areas and Species. Since 2022 the Mace Head buoy has been funded through the EMFAF Sentinels Site project. Time-series resolution: For the period 2018 to 2022 measurements were taken every 30 minutes. Since 2023 measurements have been made every 10 minutes. There may be short term data gaps caused by maintenance, re-deployments, or technical difficulties. Sensor deployments usually last 6 months and data are uploaded and reviewed shortly after each sensor recovery. For details of the real-time data feed from the Mace Head Buoy, see the separate Data Catalogue record (https://data.marine.ie/geonetwork/srv/eng/catalog.search#/metadata/ie.marine.data:dataset.4268).