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Seamless nearshore topo-bathymetry reconstruction from lidar scanners: A Proof-of-Concept based on a dedicated field experiment at Duck, NC
No full textInternational audienceAccurate observations of the nearshore bathymetry, including within the breaking wave region, are critical for the prediction of coastal hazards, and improved understanding of sandy beach morphological response to storms. In this paper, we implement the recent Boussinesq theory-based depth inversion methodology of Martins et al. (Geophys. Res. Lett., 50 (2023), Article e2022GL100498) to single-and multibeam lidar datasets collected during a dedicated field experiment on a sandy Atlantic Ocean beach near Duck, North Carolina. Compared with common approaches based on passive remote sensing technology (e.g., optical imagery), lidar scanners present several key advantages, including the capacity to directly measure the beach topography, waveforms and the cross-shore variations in mean water levels due to wave action (e.g., the wave setup), leading to the seamless reconstruction of a vertically-referenced beach topo-bathymetry. Given the potentially gappy nature of lidar data, particular attention is paid to the robust computation of surface elevation spectral and bispectral quantities, which are at the base of the proposed non-linear depth inversion methodology. Promising results on the final topo/bathymetry are obtained under contrasting wave conditions in terms of non-linearity and peak period, with an overall root-mean square error below 0.3 m obtained along a cross-shore transect covering both shoaling and breaking wave conditions. The accuracy of the final bathymetry in the shoaling and outer surf regions is generally found to be excellent, with similar skills as previously obtained in laboratory settings (relative error < 10 -15%). Under the most energetic conditions, an underestimation of the wave phase velocity spectra is observed within the surf zone with all theoretical frameworks, potentially owing to surf zone vortical motions not yet accounted for in the present methodology. This underestimation of the wave phase velocities results in a relatively large overestimation of the mean water depth, between 30% to 100% depending on the theoretical framework. With the methodology described herein, lidars bring new perspectives for seamlessly mapping the nearshore topo/bathymetry, and its temporal evolution across a wide range of scales. Although currently limited to a single cross-shore transect, we believe that opportunities exist to integrate multiple remote sensors, which could address individual sensor limitations, such as coverage (lidar) or the incapacity to directly measure waveforms (optical imagery).</div
Addressing Out-of-Label Hazard Detection in Dashcam Videos: Insights from the COOOL Challenge
No full textInternational audienceThis paper presents a novel approach for hazard analysis in dashcam footage, addressing the detection of driver reactions to hazards, the identification of hazardous objects, and the generation of descriptive captions. We first introduce a method for detecting driver reactions through speed and sound anomaly detection, leveraging unsupervised learning techniques. For hazard detection, we employ a set of heuristic rules as weak classifiers, which are combined using an ensemble method. This ensemble approach is further refined with differential privacy to mitigate overconfidence, ensuring robustness despite the lack of labeled data. Lastly, we use state-of-the-art vision-language models for hazard captioning, generating descriptive labels for the detected hazards. Our method achieved the highest scores in the Challenge on Out-of-Label in Autonomous Driving, demonstrating its effectiveness across all three tasks. Source codes are publicly available at https://github.com/ffyyytt/COOOL_2025
Mercury speciation and stable isotopes in emperor penguins: First evidence for biochemical demethylation of methylmercury to mercury-dithiolate and mercury-tetraselenolate complexes
No full textInternational audienceApex marine predators, such as toothed whales and large petrels and albatrosses, ingest mercury (Hg) primarily in the form of methylmercury (MeHg) via prey consumption, which they detoxify as tiemannite (HgSe). However, it remains unclear how lower trophic level marine predators, termed mesopredators, with elevated Hg concentrations detoxify MeHg and what chemical species are formed. To address this need, we used high energy resolution X-ray absorption near edge structure spectroscopy paired with nitrogen (N) and Hg stable isotopes to identify the chemical forms of Hg, Hg sources, and species-specific δ202Hg isotopic values in emperor penguin, a mesopredator feeding primarily on Antarctic silverfish. The penguin liver contains variable proportions of MeHg and two main inorganic Hg complexes (IHg), Hg-dithiolate (Hg(SR)2) and Hg-tetraselenolate (Hg(Sec)4), each characterized by specific isotopic values (δ202MeHg = 0.3 ± 0.2 ‰, δ202Hg(SR)2 = -1.6 ± 0.2 ‰, δ202Hg(Sec)4 = - 2.0 ± 0.1 ‰). Using δ15N as a tracer of food source, we show that Hg(SR)2 is likely not obtained through dietary intake, but rather is present as a biochemical demethylation product. Furthermore, on average, female penguins transferred Hg to the egg strictly as MeHg in the egg albumen but as mixtures of MeHg and IHg in the membrane (89 % and 11 %, respectively) and yolk (32 % MeHg and 68 % Hg(Sec)4). Despite IHg species in eggs, MeHg is still the main species quantitatively transferred by the mother to the chick because of the disproportionate mass of the MeHg-rich albumen compared to the yolk. This work highlights the transformation of MeHg to Hg(SR)2 during demethylation for the first time in multicellular organisms, but further work is needed to understand the formation of Hg(SR)2 in the presence of relatively abundant Se biomolecules in lower trophic level predator species
Electrochemical processes occurring on previously cathodically polarized AISI 316L stainless steel electrodes during emersion in marine atmosphere
No full textInternational audienceCarbon and low alloy steel structures immersed in seawater are commonly protected against corrosion by cathodic protection. In some complex structures, even though care is taken to avoid galvanic coupling, other metallic materials may be in contact with the protected carbon/low alloy steel and thus cathodically polarized too. The present study deals with complex structures that undergo immersion / emersion cycles. It is focused on the behavior of AISI 316 L stainless steel parts affected by cathodic protection and aims to provide information about the electrochemical behavior of stainless steel during emersion periods. For that purpose, AISI 316 L electrodes were polarized at -850 mV/ Ag-AgCl-sw or -1050 mV/ Ag-AgCl-sw during two months in natural seawater at 10 • C and subsequently left at open circuit potential in a marine atmosphere for two weeks. µ-Raman spectroscopy analysis showed that the deposits were in any case mainly composed of aragonite CaCO 3 but XRD analysis revealed the presence of brucite Mg(OH) 2 at -1050 mV/ Ag-AgCl-sw . Linear polarization resistance and electrochemical impedance spectroscopy measurements were carried out during the emersion period and showed that the calcareous deposit formed at -1050 mV/ Ag-AgCl-sw retained more water during emersion than the deposit formed at -850 mV/ Ag-AgCl-sw . Moreover, it delayed the increase in OCP associated with the interruption of cathodic protection. These differences are attributed to the underlying brucite film only present at -1050 mV/ Ag- AgCl-sw that tends to dissolve when cathodic protection is interrupted, thus maintaining a higher pH at the metal/ seawater interface.</div
Les fouilles de Troesmis
No full textLa Fabrique consulaireÉdouard Engelhardt (1828-1916) was a diplomat and jurist. From 1856 to 1867 he was a delegate of France to the European Danube Commission and stayed at the commission's headquarters in the Danube port of Galaţi throughout his term of office. In the summer of 1862, he identified the site of Iglitza, known since 1860 as an "ancient Roman city", as that of Troesmis, the seat of several Roman legions. He mentioned the site in a booklet published in 1862 in Galati in which he studied the ancient and contemporary geography of the Danube delta. At his instigation, a French archaeological mission completed its own research in 1865. The surveys carried out on this occasion illustrate the beginnings of an evolution in archaeological practices that are beginning to emerge from exclusively artistic and epigraphic research
Energyscapes pinpoint marine megafauna feeding hotspots in the Mediterranean
No full textInternational audienceOcean giants shape the structure and functioning of marine food webs via trophic top–down controls, landscapes of fear, vertical and horizontal redistribution of nutrients, energy, and matter. Yet, they face threats from overfishing, pollution, habitat degradation, and climate change, and one-third of marine megafauna species are at risk of extinction, ultimately endangering the resilience of entire ecosystems. In such a context, knowing when and where megafauna find resources to balance their substantial energy requirements is critical for their management. Through an energyscape approach integrating abundance censuses, diet, and energy requirements, we investigated the prey consumption patterns of Mediterranean marine megafauna during the summer. We thereby shed light on a diverse guild of species composed of fishes, mammals, reptiles, and birds and estimated that 4.1 million individuals consume 1.6 million tons of prey each summer, pelagic cephalopods being the primary food resource and cetaceans and tunas being key players in the community. Spatial patterns in prey consumption reflected the diverse distribution and needs of the megafauna species and underlined the critical importance of the western Mediterranean for the megafauna community. Conservation strategies should prioritize spatial and biological diversity to safeguard megafauna and ecosystem functions across the Mediterranean basin
