Éditeur(s) : American Geophysical Union
Résumé : As part of the French CLIPPER project, an eddy permitting model of the Atlantic circulation has been run for 22 years. The domain has open boundaries at Drake passage and at 30 degreesE, from Africa to Antarctica. The simulated mean circulation, as well as the eddy activity, is satisfactory for a 1/3 degrees model resolution, and the meridional heat transport at 30 degreesS is within the range estimated from observations. We use the "mixed" open boundary algorithm of Barnier et al. [1998], which has both a radiation condition and a relaxation to climatology. The climatological boundary forcing strongly constrains the solution in the whole domain. The model heat balance adjusts through the surface (heat flux retroaction term) more than the open boundaries. The radiation phase velocities calculated within the algorithm are analyzed. This shows, quite surprisingly, that both the eastern and western boundaries have a similar behavior, regardless of the preferred directions for advection (mainly eastward) and wave propagation (mainly westward). Our results confirm that open boundary algorithms behave differently according to the dynamics of the region considered. The passive boundary condition that Penduff et al. [2000] applied successfully in the north eastern Atlantic does not work in the present South Atlantic model. We emphasize the need for a careful prescription of the climatology at the open boundary, for which a new approach based on synoptic sections is implemented.
Journal of Geophysical Union - Research C - Oceans (0148-0227) (American Geophysical Union), 2001-10 , Vol. 106 , N. C10 , P. 22115-22129

Droits : 2001 American Geophysical Union
http://archimer.ifremer.fr/doc/2001/publication-454.pdf
DOI:10.1029/2000JC000376
http://archimer.ifremer.fr/doc/00000/454/

Éditeur(s) : Montpellier 1
Résumé : Understanding bioaccumulation mechanisms of persistent organic pollutants (POPs) is a major issue for environmental risk assessment. In this work, polychlorinated biphenyls (PCBs), a model contaminant family, has been studied in the European hake (Merluccius merluccius), a high trophic level species from the Gulf of Lions. High concentrations of PCBs were measured in hake from this area compared to those encountered in the population of the Bay of Biscay. PCB biomagnification was highlighted along its food web from marine phytoplankton, suggesting a strong influence of diet on contamination levels. The role of other biological processes was also apprehended in order to understand the high variability of observed levels. Thus, growth, sex, and also the degree of sexual maturity appear as major factors explaining the measured concentrations in fish. A PCB bioaccumulation model in the hake, based on the Dynamic Energy Budget theory (DEB), was developed. This approach is based on a bioenergetic model, reproducing the main physiological functions of an organism (feeding, growth and reproduction), coupled with a kinetic model of contaminants. The growth and evolution of contamination levels of several PCB congeners during the life of male and female hakes is satisfactorily simulated, both in the Gulf of Lions and in the Bay of Biscay, validating the processes taken into account. This combined modelling approach appears well adapted to study the fate of contaminants in fish, and paves the way for a realistic understanding of their effects on major biological functions of fish.
La compréhension des mécanismes de bioaccumulation des contaminants organiques persistants (POP) est un enjeu majeur pour l'évaluation des risques environnementaux. Lors de ce travail, le devenir d'une famille de contaminants modèles, les polychlorobiphényles (PCB), a été étudié chez une espèce de rang trophique élevé du golfe du Lion, le merlu Européen (Merluccius merluccius). Des concentrations élevées en PCB ont été mesurées dans les merlus de ce secteur en comparaison à celles rencontrées dans la population du golfe de Gascogne. La mise en évidence d'une bioamplification des PCB le long de son réseau trophique, depuis le phytoplancton marin, suggère une influence importante de l'alimentation sur les niveaux de contamination. Le rôle d'autres processus biologiques a également été appréhendé afin de comprendre la forte variabilité des niveaux observés. Ainsi, la croissance, le sexe, mais également le degré de maturité sexuel apparaissent comme des facteurs explicatifs majeurs des concentrations en PCB mesurées dans les poissons. Un modèle de bioaccumulation des PCB chez le merlu, basé sur la théorie de Budget d'Energie Dynamique (DEB), a été développé. Il s'agit d'une approche basée sur le couplage d'un modèle bioénergétique, reproduisant les principales fonctions physiologiques de l'organisme (nutrition, croissance et reproduction), avec un modèle de cinétique des contaminants. La croissance et l'évolution des niveaux de contamination de plusieurs congénères de PCB au cours de la vie des merlus mâles et femelles est simulée de manière satisfaisante, tant dans le golfe de Gascogne que dans le golfe du Lion, validant ainsi les processus pris en compte. Cette approche combinée de modélisation apparaît tout à fait adaptée à l'étude du devenir des contaminants chez les poissons, et ouvre la voie à une compréhension réaliste de leurs effets sur les grandes fonctions biologiques de ces organismes.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2008/these-6490.pdf
http://archimer.ifremer.fr/doc/00000/6490/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Laboratory models have been conducted to improve our understanding of the role that the resistance of the slab to bending and its coupling to the ambient mantle play in subduction dynamics over geological time scales. Our models are set up with a viscous plate of silicone (lithosphere) subducting under negative buoyancy in a viscous layer of glucose syrup (mantle). For our study, the lithosphere/upper mantle viscosity contrast has been systematically varied, from similar to 10 to similar to 10(5) in order to explore the parameter space between weak and strong slab dynamics. We found that subduction is characterized by a retreating mode for viscosity ratios > 10(4), by the coexistence of a retreating mode and an advancing mode for viscosity ratios between similar to 10(4) and similar to 10(2), and quasi-stationary, Rayleigh-Taylor like behaviour for ratios < 10(2). By combining our experimental results and kinematic data from current subduction zones in four reference frames which differ in the amount of net rotation, we infer that a lithosphere/upper mantle viscosity contrast of 150-500 is necessary to obtain realistic trench/subducting plate velocity ratios as well as the variability of subduction styles observed in nature.
ISSN: 0012-821X

hal-00412008
https://hal.archives-ouvertes.fr/hal-00412008
DOI : 10.1016/j.epsl.2008.04.006

