The Mace Head buoy is located 2 km offshore from the Mace Head atmospheric research station in Connemara, County Galway and is one of the Sentinel sites. Initially installed in May 2018, sensors have been deployed for the measurement of Temperature, Salinity, Dissolved Oxygen, Nitrate, pH, and pCO2. In addition, an Airmar weather station was installed for measuring wind speed and direction, air temperature, and atmospheric pressure at this site. This work was initially facilitated by 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. Data telemetry: For the period 2018 to 2022 measurements were taken every 30 minutes and transmitted every 12 hours to the Marine Institute Headquarters in Rinville, Galway. Since 2023 measurements have been made every 10 minutes and transmitted every 2 hours to the Marine Institute. Disclaimer: These data are real-time (GMT) and raw - they have not yet been through the full quality checking procedures. There may be short term data gaps caused by maintenance, re-deployments, or technical difficulties.