Modern sedimentation and geochemical imprints in sediments from the NW Madagascar margin
The NW Madagascar continental margin receives high loads of terrigenous particulate organic matter during the wet season and especially linked to extreme events, originating from two major rivers, the Betsiboka and the Mahavavy Rivers. This particulate matter contains a high content of iron minerals from the weathering of red ferruginous/ferralitic soils of Madagascar. The presence of pockmarks, i.e. gas or fluid expulsion features on the continental slope, testifies to past/present methane migration through the sedimentary column, associated with early diagenetic processes. This study globally aims at deciphering the interactions between episodic sedimentation and geochemical processes influenced by fluids upward migration, using a sediment trap mooring and interface sediment cores at two sites on the continental slope. The present-day sedimentation along this margin undergoes two patterns. During the wet season, high continental fluxes generally result in an increase in particle fluxes on the slope. Longshore currents may deflect river plumes alongslope resulting in some periods of low particle flux on the slope during the wet season. During the dry season, the particles collected in the water column are probably originated from sediment remobilization from the shelf and slope. The observed progradation of the Mahavavy River delta and prodelta between 1984 and 2016 argues for an increase in temporary connections of the river with the canyon head during extreme events, inducing pulsed sedimentation offshore. This pulsed sedimentation could be responsible for enhancing pyritization on surface sediments, due to higher inputs of terrigenous organic matter and iron oxides. Finally, methane upward migration also influences the pyritization process through anaerobic oxidation of methane using sulfate as an electron acceptor and methanotrophs associated with this reaction significantly impact the δ13C of organic carbon towards more negative values.
(Marine Geology. vol. 426, n° 0025-3227, pp. 106184, 01/08/2020)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
North Atlantic climate far more predictable than models imply
(Nature. vol. 583, n° 0028-0836, pp. 796-800, 30/07/2020)
MOHC, EMPS, CMCC, BCCR, BIO / UiB, UiB, BSC-CNS, LOCEAN-VARCLIM, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, NERSC, NCAR, GFDL, NOAA, ICREA, CCCma, ECCC, AORI, UTokyo, JAMSTEC, MPI-M, DWD, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Extreme Morphological Plasticity Within Orbulina-“Praeorbulina-Like” Assemblages Related to Environmental Stress
Planktic foraminifera, unicellular microzooplankton with a calcitic shell, have produced an exceptional fossil record, revealing an invaluable archive of biodiversity, morphological and evolutionary changes. The evolutionary lineage starting from Trilobatus Spezzaferri 2015 (= “Globigerinoides”) culminating in Orbulina universa d’Orbigny 1839 is a fascinating example of peramorphic spherisation lineage (increasing involution, coupled with increasing shell curvature). This chapter focuses on the extreme morphological variability observed in the Orbulina group in some horizons from Chélif Basin in Algeria, just preceding the well-known Messinian (Late Miocene) salinity crisis in the Mediterranean basin. Surprisingly, in such horizons, spherical Orbulina universa lineage end-member specimens coexist with ancestor-like morphotypes, such as Orbulina suturalis Brönnimann 1951 and the supposed extinct Praeorbulina Olsson 1964, as well as with malformed specimens. Many authors considered in fact that Praeorbulina last occurred within the Langhian stage in the Middle Miocene. A similar recovery of individuals which show an intergradation between a typical Orbulina morphology and morphologies close to the ancestors Orbulina suturalis and Praeorbulina was also reported in Last Glacial Maximum sediments from the northern Arabian Sea. In this Late Pleistocene case, AMS 14C data showed clearly unreworked character of this “Praeorbulina-like” populations. We discuss the possible link between this extreme morphological plasticity of Orbulina group in specific time horizons and possible stress conditions of the water column.
