Comportement biogéochimique d’antimoine (Sb) et de tellure (Te) dans le milieu côtier : vers des scénarios de dispersion des radionucléides de Sb et de Te en cas de rejets accidentels de centrales nucléaires (projet AMORAD, ANR-11-RSNR-0002)
Antimoine (Sb) et tellure (Te), sont des contaminants peu étudiés (isotopes stables) et leurs radionucléides artificiels peuvent être rejetés dans le milieu aquatique lors des accidents nucléaires. La connaissance de leurs comportements biogéochimiques respectifs est nécessaire à l'évaluation du risque radiologique post-accidentel.Ce travail présente des données originales sur le comportement biogéochimique de Sb et de Te dans les systèmes de transition continent-océan, tels que l'estuaire de la Gironde et la rivière du Rhône. Un suivi de 14 ans et des campagnes océanographiques dans le bassin versant de l’estuaire de la Gironde ont permis d’identifier des concentrations, des flux, et des réactivités (variabilités spatio-temporelles et distribution solide/liquide) plus élevés pour Sb que pour Te, mettant en évidence un comportement additif pour Sb et de soustraction pour Te le long des gradients de salinité et de turbidité estuariennes. Des expériences couplant l’adsorption d’isotopes marqués sur des matières en suspension (MES) et des extractions sélectives des phases porteuses, suggèrent que les formes apportées de Sb et de Te sont plus mobiles et potentiellement plus biodisponibles que leurs équivalents naturels. De plus, l’observation de la bioaccumulation non-négligeable de Sb et de Te naturels dans les huîtres sauvages à l’embouchure de l’estuaire permet d’envisager une absorption potentielle de leurs homologues radioactifs.Ainsi, le développement de scenarios de dispersion de radionucléides rejetés dans les zones de transition dépendra (i) de la position géographique de la source (Rhône) et/ou de la zone de turbidité maximale (ZTM; système fluvio-estuarien de Gironde), (ii) de la situation hydrologique pendant et post accident, ainsi que (iii) de la réactivité biogéochimique et des temps de demi-vies des radionucléides. Les premiers scénarios de dispersion de radionucléides dans l'estuaire de la Gironde suggèrent (i) un transport préférentiel de Sb dissous vers la zone côtière, et (ii) une forte rétention de Te radioactif dans la ZTM si la dernière est présente en aval du site d’accident, impliquant le risque de migration saisonnière de la radioactivité vers la ville de Bordeaux pendant l’étiage suivant. Ainsi, la dynamique intra estuarienne (marée, débit et migration de la ZTM) sera le facteur prédominant dans le devenir de Te radioactif, depuis son rejet jusqu’à sa désintégration complète en iode radioactif. L’ensemble de ce travail met en évidence la nécessité d’une évaluation plus approfondie de la radiotoxicité potentielle de Sb et Te lors de leurs rejets en milieu aquatique.
(11/01/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Tellurium radionuclides produced by major accidental events in nuclear power plants
Environmental contextHistorical accidents in nuclear power plants have released radionuclides of several elements, including tellurium, to the environment. Although tellurium radionuclides are significant radioactive emission products, and show medium-term persistence in the environment, the mechanisms behind their widespread dispersion are unknown. Future research into the biogeochemical behaviour of stable tellurium is proposed as an appropriate approach to develop tellurium dispersion scenarios fundamental for post-accident management. AbstractTellurium (Te) is a technology critical element (TCE) and a non-negligible fission product in nuclear facilities. This work compiles the environmental releases of Te radionuclides registered after two nuclear power plant (NPP) major accidental events in human history (Chernobyl and Fukushima Daiichi). Despite the registered non-negligible activities and environmental persistence, Te radionuclides are scarcely monitored, which limits the current understanding of their biogeochemical behaviour, dispersion and fate in all environmental compartments. This lack of knowledge implies an underestimation of the role of Te radionuclides during and after accidents and its consideration in dispersion scenarios, which are fundamental for post-accidental risk assessment and management.
