Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
For the first time, an albite orthogneiss has been recognised and dated within the HP-LT blueschist facies metabasites and metapelites of the Ile de Groix. It is characterised by a peraluminous composition, high LILE, Th and U contents, MORB-like HREE abundances and moderate Nb and Y values. A U-Pb age of 480.8 ± 4.8 Ma was obtained by LA-ICP-MS dating of zircon and titanite. It is interpreted as the age of the magmatic emplacement during the Early Ordovician. Morphologically different zircon grains yield late Neoproterozoic ages of 546.6-647.4 Ma. Zircon and titanite U-Pb ages indicate that the felsic magmatism from the Ile de Groix is contemporaneous with the acid, pre-orogenic magmatism widely recognised in the internal zones of the Variscan belt, related to the Cambro-Ordovician continental rifting. The magmatic protolith probably inherited a specific chemical composition from a combination of orogenic, back-arc and anorogenic signatures because of partial melting of the Cadomian basement during magma emplacement. Besides, the late Devonian U-Pb age of 366 ± 33 Ma obtained for titanite from a blueschist facies metapelite corresponds to the age of the HP-LT peak metamorphism.
ISSN: 1437-3254

insu-00714570
https://hal-insu.archives-ouvertes.fr/insu-00714570
DOI : 10.1007/s00531-011-0732-5

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Slices of polycyclic metasediments (marbles and meta-cherts) are tectonically amalgamated with the polydeformed basement of the Dent Blanche tectonic system along a major Alpine shear zone in the Western Alps (Becca di Salé area, Valtournenche Valley). A combination of techniques (structural analysis at various scales, metamorphic petrology, geochronology and trace element geochemistry) was applied to determine the age and composition of accessory phases (titanite, allanite and zircon) and their relation to major minerals. The results are used to reconstruct the polyphase structural and metamorphic histories, comprising both pre-Alpine and Alpine cycles. The pre-Alpine evolution is associated with low-pressure high-temperature metamorphism related to Permo-Triassic lithospheric thinning. In meta-cherts, microtextural relations indicate coeval growth of allanite and garnet during this stage, at ~ 300 Ma. Textures of zircon also indicate crystallisation at HT conditions; ages scatter from 263 to 294 Ma, with a major cluster of data at ~ 276 Ma. In impure marble, U-Pb analyses of titanite domains (with variable Al and F contents) yield apparent 206Pb/238U dates range from Permian to Jurassic. Chemical and isotopic data suggest that titanite formed at Permian times and was then affected by (extension-related?) fluid circulation during the Triassic and Jurassic, which redistributed major elements (Al and F) and partially opened the U-Pb system. The Alpine cycle lead to early blueschist facies assemblages, which were partly overprinted under greenschist facies conditions. The strong Alpine compressional overprint disrupted the pre-Alpine structural imprint and/or reactivated earlier structures. The pre-Alpine metamorphic record, preserved in these slices of metasediments, reflects the onset of the Permo-Triassic lithospheric extension to Jurassic rifting.
ISSN: 0024-4937

hal-00758123
https://hal.archives-ouvertes.fr/hal-00758123
DOI : 10.1016/j.lithos.2012.05.007

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Analysis of short-term deformation along the southern part of Dead Sea Fault (DSF) provides a systematic view of kinematics this part of the continental transform. The southern DSF consists of two principal segments: the Wadi Araba and Jordan Valley faults. In addition to other regional continuous GPS data, this study uses new data from 25 survey sites and 4 continuous GPS stations in Jordan for improved near-field observations. Resulting velocities are reported with 1-sigma uncertainties ranging from 0.4-1.0 mm/yr. Application of elastic dislocation models yields estimates of slip rates for Wadi Araba and Jordan Valley faults are 4.9 +/- 0.4 mm/yr and 4.7 +/- 0.4 mm/yr, respectively. Modeling also suggests different depths of effective fault locking with 15 +/- 5 km and 8 +/- 5 km for the Wadi Araba and Jordan Valley faults, respectively. These slip rates are generally consistent with the upper end of the range of slip rates estimated from late Quaternary geology. Spatial variations in effective fault locking generally correspond with a heterogeneous mantle lithosphere. A similar observation can be observed along the southern San Andreas Fault, and this may reflect the influence of heterogeneity in the uppermost mantle on crustal faulting processes.
ISSN: 1525-2027

hal-00689031
https://hal.archives-ouvertes.fr/hal-00689031
DOI : 10.1029/2011GC003736

