Éditeur(s) : HAL CCSD Elsevier Masson
Résumé :  
Modeling soil water availability for tropical trees is a prerequisite to predicting the future impact of climate change on tropical forests. In this paper we develop a discrete-time deterministic water balance model adapted to tropical rainforest climates, and we validate it on a large dataset that includes micrometeorological and soil parameters along a topographic gradient in a lowland forest of French Guiana. The model computes daily water fluxes (rainfall interception, drainage, tree transpiration and soil plus understorey evapotranspiration) and soil water content using three input variables: daily precipitation, potential evapotranspiration and solar radiation. A novel statistical approach is employed that uses Time Domain Reflectometer (TDR) soil moisture data to estimate water content at permanent wilting point and at field capacity, and root distribution. Inaccuracy of the TDR probes and other sources of uncertainty are taken into account by model calibration through a Bayesian framework. Model daily output includes relative extractable water, REW, i.e. the daily available water standardized by potential available water. The model succeeds in capturing temporal variations in REW regardless of topographic context. The low Root Mean Square Error of Predictions suggests that the model captures the most important drivers of soil water dynamics, i.e. water refilling and root water extraction. Our model thus provides a useful tool to explore the response of tropical forests to climate scenarios of changing rainfall regime and intensity.
ISSN: 0168-1923

hal-01032181
https://hal.archives-ouvertes.fr/hal-01032181
DOI : 10.1016/j.agrformet.2011.04.012

Éditeur(s) : HAL CCSD Elsevier
Résumé : In this study, we assessed past and present influence of ancient mining activity on metal(loid) enrichment in sediments of a former mining watershed (Gardon River, SE France), that is now industrialized and urbanized. A sedimentary archive and current sediments were characterized combining geochemical analyses, zinc isotopic analyses and sequential extractions. The archive was used to establish local geochemical background and recorded (i) increasing enrichment factors (EFs) for Pb, Zn, Cd, Tl, Hg, As and Sb throughout the industrial era, (ii) a contamination peak in 1976 attributed to a tailings dam failure, and (iii) current levels in 2002 and 2011 similar to those of 1969, except for Sb and Hg, reflecting a persisting contamination pattern. Inter-element relationships and spatial distribution of EF values of current sediments throughout the watershed suggested that both ancient and current contamination had a common origin for Pb, Zn, Cd, Tl and As related to the exploitation of Pb/Zn mineralization while old Sb mines and coal extraction area were the main sources for Sb and Hg respectively. This prevailing mining origin was reflected for Zn by a relatively uniform isotopic composition at δ66Zn = 0.23 ± 0.03‰, although slight decrease from 0.23‰ to 0.18‰ was recorded from upstream to downstream sites along the river course in relation with the contribution of the lighter δ66Zn signature (~ 0.08‰) of acid mine drainage impacted tributaries. Results from sequential extractions revealed that the potential mobility of the studied metal(loid)s varied in the order Sb < Tl ≈ As < Zn < Pb < Cd, with an increase of the mobile pool for Cd, Pb, Zn and to a lesser extent for As and Tl associated to increased enrichment. Altogether, these results tend to demonstrate that ancient mining activity still contributes to metal enrichment in the sediments of the Gardon River and that some of these metals may be mobilized toward the water compartment.
ISSN: 0048-9697

hal-01054163
https://hal.archives-ouvertes.fr/hal-01054163
DOI : 10.1016/j.scitotenv.2014.02.078

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This study analyses the interactions between deformation and reactive fluid and melt percolation, and their effects on sub-arc mantle seismic properties based on microstructural observations on mantle xenoliths extracted by the Tubaf and Edison seamounts close to the Lihir Island, in the Papua New Guinea archipelago. These xenoliths sample an oceanic lithosphere, which has experienced high-temperature deformation in the presence of fluids or melts. This was followed by metasomatism under static conditions. Syn-kinematic percolation of reactive Si-rich melts or fluids in peridotites has produced pyroxene-enrichment, grain size reduction, and dispersion of olivine crystal preferred orientation (CPO). Fourier transform infrared spectroscopy analyses show that olivine has very low water contents (1-4 wt. ppm H2O), similar to spinel peridotites from other subduction zones. These low values may record both low water solubility in olivine at low pressure and dehydration during transport and exhumation. Water contents in pyroxenes are highly variable and likely result from spatially heterogeneous melt or fluid percolation. Analysis of olivine CPO indicates dominant activation of both (010)[100] and (001)[100] slip systems, which are characteristic of deformation under high temperature, low stress, low pressure and low to moderate hydrous conditions. Fast S-wave polarization and P- and Rayleigh propagation directions are thus parallel to the mantle flow direction. The pyroxene enrichment by melt-rock reactions is accompanied by dispersion of olivine CPO and induces a significant decrease of the maximum S-wave and P-wave anisotropy in the peridotites. The calculated seismic properties also show that the lowest Vp/Vs ratios (< 1.7) mapped in fore-arc mantle may only be explained by taking in consideration the CPO-induced elastic anisotropy of the peridotites.
ISSN: 0040-1951

