Vers une vision multipression explicative des niveaux de contamination biodisponible et de toxicité des cours d'eau.
(01/09/2022)
RiverLy, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR REVERSAAL, INRAE, UR EABX, INRAE
Wave-Current Impact on Shear Stress Patterns around 3D Shallow Bedforms
Observations from wave basin experiments and wave-resolving numerical simulations demonstrate the effect of wave-current interaction on shear stress around a sandy mound. Observations from the wave basin show that the mound deformation rate and morphological patterns depend on the mixture of waves and currents in the incident flow conditions. A SWASH nonhydrostatic numerical model was used to expand the parameter space of wave-current conditions observed in the flume and characterize the response of the near-bed shear stress to the mound. The model was validated with observations from wave-alone, current-alone, and wave-current flume tests and then ran for a suite of numerical flow conditions which isolate the impact of the ratio of wave-current energy on the bed shear stress. Results show how the current-to-wave ratio impacts the spatial heterogeneity of shear stress across the mound, with the region of shear stress intensification around the mound and the location of the peak shear stress becoming asymmetric with more mixed wave-current flows. These results show the nonlinear response of shear stress patterns to combined wave-current flows and how these patterns may impact eventual sediment transport and mound evolution.
(Journal of Marine Science and Engineering. vol. 10, n° 2077-1312, pp. 1178, 01/09/2022)
TU Delft, OSU, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Global carbon isotopic events in a Campanian–Maastrichtian deltaic succession (Tremp-Graus Basin, Spain) and multiproxy stratigraphy for high sedimentation rate environments
The Campanian to Maastrichtian sedimentary succession of the Tremp-Graus Basin (NE Spain) is characterized by the offshore-to-prodeltaic upper Vallcarga Fm giving way to prograding deltaic units (the Aren Fm), which are overlain by transitional facies (the Grey Unit) that correspond to the basal part of the Tremp Group. This work aims to improve the stratigraphical scheme of these deposits using a new dataset of δ13Ccarb and δ13Corg, δ18O and TOC variations through time, supported by a new biostratigraphical analysis and compiling previous biostratigraphical and paleomagnetic data. The comparison of isotopic signals from marine reference sections where δ13Ccarb is well calibrated in the Tethys realm allows recognition of global isotopic events that can be used as correlative marker events. Significant high-frequency δ13C variations defined in the δ13Ccarb are identified in the studied succession despite the different sedimentary setting and some can be related to global geochemical events such as the Late Campanian Event (LCE) and the Campanian–Maastrichtian Boundary Event (CMBE), in good agreement with the magnetic chrons at the base of the Tremp Group, and with some new biostratigraphic constraints. From multiple geochemical and petrographic analysis of the organic matter we suggest that the geochemical signal corresponds to global changes, but at higher resolution, sedimentary dynamics are also reflected in the geochemical signals, particularly inputs of surface water in the deltaic signal.
(Cretaceous Research. vol. 137, n° 0195-6671, pp. 105222, 01/09/2022)
Bordeaux INP, UBM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CR2P, MNHN, SU, CNRS, iSTeP, INSU - CNRS, SU, CNRS, ITES, ENGEES, UNISTRA, INSU - CNRS, CNRS, EOST, UNISTRA, INSU - CNRS, CNRS
Wave runup on composite beaches and dynamic cobble berm revetments
The effects of climate change and sea level rise, combined with overpopulation are leading to ever-increasing stress on coastal regions throughout the world. As a result, there is increased interest in sustainable and adaptable methods of coastal protection. Dynamic cobble berm revetments consist of a gravel berm installed close to the high tide shoreline on a sand beach and are designed to mimic naturally occurring composite beaches (dissipative sandy beaches with a gravel berm around the high tide shoreline). Existing approaches to predict wave runup on sand or pure gravel beaches have very poor skill for composite beaches and this restricts the ability of coastal engineers to assess flood risks at existing sites or design new protection structures. This paper presents high-resolution measurements of wave runup from five field and large-scale laboratory experiments investigating composite beaches and dynamic cobble berm revetments. These data demonstrated that as the swash zone transitions from the fronting sand beach to the gravel berm, the short-wave component of significant swash height rapidly increases and can dominate over the infragravity component. When the berm toe is submerged at high tide, it was found that wave runup is strongly controlled by the water depth at the toe of the gravel berm. This is due to the decoupling of the significant wave height at the berm toe from the offshore wave conditions due to the dissipative nature of the fronting sand beach. This insight, combined with new methods to predict wave setup and infragravity wave dissipation on composite beaches is used to develop the first composite beach/dynamic revetment-specific methodologies for predicting wave runup.
(Coastal Engineering. vol. 176, n° 0378-3839, pp. 104148, 01/09/2022)
BRGM, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UFRN, UC
Aluminium in aquatic environments: abundance and ecotoxicological impacts
Aluminium (Al) is a common chemical element released into the aquatic environment from the Earth’s crust and many anthropogenic activities. It may be present in various dissolved and precipitated forms [Al3+, AlOH2+, Al(OH)2+, Al(OH)03, Al(OH)4−, etc.], which are potentially toxic for organisms. This review summarizes information about the concentrations of Al detected in aquatic ecosystems and its effects on both freshwater and marine organisms (such as growth disturbance, reproduction, and respiration alterations). As the chemistry of Al is different in freshwater and marine systems, we discuss the behaviour of aluminium and its effects on marine or freshwater fauna. Therefore, the solubility of Al, as other metals, is highly pH dependent, which increases when pH decreases. We are assuming that ocean acidification, linked to climate change, would affect the Al bioavailability in the aquatic environment, which may increase its ecotoxicological effects on semi-closed (Bays, Mediterranean Sea, etc.) or closed (lakes, etc.) aquatic ecosystems.
(Aquatic Ecology. vol. 56, n° 1386-2588, pp. 751-773, 01/09/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BiOSSE, UM, IMMM, UM, INC-CNRS, CNRS
Turbulence de type Burgers dans la zone de surf
Dans cette article nous montrons que la turbulence d'onde en zone de surf interne a de nombreuses similarités avec la turbulence de Burgers. En nous appuyant sur des résultats théoriques concernant la turbulence de Burgers nous proposons un modèle décrivant les spectres d'énergie en zone de surf interne. Notre modèle est ensuite validé par rapport à des données expérimentales. A partir de mesures de l'élévation des vagues, notre modèle permet d'estimer le coefficient de diffusion turbulente et de prédire le spectre de dissipation de l'énergie.
(29/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Charcoal in deep-sea sediments: fire history and climate change
Fire results today from interactions between climate, vegetation and human activities and occurs in most terrestrial ecosystems. It has potential feedbacks to climate, through the emission of CO2, trace gases and aerosols that influence the global carbon cycle, the atmospheric chemistry and the radiative balance. How fire regimes (including frequency and intensity) may respond to climatic change can be explored by modelling. Empirical-based models however lack the impact of climatic change on vegetation and it is necessary to evaluate process-based models with paleofire data. Marine sedimentary charcoal records provide the opportunity to explore drivers of fire beyond the range of recent climates at different time-scales (from centennial, millennial to orbital scales). I will focus on two subtropical regions, the southwestern Iberian Peninsula and the southern Africa where millennial- and orbital-scale fire variability was observed. Results suggest a strong orbital and millennial climate control on fires and highlight the main role of vegetation type and fuel amount in driving fires in these subtropical regions. Contrary to the conventional expectation that fire increases with higher temperatures and increased drought, fires may increase also under cooler and/or wetter climates. Data-model comparison is still challenging as paleofire records provide charcoal measurements (abundance and morphology) not directly comparable to fire regime metrics. I will develop on calibrating charcoal in marine sediments showing recent results from the Mediterranean region and off the African continent. Results suggest the abundance and morphology of charcoal detect specific fire regimes, in particular fires of high intensity in mixed vegetation in Iberia and in graminoid-mixed ecosystems in Africa. These results might be a springboard for converting marine charcoal records into past fire regime history.