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The analysis of field relationships between allochthonous crystalline slivers, ultramafic units and associated sedimentary cover in the high-pressure Schistes Lustrés units of northern Corsica allows reconstruction of the pre-orogenic architecture of a fossil Mesozoic Ocean-Continent Transition (OCT) of the Tethys basin. The studied area, encompassing the Serra di Pigno and Col de Téghime areas (Cap Corse) is composed of an assemblage of prealpine basement sheets made up of serpentinized mantle rocks, Permian gabbros and gneisses, locally associated with Paleozoic metabasites and micaschists. The sedimentary cover includes numerous intervals of calc-schists, marbles, quartzites, micaschists and dolomitic metabreccias yielding a great variety of lithostratigraphical successions. The metasedimentary sequences do not show affinities with the typical cover series of the Prépiémontais margin domains. This implies an origin from a more internal domain (oceanward) for the studied units. In addition, the sedimentary cover of the ultramafic basement units do not display the characters of the classical Alpine ophiolites but bear lithological features showing affinities with both continental and oceanic environments. We assume that the high variability of the sedimentary successions as well as the presence of a basement composed of continental and upper-mantle rocks is consistent with an origin at an OCT. The acidic basement slivers are regarded as former extensional allochthons of continental crust abandoned during breakup on a newly exhumed seafloor of peridotite composition. Such extensional allochthons, will then logically constitute the most internal continental slices buried at great depth during Alpine subduction. This work shows that a lot has to be expected from a revision of the Schistes Lustrés lithostratigraphy in the light of the new concepts of the evolution of the OCT domains.
ISSN: 0040-1951

hal-00795578
https://hal.archives-ouvertes.fr/hal-00795578
DOI : 10.1016/j.tecto.2012.06.013

Éditeur(s) : Pêche thonière et dispositifs de concentration de poissons, Caribbean-Martinique, 15-19 Oct 1999
Résumé : The original baitboat fishing technique using a permanent association between the fishing boat and the tuna school has been developed by the baitboat fleet of Dakar, Senegal and is also in use in the Canary Islands. This new fishing technique, the result of 20 years of improvements still on, has induced a dramatic increase of the catch yields which, in turn, has sustained the survival and even a recent development of the fleet. This technique is based on the aggregating behaviour of tropical tunas. However, it contains a dynamic component which is not found in tuna fishing on drifting or anchored fads. The specifications of the method, its refinement over the years and its main consequences for the fishery are described together with the school exchanges between baitboats over months even from one year to the next. Based on the analysis of 1228 recoveries from 5500 tagged fish, tuna movements among associated schools, between associated schools and free schools fished by purse seiners and movements in and out of the baitboat fishing grounds help to better understand the dynamics of tunas and schools of this peculiar tuna association. These data show a very high recovery rate, a remarkable tuna fidelity to the original school for all species, a small number of recoveries within the purse seine catch as well as the rare tuna movements outside the baitboat area. The study highlights the complexity and the numerous consequences of tuna and school behaviour.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00042/15304/12637.pdf
http://archimer.ifremer.fr/doc/00042/15304/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Interactions between deformation and melt percolation yield important consequences for the evolution of the mantle lithosphere, controlling its composition and mechanical behavior. In the Lherz massif (Pyrenees, France), the analysis of structural relationships between harzburgites, lherzolites and pyroxenites and of the crystal-preferred orientations (CPO) of olivine and pyroxenes highlights a strong feedback between percolation of basaltic melts and deformation under near-solidus conditions at the lithosphere–asthenosphere boundary. Elongated harzburgite bodies up to tens of meters wide, which are the remnants of an old lithospheric mantle, preserve a constant foliation. This foliation is locally outlined by cm-scale flattened websteritic lenses. At the contact with the enclosing lherzolites, the harzburgite foliation is crosscut by the lherzolites foliation and by cm-wide websterite bands parallel to the contact. Strain intensity in the lherzolites increases with distance to the harzburgites. Based on these observations, we propose that reactive percolation was synchronous to the deformation and propose that variations in instantaneous melt fraction, due to pyroxenes and spinel crystallization during reactive melt transport, guided strain localization. Accordingly, the observed decrease in olivine CPO intensity and change in CPO patterns from harzburgites to distal lherzolites are interpreted as recording changes in the relative contribution of dislocation glide and diffusion processes, which is ruled by a balance between the instantaneous melt fraction and the local strain rate. We also propose that the pervasive websteritic layering in the refertilized lherzolites may result from deformation-assisted melt segregation in a system with decreasing permeability due to refertilization reactions. Finally, we discuss the possible timing and geodynamical context of the refertilization episode.
ISSN: 0012-821X

hal-00411724
https://hal.archives-ouvertes.fr/hal-00411724
DOI : 10.1016/j.epsl.2008.07.053

