Contribution relative des forçages climatiques et des processus sédimentaires dans la répartition spatio-temporelle des sédiments des mers nordiques (mers de Norvège, du Groenland et de Barents)
Ce travail présente une analyse des environnements sédimentaires marins profonds des mers nordiques à l’interface de l’Atlantique nord et de l’Arctique (mers du Groenland, de Norvège, de Barents et d’Islande) au cours du dernier million d’années. Il se base sur une base de données acoustiques (bathymétrie, imagerie multifaisceau) et sédimentologique (carottes calypso) issues de deux campagnes réalisées par le Shom. Les enregistrements sédimentaires ont montré une très grande variabilité des processus de sédimentation en jeu dans ces mers en fonction des périodes climatiques, avec notamment une sédimentation glaciomarine, gravitaire, contouritique, et hémipélagique. Ils ont également permis de se concentrer sur la chronologie des périodes de développement ou de retrait des calottes continentales périphériques (calotte du Groenland, calotte Fennoscandie et calotte de Barents et Svalbard), et du couvert de glace de mer. Une étude stratigraphique détaillée a été réalisée sur la base de différents outils (datations radiocarbones, géochimie isotopique, géochimie élémentaire, biostratigraphie sur microfossiles et nannofossiles calcaires, et analyses sédimentologiques). La reconstitution de l’historique d’évolution des apports sédimentaires et des processus responsables de ces apports depuis le Quaternaire moyen (début de la Mid-Pleistocene Transition, MPT) jusqu’à l’Holocène terminal, a permis de mieux caractériser l’impact des variations d’extension des calottes continentales sur la sédimentation des mers nordiques, mais aussi d’identifier les périodes de forte influence du couvert de glace Arctique (y compris calotte potentielle en maxima glaciaire) sur les mers nordiques, et les variations de l'influence des courants de surface et de fond dans la zone nord et la zone sud de ces bassins boréaux. Notamment, les variations d’influences des eaux de surface chaudes et salées de l’Atlantique nord ont pu être identifiées pour certaines périodes de temps.
(22/02/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Bi-decadal variability in physico-biogeochemical characteristics of temperate coastal ecosystems: from large-scale to local drivers
Coastal marine ecosystems, which play a crucial role in the biogeochemical and ecological functioning of the Earth, are highly sensitive to the combined effects of climate and human activities. Because of their location, coastal ecosystems are directly influenced by human activities, but it remains challenging to assess the spatial and temporal scales at which climate influences coastal ecosystems. We monitored 12 sampling stations, distributed in 8 ecosystems in France, over 2 decades for physico-biogeochemical parameters (temperature, salinity, concentrations of dissolved oxygen, nutrients and particulate material). The study encompasses a large diversity of temperate coastal ecosystems with respect to e.g. geomorphology, trophic status, tidal regime, river influence and turbidity. Time-series analysis coupled with standardised 3-mode principal component analyses, partial triadic analyses and correlations were used to assess bi-decadal variability and ecosystem trajectories, and to identify large-scale, regional and local drivers. Our results highlighted 2 abrupt changes in 2001 and 2005. The bi-decadal changes were related to changes in large-scale and regional climate, detected through proxies of temperature and atmospheric circulation, as well as through river discharge. Ecosystem trajectories tended to move towards an increase in temperature and salinity, and/or a decrease in chlorophyll a , nutrients and particulate matter. However, the magnitude of change, the year-to-year variability and the sensitivity to the 2001 and 2005 changes varied among the ecosystems. This study highlights the need for establishing long-term time series and combining data sets as well as undertaking multi-ecosystem and local studies to better understand the long-term variability of coastal ecosystems and its associated drivers.
