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Sediment characteristics and microbial mats in a marine mangrove, Manche-à-eau lagoon (Guadeloupe)
No full textInternational audiencePurposeMarine mangrove sediments in the Manche-à-Eau lagoon (Guadeloupe, Caribbean Sea) harbor locally extensive, white microbial mats. These mats cover the surface of reduced sediments near the roots of red mangrove trees, Rhizophora mangle, and are mainly composed of sulfur-oxidizing bacteria belonging to the Beggiatoaceae family, with some filamentous cyanobacteria. The goal of this study was to investigate the possible influence of sediment characteristics on the presence of these microbial mats.Materials and methodsFour push cores were collected in April 2013, two from zones with microbial mats and two from zones without mats. Sediment characteristics (grain-size distribution, mineralogy, total organic carbon (TOC) and total nitrogen (TN) contents, atomic TOC/TN ratios, and organic matter (OM) δ13C values) were compared for all four cores.Results and discussionSignificant differences were observed between sediments below microbial mats and those without mats. Sediments with microbial mats contained greater amounts of clay, and higher TOC, TN, and TOC/TN ratios, with lower total carbonate content and δ13C values. The higher clay content most likely results from lower fluid flow velocity near to mangrove roots, while higher TOC/TN ratios and lower δ13C values indicate higher inputs of OM from mangrove trees. These results are consistent with the fact that microbial mats were observed near the roots of mangrove trees, which trap OM from terrestrial vegetation and fine sediments.ConclusionsThe grain-size distribution of sediment particles, the total carbonate content, and the δ13C values are the main parameters discriminating between zones with microbial mats and those without mats. Variations in total carbonate content, which is mainly of biogenic origin, result from conditions that are more favorable for benthic organisms in zones without microbial mats. Variations of the TOC/TN ratios are controlled by the presence of a non-negligible amount of inorganic nitrogen bound to surface clay mineral particles and/or by microbial processes
Mare Incognitum: A Glimpse into Future Plankton Diversity and Ecology Research
No full textInternational audienceWith global climate change altering marine ecosystems, research on plankton ecology is likely to navigate uncharted seas. Yet, a staggering wealth of new plankton observations, integrated with recent advances in marine ecosystem modelling, may shed light on marine ecosystem structure and functioning. A EuroMarine foresight workshop on the “Impact of climate change on the distribution of plankton functional and phylogenetic diversity” (PlankDiv) identified five grand challenges for future plankton diversity and macroecology research: 1) What can we learn about plankton communities from the new wealth of high-throughput ‘omics’ data? 2) What is the link between plankton diversity and ecosystem function? 3) How can species distribution models be adapted to represent plankton biogeography? 4) How will plankton biogeography be altered due to anthropogenic climate change? and 5) Can a new unifying theory of macroecology be developed based on plankton ecology studies? In this review, we discuss potential future avenues to address these questions, and challenges that need to be tackled along the way
: Angelija Bučienė, Sébastien Gadal, Jelena Galinienė, Viktoras Gailius36AngelijaBučienė, SébastienGadal, JelenaGalinienė, ViktorasGailiusThe Geographic-Restrospective Analysis of Landscape in Žemaičių Naumietis Ward
No full textNational audienceResearch aim was to analyse seminatural and agrarian urban landscape components of Žemaičių Naumiestis ward as well as social demographic factors and their changes within the ward boundaries and time scale (from soviet time till recent years) in order to distinguish the common tendencies of these changes. The seminatural landscape components – forests, water bodies and their area as well as agrarian urban components (agricultural land use with arable land, pastures and meadows, builtup territories) and their changes in time and space were analysed of social demographic factors, population, density and settlement size were focused on. The statistical and historical document analysis methods as well as distance and GIS modelling were applied. Land cover mapping of the territorial and geographic changes were computed by remote sensing using Landsat series satellite images of the studied area around Žemaičių Naumiestis town (297km2) in 