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International audience; Because of its size and geographical position, the Cherbourg roadstead appears as a favourable site for Marine Renewable Energy (MRE) industry. As a result, Cherbourg harbour has undergone profound changes (2015 and 2016) due to the installation of industrial infrastructures to service the needs of expanding MRE further offshore. However, little is known about the morpho-sedimentary distribution and associated dynamics of seabed sediments before and after harbour transformations. This study focuses on sedimentary dynamics using detailed morphological and sedimentological analyses based on data acquired before changes (2012). The main map includes a unique bathymetric map (1:35,000) and sedimentary maps showing the percentage of the characteristic grain size fractions of 184 seabed samples. Despite the high tidal conditions, the roadstead construction had a significant impact on the sedimentary facies and distribution. This study provides a basis for future investigations on geomorphological evolution linked to the impact of anthropogenic development.

Anthropocene mineral diversity is the result of the purification of metals naturally combined with other chemical elements in natural environment. Moreover, the advent of human mining and manufacturing mineral-like compounds has experienced a punctuation event in diversity and distribution owing to the pervasive impact of human activities. In this context, the wastes of an abandoned historical mine, Huelgoat mine (Brittany, France), famous during the eighteenth and the nineteenth century contain significant amounts of chemical elements potentially dangerous to the environment. Lead concentration and Pb-bearing phases were quantified in 7 sediments samples located from mine upstream to the Aulne estuary (100 km downstream to the mine). Results show very high concentrations of lead in the stations located upstream and downstream of the Huelgoat mine, using X-ray fluorescence spectroscopy, ranging from 7000 mg/kg downstream of the mine to a natural concentration of about 80 mg/kg upstream. At the same time, Pb-bearing phases were identified depending on the particle sizes, fine ( 50 μm), using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), total organic carbon (TOC), and pH analyses. For the first time, evidence of anthropogenic mineral “iodoplumbate” formation has been described in a natural environment.

Anthropocene mineral diversity is the result of the purification of metals naturally combined with other chemical elements in natural environment. Moreover, the advent of human mining and manufacturing mineral-like compounds has experienced a punctuation event in diversity and distribution owing to the pervasive impact of human activities. In this context, the wastes of an abandoned historical mine, Huelgoat mine (Brittany, France), famous during the eighteenth and the nineteenth century contain significant amounts of chemical elements potentially dangerous to the environment. Lead concentration and Pb-bearing phases were quantified in 7 sediments samples located from mine upstream to the Aulne estuary (100 km downstream to the mine). Results show very high concentrations of lead in the stations located upstream and downstream of the Huelgoat mine, using X-ray fluorescence spectroscopy, ranging from 7000 mg/kg downstream of the mine to a natural concentration of about 80 mg/kg upstream. At the same time, Pb-bearing phases were identified depending on the particle sizes, fine (50 μm) and coarse (50 μm), using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), total organic carbon (TOC), and pH analyses. For the first time, evidence of anthropogenic mineral "iodoplumbate" formation has been described in a natural environment.

The remediation of metal-polluted water using bacterial biofilms is a promising technology. In order to help its development, the present study aims to evaluate the feasibility to utilize XRF spect...

International audience; Geochemistry and sedimentary studies allow to highlight surface processes. Traditional geochemistry studies use mapping techniques (GIS) and multivariate analyzes (PCA and HAC) to highlight the spatial distribution of concentrations of one or several chemical parameters (Delgado et al., 2010; Coura Borges et al., 2014; El-Amier et al., 2017; Hou et al., 2017; Bodrud-Doza et al., 2019; Jin et al., 2019). Granulometric parameters are used to study sedimentary transport, especially through the Grain Size Trend Analysis (GSTA) approach, which integrates three parameters: mean, sorting and skewness (MacLaren, 1982; Gao and Collins, 1994, Poizot et al., 2006). In the context of the increasing pressure of human activities on marine coastal ecosystems, the study of sedimentary disturbances remains a challenge. The eastern part of the Bay of Seine (France) is very anthropized by the presence of harbour activities. The dredging sediments of The Havre Harbour are deposited on subtidal area. To understand sedimentary mechanism in this mixed area, a geochemical and sedimentological study was conducted at the beginning of 2016 (Baux et al., 2019). A sampling of 179 subtidal stations and 16 stations in the harbour basins and in the Seine estuary were studied. Geochemical elemental composition (18 calibrated elements) was obtained through X-Ray Fluorescence spectrometry and infrared spectrometry (TOC). On this dataset, multi-treatments were applied and the results compared:-Mapping of the spatial distribution of the concentrations of each chemical element.-PCA analyzes and selection of the information-bearing parameters and mapping of the PCA results.-Application of the "classical" GSTA approach on the three granulometric parameters.-"Innovative" integration of the chemical parameters and PCA results in the GSTA approach. The results show the necessity of multidisciplinary research and the interest of geochemical tracers to study coastal sediment dynamics and to highlight the impact generated by anthropogenic activities. The geochemical GSTA approach confirms the sedimentary dynamics observed by Baux et al. (2019) and appears more robust than the methods conventionally used. To generalize this approach, an adaptation of the concepts governing the GSTA approach will be developed.

