A 30-month data set of glider physico-chemical data off Mayotte Island near the Fani Maoré volcano

In May 2018, an unprecedented long and intense seismo-volcanic crisis broke out off the island of Mayotte (Indian Ocean) and was associated with the birth of an underwater volcano (Fani Maoré). Since then, an integrated observation network has been created (REVOSIMA), with the objective of monitoring and better understanding underwater volcanic phenomena. Recently, an autonomous ocean glider (ALSEAMAR's SeaExplorer) was deployed to supplement the data obtained during a series of oceanographic surveys (MAYOBS) carried out on an annual basis. Operated by ALSEAMAR in collaboration with IFREMER, the glider performed a continuous monitoring of the water column, from the sea surface to 1250 m water depth, over 30 months between September 2021 and April 2024 with the objective of acquiring hydrological properties, water currents and dissolved gas concentrations. This monitoring showed the feasibility and value of measuring autonomously, continuously and at a high spatio-temporal scale the physical (temperature, salinity, ocean current) and biogeochemical parameters (O2, CH4, CO2, bubbles/droplets, vertical speed anomalies related to droplets) over several months using a glider. In particular, innovating sensing capabilities (e.g. MINICO2, acoustic Doppler current profiler (ADCP)) have shown great potential in the context of the Mayotte seismo-volcanic crisis despite technical challenges (complex algorithms, sensor capabilities, etc.). Data described in this paper can be accessed at the SEANOE repository under DOI: https://doi.org/10.17882/99960 (Heumann et al., 2024).