French Research Institute for Exploitation of the Sea
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Performance evaluation of optical dissolved oxygen sensor, ARO-FT
No full textThe temporal drift of the ARO-FTs, the new optical dissolved oxygen (DO) sensors mounted on 13 Argo floats, was analyzed for two periods: the storage period before float deployment and the period after float deployment. ARO-FTs exhibited a common issue of optical DO sensors, resulting in greater deviations from the reference data at higher concentrations. The storage drift of the ARO-FTs mounted on floats in this study was on the order of 5 μmol kg–1. Although this storage drift was larger than that of the Aanderaa Optode 4330, the first ARO-FT DO profiles could be corrected to within ± 2% of the ship-based bottle sampling data, even at layers with large vertical DO gradients, using a linear first-order equation, owing to the fast response time of ARO-FTs. The average temporal drift of ARO-FTs after float deployment was estimated at – 0.31 ± 0.17% year–1 in oxygen concentration using the method of a previous study. Although the drift of ARO-FTs was greater than that of the Aanderaa Optode 4330 for both periods, the DO profiles corrected for drift remained within ± 2% of the nearby reference data at 210 days after float deployment. The seasonal variations in oxygen saturation rate near the surface and their amplitudes during the study period were consistent with those observed in monthly climatology. These results indicate that the corrected DO measurement by ARO-FTs was comparable to that of the Aanderaa Optode 4330
Hydrothermal vent temperatures track magmatic inflation and forecast eruptions at the East Pacific Rise, 9°50’N
No full textHydrothermal vent temperatures fluctuate in response to transient magmatic and tectonic activity at the axis of mid-ocean ridges (MORs) and modulate energy fluxes from the deep Earth to the ocean. Such fluctuations have thus far only been documented on time scales of minutes to years, because of the scarcity of long, continuous observations. Here, we assemble a ~35-year-long time series of exit fluid temperatures from five hydrothermal vents on the East Pacific Rise axis, between 9°46’-51’N. This dataset reveals a steady increase in maximum venting temperatures atop the central part of the axial magma lens (AML), from ~350 °C to ~390 °C between the 1991–92 and 2005–06 eruptions. Temperatures decreased back to ~350 °C shortly after the 2005–06 eruption and have been rising ever since. We interpret the temperature increase as a result of a steady decrease in upflow zone permeability caused by the steady inflation of the AML compressing the oceanic upper crust. Using laboratory-determined pressure–permeability relations, we estimate crustal pressurization rates of 0.38 MPa/y (1992–2005) and 0.33 MPa/y (post-2006), consistent with geodetic observations from 2009–2011. Decadal fluctuations in hydrothermal vent temperatures likely mimic the rate of AML pressurization, yielding valuable new constraints on the dynamics of magmatic replenishment and eruptions at MORs. Notably, this temperature time series underpinned our forecast of the April 2025 eruption at the study site
Le partage des avantages financiers issus de l’exploitation des grands fonds marins : Une illustration des mutations récentes de la notion de patrimoine commun de l’humanité ?
No full textThis contribution aims to analyse the concept of the common heritage of humankind (CHM) from the perspective of its implementation in the international law of the sea. In this context, the fair and equitable sharing of benefits arising from the exploitation of the resources of the Area is considered an essential element in defining the CHM. The terms and modalities of this sharing are currently being clarified in the context of a potential exploitation of the mineral resources of the Area. However, discussions within the International Seabed Authority (ISA) appear to be moving away from the inter-State vision of the CHM embodied in UNCLOS, favouring instead an intergenerational conception. Our hypothesis is that this shift towards a cosmopolitan vision of the CHM can be explained by changes in the negotiation contexts that have shaped discussions relating to the Area in 1982, 1994, and today. This contribution adopts a methodology based on a textual and historical analysis of UNCLOS and the 1994 Implementation Agreement, as well as current debates within the ISA, in order to assess this evolution.Cette contribution vise à analyser la notion de patrimoine commun de l’humanité (PCH) du point de vue de sa mise en oeuvre en droit international de la Mer. Dans ce cadre, le partage juste et équitable des avantages issus de l’exploitation des ressources de la Zone est considéré comme un élément essentiel de définition du patrimoine commun de l’humanité. Les termes et modalités de ce partage se précisent actuellement dans le cadre d’une éventuelle exploitation