The Arcachon Bay is a unique and ecologically important meso-tidal lagoon on the Atlantic coast of south-west France. The Arcachon Bay has the largest area of dwarf seagrass (Z. noltei) in Europe, the extent of which was stable in their extent between the 1950s and 1990s, but a decline in seagrass was observed in mid-2000. The decline of Zostera (seagrass) may have a significant impact on sedimentation in this coastal ecosystem rich in marine life. Interface cores were collected in September 2022 to determine sediment and mass accumulation rates (SAR, MAR) in the Arcachon Bay. Ten study areas were selected, distributed over most of the areas where seagrass meadows are actually observed. Two sites were visited each time, one with the presence of Zostera noltei in good condition (Healthy) and the other where the sediment was bare (Bare). Maximum water heights during spring tides range from 3.44 m for the deepest site (Garrèche) to 2.09 m for the shallowest site (Fontaines). A total of 20 sediment cores were sampled and carefully extruded every 1 cm from the top to the bottom of the core. The sediment layers were used to determine dry bulk density and selected radioisotope activities: DBD, 210Pb, 226Ra, 137Cs, 228Th and 40K expressed as %K). 

The general objective of the PEACETIME cruise is to study the fundamental processes and their interactions at the ocean-atmosphere interface, occurring after atmospheric deposition (especially Saharan dust) in the Mediterranean Sea, and how these processes impact the functioning of the pelagic ecosystem. During the proposed 33 days cruise in the western and central Mediterranean Sea in May 2017, we will study the impact of atmospheric deposition on the cycles of chemical elements, on marine biogeochemical processes and fluxes, on marine aerosols emission and how ongoing changes will impact the functioning of Mediterranean Sea communities in the future. The cruise is designed to explore a variety of oligotrophic regimes. Combining in situ observations both in the atmosphere and the ocean, and in situ and minicosm-based on-board process studies, the 40 embarking scientists from atmosphere and ocean sciences will characterize the chemical, biological and physical/optical properties of both the atmosphere and the sea-surface microlayer, mixed layer and deeper waters. The PEACETIME strategy (season and cruise track) associated to a combination of dust transport forecasting tools and near real-time satellite remote sensing is designed to maximize the probability to catch a Saharan dust deposition event in a stratified water column in order to follow the associated processes in-situ. This coordinated multidisciplinary effort will allow us to fill the current weaknesses/lacks in our knowledge of atmospheric deposition impact in the ocean and feedbacks to the atmosphere in such oligotrophic systems. As a key joint-project between MERMEX and CHARMEX : The PEACETIME project comes in the scope of the regional multidisciplinaryprogramme MISTRALS (Mediterranean Integrated STudies at Regional And Local Scales ), which aims at predicting the evolution of this region following strong expected changes in climate and human pressures. In this framework, the PEACETIME project constitutes a key joint project between the ChArMEx (the Chemistry-Aerosol Mediterranean Experiment) and MERMEx (Marine Ecosystems Response in the Mediterranean Experiment) initiatives, enabling to gather communities of atmospheric chemists and marine biogeochemists around the common question of assessing the impact of atmospheric deposition on the marine biogeochemical processes and air-sea exchanges.

Data collected by the Spindrift 2 Sails of Change vessel during its attempt at the round-the-world sailing record, the Jules Verne Trophy. More information at https://spindrift-racing.com/fr/.

The Argo program provides an unprecedented volume of oceanographic data, yet the complexity of its dataset — involving multiple data modes, quality control flags, and metadata conventions — often hinders its direct usage. The EasyOneArgo initiative addresses this challenge by delivering simplified, high-quality subsets of Argo data, specifically designed to streamline user access and integration. The EasyOneArgo data product is comprised of 4 datasets: - EasyOneArgoTS – A curated selection of temperature-salinity profiles filtered by strict quality criteria and optimized across raw, real-time adjusted, and delayed-mode status. - EasyOneArgoTSLite – The vertically interpolated counterpart of EasyOneArgoTS, with standardized pressure levels between 2 and 6000 dbar. - EasyOneArgoBGC – A curated selection of biogeochemical profiles filtered by strict quality criteria. The BGC parameters include DOXY, NITRATE, PH, CHLA, BBP, and various radiometry parameters. All BGC data are adjusted either in real-time or in delayed-mode. Accompanying TS measurements are also included. - EasyOneArgoBGCLite – The vertically interpolated counterpart of EasyOneArgoBGC, with the same standardized pressure levels as EasyOneArgoTSLite. Note: The BGC vertical interpolation process involves pre-filtering the original data before interpolation. Hence the magnitudes of some of the features are modulated in the BGCLite dataset. Each profile in EasyOneArgo is packaged as a standalone CSV file, with metadata and indexes for seamless retrieval. This work represents a user-centric shift in Argo data delivery: no QC flags, no data modes, no data manuals — just good, clean, structured ocean data ready for immediate scientific application. The EasyOneArgo data product is publicly available through monthly FAIR-compliant releases. We invite community feedback for continued refinement. Please send any comments to Annie Wong (apsw.uw@gmail.com) or Thierry Carval (Thierry.Carval@ifremer.fr).