(pp. 111-127, 24/07/2020)
CR2P, MNHN, SU, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UNIL, UNIL
Caractérisation du comportement de nanoplastiques représentatifs de l'environnement dans un gradient de salinité : évaluation de leurs impacts écotoxicologiques sur les huitres de palétuviers Isognomon alatus
La pollution mondiale des eaux de surface par les plastiques ne cesse de croitre et soulève des problèmes économiques et écologiques. D'après de récentes études, les macro-déchets plastiques marins se dégradent en microparticules puis en nanoparticules par des effets mécaniques et photochimiques. La fraction nanométrique des plastiques environnementaux est encore inconnue car cela reste un challenge analytique pour les caractériser à l'état d'ultra-trace. Ces particules sont potentiellement toxiques par leur composition, leur taille et leur forme, mais peuvent le devenir encore plus, par l'agrégation avec de la matière organique, ou bien par l'adsorption de métaux trace ou de polluants organiques à leur surface. Le comportement des nanoplastiques dans les eaux de transition comme les estuaires ou les mangroves est encore méconnu et peu étudié. Le but de cette thèse est de (i) caractériser le comportement physico-chimique de nanoparticules de plastiques modèles dans un gradient de salinité, avec une technique originale utilisant la microfluidique ; (ii) étudier l’impact écotoxicologique de ces nanoparticules sur des bivalves, avec un mode d’exposition représentatif des conditions d’exposition in situ.Des latex de polystyrène, ainsi que des nanoplastiques mécaniquement vieillis provenant soit de pellets de polystyrène, soit de macroplastiques prélevés sur des plages de Guadeloupe (polyéthylène, polypropylène), ont été soumis à un gradient de salinité dans des conditions dynamiques à l'intérieur de micro-puces. Les résultats ont été comparés à ceux des protocoles classiques qui consistent à disperser des nanosphères standards dans un milieu salin homogène en condition statique. Les tailles, concentrations, morphologies et stabilité de ces nanoparticules, ont été mesurées en fonction des conditions physico-chimiques du milieu.L'impact écotoxicologique des nanoplastiques modèles, dispersés via un gradient de salinité, a ensuite été étudié sur des huitres des palétuviers : Isognomon alatus. Les expositions ont été réalisées par voie directe à des concentrations environnementales. Différents marqueurs tels que la production de métallothionéines et l’expression précoce des gènes ont été utilisées pour évaluer la toxicité des nanoplastiques. Cette thèse a également permis le développement d’un des instruments les plus sensibles pour l'analyse de nanoparticules à l'état d'ultra-traces : la détection de plasmas induits par laser (LIBD). Ces travaux mettent en évidence l’impact des gradients de salinité sur le comportement des nanoplastiques et leur importance dans l’évaluation de la toxicité sur les bivalves lors de la transition eau douce-eau de mer.
(16/07/2020)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Classification of Atlantic Coastal Sand Dune Vegetation Using In Situ, UAV, and Airborne Hyperspectral Data
Mapping coastal dune vegetation is critical to understand dune mobility and resilience in the context of climate change, sea level rise, and increased anthropogenic pressure. However, the identification of plant species from remotely sensed data is tedious and limited to broad vegetation communities, while such environments are dominated by fragmented and small-scale landscape patterns. In June 2019, a comprehensive multi-scale survey including unmanned aerial vehicle (UAV), hyperspectral ground, and airborne data was conducted along approximately 20 km of a coastal dune system in southwest France. The objective was to generate an accurate mapping of the main sediment and plant species ground cover types in order to characterize the spatial distribution of coastal dune stability patterns. Field and UAV data were used to assess the quality of airborne data and generate a robust end-member spectral library. Next, a two-step classification approach, based on the normalized difference vegetation index and Random Forest classifier, was developed. Results show high performances with an overall accuracy of 100% and 92.5% for sand and vegetation ground cover types, respectively. Finally, a coastal dune stability index was computed across the entire study site. Different stability patterns were clearly identified along the coast, highlighting for the first time the high potential of this methodology to support coastal dune management.
(Remote Sensing. vol. 12, n° 2072-4292, 11/07/2020)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IMS, UB, CNRS, LPG, UA, UN UFR ST, UN, INSU - CNRS, CNRS
A revision of the French Telothelepodidae and Thelepodidae (Annelida, Terebelliformia), with descriptions of three species and first European record of a non-indigenous species
Telothelepodidae and Thelepodidae from French waters are revised based on material available in French marine stations and newly collected specimens. This work is the second part of the Spaghetti Project aiming to revise French species of “Spaghetti” worms. It describes three new species using both morphological and molecular tools: Streblosoma cabiochi n. sp., Streblosoma lindsayae n. sp. and Thelepus corsicanus n. sp. This study also permitted us to detect the presence of an Asiatic species, Thelepus japonicus, in Arcachon Bay and Normandy, introduced via oysters transfers. An identification key for European species of both families is also provided.
