The influence of substrate type for alpine community composition and change under global change
(12/06/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR LESSEM, IRSTEA, UGA [2016-2019], Fédération OSUG, LECA, USMB [Université de Savoie] [Université de Chambéry], CNRS, UGA [2016-2019]
Bathymetric Controls on Rotational Surfzone Currents
A multibeach Lagrangian data set was used to determine bathymetric controls on flow variability within the surfzone. Seven microtidal flow regimes were examined, six containing rip channels, under moderate shore normal waves. Three selected zones exemplified varying bathymetric control: (i) a alongshore uniform zone; (ii) a shallow rip channel at an oblique angle to shore normal; and (iii) a deep, shore-normal rip channel. Bathymetric variables included alongshore nonuniformity (φ) and channel angle relative to shore normal (α). Low-frequency flow (0.01 Hz) was described by velocity (U), velocity standard deviation (σU), angular deviation (σθ), and bias in direction of eddy rotation (ζbias). Observations of the exemplar zones indicated the following: (i) near-zero mean flow with transient eddies within the alongshore uniform zone; (ii) low mean flow with high ζbias within the oblique channel; and (iii) strong mean flow with low ζbias in the deep channel. Bathymetry and flow variables were spatially averaged and linearly correlated, scaling for wave forcing. Normalized flow variables were found to be interdependent and were correlated with bathymetric variability, with [U ∝ φ], [(U/σU) ∝ φ], and [σθ ∝ − φ], all with (R2 ≥ 0.8). A correlation was determined between α and ζbias (R2 ≥ 0.7, increasing as zone width is decreased), with peak ζbias within oblique channels. Based on these results, a conceptual model is introduced to predict flow behavior for known bathymetry. Surfzone currents were found to span a dynamic continuum from transient eddies on alongshore uniform bathymetry, to channelized rip currents, forced by bathymetric three-dimensionality and mediated by channel geometry.
(Journal of Geophysical Research: Earth Surface. vol. 123, n° 2169-9003, pp. 1295-1316, 01/06/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Historical Nankai-Suruga megathrust earthquakes recorded by tsunami and terrestrial mass movement deposits on the Shirasuka coastal lowlands, Shizuoka Prefecture, Japan
Geological investigations of coastal sediment sequences play a key role in verifying earthquake and tsunami characteristics inferred from historical records. In this paper, we present a multi-proxy investigation of a coastal lowland site facing the Nankai-Suruga megathrust and appraise evidence for tsunamis and earthquake-triggered terrestrial mass movements occurring over the last 800 years. Combining a high-resolution chronology with X-ray computed tomography and analyses of particle size, diatoms, pollen, non-pollen palynomorphs and aerial photographs, we present the most compelling geological evidence of the 1361 CE Kōan (also known as Shōhei) tsunami reported to date from any site along the megathrust. This finding is consistent with either of two recent hypotheses: a single larger rupture of both the Nankai and Tōnankai regions or two smaller ruptures separated by a few days. Enhancing the site chronology using Bayesian age modelling, we verify evidence for inundation during the 1498 CE Meiō tsunami. While previous investigations identified evidence for historically recorded tsunamis in 1605, 1707 and 1854 CE and a storm surge in 1680 or 1699 CE, we encountered a thick sand layer rather than discrete extreme wave deposits in this interval. The overprinting of evidence highlights the potential for geological records to underestimate the frequency of these events. A terrestrial mass movement also deposited a sand layer at the site; radionuclide dating and aerial photographs provide independent confirmation that this may have been triggered by intense shaking in 1944 CE during the most recent great Nankai-Suruga megathrust earthquake.