des ressources minérales de la Zone. Or, les discussions au sein de l’AIFM semblent s’éloigner de la vision interétatique du PCH au sein de la CNUDM pour favoriser au contraire une conception intergénérationnelle. Notre hypothèse est que ce glissement vers une vision cosmopolitique du PCH s’explique par les changements dans les contextes de négociation, qui ont présidé aux discussions relatives à la Zone en 1982, 1994 et aujourd’hui. Cette contribution adopte une méthodologie basée sur une analyse textuelle et historique de la CNUDM et de l’Accord de mise en oeuvre de 1994, ainsi que des débats actuels au sein de l’AIFM afin d’apprécier cette évolutionEsta contribuição tem como objetivo analisar o conceito de patrimônio comum da humanidade (PCH) sob a perspectiva de sua implementação no direito internacional do mar. Nesse contexto, a partilha justa e equitativa dos benefícios resultantes da exploração dos recursos da Área é considerada um elemento essencial na definição do PCH. Os termos e modalidades dessa partilha estão atualmente sendo definidos no contexto de uma possível exploração dos recursos minerais da Área. No entanto, as discussões no âmbito da Autoridade Internacional dos Fundos Marinhos (AIFM) parecem afastar-se da visão interestatal do PCH consagrada na CNUDM, favorecendo, ao contrário, uma concepção intergeracional. Nossa hipótese é que essa mudança para uma visão cosmopolita do PCH se explica pelas transformações nos contextos de negociação que orientaram as discussões relativas à Área em 1982, 1994 e atualmente. Esta contribuição adota uma metodologia baseada em uma análise textual e histórica da CNUDM e do Acordo de Implementação de 1994, bem como dos debates atuais no âmbito da AIFM, a fim de avaliar essa evolução
Mo isotope chemostratigraphy of the 2.87 Ga Red Lake Carbonate Platform and implications for incipient oxidative Mo cycling during the Archean
No full textPrior to 2.5 billion years ago, the Earth system was dramatically different from today, and the Archean oceans were largely anoxic except for local oxygen oases in shallow seas. This study reports a complete molybdenum (Mo) stable isotope chemostratigraphy based on two correlative cored drill holes through Earth's earliest thick carbonate platform, preserved in the 2.87-billion-year-old (Ga) Ball Assemblage of the Red Lake Greenstone Belt (Ontario, Canada). Previous studies have suggested the presence of an oxygen oasis at this site based on negative Ce anomalies and Mo isotope data obtained from outcrop samples (McIntyre and Fralick, 2017; Thoby et al., 2019), which is further supported by La-Ce geochronological data indicating that the Ce anomalies are syngenetic (Patry et al., 2025). delta Mo-98/95 values across diverse lithologies, including stromatolitic dolostones, microbialitic limestones, oxidefacies banded iron formations, black shales, and sulfidic shales, range from -2.22 %o to 0.53 %o, clearly demonstrating important redox-driven Mo isotope fractionation as far back as 2.87 Ga. Despite non-negligible authigenic Mo enrichments in carbonate and iron formation (IF) samples relative to the crust, Mo concentrations determined by isotope dilution remain significantly below crustal values (mean values of ca. 300 ppb and 60 ppb for IF and carbonates, respectively). Mo stable isotopes in carbonate samples are generally unfractionated from crustal values, indicating a small Mesoarchean seawater Mo reservoir of near-zero delta Mo-98/95 composition. The few outcrop carbonate samples previously analyzed from Red Lake showing heavy Mo isotope compositions (Thoby et al., 2019) may therefore represent a false positive for the presence of O2 due to recent (<20 Ka) surface contamination. In contrast, shales and IF are generally characterized by isotopically lighter values, consistent with fractionation during Mo adsorption onto Mn-/Fe-oxides or partial uptake by reducing sediments, respectively, from a dissolved seawater reservoir that was near 0 %o. The systematic presence of mild positive Ce anomalies in all samples showing the lightest Mo isotope compositions point to a role for Mn-oxide shuttling during deposition, consistent with previous reports of the establishment of an oxygen oases at Red Lake. Combined, this evidence suggests that any oxidative processing of Mo occurring during the deposition of the Red Lake platform did not result in the establishment of an isotopically heavy seawater Mo reservoir, as occurs today. Instead, the results point to a largely unfractionated seawater Mo reservoir derived from weathering under low O2 conditions and/or from hydrothermal sources. To investigate the conditions enabling such a reservoir, we employ a steady-state isotope mass balance model to examine the Mesoarchean Mo cycle. Our results suggest that, despite incipient oxidative processing in the marine realm, a well-mixed Mo reservoir with a nonfractionated delta Mo-98/95 is the likely result for a Mesoarchean ocean subject to reduced riverine Mo fluxes, modern to elevated hydrothermal Mo input fluxes, and for a variety of plausible reservoir sizes, providing important perspective on the application of Mo isotope redox proxies at the onset of Earth system oxygenation
Synthèse de l’état des stocks dans le golfe Normand-Breton. Réponse à une demande d'expertise
No full textThis report incorporates the latest available information on the state of stocks fished in the Normandy-Breton Gulf. For whelk, the standardised LPUE, used here as a proxy for abundance, suggests a steady decline in stock biomass since 2017, with a further decline observed in 2024. Landings are following this trend, generally with a one-year lag. This stock seems to be more fragile than ever. A number of factors suggest that rapidly changing environmental conditions in the Western Channel could be a major contributor to this deterioration in the state of the stock. For spider crab, abundance has particularly increased in the Norman-Breton Gulf in recent years, the main fishing area in France. However, this situation is highly heterogeneous, with spider crab abundance currently lower in other areas, such as southern Brittany. We still lack the information needed to understand this dynamic, but the milder winter conditions, with cooler temperatures, are likely to favour the survival of juveniles. For edible crab, LPUE trends indicate that the state of the stock is low. Low recruitment in recent years and/or an increase in mortality unrelated to fishing could explain this sharp drop in landings; work is underway to validate these hypotheses. The state of the lobster stock is considered to be generally good, although no length-based indicators or other stock assessments are yet available for these stocks, except in Granville Bay, where the decline has been confirmed for 10 years now. Some work is underway to develop assessments that will be adjusted using a global SPiCT model. For scallops, the CMSY+ and SPiCT models have been used to assess the Normandy-Breton Gulf stock. The stock in the Bay of Saint-Brieuc has shown a steady increase in biomass and abundance indices over the last 10 years. The model results confirm that the stock is in excellent condition, with catches below the estimated MSY. No information is available for other bivalve stocks.Ce rapport intègre les derniers éléments disponibles concernant l’état des stocks pêchés dans le Golfe Normand-Breton. Pour le buccin (bulot), La LPUE standardisé, utilisé ici comme proxy de l’abondance, suggère une baisse continue de la biomasse du stock depuis 2017, avec une nouvelle diminution observée en 2024. Les débarquements suivent cette dynamique avec généralement un décalage d’une année. Ce stock semble être plus fragilisé que jamais. Plusieurs éléments suggèrent que l’évolution rapide des conditions environnementales en Manche Ouest pourrait contribuer de façon importante à cette dégradation de l’état du stock. Pour l’araignée, l’abondance a particulièrement augmenté dans le golfe Normano-breton ces dernières années, principale zone de pêche française. Mais cette situation est très hétérogène puisque sur d’autres secteurs l’abondance en araignée est plus faible actuellement, comme en Bretagne Sud. Les éléments pour comprendre cette dynamique manquent encore, mais les conditions hivernales plus clémentes, avec des températures moins froides favoriseraient la survie des juvéniles. Pour le tourteau, les tendances de LPUE indiquent que l'état du stock est bas. Un faible recrutement ces dernières années et/ou une augmentation de la mortalité non liée à la pêche pourraient expliquer cette nette diminution des débarquements ; des travaux sont en cours pour valider ces hypothèses. L'état du stock de homard est considéré comme généralement bon, bien qu'aucun indicateur basé sur la longueur ni aucune autre évaluation du stock ne soient encore disponibles pour ces stocks, sauf dans la baie de Granville, où la diminution est confirmée depuis 10 ans maintenant. Certains travaux sont en cours pour développer des évaluations qui seront ajustées à l'aide d'un modèle global SPiCT. Pour la coquille Saint-Jacques, les modèles CMSY+ et SPiCT ont été utilisés pour évaluer le stock du golfe normand-breton. Le stock de la baie de Saint-Brieuc montre une progression constante en biomasse et indices d’abondance depuis 10 ans. Les résultats des modèles confirment un excellent état du stock, avec des captures en dessous de l’estimation RMD. Il n'y a pas d'information disponible pour les autres stocks de bivalves
Qualité du Milieu Marin Littoral. Bulletin de la surveillance 2022. Département des Alpes Maritimes, Bouches du Rhône, Var, Haute-Corse et Corse-du-Sud
No full textL’Ifremer coordonne, sur l’ensemble du littoral métropolitain, la mise en œuvre des réseaux d’observation et de surveillance de la mer côtière. Ce bulletin contient une synthèse et une analyse des données collectées au cours de l’année 2022 par l’ensemble des réseaux pour les départements des Alpes maritimes, Bouches du Rhône, Var, Haute Corse et Corse-du-Sud. Des représentations graphiques homogènes, assorties de commentaires, donnent des indications sur les niveaux et les tendances des paramètres mesurés