(Marine Ecology Progress Series. vol. 660, n° 0171-8630, pp. 19-35, 18/02/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA, AD2M, SU, CNRS, SBR, SU, CNRS, SBR, SU, CNRS, LOMIC, INSU - CNRS, SU, CNRS, OOB, SU, CNRS, LEMAR, IRD, IFREMER, UBO EPE, CNRS, LOV, INSU - CNRS, SU, CNRS, IMEV, INSU - CNRS, SU, CNRS, MIO, IRD, AMU, INSU - CNRS, UTLN, CNRS, IUEM, IRD, INSU - CNRS, UBO EPE, CNRS, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], OOB, SU, CNRS, LGSR, UR, IPG Paris, IPGP - UMR_7154, INSU - CNRS, IGN, UR, IPG Paris, CNRS, UPCité, FR2424, SBR, SU, CNRS
Rôle des interactions biophysiques dans la dynamique dunaire en réponse aux perturbations
Les dunes littorales le long des côtes sableuses ont souvent été fixées, voire reprofilées, pour protéger des inondations et des vagues de tempêtes les biens socio-économiques situés en arrière. Mais ces méthodes de gestion ont parfois mené à la dégradation de l’écosystème des dunes et de leur résilience face aux événements extrêmes. Depuis quelques années, plusieurs études dans le monde ont porté sur la réintroduction de la dynamique naturelle dans les systèmes de dunes côtières. C’est dans ce contexte que nous avons réalisé une expérimentation pionnière en France par la mise en place de brèches dans un système dunaire du sud-ouest de la France. Après 3 ans de suivis morphologiques (photogrammétrie par drone) et écologiques (in situ), les résultats ont mis en avant que les brèches ont favorisé le transport de sable chargé en nutriments vers l’arrière dune, menant à une augmentation de la diversité des espèces. Ces travaux ont donc des implications importantes pour les stratégies de gestion des dunes côtières et le développement durable de ces systèmes, tout particulièrement dans les environnements en érosion chronique.
(15/02/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Variable inter and intraspecies alkaline phosphatase activity within single cells of revived dinoflagellates
Variable inter-and intra-species alkaline phosphatase activity within single cells of revived dinoflagellates
(The International Society of Microbiologial Ecology Journal, n° 1751-7362, 10/02/2021)
CRPP, UB, INC-CNRS, CNRS, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IUF, M.E.N.E.S.R.
Microplastiques en estuaire de Seine : synthèse des connaissances du projet Plastic-Seine sur les matrices abiotiques (2017-2020)
Microplastiques en estuaire de Seine : synthèse des connaissances du projet Plastic-Seine sur les matrices abiotiques (2017-2020) GASPERI Johnny Le projet PLASTIC-Seine (Flux et impacts des microplastiques dans l’estuaire de la Seine, 2017-2020) avait pour objectif d’étudier de manière intégrée l’occurrence et les niveaux d’imprégnation de l’estuaire de la Seine par les microplastiques (MP), qu’il s’agisse de la colonne d’eau, du sédiment ou du biote. Structuré autour de trois tâches, le projet visait à 1) dresser un état des lieux de la contamination des compartiments abiotiques sur le fleuve, 2) étudier la contamination par les MP de sept espèces représentatives du réseau trophique de l’estuaire de Seine et 3) mieux comprendre le transfert, le devenir et les effets des MP dans trois des sept espèces sélectionnées. Sur le premier point, les travaux menés démontrent l’ubiquité des MP au sein des matrices abiotiques. Ils soulignent d’une part le rôle majeur joué par le sédiment dans le transfert et le devenir des MP. Ils mettent également en évidence une évolution des concentrations en MP le long du gradient salin. L’étude de deux cycles de marée a montré l’existence des forts gradients de concentration au cours du temps, mais également au sein de la colonne d’eau. Ces gradients peuvent s'expliquer à la fois par la remise en suspension des sédiments de fond, riches en MP, lors du flot et par la sédimentation des particules lors du jusant. Ces travaux ont été financés par le GIP Seine Aval et l'Agence de l'Eau Seine Normandie.