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : Zircon and apatite fission track (ZFT and AFT) and (U-Th)/He, ;40;Ar/;39;Ar hornblende, and U-Pb zircon ages from the granites of Tinos Island in the Aegean Sea, Greece, suggest, together with published ZFT data, that there are three extensional detachments on Tinos. The Tinos granites crosscut the Tinos detachment. Cooling of the granites was controlled by the Livadi detachment, which occurs structurally above the Tinos detachment. Our U-Pb zircon age is 14.6 ± 0.2 Ma and two ;40;Ar/;39;Ar hornblende ages are 14.4 ± 0.4 and 13.7 ± 0.4 Ma. ZFT and AFT ages go from 14.4 ± 1.2 to 12.2 ± 1.0 Ma and 12.8 ± 2.4 to 11.9 ± 2.0 Ma. (U-Th)/He ages are from 10.4 ± 0.2 to 9.9 ± 0.2 Ma (zircon) and 11.9 ± 0.5 to 10.0 ± 0.3 Ma (apatite). All ages decrease northeastward in the direction of hanging wall transport on the Livadi detachment and age-distance relationships yield a slip rate of 2.6 (+3.3 / −1.0) km Ma;−1;. This rate is smaller than a published slip rate of 6.5 km Ma;−1; for the Vari detachment, which is another detachment structurally above the Tinos detachment. Because of the different rates and because published ZFT ages from the footwall of the Vari detachment are ∼10 Ma, we propose that the Vari detachment has to be distinguished from the older Livadi detachment. We discuss various models of how the extensional detachments may have evolved and prefer a scenario in which the Vari detachment cut down into the footwall of the Livadi detachment successively exhuming deeper structural units. The thermochronologic ages demonstrate the importance of quantitative data for constraining localization processes during extensional deformation.
ISSN: 0278-7407

hal-00407638
https://hal.archives-ouvertes.fr/hal-00407638
DOI : 10.1029/2006TC001969

Éditeur(s) : CM. 1982/K : 8
Résumé : Since 1978, the habits of the french fishermen working with bottom trawl in the Irish Sea and in the Celtic Sea were altered (CHARUAU et M0RIZUR, 198l) under the pressure of the new mesh regulation. Two facts are pointed out: - the shifting, stabilized during 1980 and 198l, of a part of the effort of the vessels fishing for gadoids, from the area VIIa to the areaVIIf - a tendancy inside the area VIIg of a part of the effort of the Nephrops trawlers to be transferred on benthic fishes when the yield of Nephrops is low.
Cette communication décrit l'évolution des habitudes des pêcheurs français travaillant au chalut de fond en Mer d'Irlande (division CIEM VIIfa) et sur le Plateau Celtique (divisions CIEM VIIf et g) sous la pression des nouvelles réglementations de irai liage. Elle fait suite à la communication de CHARUAU et M0RIZUR(198l) sur le même sujet. Deux phénomènes simultanés se sont produits depuis 1978 : - un repli qui semble s'être stabilisé entre 1980 et 198l, d'une partie de la flottille des bateaux spécialisés dans la pêche du poisson, de la division VIIa vers la division VIIf, - un report, à l'intérieur de la division VIIg, d'une partie de l'effort des langoustiniers vers le poisson. Ce changement qui s'explique surtout par des raisons socio-économiques n'est pas analysé. Seules les tendances par rapport a 1980 sont constatées.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/1982/acte-2342.pdf
http://archimer.ifremer.fr/doc/00000/2342/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Whole-rock concentrations of Se and Te were determined in 53 peridotite samples collected in orogenic bodies from the Eastern Pyrenees, including the Lherz massif (33 samples), the type-locality of Iherzolite. Orogenic Iherzolites tectonically emplaced into the continental crust escaped devolatilisation that may strongly alter concentrations of those volatile trace elements in basalt-hosted peridotite xenoliths. The Se and Te concentration ranges (<3.5-100.7 ppb; <1-11 ppb) are consistent with the few analyses of mantle samples yet available, yet extending to higher Se concentrations. In-situ analyses performed by LAM-ICPMS on base metal sulfides indicate that the Se budget is controlled by sulfides whereas a large fraction of Te (50 +/- 30%) does not reside in sulfides. The missing fraction is accounted for by fractional crystallization of Pt-Pd tellurides from Cu-Ni sulfide melts. A maximum of one third of the S budget of Eastern Pyrenean peridotites was added by assimilation of crustal sulfides, which crystallized as pyrite. Disregarding those contaminated samples, some features of the Se and Te systematics (e.g. bivariate plots vs. fertility index) cannot be explained by partial melting processes. The best fit for 33 peridotites (mostly from Lherz) yields higher than chondritic S/Se (3.1213 +/- 500; r(2) = 0.96) for near chondritic Se/Te (8.6 +/- 2; r(2) = 0.9). Our study suggest that such superchondritic S/Se ratios are better explained by petrogenetic processes involving refertilization of harzburgitic lithosphere by metal (Cu,Ni)-rich sulfide melts precipitated along with clinopyroxene and Al-spinel from silicate melts en-route to the surface.
ISSN: 0009-2541

hal-00544577
https://hal.archives-ouvertes.fr/hal-00544577
DOI : 10.1016/j.chemgeo.2010.09.007

