The Mayotte volcanological and seismological monitoring network (REVOSIMA) was created in response to the sub-marine eruption that started in May 2018. Composed by IPGP, BRGM, IFREMER and CNRS, its main missions are: - 1) to observe and study volcanic phenomena through real-time volcano monitoring, - 2) to conduct research programs, - 3) to communicate, disseminate and inform authorities and civil society. These real-time observations and research can contribute to the prevention, and mitigation of seismic and volcanic risks. The main objective is to collect geological, geophysical and geochemical data over long periods of time to improve the understanding and modeling of volcanic processes at active volcanoes, to allow the systematic elaboration of long-term multi-parameters databases available to the scientific community, and to inform the authorities in charge of civil protection of any change in the volcano activity and after periods of local and regionally felt earthquakes. The MAYOBS campaigns are carried out to monitor the evolution of the seismic and volcanic phenomenon which has affected the island of Mayotte since May 2018. They are carried out as part of an action program financed by the Ministry of Research, the General Directorate of prevention and risks of the Ministry of Ecological and Inclusive Transition, with the support of the interministerial delegate for major risks overseas and in conjunction with the other ministries and institutes involved (IPGP, IPGS, BRGM, IFREMER). They focus on the region east of Mayotte. The bathymetric surveys carried out by SHOM in the volcano area also contribute to the MAYOBS project. IFREMER carried out water column geochemistry measurements during MD220-MAYOBS cruise. In the present database, 5 stations were investigated between 15th and 17th May 2019 using in situ measurements embedded in a CTD-Rosette. Samples (max. 16 bottles per station) were anaylized onboard and onshore depending on the parameters. The quality controlled and process data are: - In situ: salinity (conductivity), temperature, depth, dissolved oxygen, turbidity - Onboard: pH, alkalinity, dissolved inorganic carbon - Onshore: dissolved CO2 CH4 H2, silicates