(IF 3.78; Q1); International audience; Dredged sediments have different physical and chemical characteristics compared with the sediments in place, which generates multiple effects on the environment.In this study, we show that the sampling strategy used to monitor the effects of dredge spoil deposition on the surrounding environment can lead to different interpretations. It appears that sediment sample replicates may or may not be necessary, depending on the studied area, the prevailing environmental forcings before sediment sampling and the combination of these two factors. The proposed modus operandi allows us to optimize both the confidence on the obtained results and the cost of the sediment studies (sampling and laboratory analyses). The results are based on the sediment fine fraction, which is considered as a key environmental component due, for example, to its strong association with the structure of benthic faunal communities as well as its role in the build-up of pollutants.

International audience; Microbial contamination of aggregates collected near an Atlantic salmon farm, in the Cherbourg roadstead, was followed monthly over one year to study the dynamics of Vibrio spp. and explore their impact on farmed fish. Salmon state of health was followed through blood and histopathological analyses. Vibrio were systematically found in aggregates with particularly high concentration in August. The Splendidus clade was strongly dominant in aggregates as well as in gills, and an increase in Vibrio diversity was observed in summer and autumn. Results did not demonstrate that aggregates directly impact the bacterial community of gills, but they suggested an aggregates-gills interaction. Gill contamination was correlated with water temperature and probably impacted by amoebae. Vibrio renipiscarius and Vibrio toranzoniae were isolated in North Atlantic for the first time. A better understanding of the interaction between marine aggregates, Vibrio spp. and fish is essential to improve salmon cage farming.

In the shallow waters of the Bay of Concarneau (South Brittany, France), previous studies reported a dense settlement of the species Haploops (tube-dwelling bioengineer amphipod) that perfectly overlaps a field of pockmarks. A possible mechanistic link may therefore exist between the Haploops colonies and the shallow pockmarks. To test this hypothesis, interferometry sonar and sub-bottom profiler chirp data were acquired in two new areas located in the marine estuary of the Loire River, “La Lambarde” and “Le Croisic”. The new sites share the same sedimentary and geological characteristics as those found in the Bay of Concarneau. The three sites are similarly located in shallow and muddy environments above a faulted Middle Eocene formation that is incised by paleo-valleys. Despite different hydrodynamic conditions and estuarine influence, in the two new investigated areas, the Haploops also settle within the pockmarks field limits. To better constrain the association pockmarks/Haploops, we compared the sedimentary features, seismic signatures and total organic carbon (TOC) content of the sediment. Active pockmark chimneys displaying highly reworked profiles and slightly higher TOC contents suggest a local deeper source of organic matter, which might be an important source of nutrient for the Haploops. In Southern Brittany the pockmarks/Haploops spatial overlap is not a simple coincidence and may therefore present a general pattern for identification of settlement preferences of the specie.

