Institut Pytheas

Abstract. The science guiding the EUREC4A campaign and its measurements is presented. EUREC4A comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic – eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EUREC4A marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10 000 profiles), lower atmosphere (continuous profiling), and along the air–sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EUREC4A explored – from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation – are presented along with an overview of EUREC4A's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement.

The differential response of marine populations to climate change remains poorly understood. Here, we combine common garden thermotolerance experiments in aquaria and population genetics to disentangle the factors driving the population response to thermal stress in a temperate habitat-forming species: the octocoral Paramuricea clavata. Using eight populations separated from tens of meters to hundreds of kilometers, which were differentially impacted by recent mortality events, we identify 25 °C as a critical thermal threshold. After one week of exposure at this temperature, seven of the eight populations were affected by tissue necrosis and after 30 days of exposure at this temperature, the mean % of affected colonies increased gradually from 3 to 97%. We then demonstrate the weak relation between the observed differential phenotypic responses and the local temperature regimes experienced by each population. A significant correlation was observed between these responses and the extent of genetic drift impacting each population. Local adaptation may thus be hindered by genetic drift, which seems to be the main driver of the differential response. Accordingly, conservation measures should promote connectivity and control density erosion in order to limit the impact of genetic drift on marine populations facing climate change.

Abstract Today, aquatic biodiversity suffers from many pressures linked to human activities, including climate change, which particularly affects alpine areas. Many alpine freshwater species have shifted their geographical distribution to colder areas, but a reduced availability of suitable habitats is also forecasted. New artificial water bodies could provide habitat enhancement opportunities, including small mountain reservoirs built to overcome a lack of snow during winter. To investigate the role of reservoirs as a habitat for freshwater invertebrates, a case study was conducted on eight reservoirs in the Swiss Alps. The study aimed to compare the water quality and freshwater biodiversity of the reservoirs with those of 39 natural and newly excavated ponds. Data were collected on physico‐chemistry, freshwater habitat structure, and aquatic insects (dragonflies and aquatic beetles). The study showed that the mountain reservoirs investigated did not differ from natural ponds in terms of surface area, conductivity, and trophic level. Similarly to natural ponds, reservoirs showed signs of impairment owing to surface run‐off carrying pollutants linked to ski tourism. They presented a low diversity of mesohabitats, and in particular lacked vegetation. Compared with natural ponds, the species richness in reservoirs was lower for dragonflies but not for beetles. At the regional scale, the community from the reservoirs was a subset of the natural ponds community, supporting 38% of the regional species richness for these two insect groups. The results suggest that mountain reservoirs are likely to be important for biodiversity in alpine areas, both as habitats and as stepping stones for species shifting their geographical range. These water bodies can be enhanced further by some nature‐friendly measures to maximize benefits for biodiversity, including margin revegetation or the creation of adjacent ponds. Ecological engineering needs to be innovative and promote freshwater biodiversity in artificial reservoirs.

Abstract The Variscan Orogen was formed during the closure of the Rheic Ocean and the final collision between the North American and West African cratons in the Late Paleozoic. This collision led to the multistage building of the Mauritanide Belt to the east of the Variscan suture and to the building of the well-known Appalachian Belt to the west. Both led to opposite vergences in this part of the Variscan belt. The earliest records of the main collision episode begin at ∼360 Ma and end about 250 myr ago, while a late extensional phase lasted until ∼190 Ma. Three distinct stages are recognized in West Africa. The first stage ( c. 350–300 Ma) records the indentation of the Reguibat Shield into the central Appalachian margin of Laurentia. This indentation led to thrusting of the Souttoufide and Akjoujt ‘nappes’ onto the Reguibat Shield, to southward motion of the Senegalese block (SB), and to strike-slip motion in the Appalachians. The motion of the SB to the south is coeval with: (1) folding of the northern part of the Bové Basin, (2) north–south sinistral strike-slip motions in the central Mauritanides, and (3) the end of sedimentation in the Bové and Taoudeni Basins by the Late Devonian. The second stage ( c. 300–250 Ma) involves the eastward motion of the Western Thrust Block (WTB) against the SB and, likely, some of the westward thrusts in the Appalachians. This second ‘Variscan’ event includes: (1) closure of parts of the lower Diourbel Carboniferous basin, which is now concealed beneath the Senegalo-Mauritanian Basin, (2) thrusting to the east of the Simenti Group over the Koulountou Group in the Bassaride Belt, (3) thrusting to the east of the Wa-Wa Group, (4) thrusting of the Mauritanide Belt onto the Taoudeni Basin in the central Mauritanide Belt, and finally (5) thrusting of the Agualilet Group over the Akjoujt nappes and eastward motion of the western units over the Dhloat Ensour (Late Ordovician to early Devonian) autochthonous unit in the Souttoufides. West of the supposed ‘Variscan’ suture, Appalachian thrusting affected parts of Appalachian Belt. The third stage ( c. 250 to 190 Ma) began with the opening of Triassic rift basins in the Senegalo-Mauritanian basin and also in the north of Florida. As numerous previous correlations across the Variscan system do not include the West African part, our sythesis is intended to enhance these correlations.