Éditeur(s) : HAL CCSD Springer/Terra Scientific Publishing Company
Résumé : International audience
We carried out a detailed paleomagnetic, rock-magnetic, and Thellier paleointensity study of all similar to 3.6 My Pliocene lava flow succession in southern Georgia. An earlier study (Camps et al., 1996) revealed that several consecutive lava flows record an intermediate polarity direction at the base of the section followed by a thick reverse polarity zone. The transitional field was interpreted as an excursion within chron 2Ar or all upper Cochiti-Gilbert reversal. New paleomagnetic data reported here have been obtained from nearby lava successions. In total, about 170 standard paleomagnetic cores belonging to 22 lava flows were collected during the 2005 sample collection campaign. Rock-magnetic experiments showed that the remanence is carried by Ti-poor titanomagnetite in most of the samples. The fraction of grains with multidomain magnetic structure does not seem to be important. Characteristic remanent magnetization was successfully determined oil all samples. The direct correlation with the original (Thoki) sequence, previous preliminary measurements of natural remanent magnetization (Sologashvili, 1986), and field observations allowed us to establish a new magnetic stratigraphy. The lower part of section is characterized by intermediate magnetic polarity followed by thick reversely magnetized lavas. The upper sequence, represented by 18 consecutive flows yielded normal magnetic polarity. The mean paleointensity of the intermediate field is drastically reduced with respect to the post-transitional field strength. Based on all available radiometric ages and new paleomagnetic data, it may be speculated that Gilbert-Gauss (R-N) reversal was recorded at the upper part of sequence. Lower intermediate polarity flows possibly represent a form of precursor of this reversal that is similar to the Matuyama-Brunhes geomagnetic transition.
ISSN: 1343-8832

hal-00413099
https://hal.archives-ouvertes.fr/hal-00413099

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The ‘International Intercomparison Exercise of fCO₂ Systems’ was carried out in 1996 during the R/V Meteor Cruise 36/1 from Bermuda/UK to Gran Canaria/Spain. Nine groups from six countries (Australia, Denmark, France, Germany, Japan, USA) participated in this exercise, bringing together 15 participants with seven underway fugacity of carbon dioxide (fCO₂) systems, one discrete fCO₂ system, and two underway pH systems, as well as systems for discrete measurement of total alkalinity and total dissolved inorganic carbon. Here, we compare surface seawater fCO₂ measured synchronously by all participating instruments. A common infrastructure (seawater and calibration gas supply), different quality checks (performance of calibration procedures for CO2, temperature measurements) and a common procedure for calculation of final fCO₂ were provided to reduce the largest possible amount of controllable sources of error. The results show that under such conditions underway measurements of the fCO₂ in surface seawater and overlying air can be made to a high degree of agreement (±1 μatm) with a variety of possible equilibrator and system designs. Also, discrete fCO₂ measurements can be made in good agreement (±3 μatm) with underway fCO₂ data sets. However, even well-designed systems, which are operated without any obvious sign of malfunction, can show significant differences of the order of 10 μatm. Based on our results, no “best choice” for the type of the equilibrator nor specifics on its dimensions and flow rates of seawater and air can be made in regard to the achievable accuracy of the fCO₂ system. Measurements of equilibrator temperature do not seem to be made with the required accuracy resulting in significant errors in fCO₂ results. Calculation of fCO₂ from high-quality total dissolved inorganic carbon (CT) and total alkalinity (AT) measurements does not yield results comparable in accuracy and precision to fCO₂ measurements.
ISSN: 0304-4203

hal-01245605
https://hal.archives-ouvertes.fr/hal-01245605
DOI : 10.1016/S0304-4203(00)00080-3

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We review the evolution of concepts on and methods of estimating the state of stress from fault movements. Theories of failure in isotropic materials suggested a simple geometrical construction of optimal principal stress directions from a fault plane and its associated slip. These optimal directions align shear stress and slip directions and maximize the difference between shear stress and frictional resistance on the fault plane. Optimal stress directions for calcite twinning are obtained by a similar construction, with the difference that they maximize shear stress. Force representation of seismic sources independently introduced pressure, P, and tension, T, axes at positions that also maximize shear stress on both nodal planes. Frictional slip theory and the constraint that slip and shear stress directions be parallel allowed to address reactivation of pre-existing faults. This suggested that stress could also be inverted from reactivated fault and slip data or earthquake focal mechanisms. Early methods relied on geometrical constructions as a substitute for calculations, whereas later methods relied on software as these calculations became tractable with the help of computers. Similar methods were developed for the inversion of stress from crystal twin gliding with non-optimal geometry, with a different criterion that relies on a threshold of the component of shear stress along the gliding line. Even though these methods seek a common stress tensor compatible with fault and slip data, their main use is to separate polyphase data into homogeneous subsets and help deciphering complex tectonic histories. Fault and slip data can also be analyzed to constrain the strain rather than the stress tensor. In most cases this involves a summation and yields an average strain for the considered rock volume. Stress inversion thus appears better suited for differentiating heterogeneous data whereas strain analysis appears better suited for homogenizing them.
ISSN: 0040-1951

hal-00759043
https://hal.archives-ouvertes.fr/hal-00759043
DOI : 10.1016/j.tecto.2012.02.009