(IF 2.42; Q2); International audience; Geochemical studies are becoming more and more frequent in the context of the increasing pressure of human activities on marine coastal ecosystems and represent an appropriate tool to assess anthropogenic disturbances. Moreover, it is difficult to find discriminant markers. The eastern part of the Bay of Seine (English Channel) is highly impacted by the presence of harbour activities, fishing and sediment extraction. Dredged sediment from the Grand Port Maritime du Havre (GPMH) are deposited at the subtidal Octeville site, in the north-eastern part of the mouth of the Seine estuary (mixed sediment area). To understand natural and anthropogenic sedimentary mechanisms in this area, a geochemical and sedimentological study was conducted at the beginning of 2016. A dense sampling campaign including 179 stations was carried out between Cap de La Hève and Cap d’Antifer. For comparison, sampling was carried out in the harbour (13 samples in basins strongly or very weakly dredged), in the dredged grab itself and in the Seine estuary sediment (one station in the brackish zone and two stations in the river freshwater zone). Elemental compositions were determined by X-Ray Fluorescence spectrometry and infrared spectrometry. Using PCA (Principal Component Analysis), seven constituents were selected (Si, As, S, Pb, Rb, organic Br and TOC) to determine the area influenced by dumped spoil and the sediment transport directions. Sediment areas in dynamic equilibrium display a TOC gradient perpendicular to the coastline, linked to granulometric variations due to a combination of the swell and tidal currents. In the study area, dredged sediment are finer grained and have undergone changes due to the influence of diagenetic processes characteristic of the harbour environment. As a result, these sediment are enriched in sulphides, Pb, TOC and Rb, which allows us to highlight the in-situ deposited sediment spoil. Dumped sediment and the area subject to their influence are clearly identified since they locally disrupt the natural dynamic equilibrium state.

(IF 3.02 [2018]; Q1); International audience; The Rade de Cherbourg (RdC), in the North Cotentin (Normandy, English Channel) is the only French coastal zone where an offshore salmon farm has been in operation over the past three decades. Our study leads to the identification of the Ecological Quality status of benthic habitats based on a one-year survey (2013–2014) underneath and near the cages as well as in non-impacted areas lying outside the influence of salmon farming. The semi-diurnal high tide regime of the Rade de Cherbourg (5 to 8 m tidal range from neap to spring tide) should prevent any significant accumulation of Organic Matter (OM) under the cages. Nevertheless, higher Total Organic Carbon (TOC) and the presence of opportunistic species at sampling stations under and near the cages indicate an impact of salmon farming on the benthic habitats. Three benthic assemblages are identified, corresponding to three sediment types with different levels of OM enrichment. The presence of several indicator species, such as the polychaete worm Capitella minima belonging to the Capitellidae, reflects the local impact of fish farming without long-term accumulation of OM in the shallow waters of the RdC. Moreover, one of the main characteristics of the macrofauna of the RdC and neighbouring zones is the current very high abundance and dominance of the tanaid Apseudopsis latreillii in diverse sediment types. Benthic indices (AMBI, M-AMBI, and BO2A) were also able to distinguish three main zones in relation to the distance to salmon cages.

International audience; In the context of the increasing pressure of human activities on marine coastal ecosystems, the study of sedimentary disturbances remains a challenge. The eastern part of the Bay of Seine is very anthropized by the presence of harbour activities (heavy shipping, dredging and sediment dumped deposit …), fishing, sediment extraction… The dredging sediments of the Grand Port Maritime du Havre (GPMH) are deposited on the Octeville site, in the northeastern part of the Seine estuary mouth. The high hydrodynamics (swell and tide) associating with the constant supply of fines particles from both the Seine estuary and the English Channel combined with dumped sediment deposition create a mixed sedimentary zone. To understand sedimentary mechanism in this area, a geochemical and sedimentological study was conducted at the beginning of 2016. A sampling of 179 stations (distance of 500m between stations) was conducted between cape of La Hève and cape of Antifer. In addition, sampling in the harbour basins and in the dredge itself (13 samples in basins strongly or very weakly dredged) and in the Seine estuary (one station in the brackish zone and two stations in freshwater) were also studied. Geochemical elemental composition was obtained through X-Ray Fluorescence spectrometry (SPECTRO xSORT, 43 elements) and infrared spectrometry (LECO CS 744, Total Organic Carbon: TOC). Multiple PCA (Principal Component Analysis) had been conducted to reduce the large set of variables into a more concise one that retains most of the existing variations. Only seven elements had been conserved in the last PCA (Si, As, S, Pb, Rb, organic Br and TOC). Deposited sediments in the studied area have the same geochemical pattern irrespective of whether their originate from natural or dredged sources. The only difference is that dredged sediments are finer and have undergone changes under the influence of diagenetic processes which are characteristic of harbour environment. As a result, they are enriched in S, TOC, Rb and Pb, which allows to highlight in-situ the dredged deposits. To determine the area under dumped sediments influence and sediments transport directions, we sought if deposits were in a " dynamical equilibrium state ". To do that, TOC is the more accurate parameter. Area under dynamical equilibrium state display, a gradient perpendicular to the shoreline tied up to the granulometrical refinement gradients due to the swell and tide combined actions. Dumped sediments and area under their influence are clearly highlighted as they disrupt the natural dynamical equilibrium state.