1988, 1998, 2005 and 2015 and ortographic photo data method in 1997 and 2013. Žemaičių Naumiestis as a town (the old name is Naumiestis, or Nowe Miasto in Polish) was mentioned in the historical documents from the 17th century. Only in the fourth decade of the 20th century it was named Žemaičių Naumiestis – as one of the territorial administrative units of western Lithuania. The first collective farm in the ward was founded in 1959, and in the last decade of soviet governance there were two sovhozes specialised in vegetable seed husbandry, milk and meat production, one educational farm, as well as one forestry .The greatest population and its density in the ward was documented in 1970 (4,744 and 49.2 inhabitants per km2), and the greatest population in Žemaičių Naumiestis town in 1985 (2,500). At the same time rural population and its density in the ward decreased. The distinguished spatial changes of rural population decrease were observed served in the south eastern part of the ward (decrease by 40–60 and >%), where the number of small villages prevailed. A few of them, like Dekintai, Užšustis and Klebonai, were almost empty. After restoration of independence in 1990, the land reform changed drastically the configuration of agricultural land plot cover: asa result of restitution of private land, at first the plots of agricultural land decreased in size, but increased in the number of owners, at the same time some plots became abundant, because their owners were too old to manage the farm. Nowadays increase in private farm area is going on. According to the latest Censuses of land in 2003 and 2010, the number of farms in Šilutė district and in Žemaičių Naumiestis ward started to decrease, however the total agricultural area even increased. Thus the farms became larger in area.The research based on different distant methods revealed that in the beginning of the 21st century there was reduction in agrarian components of landscape and urban (builtup) areas. Seminatural components (water bodies) have remained unchanged in the area, while the forest area slightly increased. The same tendencies of landscape component plot changes from the end of soviet era up to now have been observed both in the total Žemaičių Naumietis ward territory as well as in the studied Žemaičių Naumiestis ward parcel (297km2). The secondary agricultural land consolidation and stabilisation of agrarian landscape fragmentation is to be documented in the ward nowadays.Despite different changes in land use, decrease of villages and rural population, the landscape of Žemaičių Naumiestis has remained more agrarian as compared with Silute district, on the average. The agrarian activities became more diverse, the first ecological farm appeared in 2006, and they have increased in numbers since then. The forests are slightly increasing in the area, thus the situation with natural landscape components in the ward is improving. However, the necessity to strengthen the social economic cultural status of population life remains the task of high importance
Investigating the March 28th 1875 and the September 20th 1920 earthquakes/tsunamis of the Southern Vanuatu arc, offshore Loyalty Islands, New Caledonia
No full textInternational audienceNew Caledonia's Loyalty Islands are located in the southwest region of the Pacific ocean in the highly seismogenic southern Vanuatu subduction zone and therefore may be subject to devastating local tsunamis. Over the past 150 years, two large tsunamis were triggered by major earthquakes on March 28th 1875 and September 20th 1920. In this study, we use historical observations of these tsunamis (mostly in the form of testimonials), earthquake scenarios, and tsunami modeling to derive the magnitudes of these earthquakes, as well as tsunami runup and inundation maps. Assuming that these earthquakes were located on the interplate megathrust zone, the 1875 earthquake's magnitude was Mw8.1–8.2 and the 1920 event's magnitude was Mw7.5–7.8. The tsunami damage inflicted on the Lifou and Maré islands was approximately proportional to these magnitudes, with Maré being less impacted due to favorable wave directivity. Damage at Ouvéa island may have varied irregularly with the magnitude due to the effects of resonance. This study demonstrates that the quantitative characteristics of historical tsunamigenic earthquakes may be derived from qualitative estimates of tsunami runup
Numerical analysis of a nonlinear free-energy diminishing Discrete Duality Finite Volume scheme for convection diffusion equations