hal-00950058
https://hal.archives-ouvertes.fr/hal-00950058
DOI : 10.1016/j.tecto.2013.09.024

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
A new portable sampling system was developed to extract Radium isotopes from large volumes (up to 300 L) of fresh surface- and ground-waters of low Ra-activities (<5 mBq/L). Ra is quantitatively adsorbed on a small amount (6.5 g) of MnO2-coated acrylic fibers, which are then dried and burned at 600 °C in the laboratory. The resulting Mn-oxide powder (about 2 cm3 when compacted) is then analyzed through gamma-ray spectrometry which allows measurement of the whole Ra quartet (226Ra, 228Ra, 224Ra and 223Ra) in a single counting of a few days. The usual relative standard combined uncertainties (1σ) are 2–3% for 226Ra, 228Ra and 224Ra; and less than 10% for 223Ra. This method was applied to the analysis of Ra in karstic waters of the Lez aquifer, and surface- and ground-waters of the upper and middle Vidourle watershed (South of France). The analyzed waters have relatively low 226Ra activities (1–4 mBq/L) in both cases, regardless of the contrasted geology (Mesozoic limestone vs crystalline Variscan basement), but clearly distinct (228Ra/226Ra) ratios in agreement with the differences in Th/U ratios of the two drained areas. Short-lived Ra isotopes (224Ra and 223Ra) appear to be mainly influenced by near-surface desorption/recoil processes for most of the sampling sites.
ISSN: 0969-8043

hal-01491281
https://hal.archives-ouvertes.fr/hal-01491281
DOI : 10.1016/j.apradiso.2016.12.010

Éditeur(s) : HAL CCSD De Gruyter
Résumé : International audience
Wallaba (Eperua falcata) is a tropical wood which is known to have naturally low swelling characteristics. Samples of wallaba heartwood were subjected to differential solvent extraction. Wood pieces that were extracted with methanol experienced significantly higher swelling after rehydration from oven dry to 96% relative humidity in comparison to non-extracted samples and samples extracted with other solvents. Methanol soluble wallaba heartwood extract was purified by high pressure liquid chromatography and the compounds present were characterised by nuclear magnetic resonance spectroscopy. Methanol extract was found to contain a very high relative proportion of polar compounds which are proposed to bind to the polymeric cell wall by multiple hydrogen bonds restricting the association of water and therefore acting as natural anti-swelling agents.
ISSN: 0018-3830

hal-00856942
https://hal.archives-ouvertes.fr/hal-00856942
https://hal.archives-ouvertes.fr/hal-00856942/document
https://hal.archives-ouvertes.fr/hal-00856942/file/Chemical_extractives_tropical_wood_Royer_al.pdf

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Though the root biomass of tropical rainforest trees is concentrated in the upper soil layers, soil water uptake by deep roots has been shown to contribute to tree transpiration. A precise evaluation of the relationship between tree dimensions and depth of water uptake would be useful in tree-based modelling approaches designed to anticipate the response of tropical rainforest ecosystems to future changes in environmental conditions. We used an innovative dual-isotope labelling approach (deuterium in surface soil and oxygen at 120-cm depth) coupled with a modelling approach to investigate the role of tree dimensions in soil water uptake in a tropical rainforest exposed to seasonal drought. We studied 65 trees of varying diameter and height and with a wide range of predawn leaf water potential (I-pd) values. We confirmed that about half of the studied trees relied on soil water below 100-cm depth during dry periods. I-pd was negatively correlated with depth of water extraction and can be taken as a rough proxy of this depth. Some trees showed considerable plasticity in their depth of water uptake, exhibiting an efficient adaptive strategy for water and nutrient resource acquisition. We did not find a strong relationship between tree dimensions and depth of water uptake. While tall trees preferentially extract water from layers below 100-cm depth, shorter trees show broad variations in mean depth of water uptake. This precludes the use of tree dimensions to parameterize functional models.
ISSN: 0029-8549

hal-01032433
https://hal.archives-ouvertes.fr/hal-01032433
DOI : 10.1007/s00442-013-2724-6