International audience; Dans les études sédimentaires côtières, l'équilibre dynamique est défini, comme un équilibre entre le transport des particules, l'érosion et le dépôt, en fonction des processus physico-chimiques et hydrodynamiques associés, dont la marée et la houle. En baie de Seine et dans l'estuaire, les processus de dépôt et d'érosion des particules fines sont principalement étudiés sur la base d'études sédimentologiques, de calculs de taux de sédimentation, de modélisation et/ou de leur association avec la macrofaune benthique. Dans le présent travail, une autre approche est envisagée, sur la base de traceurs géochimiques, pour comprendre les mécanismes sédimentaires présents entre le cap de La Hève et celui d'Antifer (baie de Seine Orientale). L'étude a été menée sur des prélèvements sédimentaires réalisés début 2016 à l'aide d'une benne Shipeck. Un échantillonnage de 179 stations, disposées en lignes parallèles à la côte (espacées de 500 m), a été mené entre le cap de La Hève et le port d'Antifer, zone incluant le site de dépôt de dragage du Grand Port Maritime du Havre (Octeville). Pour caractériser les sources, des prélèvements ont été effectués dans les bassins portuaires fortement et faiblement dragués (13 stations) ainsi que dans l'estuaire de la Seine, en eau saumâtre et en eau douce (trois stations). La composition géochimique a été obtenue par XRF (X-ray fluorescence, Spectro xSORT) et par analyseur carbone/soufre (LECO CS 744), pour le dosage du carbone organique total (COT). La sélection des éléments porteurs d'information a été menée progressivement par la réalisation de plusieurs Analyses en Composantes Principales (ACP). Ces dernières ont permis de sélectionner sept éléments (Si, As, S, Pb, Rb, Br organique et COT).

International audience; Harbours need to maintain a sufficient water column to allow good navigation. Dredged sediment may be deposited at sea. Nevertheless, they may have different physical and chemical characteristics compared with the sediment in place which generate multiple effects on the benthic environment. Studies on the impacts of such eco-environmental disruptions are numerous and necessary. Unfortunately, no sampling schedule patterns have been proposed despite the OSPAR Convention (www.ospar.org) covering Northwest Europe, and the London Convention (http://londonprotocol.imo.org), neither of which impose a "uniform" design for monitoring programmes. What is the best way of measuring sediment cover around a site used for dumping to obtaining the best representation of the sediment coverage? In the eastern Bay of Seine (France), sediment management and dredging practices (" Grand Port Maritime " Rouen and Le Havre) constitute one of the main anthropic pressure and driving factors in the morphological evolution of the Seine estuary and its sedimentary hydrodynamics. This study is focused on the environment surrounding the Octeville dumping site (used by the " Grand Port Maritime du Havre ").

