French Research Institute for Exploitation of the Sea
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Geochemical and mineralogical characteristics of fjord sediments in Arctic Svalbard: insights into Holocene glacial activity and weathering variability
No full textThe Svalbard archipelago at the border of the Arctic Ocean experiences substantial glacier retreat due to global warming, resulting in a retreat of glacier termini from the marine to terrestrial settings. However, the impact of these transitions on marine environments remains poorly understood. To improve our understanding of how Arctic Svalbard responds to fluctuations in climate and glaciers, we reconstructed past glacimarine environments in Hornsund, southern Svalbard, over the last 4,900 years. By tracking sediment provenance using detrital neodymium isotopes and quartz-to-carbonate ratios, we revealed a progression from nearly open-marine conditions with minimal glacial activity during the middle Holocene to gradual seaward glacial expansion into the Neoglacial period (4,000 years B.P. to 790 C.E.). Glaciers likely retreated landward during the Medieval Warm Period (MWP; 790 to 1,470 C.E.), punctuated by significant readvances at least twice. The Little Ice Age (LIA) witnessed multiple glacial advances into the marine environment, followed by an overall glacial retreat in modern times. Geochemical analysis of authigenic sediment components indicates pronounced enrichments of middle rare earth elements, particularly during rapid glacial advances such as the MWP and LIA, which we interpret as enhanced glacial erosion and accelerated sulfide oxidation. Paleo-analogues from the middle Holocene, characterized by minimal marine-terminating glaciers and reduced sulfide weathering, suggest potential future declines in sulfur-related bioessential nutrient fluxes into Arctic coastal environments and subsequently to marine ecosystems
Mid-infrared integrated spectroscopic sensor based on chalcogenide glasses: optical characterization and sensing applications
No full textA mid-infrared (mid-IR) spectroscopic sensor is developed using a chalcogenide glasses (ChGs) platform with a broad transmission band. The ridge ChGs waveguides were patterned via standard i-line photolithography and reactive ion etching, following the deposition of guiding and confinement layers through RF magnetron sputtering. The waveguides exhibit a wide transparency range from λ = 3.94 to 8.95 μm, with minimum propagation losses value of 2.5 dB/cm at λ = 7.58 μm. To validate the feasibility of the suggested sensor, a spectroscopic gas sensing experiment was performed using CO2, resulting in an estimated limit of detection (LoD) of 1.16%v at λ = 4.28 μm, achieved with an external confinement factor Γ of 6.5%. Additionally, liquid sensing experiment was carried out using isopropanol, obtaining a LoD of 300 ppmv at λ = 7.25 μm
Mesoscale induced vertical fluxes over the Iceland-Faroe Ridge
No full textMesoscale eddies play a crucial role in ocean dynamics, yet their impact on vertical heat fluxes over topographic features remains poorly understood. This study investigates the Iceland-Faroe Ridge (IFR), a key boundary between the North Atlantic and Nordic Seas, southeast of Iceland. Recent rapid warming in the region has shifted thermal structures, potentially impacting the upper cell of the global thermohaline circulation. Using newly available high-resolution SWOT altimetry and numerical modeling, we directly observe mesoscale turbulence atop the IFR for the first time and quantify its role in driving significant vertical heat fluxes. This turbulence provides a pathway for heat transfer from warming surface waters to the deep Iceland-Scotland Overflow Water, likely contributing to its observed warming over the past four decades. These findings highlight the critical role of mesoscale dynamics in heat redistribution and the need for enhanced monitoring in this climatically sensitive region
The Dynamics Of Silica Sediment At The Ecused Site In The Baie de Seine Based On The Cova Methodology: (1) Glauconite Traced By Arsenic
No full textThe English Channel, and specifically the Baie de Seine, is one of the maritime areas hosting the most human activities in Europe. The ECUSED project focuses on the cumulative impact of marine aggregate extraction activities (“Granulats Marins du Havre” concession) and dumping of dredged sediment by the Normand harbours (“Grands Ports Maritimes”) for the maintenance of navigation channels (MACHU site), which are concentrated at the outlet of the Seine estuary. To achieve this goal, we used an innovative methodology (ELCOVA) on 114 surface sediments samples according to a regular grid of 2 stations per km². Samples were separated by sieving into 16 particle size fractions and elemental geochemical analyses were carried out on the separated granulometric fractions using X-ray fluorescence spectrometry. The present work focuses on identifying the movements of the various grain sizes naturally present at the site. The mineral considered is glauconite, an alumino-silicate, traced in the elemental analysis by arsenic. The study zone reveals a complex history in terms of granulometry, geography and time. We identify two sources of material, underwater erosion, river input, transports on the seabed and in suspension and a dynamic equilibrium sedimentary state. An essential point of the results obtained is that each granulometric fraction has its own history. Grains belonging to the same sediment sample do not come from the same sources, have not been transported in the same direction, and have not been deposited at the same time under the same energy conditions. It is possible to find grains of the same size and mineralogy from different sources in the same surface sample. This directly challenges the view of sedimentologists on sedimentation
Hierarchical Neutral and Non‐Neutral Spatial Genetic Structuring in the European Sardine (Sardina pilchardus) Revealed by Genomic Analysis: Implications for Management