Éditeur(s) : Inter-research
Résumé : Environmental conditions experienced by aquatic organisms are archived in biogenic carbonates such as fish otoliths, bivalve shells and coral skeletons. These calcified structures present an accretionary growth and variations in optical properties - color or opacity - that are used to reconstruct time. Full and reliable exploitation of the information extracted from these structures is, however, often limited as the metabolic processes that control their growth and their optical properties are poorly understood. Here, we propose a new modeling framework that couples both the growth of a biogenic carbonate and its optical properties with the metabolism of the organism. The model relies on well-tested properties of Dynamic Energy Budget (DEB) theory. It is applied to otoliths of the Bay of Biscay anchovy (Engraulis encrasicolus) for which a DEB model has been previously developed. The model reproduces well-known otolith patterns and thus provides us with mechanisms for the metabolic control of otolith size and opacity at the scale of an individual lifespan. Two original contributions using this framework are demonstrated. First, the model can be used to reconstruct the temporal variations in the food assimilated by an individual fish. Reconstructing food conditions of past and present aquatic species in their natural environment is key ecological information to better understand population dynamics. Second, we show that non-seasonal checks can be discriminated from seasonal checks, which is a well-recognized problem when interpreting fish otoliths. We discuss further developments of the model and the experimental settings required to test this new promising framework.
Marine Ecology-progress Series (0171-8630) (Inter-research), 2012 , Vol. 447 , P. 151-164

Droits : 2012 Inter-Research
http://archimer.ifremer.fr/doc/00060/17082/14593.pdf
DOI:10.3354/meps09492
http://archimer.ifremer.fr/doc/00060/17082/

Éditeur(s) : Elsevier Sci Ltd
Résumé : This study analyses the impact on the oceanic mean state of the evolution of the oceanic component (NEMO) of the climate model developed at Institut Pierre Simon Laplace (IPSL-CM), from the version IPSL-CM4, used for third phase of the Coupled Model Intercomparison Project (CMIP3), to IPSL-CM5A, used for CMIP5. Several modifications have been implemented between these two versions, in particular an interactive coupling with a biogeochemical module, a 3-band model for the penetration of the solar radiation, partial steps at the bottom of the ocean and a set of physical parameterisations to improve the representation of the impact of turbulent and tidal mixing. A set of forced and coupled experiments is used to single out the effect of each of these modifications and more generally the evolution of the oceanic component on the IPSL coupled models family. Major improvements are located in the Southern Ocean, where physical parameterisations such as partial steps and tidal mixing reinforce the barotropic transport of water mass, in particular in the Antarctic Circumpolar Current) and ensure a better representation of Antarctic bottom water masses. However, our analysis highlights that modifications, which substantially improve ocean dynamics in forced configuration, can yield or amplify biases in coupled configuration. In particular, the activation of radiative biophysical coupling between biogeochemical cycle and ocean dynamics results in a cooling of the ocean mean state. This illustrates the difficulty to improve and tune coupled climate models, given the large number of degrees of freedom and the potential compensating effects masking some biases.
Ocean Modelling (1463-5003) (Elsevier Sci Ltd), 2013-12 , Vol. 72 , P. 167-184

Droits : 2013 The Authors. Published by Elsevier Ltd. All rights reserved.
http://archimer.ifremer.fr/doc/00170/28102/26612.pdf
DOI:10.1016/j.ocemod.2013.09.001
http://archimer.ifremer.fr/doc/00170/28102/

Éditeur(s) : CNEXO
Résumé : This book constitutes the first of a series of three volumes, the purpose of which is to cover the principal methods used in fish population dynamics. It is devoted to the definition of the main concepts, ami the presentation of the usual mathematical models. The second volume will deal with the fitting of the models, and the estimation of parameters. The third will be devoted to sampling problems. These volumes will be recollections of communications presented during ad hoc seminars, hold in Brest (GSG/COB) in 1980 and 1981. The first part deals with the basic concepts related to the two components whose relationship is being described by the population dynamics, namely the fish stock, to its relations with biological populations, and to the partition of catchabtiity into its components (vulnerability, availability...). The second chapter of this part is devoted to the quantification of exploitation. This leads to a discussion of nominal and effective fishing effort and fishing intensity. A brief review of the use of catch per unit of effort as an index of abundance is followed by a discussion of the concept of fishing power. The second part starts with some general remarks on mathematical modelling (chapter III), then comes to the two classical categories of models : global (surplus production) models (chapter IV), and structural models (chapter V). Chapter IV is mainly a review, based upon the SCHAEFER and PELLATOMLINSON models. Some less classical formulas from the recent literature are also introduced. Attention is paid to the underlying hypotheses and to the limitation of such models. The reader is finally referred to papers presenting the developments that could make it possible to overcome some of these limitations. Chapter V is based upon the classical BEVERTON and HOLT and RlCKER models, and the yield per recruit concepts. This field is however inlarged. Other commonly used variants of structural models are presented with an effort being made to clarify the real differences between all these variants. Special attention is also paid to so-called regenerative models and to the use of spawing-biomass or fecundity per recruit, which are likely to become commonly used in the coming years. In all cases, special attention is paid to the presentation of the basic formulas, that the reader might have to use if faced with a practical problem. Finally, a discussion of the underlying hypotheses takes place, before a brief review of the main developments, where the reader is referred to the appropriate literature.
Ce livre constitue le premier volet d'un tryptique destiné à effectuer une revue des méthodes essentielles en dynamique des populations marines exploitées. Il est consacré à la définition des concepts de base, à la présentation des modèles courants. Dans la discussion des concepts, ce volume s'attache à clarifier les notions relatives aux deux parties dont les relations font l'objet de la dynamique des populations exploitées : le stock et la flottille de pêche. Ceci amène notamment à préciser la définition d'un stock, sa relation avec la notion de population biologique, à analyser les problèmes de définition de la capturabilité. Les concepts d'intensité, d'effort, de puissance de pêche, une analyse des relations entre abondance et capture par unité d'effort sont ensuite présentés. Après une brève réflexion générale sur la modélisation, la deuxième partie de cet ouvrage présente les modèles eux-mêmes, en abordant successivement les modèles dits globaux et structuraux. Un effort est fait pour couvrir non seulement les versions les plus anciennes, mais aussi les variantes récentes, pour détailler les relations entre ces différentes variantes, offrir un formulaire de base, enfin, discuter les hypothèses majeures et les prolongements souhaitables ou en cours.
Publications du C.N.E.X.O. Série "Rapports scientifiques et techniques" (0339-2899) (CNEXO), 1981 , N. 45 , P. 1-120

Droits : Centre National pour l'Exploitation des Océans, 1981
http://archimer.ifremer.fr/doc/1981/rapport-1126.pdf
http://archimer.ifremer.fr/doc/00000/1126/