(Environmental Chemistry. vol. 16, n° 1448-2517, pp. 296-302, 01/01/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Characteristics of drowning victims in a surf environment: a 6-year retrospective study in southwestern France.
Drowning is the third cause of non-intentional injury death worldwide. Beaches of Gironde, in southwestern France, are exposed to strong environmental conditions, leading to rip currents and shore breaks. Bathing season usually lasts from April to October and is supervised from June till mid-September. The objective of this study was to study the characteristics of drowning victims along Gironde surf beaches and to identify peculiarities compared to national figures. All calls originating from beaches to the emergency call center of Gironde from 2011 to 2016 were analyzed. Patient data, filled by a physician based on information given by pre-hospital care team (lifeguards, paramedics or emergency physicians), were extracted from the emergency call center database. We used Szpilman classification (0 = rescue to 6 = cardiac arrest) to assess severity. Rescues are patients without respiratory impairment who needed lifeguards or helicopter intervention. We compared our findings with national studies carried every three years (2012 and 2015). We analyzed 5680 calls from beaches and included 4398, 576 of which were rescued from the water, including 352 without respiratory impairment (stage 0). Among drownings, 155 had cough only (stage 1), 26 pulmonary rales (stage 2), 9 pulmonary edema (stage 3) and 1 had pulmonary edema with hypotension (stage 4). Five rescued people were in respiratory arrest and 28 were in cardiac arrest. 77.5% were bathers, others were mainly surfers or body-boarders. Drowning victims median age was 24 (quartiles: 17-40), and sex-ratio was 1.44 Male/Female. Men were significantly older than women (34 vs. 26 years old), and severity from stage 1 to 4 was positively associated with age. Compared to national data, Gironde drownings had a higher proportion of 15-44 year-old victims, and the case-fatality was lower in Gironde (11.5%) than at the national level (27.4%, < 0.001). Along Gironde coast, drowning is rarely severe, concerns mostly young men; the age distribution could explain the different case-fatality. Further study is needed to identify environmental predictors of drowning.
(Injury Epidemiology. vol. 6, pp. 17, 01/01/2019)
ISPED, CHU Bordeaux, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
BINCOR: An R package for Estimating the Correlation between Two Unevenly Spaced Time Series
This paper presents a computational program named BINCOR (BINned CORrelation) for estimating the correlation between two unevenly spaced time series. This program is also applicable to the situation of two evenly spaced time series not on the same time grid. BINCOR is based on a novel estimation approach proposed by Mudelsee (2010) for estimating the correlation between two climate time series with different timescales. The idea is that autocorrelation (e.g. an AR1 process) means that memory enables values obtained on different time points to be correlated. Binned correlation is performed by resampling the time series under study into time bins on a regular grid, assigning the mean values of the variable under scrutiny within those bins. We present two examples of our BINCOR package with real data: instrumental and paleoclimatic time series. In both applications BINCOR works properly in detecting well-established relationships between the climate records compared.
(The R Journal. vol. 11, pp. 170-184, 01/01/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Mid-Holocene deepening of the Southeast Pacific oxycline
This study presents new high resolution sedimentary δ15N records from piston cores collected within and outside the present-day eastern south Pacific oxygen minimum zone along a latitudinal transect from 3.5°S to 15°S. Radiocarbon dating of foraminifera and organic matter show that the cores cover the Holocene and the last deglaciation with high sedimentation rate allowing interpretations at millennial to centennial timescale. High δ15N values, reaching 10‰ and large amplitude changes, with a magnitude of ~4‰, are observed in the southern part of the studied area during the last 18 ka BP. In contrast, the northern Peruvian cores located on the edge of the OMZ show low δ15N values varying from 4 to 6‰ with amplitude of only 1‰, during the same time period. δ15N values decrease in all the studied cores from the last deglaciation to the early Holocene (17 to 8.5 ka BP) and reach a minimum value during the mid-Holocene. The δ15N variations are attributed to microbial N-loss to N2, e.g. denitrification and/or anammox, and the characteristic 15N-enriched signal that is recorded in the underlying sediments under suboxic to anoxic conditions where denitrifiers thrive. Surprisingly, δ15N values from cores located within the OMZ show similar values as the more northern cores located outside the OMZ between 5 and 8.5 ka BP. This minimum is not related to local changes in export production, reconstructed from sedimentary organic carbon, total nitrogen and bromine, but appears to be controlled by changes in the ventilation of the area. The low δ15N values recorded between 8.5 and 5 ka BP are well correlated with more arid conditions developed along the Peruvian margin and an increase of the sea surface temperature gradient along the Peruvian margin and between the West and East Pacific along the equator, implying an intensification of the Hadley circulation and climatic conditions similar to La Niña-like state. Consequently, these mid-Holocene conditions led to greater ventilation of subsurface waters that deepened the Peruvian oxycline then revealing similar conditions as observed today in the northern part of the study area.