No full textThe European sardine (Sardina pilchardus) sustains some of the most important East Atlantic fisheries and is exhibiting pronounced phenotypic and distributional changes linked to environmental changes. The application of high‐resolution genomic methods is recommended to provide insights into population demographics and patterns of ecological and evolutionary diversification. This study performed genome wide SNP analysis of samples collected across understudied NE Atlantic waters as well as geographical outgroup samples from Morocco and the Western Mediterranean. The data revealed pronounced differentiation of three regional groups (NE Atlantic, Morocco, and Western Mediterranean) that can be linked to glacial vicariance and contemporary dispersal limitations. Structuring was also apparent at outlier loci adding to evidence that genome architecture and non‐neutral processes are influencing sardine populations at various spatial scales. The highly resolved Morocco group may be a previously undescribed and localized lineage and confirms complex stock structure along the North African coast. Among the NE Atlantic samples, genome wide patterns confirm restricted gene flow between Biscay and North Sea sardine with signatures of isolation by distance. FST, individual assignment, and introgression tail analyses of outlier loci revealed further structuring and identify a North Sea—Eastern Channel group distinct from a Bay of Biscay‐Celtic Sea‐Western Channel group. This pattern contradicts current management boundaries and indicates that increasing sardine numbers in the North Sea reflect an expansion of an eastern English Channel‐North Sea fringe population. While this confirms the ability of the species' northern peripheral populations to expand in response to changing conditions, the genetically differentiated southern populations may differ in this regard. Overall, this study adds to a developing genetic framework for understanding sardine biocomplexity and provides resources for management
Proper account of auto-correlations improves decoding performances of state-space (semi) Markov models
No full textState-space models are widely used in ecology to infer hidden behaviors. This study develops an extensive numerical simulation-estimation experiment to evaluate the state decoding accuracy of four simple state-space models. These models are obtained by combining different Markovian specifications (Markov and semi-Markov) for the hidden layer with the absence (model AR0) and presence (AR1) of auto-correlation for the observation layer. Model parameters are issued from two sets of real annotated trajectories. Three metrics are developed to help interpret model performance. The first is the Hellinger distance between Markov and semi-Markov sojourn time probability distributions. The second is sensitive to the overlap between the probability density functions of state-dependent variables (e.g., speed variables). The third quantifies the deterioration of the inference conditions between AR0 and AR1 formulations. It emerges that the most sensitive model choice concerns the auto-correlation of the random processes describing the state-dependent variables. Opting for the absence of auto-correlation in the model while the state-dependent variables are actually auto-correlated, is detrimental to state decoding performance. Regarding the hidden layer, imposing a Markov structure while the state process is semi-Markov (with negative Binomial sojourn times) does not impair the state decoding performances. The real-life estimates are consistent with our experimental finding that performance deteriorates when there are significant temporal correlations that are not accounted for in the model. In light of these findings, we recommend that researchers carefully consider the structure of the statistical model they suggest and confirm its alignment with the process being modeled, especially when considering the auto-correlation of observed variables
Note de réflexion : Chalutage et Aires Marines Protégées : Mobiliser les connaissances et expertises scientifiques pour trouver des solutions ambitieuses et concertées
No full textCette note représente une réflexion scientifique volontaire, qui a émergé collectivement au sein d’Ifremer sans demande préalable et en dehors du cadre de nos projets de recherche. Son objectif est de présenter l’état de nos connaissances et les réflexions multidisciplinaires issues de nos différents champs de recherche. Quelques figures illustratives sont fournies principalement pour la façade Méditerranéenne, pour laquelle les informations quantitatives étaient déjà disponibles. Un travail similaire pourrait être conduit pour les autres façades. Ifremer est un institut de recherche uniquement dédié aux sciences de l’océan, des abysses à la surface et de la côte au large. C’est un lieu de rencontre entre différentes disciplines scientifiques, différentes compétences et différentes sensibilités citoyennes. En mettant en commun nos savoirs et nos expertises, nous espérons ainsi contribuer au débat public et venir en appui des politiques publiques, pour protéger l’océan et exploiter ses ressources de manière responsable
Marine diseases as a threat to society: Adopting and advancing the UNDRR risk framework
No full textMarine diseases change ecosystem dynamics and functioning, and modify ecosystem service (e.g. food) provisioning. Understanding marine diseases’ occurrence and frequency, and consequences and impacts thereof, is crucial for humans and nature alike, though the implications for society beyond human health have received little attention in scientific debates yet. This study advocates for the uptake of marine diseases into hazard landscapes currently being evaluated and discusses the different components of risks that marine diseases pose to societies: Adopting the analytical lens of the UNDRR risk framework to oyster farms as a specific case, we explore disease outbreaks in those as hazards to society. Looking at associated exposure and vulnerability, potential risk reduction options are elaborated. The framework is broadened by including indirect and spill-over effects within the social-ecological system – to local coastal communities. Marine diseases management is challenged by the fluidity of the ocean and fragmented governance structures. To reduce social-ecological repercussions and overall risks for society of disease outbreaks we thus endorse for a thorough risk evaluation and sensible, anticipatory communication
Long-range propagation of airgun-array signals: Comparing numerical simulations and acoustic recordings in the Ionian sea
No full textMarine seismic surveys contribute to acoustic pollution, and the sounds they produce may be audible by marine mammals at several hundred kilometers distance. To evaluate the potential effects of such sounds on fauna and translate them into effective policies and mitigation measures, stakeholders require quantitative estimations of acoustic fields. We compare simulations of airgun-array signals produced during the Upper LIthosphere Ship Subduction Exploration survey in the Ionian Sea with the signals recorded 650 kilometers away at the cabled seabed observatory NEMO-SN1. JASCO's Applied Sciences' Airgun Array Source Model was used to predict the sound levels for two configurations of 18-element airguns, and the signal was then propagated in a realistic environment utilizing JASCO's Full-Waveform Range dependent Acoustic Model from the source to the position of the receiver station. There is a qualitative agreement between the simulated, denoised, and recorded signals of the airgun arrivals. However, the signal simulated at 650 kilometers from the source stretches and shows fewer high-frequency components compared to the received one. Our study quantitatively shows that the peaks produced by a large airgun array during a scientific cruise, at 160–180 Hz are not masked by ambient noise even in busy shipping locations at a distance of 650 km