SUCHIMED 2021 is the 10th campaign for monitoring chemical contamination and its evolution in the Mediterranean Sea. It has been designed as a platform supporting various surveillance and research activities, with the main pillar being the RINBIO network, which involves active biosurveillance through mussel caging. Regarding chemical contamination, the main results of this campaign are as follows: In Occitania region: - Chronic presence of DDT for 20 years. - Detection of terrigenous markers (Mn, As) between the mouths of the Aude and Hérault rivers, along with contamination of sediments near Port-La-Nouvelle by HAP and TCE (Pt). In PACA region: - PCB markers detected between the Rhône River and Marseille (in all matrices), originating from multiple sources with no significant changes over the past 20 years. - HAP contamination in sediments of the industrial-port zone in Fos. - Presence of TBT at the Carry-le-Rouet station above ecologically acceptable concentrations (EAC), to be confirmed in the next campaign. - Detection of metallic elements and HAP in sediments near the Marseille urban area, partly in plankton, along with TCE near the Cortiou wastewater treatment plant outfall. - Chronic marking of PCB, HAP, metals (Hg, Pb, Cu, TCE), PBDE, and/or organotin compounds (TBT) in Toulon Bay, showing no significant temporal trend over two decades for the first five compounds. - Detection of Cr, Mn, and Ni in the water column and HAP in sediments near the Var River mouth, with differences in contamination between matrices raising questions about organic matter origin. - Metal (including Pb) and HAP marking in the water column and sediment in Villefranche Bay. Around Corsica: - Strong influence of the island's geological background (i.e., high Cr and Ni content) on obtained concentrations. - Chronic marking of Cu in the water column in the ports of Porto-Vecchio and Bonifacio, stable over time, with HAP, metals (Hg, Pb, Zn), and to a lesser extent, PCB detection in Bonifacio sediment. - Marking of HAP and TCE in the sediment of the Bastia coastline. - Detection of Pb and TCE at the Golo River mouth. - Contamination of the Canari site with metals (Cr and Ni in the water column, Cu in sediment), and notably, confirmed ecotoxicity likely linked to these elements. The 2021 campaign highlighted the feasibility of researching effects on caged mussels using biomarkers. Lysosomal markers, less sensitive to trophic differences, proved to best reflect the general stress state of organisms related to their contamination. The study of trophic transfers appears to confirm the decrease in most metallic elements (Cr, Cu, Fe, Mn, Ni, Pb) and HAP, bioamplification of Hg and PCB, and specific bioaccumulation of certain elements by organisms (e.g., As or Zn by mussels, HAP by plankton). Finally, the campaign revealed the presence of micro and mesoplastics at almost all sampled sites. The measured microplastic values align with concentrations observed in the western Mediterranean, with a trend towards reduction based on available 10-year data.

The COAST-HF/Arcachon-Ferret time series characterizes the hydrology of the interface between the Arcachon lagoon, located in the South-Western France, and the Atlantic Ocean. A buoy belonging to Phares et Balises is instrumented with a multi-parametric probe that records sub-surface temperature, conductivity, depth, turbidity and fluorescence every 10 minutes since February 2018. It is opérated by the OASU and EPOC teams (Univ. Bordeaux/CNRS). COAST-HF (Coastal OceAn observing SysTem - High Frequency; www.coast-hf.fr) is a national observation network accredited by the CNRS as a national Earth Science Observatory (Service National d’Observation: SNO). It aims to federate and coordinate a set of 14 fixed platforms instrumented with high-frequency in situ measurements for key parameters of coastal waters. The COAST-HF/Arcachon-Ferret buoy is one of them. COAST-HF is part of the French Research Infrastructure dedicated to coastal ocean observations (RI ILICO, https://www.ir-ilico.fr). Data are transmitted to the Coriolis Côtier database (https://data.coriolis-cotier.org/). Data are raw data.