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Extractives can affect vibrational properties tanδ (damping coefficient) and E'/ρ (specific Young's modulus) but this is highly dependent on species, compounds, and cellular locations. This paper investigates such effects for African Padauk (Pterocarpus soyauxii Taub.), a tropical hardwood with high extractives content and a preferred material for xylophones. 5 groups of 26 heartwood specimens with large, yet comparable, ranges in vibrational properties were extracted in different solvents. Changes in vibrational properties were set against yields of extracts and evaluation of their cellular location. Methanol (ME) reached most of compounds (13%), located about half in lumen and half in cell-wall. Water solubility was extremely low. tanδ and E'/ρ were very strongly related (R2≥0.93), but native wood had abnormally low values of tanδ, while extraction shifted this relation towards higher tanδ values. ME extracted heartwood became in agreement with the average of many species, and close to sapwood. Extractions increased tanδ as much as 60%, irrespective of minute moisture changes or of initial properties. Apparent E'/ρ was barely changed (+2% to -4%) but, after correcting the mass contribution of extracts, was in fact slightly reduced (down to -10% for high E'/ρ), and increasingly so for specimens with low initial values of E'/ρ.
ISSN: 0043-7719

hal-00804236
https://hal.archives-ouvertes.fr/hal-00804236
https://hal.archives-ouvertes.fr/hal-00804236/document
https://hal.archives-ouvertes.fr/hal-00804236/file/Effect_extractives_vibrational_properties_Bremaud_al.pdf
DOI : 10.1007/s00226-010-0337-3