(The Holocene. vol. 28, n° 0959-6836, pp. 968-983, 01/06/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Aqueous chlorination of sulfamethazine and sulfamethoxypyridazine: Kinetics and transformation products identification
Sulfonamides (SNs) are synthetic antimicrobial agents. These substances are continually introduced into the environment, and they may spread and maintain bacterial resistance in the different compartments. The chlorination of 2 SNs, namely, sulfamethazine (SMT) and sulfamethoxypyridazine (SMP), was investigated to study their reactivity with chlorine at typical concentrations for water treatment conditions. Experiments conducted in purified water show an acceleration of SMT and SMP degradation of a factor 1.5 by comparison to drinking water matrix. This difference is due to pH variation and competitive reactions between SNs and mineral and organic compounds, with chlorine in drinking water. In the presence of an excess of chlorine (6.7 μmol·L−1) in ultrapure water at pH 7.2, second-order degradation rate constants were equal to 4.5 × 102M−1·s−1 and 5.2 × 102M−1·s−1 for SMT and SMP, respectively. The structures of transformation products were investigated by liquid chromatography tandem mass spectrometry analyses with equimolar concentrations between chlorine and SNs. SO2 elimination, cyclization, and electrophilic substitutions were the main pathways of by-products formation. Moreover, the toxicity of the proposed structures was predicted by using toxicity estimation software tool program. The results indicated that most by-products may present developmental toxicity.
(Journal of Mass Spectrometry. vol. 53, n° 1076-5174, pp. 614-623, 01/06/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The morphotypes of Neogloboquadrina pachyderma : Isotopic signature and distribution patterns in the Canadian Arctic Archipelago and adjacent regions
Neogloboquadrina pachyderma represents a key planktonic foraminifera species in the boreal Atlantic and has been extensively used as a paleoceanographic tool in polar to subpolar environments. The species shows an intraspecific morphological variability, displaying at least 5 different morphotypes previously documented from northern and southern oceans. The present work focuses on the distribution of these morphotypes in modern surface sediment samples from the Canadian Arctic Archipelago (CAA). Our results, obtained for the first time for this area, show the prevalence of morphotypes 1, 2 and 3 (abundance on average 19%, 48% and 22%, respectively). Two types of assemblages were observed in the inner and outer parts of the Northwest Passages on the basis of the abundance and diversity of morphotypes. Their geographical and vertical positions regarding the water depth in the CAA argue for a strong influence of water mass stratification on morphotype distribution. The detailed morphometric study of test morphology together with SEM imagery provides a way to re-evaluate and complete previous classifications of N. pachyderma morphotypes. This morphological approach is supported by stable isotope analyses that document a link between δ18O and δ13C and morphotype mean sizes. This relationship is interpreted as indicative of water column position, with large morphotypes living in relatively shallower (but also fresher, colder and more productive) waters compared to small morphotypes. The former interpretation is further supported by the increased pore concentration in larger morphotypes, which is tentatively interpreted as a strategy to increase buoyancy and to adapt to lower salinity. Consequently, we propose that a coupled approach of using morphology and stable isotopes may constitute an improved tool for oceanographic reconstructions (particularly water column stratification) when used with N. pachyderma assemblages. Furthermore, the additional morphometric criteria defined in the current work are the basis of a useful and updated identification key for N. pachyderma morphotypes.
(Marine Micropaleontology. vol. 142, n° 0377-8398, pp. 13-24, 01/06/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Réponse morphologique de la plage du Lido de Sète suite à l’installation d’un atténuateur de houle.
Plusieurs relevés topo-bathymétriques et un système de suivi vidéo sont exploités afin d’étudier la réponse morphologique de la plage du Lido de Sète (Golfe du Lion) suite à l’installation d’un ouvrage type atténuateur de houle. Les observations montrent que l’atténuateur de houle a profondément impacté la morphologie et la dynamique des barres d’avant côte et du trait de côte. Contrairement à ce qui est très souvent constaté le long des plages sans barre pré-littorale, la formation de tombolo n’a pas suivi l’installation de l’ouvrage. Un nouveau scénario est observé dans lequel l’élargissement de la plage résulte de son couplage avec la nouvelle forme de barre plus linéaire et orientée de manière parallèle à la structure. L’atténuateur de houle impacte également la dynamique de l’avant côte dans le secteur adjacent situé à plusieurs kilomètres de la structure en affectant la variabilité spatiale du phénomène de Net Offshore Migration (NOM) des barres sableuses. Cette étude montre le rôle important joué par les barres sableuses dans la réponse du trait de côte suite à l’installation d’ouvrages maritimes.