Cosmic explosions have emerged as a major field of astrophysics over the last years with our increasing capability to monitor large parts of the sky in different wavelengths and with different messengers (photons, neutrinos, and gravitational waves). In this context, gamma-ray bursts (GRBs) play a very specific role, as they are the most energetic explosions in the Universe. The forthcoming Sino-French SVOM mission will make a major contribution to this scientific domain by improving our understanding of the GRB phenomenon and by allowing their use to understand the infancy of the Universe. In order to fulfill all of its scientific objectives, SVOM will be complemented by a fast robotic 1.3 m telescope, COLIBRI, with multiband photometric capabilities (from visible to infrared). This telescope is being jointly developed by France and Mexico. The telescope and one of its instruments are currently being extensively tested at OHP in France and will be installed in Mexico in spring 2023.

The IFRECOR Guide to Ecological Engineering: The Restoration of Coral Reefs and Associated Ecosystems provides a comprehensive overview of ecological engineering techniques used in France and worldwide to restore coral reefs, seagrass beds and mangroves. Building on previous IFRECOR publications, the guide synthesizes recent scientific advances and operational feedback to support contracting authorities, environmental managers, marine protected area administrators and consultants in designing and implementing effective restoration actions. The handbook presents the theoretical foundations of ecological engineering and ecological restoration, clarifying the distinction between restoration, rehabilitation, enhancement and creation. It highlights the major conservation challenges faced by tropical marine ecosystems, including climate change, eutrophication, habitat destruction, and overexploitation. The document details restoration methods for coral reefs (transplantation, coral gardening, electrodeposition), seagrass beds and mangroves, providing practical descriptions, advantages, limitations, and cost-effectiveness metrics. Numerous case studies illustrate real-world applications across the French Overseas Territories and internationally. By integrating ecological theory, regulatory requirements, methodological guidance and field experience, the guide contributes a practical, science-based framework for restoring degraded tropical marine ecosystems and supporting the mitigation hierarchy in coastal development contexts. It also emphasizes the importance of monitoring, adaptive management and stakeholder engagement to ensure long-term restoration success.

The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Universe using the Baryon Acoustic Oscillation probe. The KPNO Mayall telescope will deliver light to 5000 fibers feeding ten broadband spectrographs. A consortium of Aix-Marseille University (AMU) and CNRS laboratories (LAM, OHP and CPPM) together with the WINLIGHT Systems company (Pertuis-France) has committed to integrate and validate the performance requirements of the full spectrographs, equipped with their cryostats, shutters and other mechanisms. An AIT plan has been defined and dedicated test equipment has been designed and implemented. This equipment simulates the fiber input illumination from the telescope, and offers a variety of continuum and line sources. Flux levels are adjustable and can illuminate one or several fibers along the test slit. It is fully remotely controlled and interfaced to the Instrument Control System. Specific analysis tools have also been developed to verify and monitor the performance and stability of the spectrographs. All these developments are described in details.