Éditeur(s) : HAL CCSD
Résumé : The present study addresses the question of increasing need in water supply. One line of research consists in investigating karst aquifers that represent significant water supplies for the areas around the Mediterranean. This work aims at developing a methodology of predictive evaluation of karst distribution and karst thickness within the carbonate massifs. It is based on the study of the Tethysian carbonate platform from the area of Montpellier, South of France. This area underwent a polyphased, complex, tectonic evolution, involving successive karst forming events. The approach is based on the relationships between eustacy and geodynamics, on one hand, and base-level variation recorded within palaeokarsts, on the other hand. Sedimentary fill of palaeokarsts allows to identify distinct karstification phases and sometimes to date them. It is a marker of base-level variations, which we attempt to quantify, that is responsible for karst formation and karst filling and sealing. For three palaeokarsts of regional extent, we analyze : karst sedimentary-fill, the distribution along upstream-downstream profile, the vertical extension of palaeokarsts, indicative of the base-level lowering. - The " Bauxite palaeokarst " results from the two-stage evolution of the " Isthme Durancien " : i) Bauxitic weathering of the Neocomian cover over the southern Massif Central , related to an inversion during Barremian ; ii) ≥1600 m uplift and exhumation during Aptian-Albian, inducing erosion of alterites, upstream, and deposition of detrital bauxites, downstream. - The " Early Paleocene palaeokarsts with marine sedimentary-fill " indicate base level variations of more than 350m in the upstream area. It is suggested here that such base-level variations, exceeding eustacy and recorded in tabular undeformed series, result from desiccation-flooding events in an endoreic silled basin. - The " Miocene palaeokarst with Cevennes-sourced sediment-fill " records a Serravalian-Tortonian base-level drop, depicted by canyon incision in the hinterland of the Gulf of Lion Margin. Uplift values of ≥ 400m upstream, about 250m in an intermediate area and 10's of m downstream, are measured. The present 3D geometry and distribution of carbonate massifs (exposed and covered) are modeled in the study area, from the Cevennes to the Mediterranean. The 3D geological model integrates seismic reflection, borehole and gravimetric data. Tectonic restoration of a N-S section, extracted from the 3D model, allows to reconstruct paleo-base-levels with respect with the carbonate massifs, at different stages of deformation and successive phases of karstification. The 3D paleo-flows through carbonates across the study area, are thus constrained, especially during the Messinian desiccation stage. Application of the results to hydrogeology leads to the following : - Uplift of upstream hinterland (Cretaceous, Miocene) produces large amplitude karsts, but they do not make significant reservoirs. - Karstification responsible for the development of important and deep karst reservoirs is related to desiccation of endoreic basins (early Paleocene and Messinian). - Theses two events have produced two main deep karst reservoirs, with a gravimetric signature : (1) Upstream of Montpellier Thrust, between Pic St Loup, Les Matelles Fault and Hérault Basin, a deep karsts developed over 900m thickness in the Malm limestone, during Paleocene. (2) Downstream (south) of Montpellier Thrust, the coastal karsts extend offshore over more than 10km, they are sealed by a thick Miocene to Quaternary cover, and they result from the Messinian event.
Cette étude s'inscrit dans un contexte de demande croissante en ressources en eau, conduisant à mieux contraindre et estimer la distribution des aquifères karstifiés qui représentent une ressource importante, notamment sur le pourtour méditerranéen. Le but de ce travail est d'élaborer une méthode prédictive de la distribution de la karstification et de l'épaisseur de massifs carbonatés karstifiés, notamment pour les karsts profonds. La méthodologie est développée à partir de l'étude des karsts de la plateforme carbonatée téthysienne du Languedoc montpelliérain; région qui a subi une histoire tectonique complexe et polyphasée, entrainant des phases de karstification successives. Elle est basée sur la compréhension des relations entre eustatisme, géodynamique et niveau de base, enregistrées par les paléokarsts de la région. Le remplissage sédimentaire des paléokarsts permet d'identifier les épisodes de karstification et de les dater ; c'est un marqueur des variations -que l'on cherche à quantifier- du niveau de base local responsable de la formation et du comblement des karsts. On analyse 3 paléokarsts d'extension régionale dont on peut étudier : le remplissage karstique, la distribution le long de profils amont-aval et l'extension verticale indicatrice de l'amplitude de l'abaissement du niveau de base dont il est issu. On en déduit les causes géodynamiques à l'origine de leur formation: - Le " paléokarst des bauxites " à remplissage caractéristique, résulte de l'évolution en 2 phases de " l'Isthme Durancien " : altération bauxitique de la couverture néocomienne sur le sud du Massif Central, liée à une inversion au Barrémien, suivi d'une surrection ≥ 1600m à l'Aptien-Albien, causant l'érosion des altérites en amont et le dépôt des bauxites détritiques en aval. - Le " paléokarst à remplissage marin paléocène inférieur " indique des variations du niveau de base local ≥350m dans la zone amont sud-cévenole. On propose que ces variations de niveau de base d'amplitude très supérieures aux variations eustatiques et dans une zone faiblement déformée, résultent d'assèchements et d'ennoiements d'un bassin endoréique à seuil. - Le " paléokarst à remplissage détritique d'origine cévenole ", enregistre la chute du niveau de base au Serravalien-Tortonien, qui se traduit par l'incision de canyons dans l'arrière-pays de la marge du Golfe du Lion. On détermine une surrection de plus de 400 mètres à l'amont, près de 250m dans les blocs faillés intermédiaires et quelques dizaines de mètres dans la zone avale. En parallèle, on établit la géométrie et la distribution actuelles des massifs carbonatés dans la zone d'étude (y compris sous couverture), en construisant un modèle géologique 3D, des Cévennes à la Méditerranée. On intègre les données de sismique réflexion, de forages et les données gravimétriques. La restauration tectonique séquentielle d'une coupe Nord-Sud extraite du modèle géologique permet d'appréhender la position des paléo-niveaux de base par rapport aux massifs carbonatés, pour chaque époque de karstification. On déduit l'organisation 3D des paléo-écoulements à travers la géométrie complexe des massifs carbonatés languedociens, notamment pendant l'évènement messinien. En terme d'évaluation de la ressource en eau, on déduit que: - Les surrections de l'arrière-pays (Crétacé " moyen ", Miocène) produisent des karsts de grande amplitude, mais ne constituent pas de réservoirs significatifs. - La karstification à l'origine de réservoirs exploitables importants et profonds est créée par l'assèchement de bassins endoréiques, qui ont affecté la région au Paléocène inférieur et au Messinien . - Ces deux évènements sont à l'origine de deux principaux réservoirs karstiques profonds qui ont une signature gravimétrique : (1) En amont du chevauchement de Montpellier, entre le Pic Saint Loup, la faille des Matelles et le bassin de l'Hérault, le karst profond se développe sur une épaisseur atteignant 900m, et est attribuée à l'événement du Paléocène. (2) Au Sud du chevauchement de Montpellier les karsts côtiers s'étendent jusqu'à plus de 10 km au large, scellés par une épaisse couverture Miocène et Plio-Quaternaire, et résultent de l'événement Messinien.
https://tel.archives-ouvertes.fr/tel-00936257

tel-00936257
https://tel.archives-ouvertes.fr/tel-00936257
https://tel.archives-ouvertes.fr/tel-00936257/document
https://tel.archives-ouvertes.fr/tel-00936257/file/thA_se_husson_couleurs.pdf

Éditeur(s) : HAL CCSD Wiley
Résumé : Seasonal variations in environmental conditions influence the functioning of the whole ecosystem of tropical rain forests, but as yet little is known about how such variations directly influence the leaf gas exchange and transpiration of individual canopy tree species. We examined the influence of seasonal variations in relative extractable water in the upper soil layers on predawn leaf water potential, saturated net photosynthesis, leaf dark respiration, stomatal conductance, and tree transpiration of 13 tropical rain forest canopy trees (eight species) over 2yr in French Guiana. The canopies were accessed by climbing ropes attached to the trees and to a tower. Our results indicate that a small proportion of the studied trees were unaffected by soil water depletion during seasonal dry periods, probably thanks to efficient deep root systems. The trees showing decreased tree water status (i.e., predawn leaf water potential) displayed a wide range of leaf gas exchange responses. Some trees strongly regulated photosynthesis and transpiration when relative extractable water decreased drastically. In contrast, other trees showed little variation, thus indicating good adaptation to soil drought conditions. These results have important applications to modeling approaches: indeed, precise evaluation and grouping of these response patterns are required before any tree-based functional models can efficiently describe the response of tropical rain forest ecosystems to future changes in environmental conditions.
ISSN: 0006-3606

hal-01032411
https://hal.archives-ouvertes.fr/hal-01032411
DOI : 10.1111/j.1744-7429.2012.00902.x

Éditeur(s) : Pergamon-elsevier Science Ltd
Résumé : We report rare earth element (REE) and neodymium (Nd) isotope data for the organic fraction of sediments collected from various depositional environments, i.e. rivers (n=25), estuaries (n=18), open-ocean settings (n=15), and cold seeps (n=12). Sedimentary Organic Matter (SOM) was extracted using a mixed hydrogen peroxide/nitric acid solution (20%-H2O2 – 0.02M-HNO3), after removal of carbonate and oxy-hydroxide phases with dilute hydrochloric acid (0.25M-HCl). A series of experimental tests indicate that extraction of sedimentary organic compounds using H202 may be complicated occasionally by partial dissolution of sulphide minerals and residual carbonates. However, this contamination is expected to be minor for REE because measured concentrations in H2O2 leachates are about two-orders of magnitude higher than in the above mentioned phases. The mean REE concentrations determined in the H2O2 leachates for samples from rivers, estuaries, coastal seas and open-ocean settings yield relatively similar levels, with ΣREE = 109 ± 86 ppm (mean ± s; n=58). The organic fractions leached from cold seep sediments display even higher concentration levels (285 ± 150 ppm; mean ± s; n=12). The H2O2 leachates for most sediments exhibit remarkably similar shale-normalized REE patterns, all characterized by a mid-REE enrichment compared to the other REE. This suggests that the distribution of REE in leached sedimentary organic phases is controlled primarily by biogeochemical processes, rather than by the composition of the source from which they derive (e.g. pore, river or sea- water). The Nd isotopic compositions for organic phases leached from river sediments are very similar to those for the corresponding detrital fractions. In contrast, the SOM extracted from marine sediments display εNd values that typically range between the εNd signatures for terrestrial organic matter (inferred from the analysis of the sedimentary detrital fractions) and marine organic matter (inferred from the analysis of local surface seawater). A notable exception is the case of organic matter (OM) fractions leached from cold seep sediment samples, which sometimes exhibit εNd values markedly different from both terrigenous and surface seawater signatures. This suggests that a significant fraction of organic compounds in these sediments may be derived from chemosynthetic processes, recycling pore water REE characterized by a distinct isotopic composition. Overall, our results confirm that organic matter probably plays an important role in the oceanic REE budget, through direct scavenging and remineralization within the water column. Both the high REE abundances and the shape of shale-normalized patterns for leached SOM also suggest that OM degradation in sub-surface marine sediments during early diagenesis could control, to a large extent, the distribution of REE in pore waters. Benthic fluxes of organic-bound REE could hence substantially contribute to the exchange processes between particulates and seawater that take place at ocean margins. Neodymium isotopes could provide useful information for tracing the origin (terrestrial versus marine) and geographical provenance of organic matter, with potential applications in paleoceanography. In particular, future studies should further investigate the potential of Nd isotopes in organic compounds preserved in sedimentary records for reconstructing past variations of surface ocean circulation.
Geochimica Et Cosmochimica Acta (0016-7037) (Pergamon-elsevier Science Ltd), 2014-09 , Vol. 140 , P. 177-198