Résumé : Pour beaucoup de cultures, un sol non travaillé est une alternative de plus en plus crédible au travail intensif du sol, en particulier pour des raisons environnementales. Mais l’ananas (ananas comosus) présente un enracinement fragile très sensible à la structure, ce qui motive souvent un travail important du sol avant plantation. L’alternative d’une plantation sans travail du sol ne va donc pas de soi. L’objet de cette thèse est de répondre à la question de la faisabilité d’une culture d’ananas sans travail du sol, en remplaçant ce dernier par une plante de service « décompactante » dont les traits racinaires seraient favorables à la (re)structuration d’un sol compact. Le travail de cette thèse a donc porté sur l’évaluation de plusieurs espèces candidates, puis sur l’étude, au champ, des effets sur le sol de la plus prometteuse (Stylosanthes guianensis ). Enfin, dans le cadre d’un essai au champ comparant un système de culture innovant ananas sans travail du sol, on a étudié l’effet de la plante de service sur le fonctionnement de la culture de l’ananas. Dans un premier essai, c’est le Stylosanthes guianensis qui, comparé à huit autres espèces (Arachis pintoï, Brachiaria decumbens, Cajanus cajan, Crotalaria juncea, Cynodon dactylon, Eleusine coracana, Pueraria phaseoloides, et le maïs), a montré les traits racinaires les plus favorables à la structuration d’un sol compact. Les valeurs supérieures du diamètre racinaire moyen et de la densité de longueur racinaire (DRL) caractérisent les principaux traits impliqués. Dans un deuxième essai, les mesures de conductivité hydraulique, d’indice des vides du sol et d’analyse d’images de blocs de sol imprégné sur la répartition surfacique des différents types de porosité ont montré que la culture du Stylosanthes guianensis avait augmenté l’indice des vides du sol et provoqué l’apparition d’une porosité fissurale de grande taille, contribuant ainsi à l’amélioration de la structure du sol. Enfin, un troisième essai mettant en comparaison (i) un système de culture innovant où la culture d’ananas est implantée sans travail du sol après une culture de S. guianensis restructurante et (ii) un système conventionnel comportant un travail profond du sol (et pas de plante de service) a montré que le rendement en fruit est similaire dans les deux systèmes. Cet essai a permis de vérifier que l’enracinement de l’ananas en condition de sol non travaillé bénéficiait du précédent S. guianensis.
For many crops, direct drilling is a well-tried alternative facing the damaging effects of intensive tillage, mainly for environmental causes. But, pineapple (ananas comosus), presents a fragile rooting system which is very sensitive to soil structure. This leads frequently to intensive soil tillage before planting. Direct drilling is not so evident. The aim of this thesis is to give an answer to the feasibility of a no till system for pineapple cultivation, by using a plant with favorable roots traits for compacted soil (re)structuration. This work consisted in evaluating several candidate species, followed by the study, on the field, of the effects the most promising on soil (Stylosanthes guianensis). Finally, through a field experiment, comparing an innovating no till pineapple cultivation system we studied the use effects of Stylosanthes guianensis on the pineapple crop functioning. In a first experiment, Stylosanthes guianensis compared with eight other species (Arachis pintoï, Brachiaria decumbens, Cajanus cajan, Crotalaria juncea, Cynodon dactylon, Eleusine coracana, Pueraria phaseoloides and corn) showed better roots traits for structuring a compacted soil. Measures of average root diameter and root length density are the main implicated roots traits. In a second experiment, the measures of hydraulic conductivity, of the soil void ratio and the analysis of blocks of resin-impregnated soil on the surface distribution of the different type of porosity, all of this showed that Stylosanthes guianensis had increased the soil void ratio and had caused the creation of large-sized cracked porosity, thus contributing to the improvement of the soil structure. Finally, a third experiment involving a comparison between (i) an innovating cultivation system where pineapple is growing in a no till soil after a structuring crop of S. guianensis and (ii) a conventional system with deep tillage (without structuring crop), showed similar fruit yield. This experiment showed evidence that the rooting of pineapple in no till soil benefited from the previous Stylosanthes.