(08/02/2021)
GERS-LEE, LEESU, ENPC, UPEC UP12, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
An experimental approach to assessing the impact of ecosystem engineers on biodiversity and ecosystem functions
Plants acting as ecosystem engineers create habitats and facilitate biodiversity maintenance within plant communities. Furthermore, biodiversity research has demonstrated that plant diversity enhances the productivity and functioning of ecosystems. However, these two fields of research developed in parallel and independent from one another, with the consequence that little is known about the role of ecosystem engineers in the relationship between biodiversity and ecosystem functioning across trophic levels. Here, we present an experimental framework to study this relationship. We combine facilitation by plants acting as ecosystem engineers with plant–insect interaction analysis and variance partitioning of biodiversity effects. We present a case-study experiment in which facilitation by a cushion-plant species and a dwarf-shrub species as ecosystem engineers increases positive effects of plant functional diversity (ecosystem engineers and associated plants) on ecosystem functioning (flower visitation rate). The experiment, conducted in the field during a single alpine flowering season, included the following treatments: (1) removal of plant species associated with ecosystem engineers, (2) exclusion (covering) of ecosystem engineer flowers, and (3) control, i.e., natural patches of ecosystem engineers and associated plant species. We found both positive and negative associational effects between plants depending on ecosystem engineer identity, indicating both pollination facilitation and interference. In both cases, patches supported by ecosystem engineers increased phylogenetic and functional diversity of flower visitors. Furthermore, complementarity effects between engineers and associated plants were positive for flower visitation rates. Our study reveals that plant facilitation can enhance the strength of biodiversity–ecosystem functioning relationships, with complementarity between plants for attracting more and diverse flower visitors being the likely driver. A potential mechanism is that synergy and complementarity between engineers and associated plants increase attractiveness for shared visitors and widen pollination niches. In synthesis, facilitation among plants can scale up to a full network, supporting ecosystem functioning both directly via microhabitat amelioration and indirectly via diversity effects.
(Ecology. vol. 102, n° 0012-9658, 01/02/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Simulating storm waves in the nearshore area using spectral model: current issues and a pragmatic solution
Short waves are of key importance for nearshore dynamics, particularly under storms, where they contribute to extreme water levels and drive large morphological changes. Therefore, it is crucial to model accurately the propagation and dissipation of storm waves in the nearshore area. In this paper, field observations collected in contrasted environments and conditions are combined with predictions from a third-generation spectral wave model to evaluate four formulations of wave energy dissipation by depth-induced breaking. The results reveal a substantial over-dissipation of incident wave energy occurring over the continental shelf, resulting in a negative bias on significant wave height reaching up to 50%. To overcome this problem, a breaking coefficient dependent of the local bottom slope is introduced within depth-induced breaking models in order to account for the varying degrees of saturation naturally found in breaking and broken waves. This approach strongly reduces the negative bias observed in the shoreface compared to default parameterizations, yielding significant improvements in the prediction of storm waves. Among the implications of this study, our new parameterization of the breaking coefficient results in systematically increased predictions of the wave setup near the shoreline compared to the default parameterization. This increase reaches a factor 2 for gently sloping beaches.
(Ocean Modelling. vol. 158, n° 1463-5003, pp. 101737, 01/02/2021)
LIENSs, INSU - CNRS, ULR, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Cumulative effects of marine renewable energy and climate change on ecosystem properties: sensitivity of ecological network analysis
In an increasingly anthropogenic world, the scientific community and managers have to take interactions between the drivers of ecosystems into consideration. Tools like ecological network analysis (ENA) indices offer the opportunity to study those interactions at the ecosystem level. However, ENA indices have never been used to test the incidence of cumulative drivers. The present study uses models combining the effects of (i) the reef caused by the future offshore wind farm of Courseulles-sur-Mer and (ii) climate change on species distribution, to test the response of multiple ENA indices. ENA indices proved sensitive to this cumulative impact, displaying a wide variety of cumulative effects. They were also very powerful to characterize the role of the cumulative impact on ecosystem functioning. These results demonstrate the capacity of ENA indices to describe and understand cumulative effects at the ecosystem scale. Using a sensitivity analysis approach, this study shows that ENA indices could be viable tools for managers. To help them in their tasks, the next step could be to link ecosystem services to ENA indices for a more practical use.
