MODEX: LABORATORY EXPERIMENT EXPLORING SEDIMENT SPREADING OF A MOUND UNDER WAVES AND CURRENTS
The dispersal of sand from submerged mounds in the nearshore is driven by the interplay of processes such as converging and recirculating flows, changing roughness, bed slope effects and wave focusing/refraction. This morphological diffusivity is key to understanding sand bars in shallow seas, tidal inlets, estuaries, and the nearshore response to human interventions such as nourishments and dredging. Most of the work on the evolution of submerged mounds has been based on fluvial studies, focusing on flow without waves. In these cases, circular mounds tend to deform to crescentic (barchan) shapes. In contrast, observations of sandbars and berms in the nearshore subjected to waves show much more complex translation and deformation behavior. This contribution introduces the laboratory MOrphological Diffusivity Experiment (MODEX) aimed at examining morphological diffusivity under different forcing conditions. The experiment particularly addresses the linkages between small scale (local) effects (e.g. bed slope, bedforms) on the adjustment of sandy mounds.
(01/06/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, AGBAR, UB
Gene expression patterns and related enzymatic activities of detoxification and oxidative stress systems in zebrafish larvae exposed to the 2,4-dichlorophenoxyacetic acid herbicide.
The present study aims to assess the effects of 2,4-D herbicide on biotransformation and oxidative stress status of zebrafish larvae. Animals were exposed to a range of sublethal concentrations (0.02-0.8 mg/L) and biomarkers at transcriptomic level and biochemical level were assessed. Chemical analysis with showed that the bioaccumulation of 2,4-D in 96 hpf zebrafish larvae were increased in a concentration-dependent manner. This herbicide induced significant effects at both gene expression and enzymatic activities levels after at 96 hpf. Results of mRNA expression showed a differential transcription regulation with all target genes depending on the tested concentrations. The mRNA level of gsr and cyp1a were up regulated at the highest dose of herbicide (0.8 mg/L). The gene expression of gstp1 showed an up regulation at lower dose (0.02 mg/L) and a down regulation at the highest dose (0.8 mg/L) of 2,4-D. A significant induction of EROD activity and inhibition of GST activity were noted in groups exposed to 0.8 mg/L of 2,4-D. Considering the antioxidant defenses, the activity of CAT was increased in larvae exposed to 0.8 mg/L of herbicide and GPx activity was induced at lower doses of 2,4-D (0.02 and 0.051 mg/L). Moreover, peroxidative damage, assessed as MDA content, was markedly increased in larvae exposed to high 2,4-D concentration. Overall, the present study data indicate that bioaccumulation of 2,4-D in 96 hpf zebrafish larvae and alterations in detoxification and oxidative stress related parameters, likely associated with ROS production, which may endanger the embryo-larval stages development of fish.
(Chemosphere. vol. 224, n° 0045-6535, pp. 289-297, 01/06/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Formation and evolution of glauconite in the Demerara Contourite depositional system related to NADW circulation changes during late Quaternary (French Guiana)
The Demerara Plateau is a marginal plateau which forms a bathymetric relief on the sea floor. Here, contourite deposits have been studied in detail, following the recent discovery of contourite sequences likely related to the bottom currents and linked both to contour current and peculiar sea-floor morphology. A chronostratigraphic framework, based on δ18O relative variations and palaeomagnetic events in sediment cores allows correlating sediment processes to current intensity changes and major climate phases (glacial or interglacial). The studied sediments are enriched in glauconitic grains. In addition, the glauconite mineralogical maturity can easily correlate to low sedimentation rate and slightly energetic bottom currents on the seafloor. Based on these data and using the glauconitic authigenic mineral as proxy for inferring the degree of winnowing at the sediment-water interface, we might put forward the hypothesis that the intensity of NADW is higher during the glacial stages and lower during interglacial periods.