Turbulent fluxes at the air–sea interface were estimated with data collected in 2011–2020 with a low‐profile platform named OCARINA during eight experiments in five regions: 2011, 2015, and 2016 in the Iroise Sea; 2012 in the tropical Atlantic; 2014 in the Chilie–Peru upwelling; 2017 and 2018 in the Mediterranean Sea, and 2018 and 2020 in Barbados. The observations were carried out with moderate winds (2–10 m s −1 ) and average wave heights of 1.5 m. In this study, the authors used the fluxes calculated by the bulk method using OCARINA-sampled data as the input. These data can validate the fluxes estimated from ERA5 reanalysis data. The OCARINA and ERA5 data were taken concomitantly. To do this, the authors established an algorithm to extract the OCARINA data as closely as possible to the reanalysis data in time and position. The measurements of the OCARINA platform can conclude on the relevance of the widely used reanalysis data.

Abstract In Sicily, H. helix is the unique known native species whereas H. helix susbsp. poetarum is putatively naturalized in some forests and H. canariensis cultivated in various urban’s garden. Trichome morphology and genome size of some ivies from various west Mediterranean forests were compared to Sicilian ones. Ivies from southern Italy, continental France, Corsica and Mallorca belong to typical European diploid stellate trichomes Hedera helix . Hexaploid ivies from southern Spain have been identified as native H. iberica . Contrariwise, Sicilian ivies studied are related to western European H. hibernica (tetraploids with stellate trichomes). Is H. helix the most widespread and indigenous ivy in Sicily? Therefore, it would be the first time that tetraploid would be reported in Sicily where it could possibly correspond to an unnoticed autochthonous taxon. However, our results let us think it rather represents an invasive which impact on this island rich in endemic species could be considerable.

The Peruvian coastal upwelling system (PCUS) is one of the most productive in the world ocean. The Peruvian Marine Research Institute (IMARPE) has been monitoring the PCUS  since the 1960’s with an increase in the frequency and spatial distribution of measurements since the early 2000’s focusing on temperature, salinity and oxygen. In recent years, autonomous gliders have started to be routinely deployed by IMARPE, collecting a large amount of profiles. However, there is still a gap for the high-resolution  sampling of biogeochemical parameters such as nutrients (nitrate, phosphate and silicate).New  methods using machine learning to reconstruct missing data have been developed recently with promising results (Sauzède et al, 2017; Bittig et al., 2018; Fourrier et al., 2020). In particular, a recent global approach using neural networks (NN) named CANYON-B (CArbonate system and Nutrientes concentration from hYdrological properties and Oxygen using a Neural network) was developed in order to fill those gaps and infer nutrients’ concentrations from the more sampled variables of temperature, salinity and oxygen (Bittig et al., 2018).In this work we show the application of this global CANYON-B algorithm to the PCUS using all the historical IMARPE’s CTD casts. Moreover, we trained a new NN and compared its outputs with the ones from CANYON-B, demonstrating the benefits of training the NN with the extensive regional data set collected by IMARPE.

Potential competing interests: No potential competing

In January-February 2020, the EUREC4A-OA/ATOMIC experiment took place in the Northwest Tropical Atlantic with the overall goal of understanding the role of fine-scale processes in internal ocean dynamics and air-sea interaction. Four oceanographic ships, the French Atalante, the German Maria S. Merian and Meteor, and the US Ron Brown, were closely coordinated with airborne observations and autonomous ocean platforms (gliders, ©Saildrones, Argo floats, and drifters) to simultaneously measure the ocean and atmosphere from east of Barbados to the northern border of French Guyana. The multiple observations of the ocean, atmosphere, and their interface have revealed more complex ocean dynamics than expected, in particular a strong interaction between the Amazon River outflow (despite its reduced winter discharge), the North Brazil Current (NBC), and several mesoscale eddies (including the highly energetic NBC rings). This leads to even richer submesoscale dynamics that shape an important fraction of the air-sea exchange of heat, momentum, and CO2, and efficiently isolates the NBC northward flow waters from intense and continuous interactions with the atmosphere. Owing to the many complementary observations from ships and autonomous platforms, we have been able to quantify some of these processes, including the diurnal cycle and the 3D dynamics of different mesoscale eddies, as well as to map and quantify different terms of the air-sea fluxes and their impacts on the marine atmospheric boundary-layer water budget. The results have been widely used not only to validate numerical simulations of the region, but also to guide their analyses and to improve various numerical parameterizations.The collection of these observations was the result of an important international coordination between many different groups of ocean and atmospheric scientists. In addition, the special strategy for targeted data collection of meso- and submesoscale processes relied on daily planning of the field experiment and on detailed analysis of the near-real-time satellite data and the observations already obtained during the experiment, which was essential for providing the right snapshots of the ocean and atmosphere for the quantification of many processes. The lessons learned from this experiment will be implemented and extended in the upcoming major high-resolution oceanographic endeavor, the WHIRLS experiment, which will take place in June-July 2025, southwest of Africa.