Wild and farmed Saccharina latissima in Europe: genetic insights for sustainable cultivation, traceability and environmental challenges
No full textInternational audienceAbstract Kelp cultivation is expanding rapidly worldwide, although the aquaculture of Saccharina latissima (sugar kelp) in Europe remains in its early stages. However, major concerns have emerged about the potential impact of selected cultivars of the species on native populations of S. latissima which are already vulnerable to stressors including climate change. To address these concerns and support sustainable cultivation, it is essential to characterise genetic diversity and structure of wild kelp populations to monitor potential farm-to-wild gene flow. In this study we used 21 microsatellite loci to characterise the genetic structure of 24 natural and 3 farmed populations of S. latissima along European coasts. Results confirmed strong genetic differentiation between the northern and southern coasts, refining the boundaries between these two clusters compared to previous studies. Within each cluster, a clear genetic substructure was detected, with population differentiation being far more pronounced in the southern cluster. Cultivated sporophytes exhibited pedigrees that were all traced back to the local parent populations. Bayesian model-based structure analysis, discriminant analysis of principal components and assignment tests revealed no significant genetic differentiation between the farms and their wild populations. This indicates that farmed populations and neighbouring populations share the same gene pool, reflecting current cultivation practices. These findings contribute to understanding risks of gene flow between wild and farmed populations and demonstrate that strain traceability is feasible. Additionally, the study highlights the challenge European seaweed farmers face in securing reliable seedling stock, especially in the context of global change
Combining transient dynamics and logistic‐asymptotic growth to study the recovery of two seabird populations after rat eradication
No full textInternational audienceUnderstanding demographic processes is crucial in ecology and conservation biology to assess how populations respond to environmental pressures. Although demographic parameters often react to disturbances, populations may remain in unstable age structures (transient dynamics) following such events. To explore the influence of transient dynamics in masked booby and red‐footed booby populations on Tromelin Island 15 years after rat eradication, we compared observed, transient, and asymptotic growth using count and capture–recapture (CR) data. CR data were used to estimate survival probability from Cormack–Jolly–Seber models and other vital rates such as breeding frequency and age at first breeding. We coupled asymptotic growth with a density‐dependent model for breeding site availability to project long‐term population growth. Both populations exhibited high adult survival (0.91–0.96) and breeding success (0.46–0.54). The masked booby juvenile survival was also high (0.86). Populations are expected to grow until breeding sites are saturated, in about a century. Comparison of asymptotic and transient growth suggests that population growth is linked to an intrinsic process and that both populations have undergone disruption in their age structure likely due to past predation by rats. Although the observed population growth appears to align more closely with transient growth, we could not entirely exclude the possibility that differences between asymptotic and observed growth rates may be due to data scarcity or age‐related variation in demographic parameters. Nevertheless, the study of transient dynamics allowed a better understanding of the differences observed between field counts and estimated asymptotic growth rates based on matrix population models
Mesurer la contribution de l’écopâturage au cadre de vie
No full textInternational audienceMethods for assessing the social and environmental performance of agricultural systems often overlook their impacts on the living environment. Based on the case study of the Nantaise Cow’s local chain and on interviews with local stakeholders, we develop a set of indicators that integrates social and landscape amenities generated by urban pasture practices. This framework broadens impact assessment to include territorial socio-environmental sustainability.Les méthodes d’évaluation sociale et environnementale des systèmes agricoles négligent souvent leurs impacts sur le cadre de vie. En nous appuyant sur le cas de la filière locale de la Vache Nantaise et à partir d’enquêtes auprès d’acteurs du territoire, nous construisons un tableau de bord intégrant les aménités sociales et paysagères issues de l’écopâturage. Ce cadre permet d’élargir l’analyse des impacts à la durabilité socio-environnementale du territoire