(01/06/2018)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UM
Oyster transcriptome response to Alexandrium exposure is related to saxitoxin load and characterized by disrupted digestion, energy balance, and calcium and sodium signaling
Harmful Algal Blooms are worldwide occurrences that can cause poisoning in human seafood consumers as well as mortality and sublethal effets in wildlife, propagating economic losses. One of the most widespread toxigenic microalgal taxa is the dinoflagellate Genus Alexandrium, that includes species producing neurotoxins referred to as PST (Paralytic Shellfish Toxins). Blooms cause shellfish harvest restrictions to protect human consumers from accumulated toxins. Large inter-individual variability in toxin load within an exposed bivalve population complicates monitoring of shellfish toxicity for ecology and human health regulation. To decipher the physiological pathways involved in the bivalve response to PST, we explored the whole transcriptome of the digestive gland of the Pacific oyster Crassostrea gigas fed experimentally with a toxic Alexandrium minutum culture. The largest differences in transcript abundance were between oysters with contrasting toxin loads (1098 transcripts), rather than between exposed and non-exposed oysters (16 transcripts), emphasizing the importance of toxin load in oyster response to toxic dinoflagellates. Additionally, penalized regressions, innovative in this field, modeled accurately toxin load based upon only 70 transcripts. Transcriptomic differences between oysters with contrasting PST burdens revealed a limited suite of metabolic pathways affected, including ion channels, neuromuscular communication, and digestion, all of which are interconnected and linked to sodium and calcium exchanges. Carbohydrate metabolism, unconsidered previously in studies of harmful algal effects on shellfish, was also highlighted, suggesting energy challenge in oysters with high toxin loads. Associations between toxin load, genotype, and mRNA levels were revealed that open new doors for genetic studies identifying genetically-based low toxin accumulation.
(Aquatic Toxicology. vol. 199, n° 0166-445X, pp. 127-137, 01/06/2018)
LEMAR, IRD, IFREMER, UBO EPE, CNRS, IFREMER, GENOTOUL, UT3, Comue de Toulouse, ENVT, Toulouse INP, INSERM, CNRS, Toulouse INP, Comue de Toulouse, INRAE, MIAT INRAE, INRAE, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GeT-PlaGe, GET, GENOTOUL, UT3, ENVT, INSERM, CNRS, Toulouse INP, INRAE, INRAE, NMFS, NOAA
Premières observations de la dynamique hydro-sédimentaire de l'estuaire Maroni (Guyane)
En comparaison aux estuaires des zones tempérées, les estuaires tropicaux entourés par la mangrove sont moins connus et documentés. Dans le cadre du projet EFHEMAR financé par l’Office de l’Eau de la Guyane (2016-2018), les premières données hydromorpho-sédimentaires de l’estuaire du Maroni ont été collectées, dans le but de réaliser une description actualisée de l’estuaire, ainsi que dans le but d’alimenter un modèle en cours de développement. L’analyse des enregistrements de marée indique que l’estuaire, au moins pour sa partie aval, est convergent, avec une amplification du marnage au moins jusqu’à Crique-Vache , situé à 8 km de l’embouchure. Les courants de marée mesurés suivent les oscillations semi-diurnes de flot et de jusant ; en saison sèche ils induisent des remises en suspension de sédiments fins en amont de l’estuaire ; en saison humides ils sont complètement dominés par l’écoulement fluvial. Les mesures de salinité montrent de forts contrastes saisonniers en termes de stratification, contrôlée par le régime fluvial. En saison sèche l’estuaire est partiellement mélangé aussi bien à marée haute qu’à marée basse. En saison humide, un coin salé est bien identifié à marée haute, mais à marée basse le gradient salin est expulsé de l’estuaire. L’analyse des premières mesures de turbidité montre que des contrastes forts existent aussi en termes de concentration en matière en suspension, avec un estuaire très turbide en saison sèche, et des eaux plus claires en saison humide. Un "bouchon vaseux" semble persister près de l’embouchure en saison humide, tandis qu’en surface les eaux douces fluviales arrivent chargées en matières en suspension plus récentes.
