In May 2018, an unprecedented long and intense seismic-volcanic crisis broke out off the island of Mayotte (Indian Ocean) and was associated with the birth of the Fani Maoré underwater volcano. Since then, an integrated observation network has been created (REVOSIMA), with the given objective of monitoring and better understanding underwater volcanic phenomena. Recently, an unmanned submarine glider (SeaExplorer) has been deployed to supplement the data obtained during oceanographic surveys (MAYOBS) which are carried out on an annual basis. This glider is operated by ALSEAMAR and performed a continuous monitoring of 30 months of the water column with the objective to acquire hydrological properties, water currents and dissolved gas concentrations. This monitoring already showed that it is feasible and valuable to measure autonomously, continuously and at a high spatio-temporal scale, physical (TEMP, SAL, water currents) and biogeochemical parameters (O2, CH4, PCO2, bubbles/droplets, vertical speeds) over several months from a SeaExplorer glider. In particular, innovating sensing capabilities (e.g., MINI-CO2, ADCP) have shown a great potential in the context of the Mayotte seismic volcano crisis, despite technical challenges (complex algorithms, sensor capabilities, etc.). This dataset provides these physical and biogeochemical parameters from September 17, 2021 to April 02, 2024 and the quality flags associated.    Important Note: This submission has been initially submitted to SEA scieNtific Open data Edition (SEANOE) publication service and received the recorded DOI. The metadata elements have been further processed (refined) in EMODnet Ingestion Service in order to conform with the Data Submission Service specifications.

The datasets contains selected data from the underwater glider missions in Eastern Mediterranean performed in April-May and in August 2023 by Institute of Marine Sciences, Middle East Technical University (METU-IMS). The glider was donated to METU-IMS by Is Bankasi - the national commercial bank in Turkey. The underwater glider SeaExplorer X2 of ALSEAMAR is equipped with the following instruments: 1) RBRlegato³ C.T.D (non-pumped flow) with temperature, conductivity and pressure sensors; 2) JFE Advantech Co. Rinko Fast Optical DO sensor; 3) Wet Labs ECO Puck (fluorescence and turbidity); 4) Sea-Bird Scientific Deep SUNA Ocean Nitrate Sensor; 5) Altimeter. The research area is between mainland and Cyprus bounded by a rectangle with coordinates 35.52°-36.1°N, 33.2°-33.5°E. The first mission with internal number 16 was carried out in period April, 26 – May, 16, 2023, the second mission with internal number 20 was carried out in period August, 2 – August, 27, 2023. The first and last transects from each mission are included in the dataset. The dataset is submitted as zip-archive containing 110 .gz files. Each .gz file contains instrument output acquired within one glider dive cycle.