http://www.theses.fr/2014AGUY0725/document

Éditeur(s) : Ecole Nationale Supérieure Agronomique de Rennes (ENSAR)
Résumé : Artificial Fish Aggregating Devices (FADs) are known to concentrate tropical tunas. This aggregative behaviour drastically increases the vulnerability of these species to fishing. Alternatively, FADs can be used as oceanic observatories to study the aggregative behaviour of large pelagic fish. We conducted sea surveys in Martinique (Lesser Antilles) to i) establish a typology of the pelagic fish aggregations found around moored FADs ii) study their relations with their biotic and abiotic environment and the local fishery. The mean biomass of large pelagic fish aggregations was also estimated to provide scientific inputs to achieve a sustainable management of the moored FAD fishery. The first part presents the background of the study. We introduce the regional pelagic ecosystem, the aggregative behaviour of pelagic fish around FADs and the Martinican moored FAD fishery. The second part begins with a presentation of the conceptual framework of the study: the hierarchy theory. Observation scales and survey methodology are therefore described. Repeated echosounder surveys run in a star pattern were conducted around 2 moored FADs, in combination with underwater video observations, classical fishing experiments and CTD profiles. In the third part, the elements of the [moored FAD ¿ pelagic fish - environment - fishing] system and their interactions are numerically characterised in the vertical plane. The main type of pelagic fish aggregation was a large aggregation distributed in sub-surface (40-100 m) within a radius of 400 m of the FAD. This aggregation was mostly made of 60 cm FL blackfin tunas (Thunnus atlanticus). It appeared at sunrise and mostly spread away in the late afternoon. It was observed during all daytime surveys. The average density and the vertical structure of the micronektonic sound scattering layers (SSLs) were assessed locally around a FAD for 48h cycles. These SSLs descriptors showed positive correlation with the size and the abundance of the sub-surface tuna aggregation. Whereas this aggregation accounted for about 95% of the total biomass aggregated around a moored FAD, it was nearly unexploited by the local commercial fishermen. The fourth part focuses on the sub-surface tuna aggregation. A high variability of the spatial distribution of the aggregation was evidenced in the horizontal plane at daily, day to day and monthly temporal scales. These variations were related to fluctuations of the global abundance of the aggregation. The daytime average density of sub-surface tuna was modelled as a function of the distance to FAD, within an advection-diffusion framework. Based on these results, a universal kriging model was designed to assess the mean maximum daily biomass of the sub-surface tuna aggregation. This mean biomass estimate yielded 11 tons with an estimation error of 26%. To conclude, we present a hierarchical organization in space and time of a sub-surface tuna population distributed within a network of moored FADs, from micro to meso-scale. We suggest that the spatial distribution of tunas can be explained from fine to coarse-scales by behavioural processes (self-organization, feeding, aggregative behaviour) whereas their spatial distribution is mainly forced by environmental processes at broader scales.
L'utilisation de Dispositifs de Concentration de Poissons permet de provoquer la formation de larges agrégations de thonidés autour de dispositifs artificiels, ce qui augmente considérablement la vulnérabilité de ces ressources vis-à-vis de l'exploitation halieutique. Les DCP peuvent également être utilisés en tant qu'observatoires océaniques, afin d'étudier le comportement agrégatif du macronecton pélagique. Nous avons ainsi réalisé des observations autour de DCP ancrés en Martinique, afin de définir une typologie des agrégations de macronecton et de étudier leurs relations avec leur environnement biotique, abiotique et l'exploitation halieutique locale. Nous avons ensuite estimé la biomasse moyenne de macronecton agrégé autour d'un DCP ancré, afin de fournir des éléments scientifiques nécessaires à une gestion durable de ces ressources. La première partie présente le contexte de l'étude i.e. l'écosystème pélagique régional, le phénomène d'agrégation du macronecton autour des DCP et la pêche associée aux DCP ancrés en Martinique. La deuxième partie introduit la théorie de la hiérarchie qui a fourni le cadre conceptuel de l'étude et présente les échelles et méthodes d'observation. Le principal outil d'observation est un échosondeur scientifique, mis en oeuvre le long de parcours en étoile autour du DCP. Les prospections acoustiques ont été combinées à des observations vidéo sous marines, des pêches expérimentales et un suivi in-situ de l'environnement abiotique. La troisième partie présente une typologie des éléments constituant le système [DCP ancré - macronecton - environnement - pêche] dans le plan vertical et précise leurs interactions. Le type d'agrégation de macronecton dominant est une grande agrégation composée d'une majorité de thons noirs (Thunnus atlanticus) de taille moyenne (60 cm) distribuée en sub-surface (40-100 m), dans un rayon de 300 m autour de la tête des DCP. Cette agrégation se forme au lever du soleil et se disperse presque totalement dans l'après midi. Elle a été observée de jour lors de toutes les campagnes. Une corrélation positive entre la densité et la structure moyenne des couches micronectoniques diurnes évaluée localement autour du DCP au cours de 48 h et les dimensions et l'énergie acoustique de l'agrégation de thons de subs-surface a été mise en évidence. Malgré le fait que cette agrégation représente en moyenne 95 % de l'énergie acoustique du macronecton autour des DCP, elle est presque inexploitée par les pêcheurs artisans locaux. La quatrième partie met en évidence les fortes variations conjointes de la distribution spatiale dans le plan horizontal de la densité de l'agrégation de thons de sub-surface et de son abondance globale. Ces variations ont été observées au cours du cycle nycthéméral et aux échelles inter-journalières et mensuelles. La distribution spatiale moyenne de la densité diurne de l'agrégation en fonction de la distance au centre de gravité de l'agrégation est cependant très stable et peut être modélisée au moyen d'une équation d'advection-diffusion. Un modèle de krigeage universel, utilisant les résultats du modèle d'advection-diffusion, a permis d'évaluer la biomasse maximale journalière moyenne de l'agrégation de thons de sub-surface à une dizaine de tonnes, avec un coefficient de variation d'estimation de 26%. Nous proposons une représentation hiérarchique synthétique de la distribution spatiale d'une sous-population de thons dans un réseau de DCP ancrés de la micro à la méso-échelle. Nous suggérons que la distribution spatiale des thons est déterminée principalement à l'échelle fine (100m-1km) et à l'échelle grossière (1-10 km) par des processus comportementaux (auto-organisation, agrégation, nutrition) et par des processus environnementaux à échelle plus large.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2006/these-1735.pdf
http://archimer.ifremer.fr/doc/2006/sup-1735.pdf
http://archimer.ifremer.fr/doc/00000/1735/

