Modélisation de l'écosystème pélagique en mer Ligure. Application à la campagne DYNAPROC 2 (Sep-Oct 2004).

Modelling was used as a tool for better understanding the physical and biological processes observed during the multidisciplinary cruise DYNAPROC 2 (DYNAmic of rapid PROCesses in the water column) which took place in the Ligurian Sea in September-October 2004. The aim of the cruise was to study the short-time scale physical and biological processes that occur when the ecosystem switches from summer oligotrophy to autumnal mesotrophy. One of the most striking events observed during the cruise was the crossing of two low salinity water lenses in the sampling area, which was thought to be protected from lateral inputs. In this study, we have first fitted a 1D physical-biological coupled model to the cruise data set. The simulated food-web accounted ten state variables: three nutrients, three classes of phytoplankton, two classes of zooplankton and two types of detritus. The results showed that the main differences between model and data occurred during the low salinity water intrusions. In a second step, we tested two methods of data assimilation: the introduction of a relaxation term to the temperature measurements and a new data assimilation approach (called IDA, Isopycnal Depth Adjustment) which consists in assimilating the measured variations of isopycnal depths. The evaluation of the relative performance of the different models was performed using a Taylor diagram. The IDA method appeared to be the most efficient in reproducing the observed ecosystem dynamics. This study allowed characterization of the properties of the low salinity water mass, calibration of the matter fluxes at short-time scale and provides a better estimation of the relative contribution of physical and biological processes in the production layer in offshore waters of the Ligurian Sea.La modélisation a été utilisée comme outil pour améliorer la compréhension des processus physiques et biologiques observés pendant la campagne pluridisciplinaire DYNAPROC 2 (DYNamique des PROCessus rapides dans la colonne d'eau) qui a eu lieu dans la zone centrale de la mer Ligure en septembre-octobre 2004. Cette campagne avait pour objectif l'étude des phénomènes physiques et biologiques qui agissent à courte échelle de temps lors de la transition saisonnière entre l'oligotrophie estivale et la mésotrophie automnale. L'un des éléments les plus marquants de la campagne est le passage de deux lentilles d'eau dessalée dans la zone de mesure que l'on pensait être isolée des apports latéraux. Dans ce travail, nous avons dans un premier temps appliqué un modèle 1D couplé physique-biologie aux données de la campagne. Le réseau trophique simulé comporte dix variables d'états : trois sels nutritifs, trois classes de phytoplancton, deux classes de zooplancton et deux types de détritus. Les résultats ont montré que les principales différences entre ce modèle et les mesures avaient lieu pendant les intrusions d'eau dessalée. Dans un deuxième temps, nous avons testé deux méthodes d'assimilation de données : une méthode classique de relaxation aux données de température et une méthode que nous avons développée, qui est basée sur l'assimilation des variations de profondeur des isopycnes (méthode IDA, Isopycnal Depth Adjustment). L'évaluation des performances relatives des trois modèles a été effectuée avec des diagrammes de Taylor et a montré que le modèle IDA était le plus performant dans la représentation des évènements observés. Cette étude a permis de caractériser les propriétés de la masse d'eau dessalée, de calculer les flux de matière journaliers et de définir les contributions relatives de la physique et de la biologie à l'évolution de la zone productive au large de la mer Ligure

Zooplancton : micro- et mésozooplancton

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Modélisation de l'écosystème pélagique en mer Ligure (application à la campagne DYNAPROC 2 (Septembre-Octobre 2004))