(Global and Planetary Change. vol. 172, n° 0921-8181, pp. 365-373, 01/01/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Environmental Context Mediates Biodiversity–Ecosystem Functioning Relationships in Coastal Soft-sediment Habitats
The ongoing loss of biodiversity and global environmental changes severely affect the structure of coastal ecosystems. Consequences, in terms of ecosystem functioning, are, however, difficult to predict because the context dependency of the biodiversity–ecosystem function relationships within these heterogeneous seascapes is poorly understood. To assess the effects of biological and environmental factors in mediating ecosystem functioning (nutrient cycling) in different natural habitats, intact sediment cores were collected at 18 sites on a grain size gradient from coarse sand to silt, with varying organic matter content and vegetation. To assess ecosystem functioning, solute fluxes (O2, NH4+, PO43−, Si) across the sediment–water interface were measured. The macrofaunal communities changed along the grain size gradient with higher abundance, biomass and number of species in coarser sediments and in habitats with more vegetation. Across the whole gradient, the macrofauna cumulatively accounted for 25% of the variability in the multivariate solute fluxes, whereas environmental variables cumulatively accounted for 20%. Only the biomass and abundance of a few of the most dominant macrofauna species, not the number of species, appeared to contribute significantly to the nutrient recycling processes. Closer analyses of different sediment types (grouped into coarse, medium and fine sediment) showed that the macrofauna was an important predictor in all sediment types, but had the largest impact in fine and medium sediments. The results imply that even if the ecosystem functioning is similar in different sediment types, the underpinning mechanisms are different, which makes it challenging to generalize patterns of functioning across the heterogeneous shallow coastal zones.
(Ecosystems. vol. 22, n° 1432-9840, pp. 137-151, 01/01/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Monocorophium acherusicum (Amphipoda, Corophiidae), a species commensal to Diogenidae in Arcachon Bay, Bay of Biscay
Abstract Hermit crabs are well-known to shelter many epibiotic, endobiotic or endolithic species in their shell, and examination of shells inhabited by hermit crabs in Arcachon Bay reveals the presence of several such species. Among them is the amphipod Monocorophium acherusicum, a species originally described from European waters and now known to be well distributed throughout the world, but not previously recorded to be commensal with hermit crabs, as reported herein.
(Crustaceana. vol. 92, n° 0011-216X, pp. 129-135, 01/01/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
High-resolution stratigraphic forward modeling of a Quaternary carbonate margin: Controls and dynamic of the progradation
The relationships between the margin sedimentary regime and the platform progradation are studied using forward stratigraphic numerical simulations on the Leeward (Western) prograding margin of the Great Bahama Bank (GBB) during the Quaternary (1.7–0 Ma). The corresponding sedimentary regime in the slope and the platform is well known from the ODP leg 166 and Bahamas Drilling Project wells located along the “Western line” seismic transect. However the sedimentary regime on the margin is not well established: the coral reefal margin observed before between 1.7 and 0.8 Ma in the well Clino is not active anymore at present-day, and the Holocene sedimentary regime is geometrically unable to account alone for the progradation. This study is based on three 2D high-resolution forward stratigraphic numerical modeling experiments with the software DionisosFlow that include the platform, margin and slope domains on the “Western Line Section” in the same sedimentary models. The results are compared to the six sedimentary cores and to the present day bathymetry in order to identify the more realistic scenario. The three experiments test different models of carbonate sediment production and transport. Experiment 1 shows that the highstand shedding of the fine-grained uncemented platform production is unable to reproduce the progradation and the present-day profile. Experiments 2 and 3 incorporate cemented facies in the margin, with the best results obtained with the cemented marginal wedges produced in Experiment 2 during platform emersion. From these results a high-resolution interpretation of the margin seismic section is proposed. This study shows that the platform progradation can be decoupled from the highstand shedding of the fine-grained platform production. It is dependent on the accumulation in front of the steep margin of coarse or cemented material. Before 0.8 Ma this corresponds to the coral reef identified in Clino. The transition after 0.45 Ma to 100-kyr large eustatic cycles with total platform flooding created two distinct marginal regimes: (1) during platform flooding aggrading accumulation of non-skeletal sands, and (2) during platform emersion prograding cemented marginal wedges produced in-situ.