(Zootaxa. vol. 4810, n° 1175-5326, 10/07/2020)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
IPSL-CM5A2 – an Earth system model designed for multi-millennial climate simulations
Based on the fifth phase of the Coupled Model Intercomparison Project (CMIP5)-generation previous Insti-tut Pierre Simon Laplace (IPSL) Earth system model, we designed a new version, IPSL-CM5A2, aiming at running multi-millennial simulations typical of deep-time paleocli-mate studies. Three priorities were followed during the setup of the model: (1) improving the overall model computing performance, (2) overcoming a persistent cold bias depicted in the previous model generation and (3) making the model able to handle the specific continental configurations of the geological past. These developments include the integration of hybrid parallelization Message Passing Interface-Open Multi-Processing (MPI-OpenMP) in the atmospheric model of the Laboratoire de Météorologie Dynamique (LMDZ), the use of a new library to perform parallel asynchronous in-put/output by using computing cores as "I/O servers" and the use of a parallel coupling library between the ocean and the atmospheric components. The model, which runs with an atmospheric resolution of 3.75 • × 1.875 • and 2 to 0.5 • in the ocean, can now simulate ∼ 100 years per day, opening new possibilities towards the production of multi-millennial simulations with a full Earth system model. The tuning strategy employed to overcome a persistent cold bias is detailed. The confrontation of a historical simulation to climatological observations shows overall improved ocean meridional overturning circulation, marine productivity and latitudinal position of zonal wind patterns. We also present the numerous steps required to run IPSL-CM5A2 for deep-time paleocli-mates through a preliminary case study for the Cretaceous. Namely, specific work on the ocean model grid was required to run the model for specific continental configurations in which continents are relocated according to past paleogeo-graphic reconstructions. By briefly discussing the spin-up of such a simulation, we elaborate on the requirements and Published by Copernicus Publications on behalf of the European Geosciences Union. 3012 P. Sepulchre et al.: IPSL-CM5A2 challenges awaiting paleoclimate modeling in the next years, namely finding the best trade-off between the level of description of the processes and the computing cost on super-computers.
(Geoscientific Model Development. vol. 13, n° 1991-9603, pp. 3011-3053, 08/07/2020)
CLIM, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CALCULS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, LMD, INSU - CNRS, X, IP Paris, ENPC, SU, CNRS, ENS-PSL, PSL, LOA, INSU - CNRS, CNRS, MERMAID, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CEREGE, IRD, AMU, CdF (institution), INSU - CNRS, CNRS, INRAE, LOCEAN-VARCLIM, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, IPSL (FR_636), ENS-PSL, PSL, UVSQ, CEA, INSU - CNRS, X, IP Paris, CNES, SU, CNRS, UPCité, IPGP - UMR_7154, INSU - CNRS, IGN, UR, IPG Paris, CNRS, UPCité, RSMAS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Flux estimation, temporal trends and source determination of trace metal contamination in a major tributary of the Seine estuary, France
Anthropogenic impacts on rivers have increased significantly over the past ~150 years, particularly at the beginning of the industrial revolution. Among other signs, this impact is manifested through the addition of trace metals and metalloid elements to rivers. The Eure River watershed in France covers an area of 6017 km2 and is a major tributary of the Seine estuary. It is not exempt from anthropogenic pressures and has been exposed to significant metal discharges over the last 80 years. The average concentrations of metals (i.e., Cr, Co, Ni, Cu, Zn, Ag, Cd, Sb, and Pb), in suspended particulate matter currently transported by the river are high compared to the local geochemical background. Moreover, the lack of correlation between concentration variations and the hydrosedimentary behaviour of the Eure River suggests that the river is currently under anthropogenic pressure. Analysis of sediment cores indicate strong As contamination during the 1940s, Cr, Co, Ni, Cu, Zn, Ag, and Cd contamination during the 1960s and 1970s, and Sb and Pb contamination during the 1990s and 2000s. The enrichment factors calculation suggests that total anthropogenic pressure within the Eure River watershed since the 1940s was comparable or higher than those in many other French watersheds. An estimation of particulate metal flux in 2017 shows that the Eure River watershed contributed to 7, 8, 9, 10 and 16% of total inputs to the Seine estuary in Cr, Cu, Zn, Cd and Pb respectively. Moreover, the estimation of past theoretical flux indicates that during the 1990s the Eure River watershed was the main contributor of particulate Pb to the estuary. The use of Pb isotopes has revealed that this contamination was primarily of industrial origin.