(29/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
When Eastern India Oscillated Between Desert Versus Savannah‐Dominated Vegetation
During the last glacial period, the tropical hydrological cycle exhibited large variability across orbital and millennial timescales. However, the response of the Indian summer monsoon (ISM), its related impact on terrestrial ecosystems, and associated forcing mechanisms remain controversial. Here we present a marine record of pollen-inferred vegetation changes suggesting that eastern India shifted from woody-savanna mosaics during Marine Isotopic Stage 3 to grasslands during the Last Glacial Maximum resulting from large-scale drying. Our data shows that ISM maximum is in phase with obliquity and precession maxima suggesting a dominant role of the Indian Ocean interhemispheric temperature gradient on glacial ISM variability. Persistent and abrupt dryland expansions of varying magnitude suggest rapid-scale onset of aridity during Heinrich Stadial events and during the Toba eruption. We propose that the amplitude of ISM drought events are initiated by high latitude and volcanic forcings, although modulated by precession.
(Geophysical Research Letters. vol. 49, n° 0094-8276, 28/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UAlg, IPMA, IFP, MEAE, CNRS
Probability-based preservational variations within the early Cambrian Chengjiang biota (China)
The Chengjiang biota (Yunnan Province, China) is a treasure trove of soft-bodied animal fossils from the earliest stages of the Cambrian explosion. The mechanisms contributing to its unique preservation, known as the Burgess Shale-type preservation, are well understood. However, little is known about the preservation differences between various animal groups within this biota. This study compares tissue-occurrence data of 11 major animal groups in the Chengjiang biota using a probabilistic methodology. The fossil-based data from this study is compared to previous decay experiments. This shows that all groups are not equally preserved with some higher taxa more likely to preserve soft tissues than others. These differences in fossil preservation between taxa can be explained by the interaction of biological and environmental characteristics. A bias also results from differential taxonomic recognition, as some taxa are easily recognized from even poorly preserved fragments while other specimens are difficult to assign to higher taxa even with exquisite preservation.
(PeerJ. vol. 10, n° 2167-8359, 23/08/2022)
MEC, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, U of S, UNIL
Preservation of exopolymeric substances in estuarine sediments
The surface of intertidal estuarine sediments is covered with diatom biofilms excreting exopolymeric substances (EPSs) through photosynthesis. These EPSs are highly reactive and increase sediment cohesiveness notably through organo-mineral interactions. In most sedimentary environments, EPSs are partly to fully degraded by heterotrophic bacteria in the uppermost millimeters of the sediment and so they are thought to be virtually absent deeper in the sedimentary column. Here, we present the first evidence of the preservation of EPSs and EPS-mineral aggregates in a 6-m-long sedimentary core obtained from an estuarine point bar in the Gironde Estuary. EPSs were extracted from 18 depth intervals along the core, and their physicochemical properties were characterized by (i) wet chemical assays to measure the concentrations of polysaccharides and proteins, and EPS deprotonation of functional groups, (ii) acid–base titrations, and (iii) Fourier transform infrared spectroscopy. EPS-sediment complexes were also imaged using cryo-scanning electron microscopy. EPS results were analyzed in the context of sediment properties including facies, grain size, and total organic carbon, and of metabolic and enzymatic activities. Our results showed a predictable decrease in EPS concentrations (proteins and polysaccharides) and reactivity from the surface biofilm to a depth of 0.5 m, possibly linked to heterotrophic degradation. Concentrations remained relatively low down to ca. 4.3 m deep. Surprisingly, at that depth EPSs abundance was comparable to the surface and showed a downward decrease to 6.08 m. cryo-scanning electron microscopy (Cryo-SEM) showed that the EPS complexes with sediment were abundant at all studied depth and potentially protected EPSs from degradation. EPS composition did not change substantially from the surface to the bottom of the core. EPS concentrations and acidity were anti-correlated with metabolic activity, but showed no statistical correlation with grain size, TOC, depth or enzymatic activity. Maximum EPS concentrations were found at the top of tide-dominated sedimentary sequences, and very low concentrations were found in river flood-dominated sedimentary sequences. Based on this observation, we propose a scenario where biofilm development and EPS production are maximal when (i) the point bar and the intertidal areas were the most extensive, i.e., tide-dominated sequences and (ii) the tide-dominated deposit were succeeded by rapid burial beneath sediments, potentially decreasing the probability of encounter between bacterial cells and EPSs.
(Frontiers in Microbiology. vol. 13, n° 1664-302X, 18/08/2022)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, Unibas, IC2MP [Poitiers], UP, INC-CNRS, CNRS, GEOPS, INSU - CNRS, CNRS, BIC, UB, INSERM, CNRS, AORI, UTokyo, BGS, UB, CNRS