(pp. 293-300, 31/05/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEEISA, IFREMER, UG, CNRS, Cerema Direction Eau Mer et Fleuves, Cerema, Cerema Equipe-projet HA, Cerema, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS
UHAINA : A parallel high performance unstructured near-shore wave model
UHAINA is a new phase-resolving free surface wave model for coastal engineering 21 problems. It is based on the most advanced and recent contributions in coastal 22 modelling from the french institutes EPOC, IMAG, IMB, and INRIA BSO. It solves a 23 non-classical version of the depth-integrated fully-nonlinear and weakly-dispersive 24 equations of Green-Naghdi, which allows an efficient numerical implementation. 25 UHAINA relies on libraries developed at the INRIA BSO center, such as AeroSol for 26 its hydrodynamic core, and PaMPA and SCOTCH to handle data management for 27 distributed memory parallel computation. The use of these libraries, in particular 28 AeroSol, offers a wide range of possibilities including arbitrary high-order finite 29 element discretizations, hybrid meshes (structured and unstructured), as well as an 30 advanced programming environment specially designed by the purpose of performance 31 and HPC. These properties will lead in the coming years to the release of a new efficient 32 and robust open source wave modelling platform, available for a large community of 33 users and very suitable for practical coastal applications.
(. vol. 15, pp. 47-56, 29/05/2018)
CARDAMOM, IMB, UB, Bordeaux INP, CNRS, Inria, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CAGIRE, LMAP, UPPA, CNRS, Inria, LMAP, UPPA, CNRS, IMAG, UM, CNRS, IMB, UB, Bordeaux INP, CNRS
Étude comparative des méthodes de reconstruction du champ de vagues à partir de la mesure de pression : Application à la plage de La Salie
La reconstruction du champ de vagues basée sur la théorie linéaire, communément appelée méthode de la fonction de transfert, décrit assez bien les caractéristiques moyennes des vagues. Elle est couramment utilisée pour déterminer les paramètres statistiques des vagues mais sous-estime la hauteur des plus grosses vagues. Cependant, bien estimer ces vagues énergétiques est primordial pour l'étude des risques côtiers lors d'évènements extrêmes. La reconstruction linéaire nécessite l'application d'une fréquence de coupure du spectre d'énergie qui induit une perte d'information. Des techniques empiriques qui essaient de combler artificiellement le spectre d'énergie n'améliorent que très peu les plus grosses vagues. Récemment, des formules simples à implémenter permettant des reconstructions linéaires et non-linéaires ont été développées. Nous présentons et comparons dans cet article différentes méthodes de reconstruction du champ de vagues à partir de la pression mesurée au fond lors d'une campagne de mesure réalisée sur la plage de La Salie en avril 2017. Notre étude est centrée sur des vagues très non-linéaires et faiblement dispersives. Une analyse vague à vague met en évidence la capacité de la reconstruction non-linéaire faiblement dispersive à reproduire la hauteur et l'asymétrie des plus grosses vagues contrairement à la formule linéaire couramment utilisée en ingénierie côtière. Mots-clés : Théorie linéaire, non-linéarité, capteurs de pression, reconstruction du champ de vagues.
(29/05/2018)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, DMA, ENS-PSL, PSL, CNRS