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Leaf dark respiration (R-dark) represents an important component controlling the carbon balance in tropical forests. Here, we test how nitrogen (N) and phosphorus (P) affect R-dark and its relationship with photosynthesis using three widely separated tropical forests which differ in soil fertility.R-dark was measured on 431 rainforest canopy trees, from 182 species, in French Guiana, Peru and Australia. The variation in R-dark was examined in relation to leaf N and P content, leaf structure and maximum photosynthetic rates at ambient and saturating atmospheric CO2 concentration.We found that the site with the lowest fertility (French Guiana) exhibited greater rates of R-dark per unit leaf N, P and photosynthesis. The data from Australia, for which there were no phylogenetic overlaps with the samples from the South American sites, yielded the most distinct relationships of R-dark with the measured leaf traits.Our data indicate that no single universal scaling relationship accounts for variation in R-dark across this large biogeographical space. Variability between sites in the absolute rates of R-dark and the R-dark : photosynthesis ratio were driven by variations in N- and P-use efficiency, which were related to both taxonomic and environmental variability.
ISSN: 0028-646X

hal-01559483
https://hal.univ-lorraine.fr/hal-01559483
DOI : 10.1111/nph.13992

Résumé : L’historiographie antillaise n’a donné jusqu’ici qu’une vision tronquée de la société martiniquaise. L’appréhension de l’ère coloniale s’est très tôt autocentrée sur l’économie plantationnaire sucrière à moteur externe, mais cette dernière n’a guère occupée plus de la moitié de la population de l’île au XVIIIe et dans la première moitié du XIXe siècle. Pour une grande majorité, la masse laborieuse libre ou esclave se répartit entre les villes et les exploitations de type « secondaire ». A mesure de l’appréhension de l’univers caféier, un monde à part se profile dessinant une nouvelle catégorie sociale divergente de l’élite sucrière qui apparaissait jusqu’ici comme le modèle représentatif de la population blanche propriétaire terrienne. Une catégorie intermédiaire est mise en place mettant en relief un groupe caféier économiquement faible au mode de vie difficile, présentant des comportements matrimoniaux endogames aussi bien spatialement que socialement. Cette analyse révèle un corps social pluriel dans lequel les femmes, les libres de couleur, et avec l’abolition de l’esclavage les nouveaux libres tiennent une place de choix. Ce travail a l’avantage de combler un important vide historiographique en matière d’histoire sociale de la Martinique, ainsi que de renouveler le concept de société d’habitation à travers la mise en perspective d’une catégorie sociale jusque-là restée inaperçue.
The historiography of the Antilles to date has yielded only a limited vision of society in Martinique. The scientific works of the Colonial Era were egocentrically focused on the economy of sugar plantations, but this only covered a little over half of the population of the island in the eighteenth century and the first half of the nineteenth century. The other half of the working population, whether they were free or slaves, was divided between cities and secondary enterprises. As the coffee industry took root, a separate world emerged, diverging from the elite sugar plantation owners that represented the land-owning white population. This parallel society of economically disadvantaged small farmers and coffee growers, living a hard-working, difficult lifestyle, exhibited endogamous marriage behavior. This analysis highlights a multi-faceted social body in which women, free people of color, and, with the abolition of slavery, the new free hold a special role. On the other side of the barrier, the slaves also have a unique profile, they operate in small plantations on which opportunities for advancement are greater than in the large sugarcane plantations. This work fills an important gap in the social history of Martinique, as it reexamines the perception of the elite sugar plantation society via the perspective of a social class hitherto unnoticed.