(Science of the Total Environment. vol. 724, n° 0048-9697, pp. 138249, 01/07/2020)
UNICAEN, NU, COBRA, IRCOF, UNIROUEN, NU, INSA Rouen Normandie, INSA, NU, CNRS, UNIROUEN, NU, INSA Rouen Normandie, INSA, NU, INC3M, UNICAEN, NU, ENSICAEN, NU, ULH, NU, UNIROUEN, NU, INSA Rouen Normandie, INSA, NU, INC-CNRS, CNRS, INC-CNRS, CNRS, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LDO, INSU - CNRS, UBO EPE, CNRS, IFREMER, CEREGE, IRD, AMU, CdF (institution), INSU - CNRS, CNRS, INRAE, EDYTEM, USMB [Université de Savoie] [Université de Chambéry], CNRS, Fédération OSUG, PSL
Relationship between bacterial compartment and particulate organic matter (POM) in coastal systems: An assessment using fatty acids and stable isotopes
Particulate organic matter (POM) in coastal systems is a mixture of different organic matter (OM) sources originating from land and sea. Among sources, bacterial biomass plays a large role in OM processing and carbon recycling in the ocean and is often neglected as a source in common approaches. The present study proposes to use elemental and isotopic ratio of carbon and nitrogen (C:N, δ13C, δ15N) and fatty acids to investigate the relationship between bacteria and surface water POM composition of three systems with different characteristics (two marine and one estuarine) over an annual cycle. Overall, our results highlight a positive relationship between bacterial contribution and continental degraded or undergoing degradation POM for all the studied systems and an inverse relationship with pelagic primary producers. At multisystem scale, high bacterial contribution is linked to high proportion of refractory terrestrial material characterizing estuarine stations whereas in marine systems, the occurrence of bacteria is mainly linked to river POM. Over the annual cycle, bacterial markers are more abundant during the winter period characterized by larger river and/or benthic POM contribution. This seasonal pattern is mainly driven by changes in river flows and resuspension. This study highlights the importance of bacterial compartment as a component of coastal and estuarine POM. Even though these results remains semi-quantitative, similar studies in other types of systems can help to understand microbial role in OM dynamic and to better estimate bacterial source in carbon budgets and food web studies.
(Estuarine, Coastal and Shelf Science. vol. 239, n° 0272-7714, pp. 106720, 01/07/2020)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LOMIC, INSU - CNRS, SU, CNRS, OOB, SU, CNRS, BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA, OASU, UB, INSU - CNRS, ULR, CNRS, INRAE, OOB, SU, CNRS, DGD.REVE, MNHN, MNHN
Enhanced western mediterranean rainfall during past interglacials driven by North Atlantic pressure changes
There is increasing concern with anthropogenic greenhouse gas emissions that ocean warming, in concert with summer and winter precipitation changes, will induce anoxia in multiple ocean basins, such as in the Mediterranean Sea. Although the hydrological changes in the eastern Mediterranean are quite well constrained, quantitative evidence of changes in sea surface temperature (SST) and winter rainfall in the western Mediterranean across the past interglacials is relatively scarce. In this study, we use a combination of trace element (Ba/Ca and Mg/Ca) and stable oxygen isotope composition of planktonic foraminifera from a sediment core located off the Golo River, Corsica (northern Tyrrhenian Sea) to reconstruct variations in SSTs and sea surface salinities (SSS) during the Holocene (MIS 1) and warm periods of the past two interglacials (MIS 5, 7). We also analyse PMIP3 model simulations for the mid-Holocene to investigate the mechanism for moisture transport in the western Mediterranean. Our Mg/Ca-SSTs, Ba/Ca-salinity and derived δ18O-seawater records suggest that the warm periods of the past interglacials were characterized by high river discharge and lower SSS in the northern Tyrrhenian Sea. Since this region is ideally located on the trajectory of wintertime storm tracks across the North Atlantic into the Mediterranean Sea and is also outside the influence of the ITCZ-controlled summer monsoon rains, we suggest enhanced winter rainfall during the past interglacials. Our analysis of PMIP3 model simulations for mid-Holocene also support increased south-westerly moisture transport into the western Mediterranean originating from the North Atlantic. We also find evidence that long-term amplitude of the salinity decrease tightly follows eccentricity. We suggest that these hydrologic changes in the western Mediterranean, and the northern Mediterranean borderlands as a whole, were a contributing factor, together with local cyclogenesis and African summer monsoon rainfall, to basin-wide anoxia in the past. Our findings offer new constraints to the amplitude and cause of winter rainfall changes in the Mediterranean during past warm periods.
(Quaternary International. vol. 553, n° 1040-6182, pp. 1-13, 01/07/2020)
LGO, UBS, IFREMER, UBO EPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS