OPERATIONAL CRUISE REPORT MOMARSAT 2023 WORKING ZONE - LUCKY STRIKE

The MoMARSAT cruises series (doi.org/10.18142/130) provides annual maintenance of the EMSO-Azores Observatory at the Lucky Strike hydrothermal field. This seafloor observatory has been operating since 2010 and aims to acquire time series >10 years of hydrothermal, tectonic and volcanic processes and vent ecosystems on an active hydrothermal vent field on the mid-Atlantic ridge. It is part of the European network EMSO ERIC (European Multidisciplinary Seafloor and water column Observatory - http://emso.eu/), supported in France by the EMSO-FR Research Infrastructure (MESR) which management is ensured by a collaboration Ifremer- CNRS.

The array includes an observatory infrastructure: two junction boxes (SEAMON) at the bottom which connect instruments (Fig. 1). This year, the surface buoy (BOREL2) ensuring the transfer of data, by satellite,to a server on land as well as communication with the connected instruments was removed as part of the approach towards an operational maintenance.In its current configuration (after MOMARSAT 2023 maintenance), the "connected" part of the observatory includes: a seismometer (OBS), a generic environmental measurement module (EGIM equipped with a CTD, hydrophone, oxygen sensor, turbidimeter, pressure gauge and ADCP), a biological observation module (TEMPO- with an HDTV camera and 2 projectors), an oxygen sensor, a turbiditysensor and four hydrophones (temporarily disconnected for repair). The device also includes autonomous instruments which store their data internally: 4 OBS, 2 pressure sensors, 29 autonomous temperature probes deployed within smokers and diffusion areas, 5 autonomous current meters arranged, 6 microbiological colonizers, and 9 biological colonizers. These "unconnected" elements extend the spatial coverage of monitoring during each maintenance.

The maintenance operations consisted in the replacement replacing of the BOREL-SEAMON infrastructure and connected instruments, their reconditioning on board, and their redeployment. This year the Borel buoy and the oceanographic mooring were not redeployed. In situ sampling of rocks, fluid, fauna, microorganisms and the acquisition of imaging transects on targeted sites allow multi-year monitoring of the system and supplement the infrastructure data. These measurements also make it possible to calibrate/validate the measurements carried out by the instrumental array. This year, bottom operations were carried out by the Victor6000 submersible.