Éditeur(s) : Wiley
Résumé : This paper investigates some economic consequences of creating a marine reserve on both fishing and ecotourism, when the range of controllability of fishing effort is limited and the impact of the reserve on ecosystem is considered. The issue is illustrated by the example of creating a no-take zone in part of a region where fishing is managed through a limited entry license system, and which is inhabited by two interacting stocks: a stock of prey (fish) and a stock of predators (seals). While the former is targeted by commercial fishing, the latter is not subject to harvest but is a potential basis for a commercial non-extractive activity (seal watching). Analysis is conducted with the help of a bioeconomic model combining the features of marine reserve modeling and of multispecies modeling. Following a description of the model, results of several simulation runs are presented. These show that creating a marine reserve has more complex economic implications than predicted in studies focused exclusively on one stock and/or commercial fisheries. More specifically, the model shows that the dynamics of the two interacting stocks reduces the benefits of the no-take zone for the fishing industry, while it makes the creation of this zone provide an opportunity for the development of ecotourism. Due to this dynamics, the model suggests that the optimal size of the reserve is larger when ecotourism is taken into account along with fishing activities.
Natural Resource Modeling (1939-7445) (Wiley), 2002-12 , Vol. 15 , N. 4 , P. 387–411

Droits : 2002 Rocky Mountain Mathematics Consortium
http://archimer.ifremer.fr/doc/00244/35506/34010.pdf
DOI:10.1111/j.1939-7445.2002.tb00095.x
http://archimer.ifremer.fr/doc/00244/35506/

Éditeur(s) : Université de Bretagne Occidentale
Résumé : Study of mineral suspended particulate matter (SPM) is essential to understand ecosystem dynamics. SPM influences light penetration which is closely related to primary production and carries pollutants and nutrients within the water masses. This work aims to study near-surface mineral SPM dynamics in the English Channel using two complementary methods: remote-sensing by satellites and numerical modelling. Firstly, MODIS and MERIS satellite images processed by the IFREMER semi-analytical algorithm and describing non-algal SPM, are analysed to build three statistical models which are able to estimate near-surface SPM using simple variables, e.g., tidal coefficient, significant wave height and mean chlorophyll-a concentration. Secondly, the three-dimensional hydrosedimentary model ROMS (Regional Ocean Modeling System) is applied in the English Channel. It considers tidal forcing along open boundaries, wind stress at the sea-surface, wave-current interactions in the bottom boundary layer and realistic heterogeneous bottom sediments. Results of the more sophisticated statistical model is also used to impose SPM concentrations at open boundaries. Sensitivity tests on SPM boundary conditions show the importance of prescribing realistic sediment concentrations to improve the model predictions. Biological influences on mineral SPM are also tested using settling velocity and critical shear stress for erosion which vary with seasons. Both statistical and numerical models highlight and locate respective influences of tide, waves and biology on mineral SPM. Numerical predictions indicate that near-surface SPM is mainly composed of silts (>70%). Near-surface suspended silts come largely from seabed resuspension alongshore in the Eastern Channel and from the open boundaries of our limited-area coastal model at the West of Cotentin Peninsula and offshore. Near-surface SPM variations are investigated at semi-diurnal, neap-spring tidal cycle time scales and during a wave event. Finally, dynamics of sediments in the turbidity maximum zone around the Isle of Wight is examined depending on hydrodynamical conditions in order to distinguish the role played by advection and local erosion/settling processes in this area. Keywords: Suspended particulate matter, satellite, remote-sensing, modelling, English Channel, sediments, turbidity, tide, wave
L'étude des matières en suspension (MES) minérales est essentielle pour comprendre le fonctionnement des écosystèmes en Manche : les MES influencent la pénétration de la lumière dans la colonne d'eau, paramètre clé pour la production biologique, et sont susceptibles de transporter des polluants et nutriments. Lors de ce travail, la dynamique des MES minérales de surface en Manche est étudiée à l'aide de deux méthodes complémentaires : l'observation par satellite et la modélisation numérique tridimensionnelle. Dans un premier temps, les images satellite MODIS et MERIS, traitées par l'algorithme semi-analytique développé par l'IFREMER et représentant les MES non-algales de surface, sont analysées afin d'élaborer trois modèles statistiques permettant d'estimer la MES de surface en fonction de variables basiques telles que le coefficient de marée, la hauteur significative des vagues et la concentration moyenne en chlorophylle-a. Dans un deuxième temps, le modèle hydrosédimentaire multiclasse tridimensionnel ROMS (Regional Ocean Modeling System) est implémenté en Manche. Il prend en considération le forçage par la marée aux frontières ouvertes, la contrainte exercée par le vent à la surface de la mer, l'interaction houle-courant en couche limite de fond et l’hétérogénéité spatiale réaliste du lit sédimentaire. Les résultats du modèle statistique le plus sophistiqué sont également utilisés pour forcer la concentration en MES aux frontières ouvertes du domaine de calcul. Des tests de sensibilité sur les conditions limites montrent l'importance de considérer de manière réaliste les sédiments entrant en Manche par les frontières ouvertes lors de la modélisation numérique. L'influence de la biologie sur les MES minérales est testée en utilisant une formulation de la vitesse de chute et de la contrainte critique d'érosion variant saisonnièrement. Grâce à ces deux outils associés, les influences respectives de la marée, de la houle et de la biologie sur les MES minérales sont mises en avant et localisées en Manche. Le modèle numérique prédit que les MES de surface sont composées principalement de silts (>70%). Les silts en suspension en surface proviennent majoritairement du lit sédimentaire près des côtes en Manche orientale et des frontières ouvertes du domaine de calcul à l'ouest de la presqu'île du Cotentin et au large en Manche centrale et orientale. Les variations des MES de surface sont ensuite étudiées aux échelles des cycles de marée semi-diurnes, vive-eau/morte-eau et autour d'un épisode de houles. Enfin, l'évolution de la concentration de sédiments dans la zone de forte turbidité autour de l'île de Wight peut être analysée suivant les conditions hydrodynamiques afin d'évaluer les rôles respectifs des processus locaux d'érosion/dépot et d'advection dans la génération de ces turbidités remarquables. Mots-clés : Matière en suspension, télédétection, satellite, modélisation, Manche, sédiments, turbidité, marée, houle

Droits : 2013 UBO
http://archimer.ifremer.fr/doc/00157/26783/24884.pdf
http://archimer.ifremer.fr/doc/00157/26783/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Transmission electron microscopy observations on olivine crystals deformed at moderate (≤1273 K) temperature evidenced dislocations interactions explaining the hardening observed in the experiments, but also recovery mechanisms by the absorption or emission of point defects. Thus we investigate the possibility that, at geological strain-rates, these recovery processes allow steady-state deformation by dislocation creep at low to moderate temperatures in the lithospheric mantle. We test this hypothesis using a 2.5-D dislocation dynamics (DD) model, which combines dislocation glide and recovery by climb. This model shows that diffusion-controlled recovery processes allow for steady-state deformation by dislocation creep in the lithospheric mantle at stresses <500 MPa. For stresses of 50–200 MPa, steady-state strain-rates of 10−15 s−110−15 s−1 may be attained at temperatures as low as 900 K. Fitting of the DD model produces a flow law, which represents a lower bound for the lithospheric mantle strength, since the models describe the deformation of an olivine single crystal in an easy slip orientation. Comparison of strain-rates and Moho temperatures inferred for different geodynamic environments and the predictions of this model-based flow law implies, nevertheless, that, except in incipient rifts, most of the observed deformation may be produced by stress levels ≤200 MPa, consistent with those inferred to be produced by convection. This convergence suggests that the present models, which explicitly calculate the time-dependent dislocation dynamics, may provide a correct first order estimate of the mechanical behaviour of the lithospheric mantle, which cannot be derived directly from any existing data.
ISSN: 0012-821X

hal-01277178
https://hal.archives-ouvertes.fr/hal-01277178
https://hal.archives-ouvertes.fr/hal-01277178/document
https://hal.archives-ouvertes.fr/hal-01277178/file/Boioli.pdf
DOI : 10.1016/j.epsl.2015.10.012