The diet and stable isotopic (i.e. δ15N and δ13C values) compositions of eels have been studied during each season of 2019 with a fyke net in six estuaries located along the French coast of the eastern English Channel (Slack, Wimereux, Liane, Canche, Authie and Somme estuaries) (10.1371/journal.pone.0270348).

As part of the marine water quality monitoring of the “Pertuis” and the “baie de l’Aiguillon” (France), commissioned by the OFB and carried out by setec énergie environnement, three monitoring stations were installed. Two of them were set up at the mouths of the Charente and Seudre rivers on February 6 and 27, 2019, respectively, while a third was deployed in the Bay of Aiguillon on March 24, 2021. The dataset presented here concerns the station installed in the Charente estuary. Measurements are organized into .csv files, with one file per year. Data is collected using a SAMBAT multiparameter probe, which records the following parameters: - Temperature (-5 to 35 °C) - Conductivity (0 to 10 mS/cm) - Pressure (0 to 10 m) - Turbidity (0 to 300 NTU) - Dissolved Oxygen (0 to 20 mg/L & 0 to 200 %) - Fluorescence (0 to 50 µg/l) - PH (0/14)

The network was initiated by IFREMER from 1993 to 2009 (under the acronym REMORA) to study the rearing performance of the Pacific oyster Crassostrea gigas at a national scale. To do so, the network monitored annually the mortality and growth of standardized batches of 18-month-old oysters. Starting in 1995, the monitoring of the rearing performance of 6-month-old oyster spat was integrated into this network. These sentinel batches were distributed simultaneously each year on 43 sites and were monitored quarterly. These sites were distributed over the main French oyster farming areas and allowed a national coverage of the multiannual evolution of oyster farming performances. Most of the sites were located on the foreshore at comparable levels of immersion. Field studies were carried out by the "Laboratoires Environnement Ressources" (LER) for the sites included in their geographical area of investigation. Following the increase in spat mortality in 2008, the network evolved in 2009 (under the acronym RESCO). From this date, the network selected 13 sites among the 43 sites previously monitored in order to increase the frequency of visits (twice a month) and the number of sentinel batches. More precisely, sentinel batches of oysters corresponding to different origins (wild or hatchery, diploid or triploid) and to two rearing age classes (spat or 18-month-old adults) were selected. The monitoring of environmental variables (temperature, salinity) associated with the 13 sites was also implemented. The actions of the network have thus contributed to disentangle the biotic and abiotic parameters involved in mortality phenomena, taking into account the different compartments (environment / host / infectious agents) likely to interact with the evolution of oyster rearing performance. Finally, since 2015, the network has merged the RESCO and VELYGER networks to adopt the acronym ECOSCOPA. The general objective of this current network is to analyze the causes of spatio-temporal variability of the main life traits (Larval stage - Recruitment - Reproduction - Growth - Survival - Cytogenetic abnormalities) of the cupped oyster in France and to follow their evolution on the long term in the context of climate change. To do this, the network proposes a regular spatio-temporal monitoring of the major proxies of the life cycle of the oyster, organized in three major thematic groups: (1) proxies related to growth, physiological tolerance and survival of experimental sentinel populations over 3 age classes: (2) proxies related to reproduction, larval phase and recruitment of the species throughout its natural range in France, and: (3) proxies related to environmental parameters essential to the species (weather conditions, temperature, salinity, pH, turbidity, chlorophyll a and phytoplankton) at daily or sub-hourly frequencies. Working in a geographical network associating several laboratories, ECOSCOPA provide these monitoring within 8 sites selected among the previous ones to ensure the continuity of the data acquisition. Today, these 8 sites are considered as ecosystems of common interest, contrasted, namely : - The Thau lagoon - The Arcachon basin - The Marennes Oléron basin - The Bourgneuf Bay - The bay of Vilaine - The bay of Brest - The bay of Mont Saint Michel - The bay of Veys The ECOSCOPA network is therefore one of the relevant monitoring tools on a national scale, allowing to objectively measure through different proxies the general state of health of cultivated and wild oyster populations, and this for the different sensitive phases of their life cycle. This network aims at allowing a better evaluation, on the long term, of the biological risks incurred by the sector but also by the ecosystems, in particular under the increasing constraint of climatic and anthropic changes. Figure : Sites monitored by the ECOSCOPA network