The EUREC4A experiment was conducted in January and February 2020 off the North-Eastern coast of the Barbados Island. Air-Sea fluxes and bulk variables were derived from in situ measurements performed at the top of a bow mast on the Ifremer Genavir R/V Atalante and with a wave-following platform. Comparisons between the collected in situ data will be presented first. Second, a spatial view of the flux fields will be given, with model output fields and with satellite sensor data. Third, the spatial products will be compared to the in situ data in order to get a first order estimate of the accuracy of the spatial fields. Last, the focus will be laid on the effect of the proximity of the coast, both in terms of wind and wave fetches and of model Land-Sea Mask (LSM) and blind costal satellite zones

The Aix-Marseille metropolis is the second most populated urbanized area of France. It aims at reaching carbon neutrality in 2050. Located in the south-east of France under a Mediterranean climate, this area is known as a hot-spot regarding climate change. Its west part is strongly industrialized. The local air quality monitoring agency  ATMOSUD delivers a high resolved greenhouse gas emissions inventory that represents the reference for local stakeholders in matter of emissions trajectory. However, this inventory is still quite uncertain and requires independent assessments. In this aim, in the framework of the ANR COoL-AMmetropolis projet (2019-2025) we set-up a local greenhouse gas monitoring network based on Cavity Ring Down Spectrometry analyzers. This local network comprises the OHP ICOS-France station, located 80 km north of Marseille city. Local meteorological features such as sea and land breezes impact local greenhouse gas concentrations through advection and boundary layer dynamical processes. Isotopic analysis of 14C and 13C in CO2, as well as CO2 correlations with NOx, CO, black carbon and SO2, show a strong impact of fossil fuel emissions on the CO2 local urban greenhouse gas atmospheric plumes. The identified fossil sources are mostly traffic, building, industrial and maritime activities. Modern sources such as wood burning may account for a larger part than assessed by the local inventory.

In an attempt to reconciliate air-sea momentum flux estimates derived from open sea observations, from large eddy simulation output fields, and from wind-wave tank measurements, a series of dedicated experiments were conducted in the wind-wave tank of the Large Air-Sea Facility of Marseille, France. The turbulent friction velocity, upon which the momentum flux depends, was estimated from wind measurements by applying four classical methods including the eddy-covariance method and the inertial-dissipation method. The collected data were used to investigate some characteristics of the wave-influenced boundary layer that were predicted by previous simulations, and to quantify a wave-dependent term of the turbulent kinetic energy equation, the so-called imbalance term ϕimb. Our results show that the turbulent stress decreases toward lower heights where the effect of waves is large, as in the simulations, and that ϕimb is in the range 0.3 to 0.7, which is comparable to the value found with open sea data (0.4). These preliminary results have to be confirmed with wave-following probes, because the estimated eddy-covariance flux slightly varied with height, thus it could not be strictly considered to be equal to a constant total flux.

Scripts for the analysis of transcriptome data from the article on hybridization in Mediterranean octocorals. See information and scripts in the markdown file. License CC-BY 4.0 https://creativecommons.org/licenses/by/4.0/