(Journal of South American Earth Sciences. vol. 92, n° 0895-9811, pp. 167-183, 01/06/2019)
CEFREM, UPVD, INSU - CNRS, CNRS, GM, IFREMER, CEFREM, UPVD, INSU - CNRS, CNRS, GEOPS, UP11, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Terrestrial plant microfossils in palaeoenvironmental studies, pollen, microcharcoal and phytolith. Towards a comprehensive understanding of vegetation, fire and climate changes over the past one million years
The Earth has experienced large changes in global and regional climates over the past one million years. Understanding processes and feedbacks that control those past environmental changes is of great interest for better understanding the nature, direction and magnitude of current climate change, its effect on life, and on the physical, biological and chemical processes and ecosystem services important for human well-being. Microfossils from terrestrial plants – pollen, microcharcoal and phytoliths – preserved in terrestrial and marine sedimentary archives are particularly useful tools to document changes in vegetation, fire and land climate. They are well-preserved in a variety of depositional environments and provide quantitative reconstructions of past land cover and climate. Those microfossil data are widely available from public archives, and their spatial coverage includes almost all regions on Earth, including both high and low latitudes and altitudes. Here, we (i) review the laboratory procedures used to extract those microfossils from sediment for microscopic observations and the qualitative and quantitative information they provide, (ii) highlight the importance of regional and global databases for large-scale syntheses of environmental changes, and (iii) review the application of terrestrial plant microfossil records in palaeoclimatology and palaeoecology using key examples from specific regions and past periods.
(Revue de Micropaléontologie. vol. 63, n° 0035-1598, pp. 1-35, 01/06/2019)
PACEA, UB, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UMR ISEM, Cirad, EPHE, PSL, UM, CNRS, UNIL, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, OCCR, UNIBE, LCE, CNRS, UFC, UBFC
First assessment on trace elements in sediment cores from Namibian coast and pollution sources evaluation
(Science of the Total Environment. vol. 669, n° 0048-9697, pp. 668-682, 01/06/2019)
IAEA-MEL, IAEA, GEOAZUR 7329, INSU - CNRS, UniCA, CNRS, IRD [Occitanie], UniCA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Quantification of diagenetic transformation of continental margin sediments at the Holocene time scale
Early diagenesis processes in the Bay of Biscay have been studied previously on short interface cores. In order to complete the data base and to characterize anoxic biogeochemical processes that affect Quaternary deposits, 1–3 m long gravity cores were collected at 150, 550, 1000 and 2000 m water depth on the continental slope of the south-eastern part of the Bay of Biscay. The aim of this work was to determine how a recorded signal could be changed in the several thousand-year situation of the Holocene period. For that, we determined radiocarbon and 210Pb dating, sedimentological characteristics, and the vertical distribution of particulate and pore water biogeochemical compounds. The sediment consists of a muddy facies deposited continuously during the Holocene. Results show that the distribution of redox sensitive compounds follows the well-established depth sequence of diagenetic reactions governed by the preferential use of the electron acceptor for the bacterially mediated oxidation of organic matter. Mineralization of organic matter occurs down to the bottom of the cores studied, indicating that Holocene sediment of the Bay of Biscay are in a transient state and they keep on being diagenetically transformed today. Effects of anoxic processes on buried sediments were estimated from fluxes induced by chemical gradients in pore waters. Anoxic processes consume up to 3.6 mg particulate organic carbon (POC) per g of dry sediment. They yield also precipitation of secondary calcium carbonate, which represent up to 5% of total buried carbonates. Early diagenetic reactions, which affect proxies commonly used in paleo-oceanography, such as POC, carbonates, phosphorus, or manganese, should be quantified in order to distinguish the part of a sedimentary record being the result of past environmental conditions from that due to post-depositional diagenetic processes. Diagenesis of Holocene deposits also contributes to a low, but significant fraction of N and P flux to the Bay of Biscay sea water.Previous article in issueNext art