(Sedimentary Geology. vol. 379, n° 0037-0738, pp. 77-96, 01/01/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFPEN, [Total Energies. Anciennement : Total, TotalFina, TotalFinaElf], CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS, UHH
Kleptoplastidic benthic foraminifera from aphotic habitats: insights into assimilation of inorganic C, N and S studied with sub-cellular resolution
(Environmental Microbiology, n° 1462-2912, 01/01/2019)
LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, WHOI, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, EPFL
Into the deep: A coarse-grained carbonate turbidite valley and canyon in ultra-deep carbonate setting
New high-resolution multibeam mapping images detail the southern part of Exuma Sound (Southeastern Bahamas), and its unchartered transition area to the deep abyssal plain of the Western North Atlantic, bounded by the Bahama Escarpment extending between San Salvador Island and Samana Cay. The transition area is locally referred to as Exuma Plateau. The newly established map reveals the detailed and complex morphology of a giant valley draining a long-lived carbonate platform from its upper slope down to the abyssal plain. This giant valley extends parallel to the slope of Long Island, Conception Island, and Rum Cay. It starts with a perched system flowing on top of a lower Cretaceous drowned main carbonate platform. The valley shows low sinuosity and is characterized by several bends and flow constrictions related to the presence of the small relict isolated platforms that kept alive longer than the main platform before drowning and merging tributaries. Turbidite levees on either side of the valley witness the pathway of multiple gravity flows, generated by upper slope over steepening around Exuma Sound through carbonate offbank transport, some of them locally >15°, and resulting slumping. In addition, additional periplatform sediments are transported to the main valley through numerous secondary slope gullies and several kilometre-long tributaries, draining the upper slopes of cays and islands surrounding Exuma Plateau. Some of them form knickpoints indicating surincision of the main Exuma Valley which is consistent with an important lateral supply of the main Exuma Valley. Prior to reaching the abyssal plain, the main valley abruptly evolves into a deep canyon, 5 km in width at its origin and as much as 10 km wide when it meets the abyssal plain, through two major knickpoints named “chutes” with outsized height exceeding several hundred of meters in height. Both chutes are associated with plunge pools, as deep as 200-m. In the deepest pools, the flows generate a hydraulic jump and resulting sediment accumulation. When the canyon opens to the San Salvador abyssal plain, the narrow, deep, and strong flows release significant volume of coarse-grained calcareous sediments in numerous turbidite layers interbedded with fine mixed siliciclastic and carbonate sediments transported by the Western Boundary Undercurrent (WBUC) along the Bahama Escarpment. Carbonate gravity flows exiting the canyon decelerate at the abyssal plain level and construct a several-kilometre-wide coarse-grained deep-sea turbidite system with well-developed lobe-shape levees, partially modified by the flow of strong contour-currents along the Bahama Escarpment.
(Marine Geology. vol. 407, n° 0025-3227, pp. 316-333, 01/01/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, KFUPM, IPGP, INSU - CNRS, UPD7, UR, IPG Paris, CNRS, RSMAS, CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS, UNIGE, IFPEN