(Ecological Indicators. vol. 121, n° 1470-160X, pp. 107128, 01/02/2021)
BOREA, UNICAEN, NU, MNHN, IRD, SU, CNRS, UA, M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, FEM, UMR MARBEC, IRD, IFREMER, UM, CNRS, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], ULCO, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEMAR, IRD, IFREMER, UBO EPE, CNRS
Sampling pore water at a centimeter resolution in sandy permeable sediments of lakes, streams, and coastal zones
Concentration gradients in the solid fraction and pore water of modern sediments allow to identify benthic biogeochemical processes and the associated fluxes. Gradients are often obtained from layers sampled below the sediment–water interface from sediment cores. Numerous examples in the literature show results from cores collected in impermeable porous sediments, but very few from permeable sediment cores. Indeed, the acquisition of vertical profiles in sandy permeable sediments with a spatiotemporal resolution equivalent to that of muddy sediments is a challenge. We present here a simple protocol that allows sampling of sandy sediments and their interstitial waters with a vertical resolution of 1 cm. This method is suitable for shallow environments, such as intertidal zones, lakes, lagoons, and stream beds. The method is based on rapid conditioning of hand-collected cores. The cores are pre-cut lengthwise. Immediately after recovery, they are laid horizontally, opened, and sliced. Interstitial water is collected by centrifugation on site shortly after cutting the core with tubes equipped with a 0.2 μm membrane. Optimally, 30 min is sufficient between core collection and conditioning of 12 sections of a 20-cm long core. The examples shown indicate that the method is reproducible. Reduced dissolved compounds such as Fe(II), Mn(II), and NH4+ show profiles without significant oxidation. At the time of core cutting, small volumes of pore water are seeping out of the core, but for sediments with a permeability of up to 10−10 m2, this seepage does not disturb the shape of the pore-water profiles.
(Limnology and Oceanography: Methods. vol. 19, n° 1541-5856, pp. 96-114, 01/02/2021)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
150 years of foredune initiation and evolution driven by human and natural processes
Foredunes are efficient natural coastal defenses acting as protective barriers during storm events. They also have the capacity to be an ecosystem hosting significant biodiversity. The economic development and/or recreational use of the foredune commonly results in a modification of natural functioning and the concomitant mixing of natural and anthropogenic processes. While the impact of human interventions on the short term evolution of coastal dunes is reasonably well understood, relatively less is known on their imprint at a scale of several decades. The Truc Vert beach-dune system (SW France), which has been exposed to various dune management strategies for more than a century, provides a relevant site to explore the respective contributions of natural and anthropogenic processes on coastal foredune evolution and the current coastal dune landscape. For this purpose, the coastal dune system was investigated using several approaches that combine ground penetrating radar (GPR), topographic data, aerial photographs and historical maps. A 20-m thick GPR sequence provides a stratigraphic record from which we detail ~150-year period of coastal dune change, including the initiation of the foredune. Results show a mixture of radar facies typical of natural aeolian erosion or deposition and radar facies that are the signature of human actions. These anthropogenic works include a large fence emplaced in 1860 to build and fix the foredune, and intense mechanical reshaping of the dune profile by bulldozers in 1972 followed by an intensive planting of vegetation. These various management strategies had a profound influence on coastal dune changes and, in turn, on the current coastal dune landscape. Historic archives documenting coastal dune works were critical to discriminate some of the radar facies, which could be wrongfully interpreted as natural erosion or deposition facies. Therefore, these results demonstrate the importance of coupling GPR and historical documentation wherever possible to determine, in part or fully, the contributions of human interventions and actions in modern dune evolution and morphological development.
(Geomorphology. vol. 374, n° 0169-555X, pp. 107516, 01/02/2021)
CEFREM, UPVD, INSU - CNRS, CNRS, BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ONF