The MoMARSAT cruise series ensures the annual maintenance of the EMSO-Azores observatory on the Lucky Strike vent field. This seabed observatory has been operating since 2010 and aims to acquire long time-series data (>10 years) on hydrothermal, tectonic, volcanic processes and the associated ecosystems of an active hydrothermal field located on the Mid-Atlantic Ridge. EMSO-Azores is part of the European network EMSO ERIC (European Multidisciplinary Seafloor and water column Observatory), supported in France by the Research Infrastructure (MESR) EMSO-FR whose management is ensured by a collaboration Ifremer-CNRS.

The array includes an observatory infrastructure that comprises a surface buoy (BOREL) ensuring the transfer of data by satellite to a server on land. Two junction boxes (SEAMON) deployed on the bottom communicate acoustically with BOREL and through a cable to the connected instruments. In its current configuration (after MOMARSAT 2022 maintenance), the "connected" part of the observatory includes a surface weather station, a seismometer (OBS), a bottom pressure gauge, a biological observation module (TEMPO- with an HDTV camera and 2 projectors), an oxygen sensor and a turbidity sensor, a fluid sampler (DEAFS), an EMSO generic instrumentation module (EGIM) and four hydrophones (HYDROCTOPUS).

The infrastructure also includes autonomous instruments that store their data internally: 4 OBSs, 2 pressure sensors placed on the bottom, 28 autonomous temperature probes deployed within smokers and on diffusion zones, 6 autonomous current meters placed on the bottom, 6 microbiological colonisers, 8 biological colonizers, 3 autonomous cameras (POMMEs); and an oceanographic mooring. These "unconnected" elements contribute to extend the spatial coverage of the area studied during each maintenance cruise.

Maintenance operations include the replacement of the BOREL-SEAMON infrastructure and the connected instruments, their reconditioning on board and their redeployment. In situ sampling of rocks, fluids, fauna, microorganisms and the acquisition of imaging transects on targeted sites allow the multi-year monitoring of the system and complete the infrastructure data. These measurements are also used to calibrate/validate the measurements made by the instrumental fleet. This year, bottom operations was carried out by the manned submersible Nautile. In order to optimize ship time, a physical oceanography program to study the hydrodynamic circulation on this part of the ridge was implemented during nights (project MicroRiYo@Sea 3D).

The coordination of maintenance operations and the initial data exploitation are handled by Mathilde Cannat (EMSO France manager) and Pierre Marie Sarradin (EMSO-Azores Regional team leader). The management of on-board operations is coordinated this year by Marjolaine Matabos, Pierre-Marie Sarradin and Laurent Gautier. The data acquired during the Momarsat cruises are available on the portal EMSO-Azores. The study area is part of Portugal's EEZ and is also a ¿Marine Protected Area¿ (OSPAR).

Associated projects

The MoMARSAT cruise and EMSO-Azores observatory are therefore part of the following projects:

• EMSO ERIC (European Multidisciplinary Seafloor and water column Observatory, www.emso-eu.org/, DG J. Danobeitia)
• UE H2020 iAtlantic (Integrated assessment of the Atlantic Marine Ecosystems in space and time, http://www.iatlantic.eu/, coordinator M. Roberts University of Edinburgh, grant agreement No 818123). The MoMARSAT cruises contribute to WP1, WP2, WP3 and WP4 of the project. Repeated visits at Lucky Strike support the acquisition of underwater imagery data and environmental measurements used for the spatio-temporal mapping of habitats and biological communities at the scale of the edifice and vent field (WP2, WP3).  The collection of organisms will allow the implementation of on-board and onshore experiments to determine the impact of deoxygenation on the behaviour of mussel juveniles (WP4). The data acquired by the observatory will contribute to the calibration of high resolution hydrodynamic models.
• MicroRiYo@Sea 3D  : The specific acquisition program dedicated to the study of the water column combining CTD moorings and the operation of a VMP (Vertical microprofiler) to describe the microturbulence of the water column was carried on. This programme was enriched with the deployments of the new 3D turbulence observation platform MicroRiYo@Sea 3D.
• Abyssbox: Pressurised aquarium presenting crabs and shrimps collected from the Lucky Strike hydrothermal field to the general public. PI D. Barthélémy (Océanopolis). Segonzacia mesatlantica crabs and Mirocaris fortunata shrimps will be collected, kept alive and transferred to Brest at Océanopolis for the general public exhibition "Abyssbox" started in 2012 in collaboration with Paris Sorbonne University (UPMC) and Ifremer.
• TACOS (ISBlue project, PI S. Fuchs): The biological samples will also be used for the TACOS project (Test d'efficacité de Conditionnement, d'extractiOn d'ADN et deSéquençage en direct ou différés), the objective of which is to carry out the complete molecular biology analysis (DNA extraction to sequencing) of samples directly on board using a new-generation miniature sequencer, the MinION (Oxford Nanopore Technol)
• TENSE: The TENSE (Transfer of ENergy in hydrothermal vents ¿ an in Situ Experiment) project, funded by ISblue (Interdisciplinary graduate School for the BLUE planet, FR), is a collaboration between Ifremer (FR), the University of Western Brittany (FR) and the CIIMAR (PT, Dr. Teresa Amaro. It aims at studying how Bathymodiolus azoricus influences carbon transfer in hydrothermal vent food webs. The project will study how B. azoricus influences the rates and pathways of carbon fixation within the assemblage using six small (0.07 m²) enclosures and 13C-labelled bicarbonate.
• ANR IRONWOMAN: the collection of iron-rich microbial mats will feed the IRONWOMAN project (ANR-21-CE02-0012; PI C. Rommevaux 2021-2025). The project aims at validating the hypothesis of the primordial role of marine iron-oxidizing bacteria (FeOB) in promoting the development of iron-rich mats, and impacting the iron biogeochemical cycle and the primary production in the deep oceans, according to the variations in environmental conditions.
• DEEP REST: (PI J. Sarrazin - Ifremer- EU Biodiversa grant ¿ 2022-2026) Conservation & restoration of deep-sea ecosystems in the context of deep-sea mining. DEEP REST will investigate two remarkable deep-sea ecosystems namely polymetallic nodule fields and hydrothermal vents, including their extended peripheries. Four major areas will be investigated: the Clarion Clipperton Zone (CCZ) and the DISCOL Experimental Area (DEA) in the Pacific Ocean for nodule fields and the northern Mid-Atlantic Ridge (nMAR), and the Arctic Mid-Ocean Ridge (AMOR) for active and inactive hydrothermal vents. These remote ecosystems are at risk of exploitation of their associated strategic metal resources, i.e. polymetallic nodules (PMN) and seafloor massive sulfides (SMS). However, questions about the impacts of mining and resilience of deep sea communities to anthropogenic activities are still pending. DEEP REST will enhance fundamental knowledge on species and functional diversity and their interconnections to develop effective environmental management plans and regulations to protect unique and vulnerable marine habitats. We will evaluate the effectiveness of passive and innovative active restoration approaches on the recovery of ecosystem biodiversity and assess how these actions could contribute to maintaining ecosystem functions and services.

Biological rhythms are a fundamental property of life. The circadian clock (~24-hour) is the only characterised biological clock to date, but it is not the only timekeeping system that nature provides. Marine ecosystems are shaped by environmental cycles, ranging from a few hours (tidal and solar cycles) to a year (seasons). And not only have biological rhythms been widely described in organisms, but they are also potentially present in all environments, including places where there is absolutely no solar light like deep-sea hydrothermal vents. Indeed, biological rhythms have recently been described in an hydrothermal mussel, Bathymodiolus azoricus, whose physiology and behaviour are under tidal influence at 1700 m depth. The project Audrey Mat is developping is a fundamental research project aiming at understanding the temporal functioning of the mussel B. azoricus and of its natural deep-sea environment. This includes working both at the behavioural and the molecular level to understand how B. azozicus timing system works and how it perceives its environment, synchronizes, and interacts with it. At the molecular level, she will use both genomics tools to get a big picture of the mussel, and target specific markers known for their role in the biological clock of shallow-water species. Audrey Mat initiated this work with us as a LabexMER postdoc. She recently joined the laboratory of Pr Kristin Tessmar-Raible, affiliated primarely with the University of Vienna in Austria, and also with the Alfred Wegener Institute in Germany. The work will be carried out in collaboration with Ifremer, and specifically Dr Marjolaine Matabos.

Polymer degradation : This year, we also started a prospective deployment of specimens to study the degradation of biodegradable polymers in deep environment. 5 bags of samples were deployed in the vicinity of Seamon W and will be recovered during the next cruises. In parallel, accelerated ageing tests are being carried out in the SMASH laboratory on the same materials, taking into account various environmental parameters (pressure, temperature, biological environment) in order to set up predictive models of life duration. Collaboration P. Davies (Ifremer).