No full textSpecial issue on "Advanced numerical methods: recent developments, analysis and application"International audienceWe propose a nonlinear Discrete Duality Finite Volume scheme to approximate the solutions of drift diffusion equations. The scheme is built to preserve at the discrete level even on severely distorted meshes the energy / energy dissipation relation. This relation is of paramount importance to capture the long-time behavior of the problem in an accurate way. To enforce it, the linear convection diffusion equation is rewritten in a nonlinear form before being discretized. We establish the existence of positive solutions to the scheme. Based on compactness arguments, the convergence of the approximate solution towards a weak solution is established. Finally, we provide numerical evidences of the good behavior of the scheme when the discretization parameters tend to 0 and when time goes to infinity
Identifying codes for infinite triangular grids with a finite number of rows
No full textInternational audienceLet G T be the infinite triangular grid. For any positive integer k, we denote by T k the subgraph of G T induced by the vertex set {(x, y) ∈ Z × [k]}. A set C ⊂ V (G) is an identifying code in a graph G if for all v ∈ V (G), N [v] ∩ C = ∅, and for all u, v ∈ V (G), N [u]∩C = N [v]∩C, where N [x] denotes the closed neighborhood of x in G. The minimum density of an identifying code in G is denoted by d * (G). In this paper, we prove that d * (T 1) = d * (T 2) = 1/2, d * (T 3) = d * (T 4) = 1/3, d * (T 5) = 3/10, d * (T 6) = 1/3 and d * (T k) = 1/4 + 1/(4k) for every k ≥ 7 odd. Moreover, we prove that 1/4 + 1/(4k) ≤ d * (T k) ≤ 1/4 + 1/(2k) for every k ≥ 8 even
Modélisation prospective des paysages de la Forêt Classée du Haut-Sassandra (Côte d'Ivoire) après la fin des conflits
No full textInternational audienceIl a été démontré que les conflits armés provoquent, outre les drames humains, des dégradations de la biodiversité, dans ses dimensions écosystémique et spécifique notamment (Nackoney et al., 2014). La Forêt Classée du Haut Sassandra est un cas d’étude intéressant pour ce genre de processus dans la mesure où, durant les conflits, une massive infiltration de migrants dans la forêt classée a provoqué un brusque recul de la couverture forestière et une perte notable de la diversité végétale (Barima et al., 2016). Nous avons créé un modèle issu du croisement d’un automate cellulaire et d’un système multi-agents permettant de simuler les déplacements (dans et hors de la forêt classée) et les jeux d’acteurs (liens entre chefs d’exploitation et ouvriers ; villageois exploitant les produits forestiers non ligneux et les migrants cultivant le cacao dans la forêt ; agents de la société de protection de la forêt). La simulation sociale génère, en sortie de modèle, des scénarios sous forme de cartes du défrichement dans la forêt classée. Ce modèle a d’abord été conçu comme un modèle rétro-prospectif pour tester des hypothèses sur les dynamiques sociales qui sous-tendent ce processus (Andrieu et al., 2016), après avoir travaillé sur sa justesse par la confrontation à la réalité (télédétection). Ce modèle ayant été validé, l’objectif est de présenter une modélisation prospective pour illustrer les possibles conséquences, en termes de conservation de la couverture forestière, de différents scénarios démographiques et de différents choix politiques. Par une logique géoprospective, deux scénarios seront évoqués tel que la poursuite des tendances de la période de conflit dans le modèle et une proposition de restauration écologique
The Hera Saturn Entry Probe Mission: a Proposal in Response to the ESA M5 Call
No full textInternational audienceThe Hera Saturn entry probe mission is proposed as an ESA M-class mission to be piggybacked on a NASA spacecraft sent to or past the Saturn system. Hera consists of an atmospheric probe built by ESA and released into the atmosphere of Saturn by its NASA companion Saturn Carrier-Relay spacecraft. Hera will perform in situ measurements of the chemical and isotopic composition as well as the structure and dynamics of Saturn's atmosphere using a single probe, with the goal of improving our understanding of the origin, formation, and evolution of Saturn, the giant planets and their satellite systems, with extrapolation to extrasolar planets. Hera will probe well into and possibly beneath the cloud-forming region of the troposphere, below the region accessible to remote sensing, to locations where certain cosmogenically abundant species are expected to be well mixed. The Hera probe will be designed from ESA elements with possible contributions from NASA, and the Saturn/Carrier-Relay Spacecraft will be supplied by NASA through its selection via the New Frontier 2016 call or in the form of a flagship mission selected by the NASA "Roadmaps to Ocean Worlds" (ROW) program. The Hera probe will be powered by batteries, and we therefore anticipate only one major subsystems to be possibly supplied by the United States, either by direct procurement by ESA or by contribution from NASA: the thermal protection system of the probe. Following the highly successful example of the Cassini-Huygens mission, Hera will carry European and American instruments, with scientists and engineers from both agencies and many affiliates participating in all aspects of mission development and implementation. A Saturn probe is one of the six identified desired themes by the Planetary Science Decadal Survey committee on the NASA New Frontier's list, providing additional indication that a Saturn probe is of extremely high interest and a very high priority for the international community
Morphosedimentary evolution of carbonate sandy beaches at decadal scale : case study in Reunion Island , Indian Ocean
No full textInternational audienceGlobal change introduce a lot of uncertainties concerning future trajectory of beaches by directly or indirectly modifying major driving factors. An improved understanding of the past shoreline evolution may help for anticipate future coastline response. However, in tropical environment, studies concerning carbonate beaches dynamics are scarce compared to open sandy beaches. Consequently, coral reef protected beaches morphological adjustment is still poorly understood and long-term evolution rate are poorly quantified in these specific environment. In this context, La Reunion Island, insular department of France located in Indian Ocean, constitute a favoured laboratory. This high volcanic island possesses 25 km of carbonate beaches which experience hydrodynamic forcing specific from tropical environment: cyclonic swell during summer and long period swell during winter. Because of degraded coral reef health and high anthropogenic pressure, 50% of the beaches are in erosion since 1970s. Beach survey has been conducted since 1990s by scientist and are now encompassed as pilot site within a French observatory network which guarantee long-term survey with high resolution observational techniques. Thus, La Reunion Island is one of the rare carbonate beach to be surveyed since 20 years. This study aims to examined and quantify beach response at decadal scale on carbonate sandy beaches of Reunion Island. The study focus on 12 km of beaches from Cap Champagne to the Passe de Trois-Bassins. The analyze of 15 beach profile data originated from historical and DGPS beach topographic data confirm long term trend to erosion. Sediment lost varies between 0.5 and 2 m 3 .yr −1 since 1998. However longshore current have led to accretion of some part of beach compartment with rate of 0.7 to 1.6 m 3 .yr −1. Wave climate was examined from in-situ measurement over 15 years and show that extreme waves associated with tropical cyclones and long period swell play a major role in beach dynamics. Swell frequency and intensity are both determinant for beach evolution
Computing the carbonate chemistry of the coral calcifying medium and its response to ocean acidification
No full textInternational audienceCritical to determining vulnerability or resilience of reef corals to Ocean Acidification (OA) is a clearer understanding of the extent to which corals can control carbonate chemistry in their Extracellular Calcifying Medium (ECM) where the CaCO3 skeleton is produced. Here, we employ a mathematical framework to calculate ECM aragonite saturation state (Ωarag.(ECM) and carbonate system ion concentration using measurements of calcification rate, seawater characteristics (temperature, salinity and pH) and ECM pH (pH(ECM))). Our calculations of ECM carbonate chemistry at current-day seawater pH, indicate that Ωarag.(ECM) ranges from ∼10 to 38 (mean 20.41), i.e. about 5 to 6-fold higher than seawater. Accordingly, Dissolved Inorganic Carbon (DIC) and Total Alkalinity (TA) were calculated to be around 3 times higher in the ECM than in seawater. We also assessed the effects of acidification on ECM chemical properties of the coral Stylophora pistillata. At reduced seawater pH our calculations indicate that Ωarag.(ECM) remains almost constant. DIC(ECM) and TA(ECM) gradually increase as seawater pH declines, reaching values about 5 to 6-fold higher than in seawater, respectively for DIC and TA. We propose that these ECM characteristics buffer the effect of acidification and explain why certain corals continue to produce CaCO3 even when seawater chemistry is less favourable