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
This paper presents a multicontinuum approach to model fractal temporal scaling of catchment response in hydrological systems. The temporal scaling of discharge is quantified in frequency domain by the transfer function HðxÞ, which is defined as the ratio between the spectra of catchment response and recharge time series. The transfer function may scale with frequency x as HðxÞ x2b. While the classical linear and Dupuit models predict exponents of b52 and b51, observations indicate scalings with noninteger exponents b. Such behaviors have been described by multifractal models, which, however, often lack a relation to the medium characteristics. We revisit and extend the classical linear Dupuit aquifer models and discuss their physical meanings in the light of the resulting aquifer dynamics. On the basis of these classical models, we derive a multicontinuum approach that provides physical recharge models which are able to explain fractal behaviors with exponents 1=2 < b < 2. Furthermore, this approach allows to link the fractal dynamics of the discharge process to the physical aquifer characteristics as reflected in the distribution of storage time scales. We systematically analyze the catchment responses in the proposed multicontinuum models, and identify and quantify the time scales which characterize the dynamics of the catchment response to recharge.
ISSN: 0043-1397

insu-00952537
https://hal-insu.archives-ouvertes.fr/insu-00952537
https://hal-insu.archives-ouvertes.fr/insu-00952537/document
https://hal-insu.archives-ouvertes.fr/insu-00952537/file/russian.pdf
DOI : 10.1002/2013WR014255

Résumé : The management of marine fish stocks has stayed non-spatial, considering spatial distributions and their consequences on demography as implicit. But the impacts of climate change and the anthropisation of habitats now require to consider spatial procedures explicitly. The work presented here starts with the question of evaluating population abundance, which requires the modelling of spatial distributions (section 1). Then an ecological understanding of the multi-scale nature of distributions is investigated (section 2). Last, we study how demographic population dynamics depends on the spatial organisation of life cycles (section 3). In this work, the approach has been to combine data acquisition at sea with statistical characterisation and modelling. The application of geostatistics to fisheries survey data provided a solution to abundance evaluation and mapping for many different survey designs. A variety of models were implemented (stationary, non-stationary, non-linear, multivariate, spatio-temporal), depending on the statistical characteristics of the data and the problem posed. Sampling bias were identified by combining different survey methods. New procedures for assessing stocks based on indicators including spatial ones were developed, which prepared for ecosystem assessments. (...)
La gestion des stocks de poissons marins est longtemps restée a-spatiale, considérant implicites les mécanismes d’organisation spatiale qui soutiennent la distribution géographique des ressources et leur dynamique démographique. Mais l’impact du changement climatique et l’anthropisation des habitats nécessitent d’en tenir compte explicitement. Partant de questions d’évaluation qui ont nécessité la modélisation des distributions spatiales (section 1), le déterminisme écologique de ces distributions a ensuite été abordé à différentes échelles (section 2) puis ont été envisagées les conséquences de l’organisation spatiale sur la dynamique démographique des populations (section 3). L’approche scientifique suivie intègre l’acquisition de données à la mer, la caractérisation statistique et la modélisation. L’application de la géostatistique aux données des campagnes halieutiques permet de proposer une solution à l’estimation d’abondance et la cartographie pour une variété de plans d’échantillonnage. Différents modèles sont mis en oeuvre (stationnaires, non-stationnaires, non-linéaires, multivariés, spatio-temporels) en fonction du comportement des données et du problème posé. Des biais d’échantillonnage sont identifiés en combinant différentes méthodes d’échantillonnage. Des procédures nouvelles d’évaluation de stocks à partir d’indicateurs dont des indicateurs spatiaux sont développées, qui préparent à l’évaluation des écosystèmes. (...)

Droits : Ifremer, UPMC
http://archimer.ifremer.fr/doc/00013/12410/9197.pdf
http://archimer.ifremer.fr/doc/00013/12410/

Éditeur(s) : Universite Montpellier II
Résumé : Since 1980, the expansion of a green macro-alga: Valonia aegagropila (C Agardh) is observed in Salses-Leucate lagoon (France). It is currently distributed in the north of the lagoon with important biomasses (40 gDW/m²) eroding the cover of Zostera noltii. The free form of the alga can be transported with the surface or bottom currents depending on seasons. It multiplies mainly by vegetative reproduction. There are few studies on the ecophysiological capacities of V. aegagropila. This work tries to answer why (physiological adaptation) and how (mechanical process of transport) the alga invaded the lagoon, with an approach including observations, experiments in controlled environment and biological and hydrodynamic models. The growth capacities depend on temperature and light intensities, the nutrients absorption rates and internal nitrogen and phosphorus internal quotas were measured and modelled using a Droop model based on internal quota. Vertically transport was studied with laboratory experiments and measurements of biomass transport were made into the lagoon. The biological model (growth, vertical transport, mortality) was coupled to the MARS 3D hydrodynamic model with a meshgrid of 160m. The results show an adaptation of the alga to low availability of phosphorus and an annual growth of biomass controlled by the availability of nutrient during winter. The alga seems to occupy the whole zones where growth is optimal and the risk of invasion of the southern part of the lagoon is limited. This work opens on research prospects on an ecological model (confronting physiological capacities and competition of V. aegagropila, Zostera noltii, green algae and primary production), new physiological experiments, ecological observations and potential valorisation of V. aegagropila.
Depuis 1980, est observée dans l'étang de Salses-Leucate l'expansion d'une macro-algue verte : Valonia aegagropila (C. Agardh). En 2004, elle était présente sur la presque totalité de la moitié nord de la lagune avec des biomasses importantes (jusqu'à 600 gPS/m²). L'algue envahit et érode également la couverture d'herbiers garant de la biodiversité, de la productivité et de la stabilité de l'écosystème. V. aegagropila se reproduit essentiellement de manière végétative (fragmentation des thalles) et possède la particularité de retenir de l'oxygène de la photosynthèse dans sa structure sphérique. Cet oxygène piégé lui donne la possibilité de mouvement sur la verticale et d'être transportée dans le domaine par les courants. Les conditions physico-chimiques de l'étang présentent de fortes variations saisonnières en salinité, en température et en turbidité, ainsi que des apports nutritifs faibles : la production primaire est principalement limitée par le phosphore. Il existe malheureusement peu d'informations sur V. aegagropila ainsi que trop peu de connaissances sur son écophysiologie. Elle semble vivre dans des milieux plutôt oligotrophe dans des régions tropicales à sub-tropicales. Ce travail basé sur une approche d'observations de terrain, d'expérimentations en milieu contrôlé (en laboratoire) et de modélisation des processus, a permis d'une part d'explorer les capacités adaptatives physiologiques de V. aegagropila aux conditions environnementales de l'étang et d'autre part de mettre à jour les modes de fonctionnement de la dynamique spatio-temporelle de la population. Les capacités de croissance ont été mesurées sur un large spectre de température et de lumière. Les capacités d'absorption des sels nutritifs dans l'eau et les facultés de l'algue à stocker l'azote et le phosphore dans ses tissus ont également été étudiées. D'autre part, un modèle de dynamique des populations a été conceptualisé puis développé. Les processus pris en compte dans ce modèle sont la croissance de l'algue (modèle à quota interne), la flottabilité de l'algue et la mortalité par surdensité. Ces processus ont été paramétrés en majeure partie par des expérimentations réalisées en laboratoire. Ce modèle 0D a par la suite était couplé au modèle hydrodynamique MARS3D (modèle Ifremer) mis en place sur la lagune de Salses-Leucate, utilisant deux grilles de calcul (160m ou de 80m de résolution). Les simulations réalisées permettent d'appréhender les capacités spatio-temporelles de la croissance de l'algue dans l'étang, le turnover annuel de la biomasse totale et les attracteurs de biomasse du système sous différents évènements météorologiques. Ces résultats sont comparés avec les répartitions cartographiques de la population observées in situ en 1999 et 2004 et des flux de biomasses mesurés au cours d'observations de terrain entre juin 2003 et septembre 2004. L'ensemble des résultats montre d'une part une adaptation de l'algue à évoluer dans un milieu pauvre en phosphore et d'autre part une croissance annuelle de la biomasse totale qui est principalement contrôlée par les apports hivernaux en sels nutritifs dans la lagune. Les résultats des simulations montrent également que V. aegagropila semble occuper à présent la majeure partie des zones favorables à sa croissance. Il est également montré que si sa capacité de mouvement peut favoriser la dispersion d'individus dans la lagune et accélérer la croissance de la population pour de faibles biomasses initiales, cette même capacité de mouvement joue plutôt un rôle de régulation de la population lorsque la biomasse totale devient importante. On peut penser que le risque de colonisation de l'herbier à zostère de la partie sud de la lagune (bassin de Salses) est limité. Ce travail ouvre enfin des perspectives de recherche sur l'amélioration du modèle de dynamique des populations de l'espèce, sur de nouvelles expérimentations à réaliser ou encore sur la surveillance écologique du milieu. Des propositions sont faites pour concevoir un modèle écologique confrontant les capacités physiologiques des macrophytes (algues vertes, Valonia et zostères) afin d'apréhender les phénomènes de compétitions et les modes de fonctionnement du réseau trophique de la lagune de Salses- Leucate. Des pistes sur la valorisation de la matière algale de V. aegagropila sont enfin proposées.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2006/these-2453.pdf
http://archimer.ifremer.fr/doc/00000/2453/

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We present a 2-D Contact Dynamics discrete element model for simulating initiation and motion of rock avalanches, integrating hillslope geometry, Mohr-Coulomb rock behavior, pore pressure before avalanche triggering, and avalanche trigger. Avalanche motion is modeled as a dense granular flow of dry frictional and cohesive particles. On the basis of granular physics and shear experiments, we review some of the theories for the unexpectedly long runout of rock avalanches. Different causes are evoked, according to the strength (strong or weak) of the slip surface relative to the bulk. "Mechanical fluidization'' and "acoustic fluidization'' theories state that agitation of rock particles reduces frictional strength, increasing runout. Conversely, granular mechanics suggests that, as "shear-strain'' rate increases, granular material becomes more agitated, more dissipative, and more resistant. Another theory states that dynamic fragmentation of clasts creates an isotropic pressure that drives longer runout. In contrast, granular mechanics suggests that fragmentation may induce fluidization and strengthening of the granular material, while particle size reduction (among others) induces weakening of the granular flow and enhances long runout. Runout is also enhanced for column-like rock masses collapsing from steep hillslopes. Long runout may also be linked to thermal weakening mechanisms at the slip surface (e.g., thermal pressurization, and shear melting), which may lower drastically the shear strength. The model is illustrated with a hypothetical example of a rain-triggered avalanche, mobilizing shallowly dipping layers. Several phases are identified, including slope failure, avalanche triggering resulting from slip weakening, and avalanche motion in which rocks are folded and sheared.
ISSN: 0148-0227

hal-00420883
https://hal.archives-ouvertes.fr/hal-00420883
DOI : 10.1029/2008JF001072

Éditeur(s) : HAL CCSD
Résumé : The present PhD thesis is devoted to the numerical simulation and analysis of shear on cohesive granular materials. In the framework of the Contact Dynamics method, we developed a model of cohesive bonding, which mimics cohesion by cementation. This model involves three contact strength parameters (a tensile strength, a coefficient of sliding friction, and a coefficient of rolling friction) as well as a local criterion, which controls the creation and the breaking of cohesive bonds. All contacts are cohesive at the beginning of the numerical simulations, and contact rupture leads to an irreversible loss of tensile strength (debonding). We varied systematically the three contact strength parameters and studied their influence on the shear strength, the dilatancy, and the microstructure of the granular media. Our results show that internal friction and macroscopic tensile strength have different origins at the contact scale. We also find that the microstructure of the granular media, when sheared at the steady state (also known as the `critical state"), is strongly affected by the local coefficients of sliding and rolling friction. In particular, the mechanical role of the weak network changes with these two contact parameters, which results from the formation of a new structure of force transmission. On the other hand, we also applied the same numerical simulation method to the simulation of landslides. We developed a methodology, which takes into account the initial morphology of the hillslope, the strength of geomaterials, and a triggering factor, integrating in the same model the initiation and propagation phases of the landslide. To illustrate this methodology, we applied it to the simulation of a hypothetical example of avalanche triggered by the progressive rise of a water table.
Ce travail de thèse porte sur la modélisation numérique et l'analyse du cisaillement dans les milieux granulaires cohésifs. Dans le cadre de la méthode de la Dynamique des Contacts, nous avons développé un modèle de cohésion qui cherche à imiter la cohésion par cimentation. Ce modèle fait intervenir trois paramètres de résistance au niveau des contacts (une résistance à la traction, un coefficient de frottement de glissement, et un coefficient de frottement de roulement) ainsi qu'un critère de création et de rupture des liens cohésifs. Les contacts sont cohésifs au début des simulations et leur rupture entraîne la perte irréversible de la résistance à la traction. Nous avons fait varier les trois paramètres microscopiques et nous avons étudié leur influence dans la résistance au cisaillement, la dilatance, et la microstructure du milieu. Nos résultats montrent que le frottement interne et l'adhésion macroscopiques ont des origines microscopiques différentes. Nous observons aussi que la microstructure du milieu cisaillé à l'état stationnaire (aussi connu comme ``l'état critique") est fortement affectée par l'angle de frottement et la résistance au roulement au niveau des contacts. En particulier, le rôle mécanique du réseau faible change avec ces deux paramètres microscopiques, ce qui résulte de la formation d'une nouvelle structure de transmission de forces. D'autre part, nous avons appliqué cette méthode de simulation numérique à l'étude d'un processus naturel : les glissements de terrain. Nous avons développé une méthodologie qui tient compte de la morphologie initiale du système, de la résistance des géomatériaux, et d'un mécanisme de déclanchement, ce qui permet d'intégrer dans le même modèle les phases d'initiation et de propagation du glissement. Pour illustrer cette méthodologie, nous l'avons appliquée à la modélisation d'un exemple hypothétique d'avalanche déclenchée par la montée progressive du niveau d'une nappe d'eau.
https://tel.archives-ouvertes.fr/tel-00311303

tel-00311303
https://tel.archives-ouvertes.fr/tel-00311303
https://tel.archives-ouvertes.fr/tel-00311303/document
https://tel.archives-ouvertes.fr/tel-00311303/file/these_estrada.pdf

Résumé : Cette thèse concerne la modélisation des dynamiques de maladies foliaires de cultures pérennes tropicales à différentes échelles spatiales. Cette approche de modélisation est appliquée à la cercosporiose noire du bananier. Il s’agit d’explorer et de déterminer les paramètres environnementaux et de résistance de l’hôte ayant une influence significative sur la dynamique spatiotemporelle de la maladie et d’apporter des éléments associés au contrôle de la cercosporiose noire.Deux modèles ont été développés dans le cadre de cette thèse. La dynamique épidémiologique au niveau de la plante est décrite par un modèle mécaniste décomposé en un modèle de croissance de la plante et un module épidémiologique décrivant le cycle épidémique du pathogène. L’architecture du bananier est prise en compte par le biais de compartiments foliaires positionnés dans l’espace. Le modèle a été validé par un jeu de données indépendant. Les expérimentations numériques et l’analyse de sensibilité du modèle réalisées par les méthodes de Morris et de e-FAST ont permis de mieux comprendre le fonctionnement épidémique de cette maladie et d’identifier les paramètres influant le plus la dynamique épidémique en particulier la vitesse d’extension des lésions, la durée d’incubation et l’efficacité d’infection .L’approche bayésienne a permis de prendre en compte l’information a priori disponible pour ces trois paramètres sur lesquels a porté l’inférence statistique. L’analyse de sensibilité du modèle a également permis d’identifier l’influence de deux paramètres liés à la croissance de la plante : le nombre de feuilles sur une plante et le rythme d’émission foliaire Un modèle de dynamique spatio-temporelle de la cercosporiose noire a été développé à l’échelle d’un territoire à partir d’enquêtes effectuées enMartinique pendant la période d’invasion de cette maladie de septembre 2010 à mai 2012. Les données récoltées étant censurées, l’inférence des paramètres du modèle a été réalisée dans un cadre bayésien en utilisant un algorithme d’augmentation de données. Le modèle et l’inférence développés permettent de reconstruire la dynamique spatio-temporelle de l’invasion et de prédire la fin d’invasion sur le territoire.Les deux modèles de dynamiques spatio-temporelles développés à deux échelles spatiales différentes ont permis d’acquérir des informations importantes pour construire des outils de conception de méthode de contrôle de la cercosporiose noire des bananiers.
This thesis concerns the modeling of the dynamics of foliar diseases of tropical tree crops at different spatial scales. This modeling approach is applied to black Sigatoka of banana. It is to explore and determine the environmental parameters and host resistance has a significant influence on the spatiotemporal dynamics of the disease and to provide elements associated with the control of Sigatoka noire.Deux models were developed as part of this thesis. The epidemiological dynamics at the plant is described by a mechanistic model decomposed into a growth model of the plant and an epidemiological unit describing the pathogen epidemic cycle. The architecture of the banana is taken into account through foliar compartments positioned in space. The model was validated by an independent data set. Numerical experiments and model sensitivity analysis performed by the methods of Morris and e-FAST enabled to better understand the functioning of this epidemic disease and identify the parameters affecting the most dynamic epidemic especially speed extension of the lesions, the incubation period and efficiency of Bayesian .L'approche infection allowed to take into account prior information available for these three parameters that were the statistical inference. The model sensitivity analysis also identified the influence of two parameters related to plant growth: the number of leaves on a plant and rate of leaf emission A dynamic model of space-time Black Sigatoka has been developed at the scale of a territory from surveys enMartinique during the period of invasion of the disease from September 2010 to May 2012. The data collected being censored, inference of model parameters has was performed in a Bayesian framework, using a data augmentation algorithm. The model developed and inference possible to reconstruct the spatiotemporal dynamics of the invasion and predict the end of the invasion territoire.Les two spatio-temporal dynamics models developed at two different spatial scales has been gained important information for build tools design method of control of black Sigatoka of banana.

http://www.theses.fr/2015AGUY0835/document

Éditeur(s) : HAL CCSD
Résumé : International audience
In this work, we have led an analysis of the error of different global solar radiation prediction models according to the global solar radiation variability. Different predictions models where performed such as machine learning techniques (Neural Networks, Gaussian processes and support vector machines) in order to forecast the Global Horizontal solar Irradiance (GHI). We also include in this study a simple linear autoregressive (AR) model as well as two naive models based on persistence of the GHI and persistence of the clear sky index (denoted herein scaled persistence model). The models are calibrated and tested with data from three 3 French islands: Corsica (42.15°N ; 9.08°E), Guadeloupe (16.25°N ; 61.58°W) and Reunion (21.15°S ; 55.5°E). Guadeloupe and Reunion are located in a subtropical climatic zone whereas Corsica is in a tempered climatic zone. Hence the global solar radiation variation differs significantly. The output error of the different models was quantified by the nRSME. In order to quantify the influence of the global solar radiation variability on the forecasting models error we performed a classification of typical days according to different typical days. Each class of typical day is defined by a variation of global solar radiation rate. For each class and for each location, the selected forecasting models where performed and the error was quantified. With this analysis a global solar radiation forecasting models can be selected according to the location, the global solar radiation fluctuations and hence the meteorological conditions. INTRODUCTION Large and frequent variations of solar radiation can be observed in tropical climates with amplitudes reaching 800 W/m² and occurring within a short time interval, from few seconds to few minutes, according to the geographical location. Such fluctuations can be due for example to the dynamic of clouds which can be very complex and depend on cloud type, size, speed and spatial distribution and, more generally, due to some specific local meteorological conditions. Thus, the solar energy forecasting, a process used to predict the amount of solar energy available in the current and near terms, might be a difficult task. Some of the best predictors found in literature are Autoregressive and moving average (ARMA) [5,7,8], Bayesian inferences [9,10], Markov chains [11], k-Nearest-Neighbors predictors [12] or artificial intelligence techniques as the Artificial Neural Network (ANN) [9-11]. Although these methodologies are potentially good in many areas, we observed in our previous studies on global radiation prediction [9,13,14] that the simple model based on the persistence of the clear sky index gives often very good results with acceptable errors [15] for short term forecasting time horizon (<= 1 hour). The goal of this paper is to determinate the influence of solar radiation variability regarding different classes of days on the expected error provided by different forecasting methods that the modeller can possibly implement. The paper is organized as follow: Section 2 describes the data we have used. Section 3 exposes the classification methodology and the results obtained for the three studied locations. In the two following sections, the forecasting methods are exposed and then 3 the errors on the forecasting results for each location and for each class are exposed.
The Third Southern African Solar Energy Conference (SASEC2015)
Kruger National Park, South Africa

Droits : info:eu-repo/semantics/OpenAccess
hal-01099487
https://hal.archives-ouvertes.fr/hal-01099487
https://hal.archives-ouvertes.fr/hal-01099487/document
https://hal.archives-ouvertes.fr/hal-01099487/file/article%20SASEC.pdf

Éditeur(s) : HAL CCSD Geological Society of London
Résumé : We have applied transmission electron microscopy (TEM) analyses coupled with viscoplastic self-consistent (VPSC) numerical modelling to identify the active slip systems and to better understand the crystal preferred orientation (CPO) development of the Torridon quartz mylonite (NW Scotland). TEM analyses showed evidence of activation of 1/3〈a〉{π′}, 1/3〈a〉{z} and possible 〈a〉(c) slip systems, as well as dislocation climb and dynamic recrystallization. All the CPOs generated by VPSC models share common characteristics with the Torridon quartz mylonite, but only Models 2 and 3 reproduce the [c]-axes maxima at low angle (<20°) to the foliation pole along the YZ plane, as observed in the mylonite. In Model 2, this concentration only occurs at γ≥2.6, whereas in Model 3 this maxima occurs at lower shear strains. The models that start with a previous preferred orientation acquire very strong CPOs after small-imposed strains, followed by the rapid rotation of the fabric in relation to the new imposed finite strain axes. The combined activation of 〈a〉{π′}, 〈a〉{z} and possibly 〈a〉(c) slip systems, as demonstrated by TEM analyses, suggests that the VPSC model that best predicts CPO development in the Torridon quartz mylonite is Model 2, where the critical resolved shear stress (CRSS) of 〈a〉{π/π′} is assumed to be slightly stronger than 〈a〉(c).
Deformation Mechanisms, Rheology and Tectonics: Microstructures, Mechanics and Anisotropy

hal-00688840
https://hal.archives-ouvertes.fr/hal-00688840

Éditeur(s) : Ecole Nationale Supérieure Agronomique de Rennes
Résumé : Long-line fishing has been growing on the island of La Réunion since the beginning of the 1990s. The target species is the swordfish (Xiphias gladius), fished mainly in the tropical waters surrounding the island between longitudes 45 degree E and 60 degree E, and latitudes 17 degree S and 27 degree S. From 1998 to 2000, a finalised research programme enabled the collection of precise data concerning the lines' positions and the parameters of the fishing efforts: 3,602 nettings were thus informed by the catches (in numbers of individuals caught) and 12 descriptive variables of the effort. In parallel with this collection effort, satellite maps that described the ocean's landscape of this region of the Indian Ocean exploited by La Réunion's fisheries were made available to sailors and scientists. Extractions from these environmental variables were made at the fishing lines' positions, which allowed us to propose 20 variables describing the environmental conditions of swordfish catches applied to the nettings. In an early part of this study, after a descriptive analysis and a first selection of the variables, we used several GAM (Generalised Additive Models) to model the respective effects of effort and environmental variables on the variability of swordfish catches. We thus highlighted the predominance of factors linked to fishermen (fishing effort) on oceanographic factors in the explanation of this variability. Following these results, a summary on the biology and ecology of the swordfish was proposed in order to draw up hypotheses on the characteristics of this species' population in the Indian Ocean. The aspects linked to the individual behaviour and movements of the population were particularly highlighted. In a latter part of this study and in order to complete the empirical approach by an exploratory constructivist approach, we proposed a modelling tool in order to simulate the possible movements of individuals within the oceanic landscape described by the available satellite maps. After reading in the literature about the various forms of modelling the movements of the large pelagics, we developed an original computer modelling architecture of the multi-agent type that made it possible to manipulate in a dynamic way the satellite maps (and derived products), the individual movements of "animats" whose behaviours were based on this environmental information, and agents that clarify the process of long-line fishing in a geographical way. The computer model that was implemented (MUFINS, for MUlti-Fish INdian ocean Simulator) was next used by calibrating the behaviour of the animats on the real data originally from the analysis of commercial catches proposed in the first part, using robust techniques based on fuzzy logic. The results of the simulations were compared, on the one hand, with the large-scale hypotheses of movement proposed in the first part, and, on the other hand, to swordfish catches both real and corrected for the effect of the fishing effort modelled by the GAM models. Even if the results of these simulations in this study do not allow for proposing convincing interpretations of the underlying processes, the MUFINS tool showed its ability to address questions associated with the swordfish's behaviour in the tropical oceanic landscape and to the effects of scale transfers between the individual level and the collective level. We now envisage its use in a more operational framework, as an interface for dialogue between fishermen and scientists with a goal of sustainable management of the resource.
La peche palangriere s'est developpee a l'ile de La Reunion depuis le debut des annees 1990. L'espece cible est l'espadon (Xiphias gladius), principalement exploite dans les eaux tropicales autour de l'ile entre les longitudes 45 degree E et 60 degree E, et les latitudes 17 degree S et 27 degree S. De 1998 a 2000, un programme de recherche finalisee a permis de collecter des informations precises concernant les positions des lignes et les parametres de l'effort de peche : 3602 filages sont ainsi renseignes par les captures (en nombre d'individus captures) et 12 variables descriptives de l'effort. En parallele de cet effort de collecte, des cartes satellitales ont pu etre mises a la disposition des marins et des scientifiques, decrivant le paysage oceanique de cette region de l'ocean Indien exploitee par la pecherie reunionnaise. Des extractions de ces variables environnementales ont ete effectuees aux positions des lignes de peche, nous permettant de proposer 20 variables descriptives des conditions environnementales de captures d'espadon appliquees aux filages. Dans une premiere partie de ce travail, apres une analyse descriptive et une premiere selection des variables, on a modelise par plusieurs modeles GAM (Generalized Additive Models) les effets respectifs des variables d'effort et des variables environnementales sur la variabilite des captures d'espadon. On a ainsi mis en evidence la predominance des facteurs lies aux pecheurs (effort de peche) sur les facteurs oceanographiques dans le caractere explicatif de cette variabilite. A la suite de ces resultats, une synthese sur la biologie et l'ecologie de l'espadon a ete proposee afin de degager des hypotheses sur les caracteristiques de la population de cette espece dans l'ocean Indien. Les aspects lies au comportement individuel et aux deplacements de la population ont ete particulierement mis en evidence. Dans une deuxieme partie de ce travail et afin de completer l'approche empirique par une approche constructiviste exploratoire, nous avons propose un outil de modelisation afin de simuler les deplacements possibles d'individus au sein du paysage oceanique decrit par les cartes satellitales disponibles. Apres avoir passe en revue dans la litterature les differentes formes de modelisation des deplacements des grands, pelagiques, nous avons developpe une architecture originale de modelisation informatique de type multi-agents permettant de manipuler de maniere dynamique les cartes satellitales (et les produits derives), les mouvements individuels < d'animats >, dont les comportements sont bases sur cette information environnementale, et des agents qui explicitent le processus de capture palangriere de maniere geographique. Le modele informatique ainsi implemente (MUFINS, pour MUlti-Fish INdian ocean Simulator) a ensuite ete utilise en calibrant les comportements des animats sur les donnees reelles issues de l'analyse des captures commerciales proposee en premiere partie, a partir de techniques robustes basee sur la logique floue. Les resultats des simulations ont ete confrontes d'une part aux hypotheses de deplacement a grande echelle proposees en premiere partie, et d'autre part aux captures d'espadon reelles et corrigees de l'effet de l'effort de peche modelise par les modeles GAM. Meme si les resultats de simulations presentes dans ce travail ne permettent pas de proposer d'interpretations convaincantes des processus sous-jacents, l'outil MUFINS a demontre son aptitude a aborder les questions liees au comportement de l'espadon dans le paysage oceanique tropical et aux effets des transferts d'echelle entre le niveau individuel et le niveau collectif. On envisage desormais son utilisation dans un cadre plus operationnel, comme interface de dialogue entre les pecheurs et les scientifiques a des fins de gestion durable de la ressource.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2005/these-2592.pdf
http://archimer.ifremer.fr/doc/00000/2592/

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
1] Recent statistical analysis by Lallemand et al. (2008) of subduction zone parameters revealed that the back-arc deformation mode depends on the combination between the subducting (nu(sub)) and upper (nu(up)) plate velocities. No significant strain is recorded in the arc area if plate kinematics verifies nu(up) = 0.5 vsub - 2.3 (cm/a) in the HS3 reference frame. Arc spreading ( shortening) occurs if nu(up) is greater ( lower) than the preceding relationship. We test this statistical law with numerical models of subduction, by applying constant plate velocities far away from the subduction zone. The subducting lithosphere is free to deform at all depths. We quantify the force applied on the two converging plates to sustain constant surface velocities. The simulated rheology combined viscous (non-Newtonian) and brittle behaviors, and depends on water content. The influence of subduction rate vs is first studied for a fixed upper plate. After 950 km of convergence ( steady state slab pull), the transition from extensional to compressive stresses in the upper plate occurs for vs similar to 1.4 cm/a. The effect of upper plate velocity is then tested at constant subduction rate. Upper plate retreat ( advance) with respect to the trench increases extension ( compression) in the arc lithosphere and increases ( decreases) the subducting plate dip. Our modeling confirms the statistical kinematic relationship between vsub and nu(up) that describes the transition from extensional to compressive stresses in the arc lithosphere, even if the modeled law is shifted toward higher rates of upper plate retreat, using our set of physical parameters ( e. g., 100 km thick subducting oceanic plate) and short- term simulations. Our results make valid the choice of the HS3 reference frame for assessing plate velocity influence on arc tectonic regime. The subduction model suggests that friction along the interplate contact and the mantle Stokes reaction could be the two main forces competing against slab pull for upper mantle subductions. Besides, our simulations show that the arc deformation mode is strongly time dependent.
ISSN: 1525-2027

hal-00412328
https://hal.archives-ouvertes.fr/hal-00412328
https://hal.archives-ouvertes.fr/hal-00412328/document
https://hal.archives-ouvertes.fr/hal-00412328/file/arcayG32008.pdf
DOI : 10.1029/2007GC001875

Éditeur(s) : HAL CCSD Springer Verlag/EDP Sciences
Résumé : International audience
Context : Functional - structural models (FSM) of tree growth have great potential in forestry, but their development, calibration and validation are hampered by the difficulty of collecting experimental data at organ scale for adult trees. Due to their simple architecture and morphological properties, " model plants " such as Cecropia sciadophylla are of great interest to validate new models and methodologies, since exhaustive descriptions of their plant structure and mass partitioning can be gathered. * Aims : Our objective was to develop a model-based approach to analysing the influence of environmental conditions on the dynamics of trophic competition within C. sciadophylla trees. * Methods : We defined an integrated environmental factor that includes meteorological medium-frequency variations and a relative index representing the local site conditions for each plant. This index is estimated based on model inversion of the GreenLab FSM using data from 11 trees for model calibration and 7 trees for model evaluation. * Results : The resulting model explained the dynamics of biomass allocation to different organs during the plant growth, according to the environmental pressure they experienced. * Perspectives : By linking the integrated environmental factor to a competition index, an extension of the model to the population level could be considered.
ISSN: 1286-4560

hal-00780347
https://hal-ecp.archives-ouvertes.fr/hal-00780347
https://hal-ecp.archives-ouvertes.fr/hal-00780347/document
https://hal-ecp.archives-ouvertes.fr/hal-00780347/file/Letort2011AFS.pdf
DOI : 10.1007/s13595-011-0131-x