Monitoring Long‐Term Seafloor Water Temperature Changes Using Fiber Optic Sensing on Submarine Telecommunication Cables
No full textMonitoring of ocean temperatures is crucial for climate studies, ocean circulation modeling and assessing potential ecosystem impacts. However, obtaining observations from the subsurface ocean is difficult and costly. We present a 3‐year time series of distributed fiber optic sensing (sensitive to temperature changes and strain) obtained at 3 to 6‐month intervals, using a network of telecommunication cables in Guadeloupe (Lesser Antilles). We demonstrate that this technique can track seasonal and annual seafloor water temperature changes to within 0.1°C, in a well‐mixed, shelf sea environment. We observe a marine heatwave, with a temperature increase of +1.5°C between 2022 and 2024 at the sea‐floor, causing coral bleaching with 30% mortality. These trends are confirmed by satellite observations of the Sea Surface Temperature in the same location. This successful demonstration, in a shallow‐water environment, opens the path forward for widespread use of submarine cables for long‐term environmental monitoring of the seafloor
Insight into magmatic pathways and subsurface structures from repeated UAV magnetic prospecting at Piton de la Fournaise volcano, Réunion Island
No full textVolcanic activity disturbs the existing magnetic field, and analysis of the resulting magnetic anomalies provides information about the internal structure and evolution of active systems within edifices. This study focuses on the South-East Rift Zone (SERZ) of Piton de la Fournaise, specifically the eruptive site of September 2022, which offers a unique opportunity to characterise the thermal state, the subsurface structures, and to obtain information about the global fluid dynamics of this highly active area. For this purpose, we performed high-resolution aeromagnetic surveys using an Unmanned Aerial Vehicle (UAV) in November 2022 and May 2024 to investigate the evolution of the eruptive site. At a regional scale, first order 3D modelling of the magnetic anomalies primarily reveals a negative magnetic axis with a N120° orientation. Comparative analysis with 3D Interferometric Synthetic Aperture Radar data modelling shows a significant correlation between this demagnetised axis, the depth, and the volume of magmatic intrusions along the rift-zone. This result suggests the presence of a N120°-trending mechanical weakness intersecting the SERZ that has some control over the internal dynamics of the magmatic and hydrothermal fluids in the area. In addition, we quantify the temporal evolution of the magnetic signals associated with the September 2022 lava flow by means of repeated UAV measurements from May 2024 and estimate a global increase of several hundreds of nanoteslas (between 150 and 900 nT) linked to the magnetisation caused by the lava cooling during this time. We then successfully explore on a more local scale the ability of UAV magnetic prospecting to detect lava tubes using semi-quantitative 2D models. These results demonstrate the potential of UAV magnetic surveys to characterise the spatio-temporal evolution of magnetic signals from Piton de la Fournaise. Such multi-scale analysis of magnetic structures within the edifice indicates the potential of 4D monitoring for obtaining a better understanding of the volcano’s evolution. Graphical Abstrac
Avis sur l'ouverture à la pêche de la zone gisement à éclipse 50-21, Groupe 3 "Ouest et Nord Cotentin" (Huîtres plates) ; Gisement La Caravane
No full textQuantifying widespread hydrothermal chimneys on the East Pacific Rise flanks between 9°43′ and 57′N
No full textHydrothermal circulation at mid-ocean ridges drives the exchange of heat and matter from Earth’s interior to the global ocean and supports deep-sea life. Away from the ridge axis, however, the spatial extent of hydrothermal discharge remains enigmatic. Using near-bottom data for a 25-kilometer-long section of the East Pacific Rise between 9°43′N and 9°57′N, we show that considerable hydrothermal flow occurs at variable distances from the ridge axis. Mapping the seafloor and water column along this segment using an autonomous underwater vehicle, we identified 448 candidate hydrothermal chimneys. More than half of them lie outside the axial summit trough, indicating that hydrothermal fluids discharge over a larger area than previously thought. Water column measurements show that >27% of mapped constructs are likely to be venting actively. Our results indicate that widespread active hydrothermal flow occurs over the near-axis region, with important implications for constraining total heat flux along mid-ocean ridges and for identifying previously unexplored benthic habitats