Droits : 2014 Elsevier Ltd. All rights reserved.
http://archimer.ifremer.fr/doc/00191/30250/28682.pdf
DOI:10.1016/j.gca.2014.05.016
http://archimer.ifremer.fr/doc/00191/30250/

Éditeur(s) : HAL CCSD
Résumé : This study provides additional constraints on the relations between deformation, hydration and percolation of fluids and melts in the subcontinental lithospheric mantle beneath a craton and a rift, as well as their implication on its geodynamical behaviour. I have analysed the microstructures, the CPOs, and the hydrogen content of mantle xenoliths from the Kaapvaal craton, and two sets of xenoliths from different localities along the East African Rift (North Tanzanian Divergence and SE Ethiopia).The coarse-granular microstructures and the well-defined CPOs in Kaapvaal peridotites suggest a deformation followed by a long quiescence time. Orthorhombic olivine CPOs predominates, but axial-[100] and axial-[010] are also measured. Cratonic peridotites record multiple metasomatic episodes, leading to a significant compositional heterogeneity, which cannot be imaged by seismic studies. Olivine hydrogen contents are variable, but tend to increase until 150 km depth, reaching up to 50 ppm wt. H2O. The deeper samples are almost dry. Piston-cylinder experiments on hydrogen diffusion between a volatile-rich kimberlitic melt and forsterite suggest that the presence of CO2 in the system could significantly decrease water fugacity and thus forsterite hydration. These experimental results indicate that the hydrogen contents measured in olivine were acquired during a metasomatic event rather than during xenolith extraction by kimberlites. However, this metasomatism was not followed by remobilization of the cratonic root.In the North Tanzanian Divergence, localities within the rift axis and the volcanic transverse belt (Lashaine and Olmani) show significant differences in microstructures and olivine CPO patterns. In Lashaine, coarse-granular microstructures and orthorhombic to axial-[100] CPO patterns in olivine can be explained by transpressional deformation during the formation of the Mozambique belt, or by the occurrence of a remnant of a cratonic domain embedded within the Mozambique belt. Within the rift axis, porphyroclastic to mylonitic microstructures suggest a recent rift-related deformation accompanied by syn-kinematic melt-rock reactions, and followed by variable annealing. The strong heterogeneity in microstructures and olivine CPO suggests that this deformation was acquired during multiple tectonic events probably linked to episodic magma percolation, separated by quiescence episodes. The axial-[100] patterns in olivine and the oblique fast directions reported by SKS studies are coherent with transtensional deformation within the lithospheric mantle beneath the rift.The peridotites from SE Ethiopia are less recrystallized than the rift-axis Tanzanian peridotites, displaying coarse-porphyroclastic microstructures. Microstructures and orthorhombic CPOs in olivine suggest syn- to post-metasomatic deformation. S-waves polarization anisotropies calculated for these samples cannot explain alone the delay times reported by SKS studies in this part of the East-African Rift.
Les travaux réalisés durant cette thèse apportent de nouvelles contraintes sur les relations entre déformation, hydratation et percolation de fluides et/ou de magmas dans le manteau subcontinental sous un craton et sous un rift, et leurs implications sur son comportement rhéologique. Il repose sur l'analyse des microstructures, des OPRs et des teneurs en hydrogène de xénolites mantelliques du craton du Kaapvaal, et sur deux séries de xénolites provenant de différentes localités le long du rift Est-Africain (Divergence Nord Tanzanienne et SE de l'Ethiopie). Les microstructures granulaires à gros grains et les OPRs bien définies des péridotites du craton du Kaapvaal sont cohérentes avec un épisode de déformation suivi d'une longue période de quiescence. Les OPRs de l'olivine sont majoritairement à symétrie orthorhombique, mais des symétries axiale-[100] et axiale-[010] sont aussi mesurées. Les péridotites cratoniques enregistrent de multiples épisodes métasomatiques, ayant entraîné une hétérogénéité de compositions à petite échelle ne pouvant être détectée par les études sismiques. Les