La modélisation a été utilisée comme outil pour améliorer la compréhension des processus physiques et biologiques observés pendant la campagne pluridisciplinaire DYNAPROC 2 (DYNamique des PROCessus rapides dans la colonne d'eau) qui a eu lieu dans la zone centrale de la mer Ligure en septembre-octobre 2004. Cette campagne avait pour objectif l'étude des phénomènes physiques et biologiques qui agissent à courte échelle de temps lors de la transition saisonnière entre l'oligotrophie estivale et la mésotrophie automnale. L'un des éléments les plus marquants de la campagne est le passage de deux lentilles d'eau dessalée dans la zone de mesure que l'on pensait être isolée des apports latéraux. Dans ce travail, nous avons dans un premier temps appliqué un modèle 1D couplé physique-biologie aux données de la campagne. Le réseau trophique simulé comporte dix variables d'états : trois sels nutritifs, trois classes de phytoplancton, deux classes de zooplancton et deux types de détritus. Les résultats ont montré que les principales différences entre ce modèle et les mesures avaient lieu pendant les intrusions d'eau dessalée. Dans un deuxième temps, nous avons testé deux méthodes d'assimilation de données : une méthode classique de relaxation aux données de température et une méthode que nous avons développée, qui est basée sur l'assimilation des variations de profondeur des isopycnes (méthode IDA, Isopycnal Depth Adjustment). L'évaluation des performances relatives des trois modèles a été effectuée avec des diagrammes de Taylor et a montré que le modèle IDA était le plus performant dans la représentation des évènements observés. Cette étude a permis de caractériser les propriétés de la masse d'eau dessalée, de calculer les flux de matière journaliers et de définir les contributions relatives de la physique et de la biologie à l'évolution de la zone productive au large de la mer Ligure.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

In memoriam Professor Patrice Francour

International audienc

Forecasting climate-driven changes in the geographical range of the European anchovy (Engraulis encrasicolus)

International audienceAnthropogenic climate change is already affecting marine ecosystems and the responses of living-resources to warming waters are various, ranging from the modifications in the abundance of key species to phenologic and biogeographic shifts. Here, we used a recently developed Ecological Niche Model (ENM) to evaluate the potential effects of global climate change on the future geographical distribution of the European anchovy. We first modelled the ecological niche (sensu Hutchinson) of the fish and projected its future spatial range using new IPCC representative concentration pathways (RCPs) scenarios and five of the latest generation of ocean-atmosphere global circulation models. We chose this multi-model and multi-scenario approach to evaluate the range of possible trajectories until the end of the century. Our projections indicate that substantial poleward shifts in the probability of anchovy occurrence are very likely and highlight areas where European anchovy fisheries are forecasted to change most. Whatever the warming scenario, our results project a reduction in the probability of occurrence in all the regions located under 48°N and an increase in more northern areas. However, increases or decreases in the probability of occurrence are greater under the “business-as-usual” scenario RCP8.5 than under the low-emission scenario RCP2.6

Climate-induced range shifts of the American jackknife clam Ensis directus in Europe.

International audienceMapping the future potential distribution of alien species has become an issue of great concern. Ecological niche models are increasingly used to forecast the spatial range of introduced species in the context of climate warming. Here, we studied the potential spread of the American jackknife clam Ensis directus into European waters. E. directus, a marine bivalve native to the American coasts, was observed in Europe for the first time in the German Bight at the end of the 1970s. Afterwards, the clam quickly colonized the surrounding waters of the North Sea. Although many studies focused on its biology, ecology and colonization, the extent to which E. directus may invade European and Nordic seas remained poorly known. In this study, we used two ecological niche models (ENMs), calibrated on the native area of the mollusk, to evaluate the potential distributional range of the bivalve over European seas. Under current environmental conditions, E. directus should continue to progress towards the southern coasts of France and may also invade new areas in the Adriatic Sea. Projections for the end of the century suggest that the probability of occurrence of E. directus increases from Denmark to France with both ENMs. The Tunisian coasts may also become a new suitable area for the mollusk but the results of the two ENMs differ for this region. Therefore, contrary to what is often observed, a southward range expansion of E. directus is probable, especially as climate will get warmer

Atomistic Models for Highly‐Dispersed PtSn/γ‐Al2O3 Catalysts: Ductility and Dilution Affect the Affinity for Hydrogen