http://www.theses.fr/2014AGUY0724

Éditeur(s) : HAL CCSD Springer Verlag (Germany)
Résumé : International audience
The Michaelis-Menten enzymatic reaction is sufficient to perceive many subtleties of network modeling, including the concentration and time scales separations, the formal equivalence between bulk phase and single-molecule approaches, or the relationships between single-cycle transient probabilities and steady state rates. Seven methods proposed by different authors and yielding the same famous Michaelis-Menten equation, are selected here to illustrate the kinetic and probabilistic use of rate constants and to review basic techniques for handling them. Finally, the general rate of an ordered multistep reaction, of which the Michaelis-Menten reaction is a particular case, is deduced from a Markovian approach.
Journal of Mathematical Chemistry

hal-00920806
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00920806
https://hal-univ-rennes1.archives-ouvertes.fr/hal-00920806/document
ARXIV : 1312.5468
DOI : 10.1007/s10910-013-0237-5

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The analysis of three cataclastic band sets from Provence (France) reveals that the band density, their conjugate angles, their ratio of shear displacement to compaction, and the amount of cataclasis within the bands differ and can be expressed as functions of tectonic setting and petrophysical properties. We identify (1) a dense and closely spaced network of shear-enhanced (reverse) compaction bands; (2) a regularly spaced less dense network of reverse compactional shear bands; and (3) a localized network of normal shear bands. The field data show that strain localization is favored in an extensional regime and is characterized by shear bands with a large shear to compaction ratio and a small conjugate band angle. In contrast, distributed strain is favored in a contractional regime and is characterized by compactional bands with a low ratio of shear to compaction and a large conjugate band angle. To explain the mechanical origin of this strain localization, we quantify the yield strength and the stress evolution in extensional and contractional regimes in a frictional porous granular material. We propose a model of strain localization in porous sands as a function of tectonic stresses, burial depth, material properties, strain hardening and fluid pressure. Our model suggests that stress reduction, inherent to extensional regime, favors strain localization as shear bands, whereas stress increase during contraction favors development of compactional bands.
ISSN: 0191-8141

hal-00856921
https://hal.archives-ouvertes.fr/hal-00856921
DOI : 10.1016/j.jsg.2012.11.011

Éditeur(s) : HAL CCSD Wiley
Résumé : 1. Functional traits provide insight into a variety of ecological questions, yet the optimal sampling method to estimate the community-level distribution of plant functional trait values remains a subject of debate, especially in species-rich forests. 2. We present a simulation analysis of the trait distribution of a set of nine completely sampled permanent plots in the lowland rain forests of French Guiana. 3. Increased sampling intensity consistently improved accuracy in estimating community-weighted means and variances of functional trait values, whereas there was substantial variation among functional traits and minor differences among sampling strategies. 4. Thus, investment in intensified sampling yields a greater improvement in the accuracy of estimation than does an equivalent investment in sampling design complication. 5. Notably, 'taxon-free' strategies frequently had greater accuracy than did abundance-based strategies, which had the additional cost of requiring botanical surveys. 6. We conclude that there is no substitute for extensive field sampling to accurately characterize the distribution of functional trait values in species-rich forests.
ISSN: 0269-8463

hal-01536541
https://hal.archives-ouvertes.fr/hal-01536541
PRODINRA : 343202
DOI : 10.1111/1365-2435.12433

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Background: Researchers sorely need markers and approaches for biodiversity exploration (both specimen linked and metagenomics) using the full potential of next generation sequencing technologies (NGST). Currently, most studies rely on expensive multiple tagging, PCR primer universality and/or the use of few markers, sometimes with insufficient variability. Methodology/Principal Findings: We propose a novel approach for the isolation and sequencing of a universal, useful and popular marker across distant, non-model metazoans: the complete mitochondrial genome. It relies on the properties of metazoan mitogenomes for enrichment, on careful choice of the organisms to multiplex, as well as on the wide collection of accumulated mitochondrial reference datasets for post-sequencing sorting and identification instead of individual tagging. Multiple divergent organisms can be sequenced simultaneously, and their complete mitogenome obtained at a very low cost. We provide in silico testing of dataset assembly for a selected set of example datasets. Conclusions/Significance: This approach generates large mitogenome datasets. These sequences are useful for phylogenetics, molecular identification and molecular ecology studies, and are compatible with all existing projects or available datasets based on mitochondrial sequences, such as the Barcode of Life project. Our method can yield sequences both from identified samples and metagenomic samples. The use of the same datasets for both kinds of studies makes for a powerful approach, especially since the datasets have a high variability even at species level, and would be a useful complement to the less variable 18S rDNA currently prevailing in metagenomic studies.
ISSN: 1932-6203

hal-01544766
https://hal.archives-ouvertes.fr/hal-01544766
DOI : 10.1371/journal.pone.0051263