Organic matter degradation is the engine behind the biogeochemical evolution of sediments during burial. Previous research has shown that eogenesis is the seat of a complex interplay between organic matter, microbes and the most reactive part of inorganic compounds, such as clay minerals. To explore the variability and stability of bromine and clay minerals as geochemical and mineral tracers, we selected an eastern Mediterranean core that has a high degree of stability in the quality and quantity of organic matter through time at a one-million-year scale and great variability in organic matter content at a 10 ky scale. According to the very low maximal burial depth reached by these sediments (the core length is only 36.5 m), physical parameters, such as temperature and pressure, did not significantly influence the evolution of the studied parameters during the burial history. The bulk clay mineralogy of organic-rich and organic-poor sediments is similar all along the investigated core material; smectite predominates over kaolinite. The only identified authigenic minerals are biogenetic framboidal pyrite and manganese oxides. The X-ray data and the chemical compositions of the smectite are characteristic of a montmorillonite which is representative of a detrital Nile source. At a one-million-year scale, the organic matter content has no significant influence on clay eogenesis, and detrital smectite and kaolinite remain unchanged. Bromine is present in marine organic matter as organobromine compounds. During eogenesis, bromine is released from organic matter as bromide ion, resulting in an increase in the bromide concentration in the pore water with depth. Dissolved bromide can be used as a conservative tracer of the debromination of sedimentary organic matter. For the first time, we established that solid-phase BrOrg is a reliable tracer of debromination rates in marine sediments. The rate of debromination depends on the organic matter content. The rate increases from less than 2.3 x 10(-4) mu molBrOrg mol. C-1. y(-1) to 6.3 x 10(-4) mu molBrOrg mol. C-1. y(-1) when TOC varies from 0.17 to 3%. This increase is related to the development of the bacterial population and provides the basis for further investigation of other oceanic basins. For TOC values > 4%, the rate of debromination decreases. We propose that the bioavailability of organic matter is another factor of variability in the debromination rate., La dégradation de la matière organique est le moteur de l'évolution biogéochimique des sédiments au cours de l'enfouissement. Les recherches précédentes ont montré que l'éogenèse est le siège d'interférences complexes entre la matière organique, les microorganismes et la partie la plus réactive des composés inorganiques comme les minéraux argileux. Pour étudier la variabilité et la stabilité du brome et des minéraux argileux comme traceurs géochimiques et minéralogiques, nous avons choisi une carotte de Méditerranée orientale qui présente une grande stabilité de la qualité et de la quantité de la matière organique à l'échelle de 1 million d'années et une grande variabilité de cette quantité à une échelle de 10 ka. Considérant le faible enfouissement de ces dépôts (la carotte ne fait que 36,5 m de long), les paramètres physiques comme la température et la pression, n'influencent pas significativement l'évolution des paramètres étudiés. La minéralogie des argiles demeure semblable dans toute la carotte, que les sédiments soient riches ou pauvres en matière organique ; la smectite domine sur la kaolinite. Les seuls minéraux authigéniques identifiés sont la pyrite framboïdale biogénique et des oxydes de manganèse. Les données de diffraction de rayons X et la composition chimique de la smectite correspondent à celles d'une montmorillonite représentative des apports détritiques du Nil. À l'échelle de 1 million d'années, la quantité de matière organique n'influence pas l'éogenèse des minéraux argileux, la kaolinite et la smectite détritique demeurent inchangées. Le brome est dans la matière organique marine sous forme de composés organobromés. Pendant l'éogenèse, le brome est libéré de la matière organique sous forme d'ion bromure, il en résulte une augmentation avec l'enfouissement de la concentration en bromure dans l'eau interstitielle. Le bromure dissous peut être utilisé comme un traceur conservatif de la débromination de la matière organique sédimentaire. Pour la première fois, nous avons établi que le brome organique particulaire est un traceur valide du taux de débromination dans les sédiments marins. Le taux de débromination dépend de la quantité de matière organique. Il augmente de 2,3 × 10−4 μmolBrOrg mol.C−1.a−1 à 6,3 × 10−4 μmolBrOrg mol.C−1.a−1 quand le carbone organique total (COT) varie de 0,17 à 3 %. Cette augmentation est en relation avec le développement des populations bactériennes et fournit une base pour l'étude d'autres bassins océaniques. Pour les teneurs en COT > 4 %, le taux de débromination diminue. Nous proposons que la biodisponibilité de la matière organique soit un autre facteur de variabilité du taux de débromination.

International audience; In the English Channel, the brittle-star Ophiothrix fragilis is a common epifaunal species typically found on pebbles in habitats with strong tidal currents. This species forms dense aggregations on the seafloor, supporting populations that can reach up to 7500 ind m−2 in the eastern part of the Baie de Seine, offshore from Antifer harbour. Here, O. fragilis occurs in an area with unexpected amounts of fine-grained sediment. Some of these mud deposits are made up of unusually compact black muds, an indication of the development of anoxic conditions in surficial sediments. To highlight a potential link between silting up and dense O. fragilis populations, and identify the interactions between environmental conditions and the population dynamics of this species, we analyse the data from three surveys corresponding to exceptional situations: (1) just after a Seine flood; (2) just after a storm and (3) after a period of ten months without any flood or storm. Four parameters are taken into account: number of brittle stars per 0.25 m2, Fine Fraction percentage, Total Organic Carbon and Total Sulphur. The main environmental forcings appear to be Seine river inflow, regional circulation dependent on tidal currents and the occurrence of storms. O. fragilis is able to geoengineer its environment in various ways and at different rates. Silting up is enhanced by increasing abundance of O. fragilis and takes place at a very fast rate. As a result, floods and storms reflecting instantaneous events give rise to a steady-state situation established between the abundance of this species and the fine fraction percentage. Anoxic conditions are dependent on the degradation of organic matter and require more time to be established. After many months in the absence of any disturbing events, anoxic conditions are developed in non-compacted muddy sediments (stability situation) and represent the normal surficial situation when the sediment becomes compacted (compact black muds). The development of anoxic conditions is dependent on the abundance of the O. fragilis population and occurs at a very slow rate.