(Continental Shelf Research. vol. 180, n° 0278-4343, pp. 63-74, 01/06/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LPG-ANGERS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS, LDO, INSU - CNRS, UBO EPE, CNRS
Southern Ocean sea ice and frontal changes during the Late Quaternary and their linkages to Asian summer monsoon
(Quaternary Science Reviews. vol. 213, n° 0277-3791, pp. 93-104, 01/06/2019)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Toxicity of binary mixtures of pesticides to the marine microalgae Tisochrysis lutea and Skeletonema marinoi: Substance interactions and physiological impacts
(Aquatic Toxicology. vol. 211, n° 0166-445X, pp. 148-162, 01/06/2019)
BE, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LUBEM, UBO EPE
Imidacloprid induces adverse effects on fish early life stages that are more severe in Japanese medaka (Oryzias latipes) than in zebrafish (Danio rerio)
Neonicotinoids are widely used insecticides that have frequently been found in freshwater with concentrations ranging from ng to μg/L. It is known that these compounds impact non-target invertebrates, such as bees and gammaridae, in terms of toxicity and behavior, but impacts and species differences on vertebrates such as fish are little explored. The aim of this study was to investigate and compare the effects of one widely used neonicotinoid, imidacloprid, on development and behavior of two fish model species: Zebrafish (Danio rerio) and Japanese medaka (Oryzias latipes). Fish were exposed for 5 (zebrafish) and 14 (medaka) days from 0.2 to 2000 μg/L imidacloprid by aqueous exposure. Survival, development, behavior and histological features were monitored and organism-internal concentrations and biotransformation products measured. Imidacloprid caused sublethal effects in both species but the effects were much stronger in medaka with deformities, lesions and reduced growth being the most prominent impacts. Due to the overall longer time of development, time-integrated exposure of medaka was about 2-fold higher compared to zebrafish, potentially accounting for parts of the sensitivity differences. Our results underline the importance of taking species sensitivity differences into account especially when considering that medaka responded at imidacloprid concentrations that have been measured in the environment.
(Chemosphere. vol. 225, n° 0045-6535, pp. 470-478, 01/06/2019)
EAWAG, UniMe, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IBP, D-USYS, ETH Zürich, ENAC, EPFL
Dynamics of microbial communities across the three domains of life over an annual cycle with emphasis on marine mucilage in the Southern Bay of Biscay resolved by microbial fingerprinting
Marine mucilage has been described as worldwide phenomena occurring sporadically, or frequently in certain coastal areas. They are transitory phenomena that can remain in the photic zone for several days or weeks. Their occurrence has been more frequent and persistent, and their magnitude has increased during the last decades. Their formation typically reflects an imbalance in the marine microbial communities, and has frequently be linked to global changes. Recurrent marine mucilage events have been observed in recent years in the Southern Bay of Biscay near the French coast, mainly south of the Adour estuary. In this study, we used a fingerprinting method (T-RFLP) targeting 16S and 18S rRNA genes to investigate marine microbial community composition and dynamics over an annual cycle across the three domains of life in coastal water at three depths, in the Adour River upstream of the mouth and in the marine mucilage. In line with studies conducted in marine environments we highlighted that the dynamics of marine microbial communities in the Bay of Biscay coincided with two environmental contexts: winter and spring on one hand and summer and autumn on the other hand. More interestingly, this dynamics affects also the marine pelagic mucilage that was observed during the sampling campaigns. Thus, the composition of the marine mucilage that appears in winter/spring context diverges from the composition of the marine mucilage that occurred during the summer/autumn context. We highlighted also that marine microbial communities were partly different from marine mucilage communities with an enrichment of some microorganisms suggesting that marine mucilage behaves as a microhabitat in seawater and possesses distinct microbial assemblages from the surrounding communities.
(Continental Shelf Research. vol. 186, n° 0278-4343, pp. 127-137, 01/06/2019)
IPREM, UPPA, INC-CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA, ECOBIOP, INRA, UPPA