International audienceSupported platinum-based sub-nanometric particles play a central role in many catalytic applications. In particular, platinum-tin active phases supported on γ-Al2O3 are largely employed for dehydrogenation of alkanes and catalytic reforming of naphta cuts, although geometric and electronic effects of the active phase in the presence of hydrogen still remains highly debated. Thanks to periodic density functional theory (DFT), we propose structural models of such systems containing thirteen metal atoms (PtxSn13-x with 0 ≤ x ≤ 13) deposited on the (100) γ-Al2O3 surface. We thus unravel the intricate effects of the composition (Pt/Sn ratio), of the support (γ-Al2O3) and the hydrogen coverage on the stability of platinum-tin sub-nanometric clusters, in the case where tin is reduced (Sn 0). A detailed investigation of the interaction of the supported Pt10Sn3 cluster with hydrogen by velocity-scaled molecular dynamics provides a mapping of the hydrogen coverage as a function of the operating conditions (T, P(H2)). Our study highlights significant differences between Pt13 and PtxSn13-x clusters in terms of ductility and dilution (also called ensemble) effects which may be at the origin of the different reactivities usually reported for Pt and PtSn supported catalysts

Improving predictions of invasive fish ranges combining functional and ecological traits with environmental suitability under climate change scenarios

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Expected contraction in the distribution ranges of demersal fish of high economic value in the Mediterranean and European Seas

International audienceFisheries and aquaculture are facing many challenges worldwide, especially adaptation to climate change. Investigating future distributional changes of largely harvested species has become an extensive research topic, aiming at providing realistic ecological scenarios on which to build management measures, to help fisheries and aquaculture adapt to future climate-driven changes. Here, we use an ensemble modelling approach to estimate the contemporary and future distributional range of eight demersal fish species of high economic value in the Mediterranean Sea. We identify a cardinal influence of (i) temperature on fish species distributions, all being shaped by yearly mean and seasonality in sea bottom temperature, and (ii) the primary production. By assessing the effects of changes in future climate conditions under three Representative Concentration Pathway (RCP2.6, RCP4.5 and RCP8.5) scenarios over three periods of the twenty-first century, we project a contraction of the distributional range of the eight species in the Mediterranean Sea, with a general biogeographical displacement towards the North European coasts. This will help anticipating changes in future catch potential in a warmer world, which is expected to have substantial economic consequences for Mediterranean fisheries

Modelling European small pelagic fish distribution: Methodological insights

International audienceThe distribution of marine organisms is strongly influenced by climatic gradients worldwide. The ecological niche (sensu Hutchinson) of a species, i.e. the combination of environmental tolerances and resources required by an organism, interacts with the environment to determine its geographical range. This duality between niche and distribution allows climate change biologists to model potential species’ distributions from past to future conditions. While species distribution models (SDMs) have been intensively used over the last years, no consensual framework to parametrise, calibrate and evaluate models has emerged. Here, to model the contemporary (1990–2017) spatial distribution of seven highly harvested European small pelagic fish species, we implemented a comprehensive and replicable numerical procedure based on 8 SDMs (7 from the Biomod2 framework plus the NPPEN model). This procedure considers critical issues in species distribution modelling such as sampling bias, pseudo-absence selection, model evaluation and uncertainty quantification respectively through (i) an environmental filtration of observation data, (ii) a convex hull based pseudo-absence selection, (iii) a multi-criteria evaluation of model outputs and (iv) an ensemble modelling approach. By mitigating environmental sampling bias in observation data and by identifying the most ecologically relevant predictors, our framework helps to improve the modelling of fish species’ environmental suitability. Not only average temperature, but also temperature variability appears as major factors driving small pelagic fish distribution, and areas of highest environmental suitability were found along the north-western Mediterranean coasts, the Bay of Biscay and the North Sea. We demonstrate in this study that the use of appropriate data pre-processing techniques, an often-overlooked step in modelling, increase model predictive performance, strengthening our confidence in the reliability of predictions