To characterize a sedimentary environment, it is risky to take a single sample when the spatial variability is unknown. A reference station has to reflect the natural variations in order to allow the creation of long time series. However, it can remain unclear whether the temporal changes are real or due to a spatial variation. We highlight here the importance of spatial variability at the scale of precision of the GNSS. It appears that the number and arrangement of replicates depend on the environment and the studied parameters. InC, TOC and TS show a sufficiently low spatial variability to allow temporal tracking using GNSS without multiplying samples. The fine fraction percent shows a high spatial variability over small distances. The study of this parameter in the framework of temporal tracking requires a knowledge of its spatial variability during each period of sampling, and hence leads to the multiplication of samples.

Clastic mud beds rich in continental organic matter are observed recurrently in the Nile deep-sea turbidite system. They formed during flooding periods of the river similar to those that induce sapropel formation and occurred during periods of increased density stratification of the eastern Mediterranean. The very fine-grained flood deposits are intercalated within pelagic sediments, sapropels and Bouma-type turbidites. These flood deposits form by the successive reconcentrations of surface (hypopycnal) plumes by convective sedimentation, which in turn generate a fine-grained low-energy hyperpycnal flow. Sea-level high stands seem also to favor hypopycnal plume formation and increase clastic mud bed formation. Consequently, these muddy clastic beds provide a direct link between deep-marine sedimentary records and continental climatic change through flood frequency and magnitude.

The eastern Bay of the Seine (English Channel) was the subject in 1991 of a sampling survey of superficial sediments. Geostatistic tools were used to examine the complexity of the spatial distribution of the fine-grained fraction (o50 mm). A central depocentre of fine sediments (i.e. content up to 50%) oriented in a NW–SE direction in a muddy coastal strip, in a very high energy hydrodynamical situation due to storm swells and its megatidal setting, is for the first time recognised and discussed. Within this sedimentary unit, the distribution of the fine fraction is very heterogeneous, with mud patches of less than 4000m diameter; the boundary between these mud patches and their substratum is very sharp. The distribution of this fine fraction appears to be controlled by an anticyclonic eddy located off the Pays de Caux. Under the influence of this, the suspended material expelled from the Seine estuary moves along the coast and swings off Antifer harbour, towards the NW. It is trapped within this eddy because of the settling of suspended particulate matter. Both at a general scale and a local scale the morphology (whether inherited or due to modern processes) has a strong influence on the spatial distribution of the fine fraction. At the general scale, the basin-like shape of the area facilitates the silting, and the presence of the submarine dunes, called ''Ridins d'Antifer'', clearly determines the northern limit of the muddy zone. At a local scale, the same influence is obvious: paleovalleys trap the fine sediments, whereas isolated sand dunes and ripples limit the silting. This duality of role of the morphology is therefore one of the reasons why the muddy surface is extremely heterogeneous spatially. The presence of an important population of suspension feeding echinoderm, the brittle-star Ophiothrix fragilis Abildgaard, has led to a local increase in the silting, and to the modification of the physicochemical and sedimentological parameters. A complex relationship is shown to occur between the amount of fine fraction and the number of brittle-stars (ind.m2). Classical statistical methods are not appropriate to study the spatial distribution of the mud fraction, because the spatial component of the percentage of the distribution is not integrated in the analysis. On the other hand, this is the main property of the geostatistic concepts. The use of geostatistic tools within a strict and clearly identified procedure enables the proposal of an accurate cartography. Further application of the proposed protocol (based on a semivariographic study and a conditional simulation interpolation) for surficial sediments mapping will help explain spatial and temporal variations of fine-grained fraction. Then assessments of sedimentation and erosion stages allow highlighting signature of environmental processes.

International audience; There is a paucity of studies showing long-term changes in the population dynamics of dominant benthic epifaunal species, especially echinoderms, in relation to biological and environmental factors. In the English Channel, the brittle-star Ophiothrix fragilis is a common epifaunal species, mainly found in strong tidal currents characterised by benthic habitats with pebbles. However, in the Bay of Seine, O. fragilis lives on gravel and coarse sandy sediments; more locally, it occurs where there are unexpected amounts of fine particles for such high hydrodynamic areas. This species forms dense aggregations, supporting large populations up to 7450 ind m 2. This paper analyses the long-term spatio-temporal changes of O. fragilis aggregations over the last 25 years in the eastern part of the Bay of Seine through observations obtained from several scientific programmes from 1986 to 2010. This area is characterised as a tidal environment affected by the Seine estuary and is subject to potential sediment supply from the dumping site of the Le Havre harbour dredging operations. During all surveys, there was a similar pattern: persistent patches with high abundances of O. fragilis and sites without O. fragilis, showing that there was a high heterogeneity of the spatial population pattern. Interactions between environmental conditions and ophiurid aggregations (e.g., storm waves, Seine floods and patches) are suggested to explain these patterns.

International audience; Sampling the sea bottom surface remains difficult because of the surface hydraulic shock due to water flowing through the gear (i.e., the bow wave effect) and the loss of epifauna organisms due to the gear's closing mechanism. Slow-moving mobile epifauna, such as the ophiuroid Ophiothrix fragilis, form highdensity patches in the English Channel, not only on pebbles like in the Dover Strait or offshore Brittany but also on gravel in the Bay of Seine (>5000 ind m 2 ). Such populations form high biomasses and control the water transfer from the water column to the sediment. Estimating their real density and biomass is essential for the assessment of benthic ecosystem functioning using trophic web modelling. In this paper, we present and discuss the patch patterns and sampling efficiency of the different methods for collecting in the dense beds of O. fragilis in the Bay of Seine. The large Hamon grab (0.25 m 2 ) highly under-estimated the ophiuroid density, while the Smith McIntyre appeared adequate among the tested sampling grabs. Nowadays, diving sampling, underwater photography and videos with remote operated vehicle appear to be the recommended alternatives to estimate the real density of such dense slow-moving mobile epifauna.

International audience; Multiproxy analyses were performed on core MS27PT recovered in hemipelagic sediments deposited on the Nile margin in order to reconstruct Nile River palaeohydrological fluctuations during the last 100,000 years. The strontium and neodymium isotope composition of the terrigenous fraction and the major element distribution reveal large and abrupt changes in source, oscillating between a dominant aeolian Saharan contribution during arid periods and a dominant Nile River contribution during pluvial periods. Iron content shows a strong correlation with strontium and neodymium isotopes. This allows the use of a high-resolution continuous Fe record as a proxy of Blue Nile sediment input over the last 100,000 years. The detailed Fe record, with approximately 10 years resolution during pluvial periods, is consistent with subtropical African records of well-dated lake level fluctuations and thus constitutes a first continuous high resolution record of the East African monsoon regime intensity over Ethiopia.;The detailed Fe record shows the two main known pluvial periods attributed to strengthening of the African monsoon over Ethiopia, the Nabtian period from 14 to 8 ka cal BP and the Saharan period from 98 to 72 ka BR For the first time, the last glacial period (Marine Isotope Stage (MIS) 2,3 and 4) is documented with a continuous record showing large oscillations between high and low East African palaeo-monsoon regimes.;The end of the Nabtian period occurred at 8 ka in core MS27PT, i.e. much earlier than on the East Equatorial African region where it ended around 5.5 ka. We interpret this as evidence that the southward shift of the rain belt occurred 3000 years earlier over the Eastern Ethiopian Highland and propose that the gradual southward migration of the rain belt was associated with highly variable intensity and longer rainy seasons from 8 to 5 ka. During the last glacial period, two wet periods are present around 60-50 ka BP and 38-30 ka BP. These two humid periods are in phase with the rise of atmospheric CH4 concentrations suggesting that wetland tropical African area was one of the sources of the atmospheric CH4 during the MIS 3. During the Last Glacial Maximum and MIS 4, high Saharan aeolian influxes in phase with records of aeolian dust deposited in East Antarctica are documented. This study highlights the importance of reconstructions of monsoon rainfall fluctuation at high temporal resolution to better understand the link between low- and high-latitude climate variability at millennial timescales.

International audience; This paper presents an overview of the evolution of the Nile deep-sea turbidite system during the last 200 kyr, over a series of glacial to interglacial cycles. Six individual deep-sea fans were identified from an extensive field data set. Each fan comprises a canyon, channel system and terminal lobes. Two of these fan systems were possibly active at the same time, at least during some periods. Large-scale slope failures destroyed channel segments and caused the formation of new submarine fan systems. These slope failures thus played an important role in the overall evolution of the turbidite system. During the last glacial maximum (ca 25 to 14·8 ka) the central and eastern parts of the Nile deep-sea turbidite system were relatively inactive. This inactivity corresponds to a lowstand in sea-level, and a period of arid climate and relatively low sediment discharge from the Nile fluvial system. Rapid accumulation of fluvial flood-derived deposits occurred across the shallower part of the submarine delta during sea-level rise between ca 14·8 and 5 ka. The most recent deep-sea channel–lobe system was very active during this period of rising sea-level, which is also associated with a wetter continental climate and increased sediment and water discharge from the Nile. Increased sediment deposition in shallower water areas led to occasional large-scale slope failure. The Nile deep-sea turbidite system was largely inactive after ca 5 ka. This widespread inactivity is due to retreat of the coastline away from the continental shelf break, and to a more arid continental climate and reduced discharge of sediment from the Nile. The Nile deep-sea turbidite system may be more active during periods of rising and high sea-level associated with wetter climates, than during lowstands, and may rapidly become largely inactive during highstands in sea-level coupled with arid periods. These acute responses to climate change have produced sedimentary/stratigraphic features that diverge from traditional sequence models in their nature and timing. This large-scale sedimentary system responded to monsoon-driven climate change and sea-level change in a system-wide and contemporaneous manner.

Understanding the recent formation of a sedimentary system such as a deep-sea turbidite system (DSTS) requires an accurate stratigraphic control on deposits. Due to the important terrigeneous input which disrupts the sedimentary record, DSTS is an environment where stratigraphic control is difficult to assess. Most of the time, traditional stratigraphic tools are not accurate enough. This has led to a rather limited number of studies concerning stratigraphy in DSTS. In this study, we examine several hemipelagic long piston cores collected from the Nile DSTS (eastern Mediterranean), in order to understand the recent evolution of the complex sedimentary system in this area. The first aim of this study is to show how to obtain a reliable timeframe in DSTS. Indeed, we provided a detailed ecostratigraphical scheme based on planktonic foraminiferal distribution, oxygen isotope records and lithostratigraphy (sapropels and tephra) of three cores where the sedimentation is least disturbed. We have identified 29 foraminiferal ecozones during the last 250,000 years BP, with an approximately 2000-year time resolution. The time span of each ecozone was constrained by the oxygen isotope record, 14 C AMS radiometric data, tephrochronology and the sapropel chronology. These high-resolution ecostratigraphical time subdivisions have been applied in discontinuous mixed hemipelagic/turbiditic sequences of a levee record. This example shows how to date gravity events, formation and time periods of sedimentary accumulations.

Plus qu’un triomphe commercial mondialise, Avatar illustre un tournant dans l’histoire technique des offres spectaculaires, un moment de l’imaginaire occidental et une rencontre symptomatique entre archaisme bio et innovations numeriques.

International audience; Under modern conditions, the reoxygenation of eastern Mediterranean deep water is the result of the formation of dense bottom water in the southern Adriatic Sea. Oxygen isotopic records of planktonic foraminfera used as a paleosalinity tracer show that Po River and/or the alpine glaciers meltwater are not directly responsible of the inhibition of the deep water formation in the Adriatic, during sapropel (S1) formation at 9,000 years B.P.. Sedimentological evidence indicates that fully oxygenated conditions in the deep Adriatic occurred only by 1,650-&_100 years B.P., a long time after the total reoxygenation of the deep eastern Mediterranean. Organic carbon content and isotopic ratio indicate that persistence of a reduced sediment phase until 1,650 years B.P., does not result from increased primary productivity or large input of terrestrial organic matter.

International audience