teneurs en hydrogène mesurées dans l'olivine sont variables, mais ont tendance à augmenter jusqu'à 150 km de profondeur, atteignant alors jusqu'à 50 ppm wt. H2O. En dessous de cette profondeur, les échantillons montrent des teneurs en hydrogène très faibles. Les expériences réalisées en piston-cylindre sur la diffusion de l'hydrogène issue d'un liquide kimberlitique vers de la forstérite suggèrent que la fugacité en eau pourrait fortement être diminuée par la présence de CO2, empêchant l'hydratation de l'olivine durant extraction des xénolites par les kimberlites. Ces résultats expérimentaux suggèrent que les teneurs en hydrogène dans l'olivine des péridotites du craton du Kaapvaal ont été acquises durant un épisode métasomatique en profondeur et non pendant leur extraction par les kimberlites. Ces teneurs n'ont toutefois pas à ce jour entraîné de remobilisation de la racine cratonique. Enfin, le calcul des propriétés sismiques des péridotites cratoniques révèle que les anisotropies générées par les OPRs de ces échantillons sont suffisantes pour expliquer les anisotropies mesurées par les ondes SKS et les ondes de surface.Les xénolites de la Divergence Nord-Tanzanienne, montrent des variations significatives de microstructures et d'OPR de l'olivine entre les péridotites des localités dans l'axe du rift et celles de la chaîne volcanique transverse (Lashaine et Olmani). A Lashaine, les microstructures granulaires à gros grains et les OPRs de type orthorhombique et axial-[010] peuvent être expliquée par une déformation en transpression liée à la formation de la chaîne Mozambique ou par la présence d'une relique d'un domaine cratonique à l'intérieur de la chaîne Mozambique. Dans l'axe du rift, les microstructures porphyroclastiques à mylonitiques suggèrent une déformation plus récente, accompagnée de réactions magma-roche sous des conditions proches du solidus, suivie d'un recuit variable. L'hétérogénéité des microstructures enregistrées par les échantillons du rift suggère de multiples épisodes de déformation localisée, probablement liés à l'injection percolation épisodique de magmas, espacés de périodes d'accalmie. Les OPRs de l'olivine de type axial-[100] et l'orientation des directions de polarisation des ondes SKS suggère que le rift s'est formé en régime de transtension Les péridotites du Sud-Est de l’Éthiopie présentent des microstructures porphyroclastiques à gros grains moins recristallisées qu'en Tanzanie. Les microstructures et les OPRs principalement de type orthorhombique suggèrent une déformation syn- à post-métasomatisme. Les anisotropies de polarisation des ondes S calculées pour ces échantillons sont insuffisantes pour expliquer à elles seules les déphasages des ondes SKS dans cette partie du rift.
https://tel.archives-ouvertes.fr/tel-01684759

Droits : info:eu-repo/semantics/OpenAccess
NNT : 2014MON20139
tel-01684759
https://tel.archives-ouvertes.fr/tel-01684759
https://tel.archives-ouvertes.fr/tel-01684759/document
https://tel.archives-ouvertes.fr/tel-01684759/file/43443_BAPTISTE_2014_archivage_cor.pdf

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : Climate models for the coming century predict rainfall reduction in the Amazonian region, including change in water availability for tropical rainforests. Here, we test the extent to which climate variables related to water regime, temperature and irradiance shape the growth trajectories of neotropical trees. . We developed a diameter growth model explicitly designed to work with asynchronous climate and growth data. Growth trajectories of 205 individual trees from 54 neotropical species censused every 2 months over a 4-year period were used to rank 9 climate variables and find the best predictive model. . About 9% of the individual variation in tree growth was imputable to the seasonal variation of climate. Relative extractable water was the main predictor and alone explained more than 60% of the climate effect on tree growth, i.e. 5.4% of the individual variation in tree growth. Furthermore, the global annual tree growth was more dependent on the diameter increment at the onset of the rain season than on the duration of dry season. . The best predictive model included 3 climate variables: relative extractable water, minimum temperature and irradiance. The root mean squared error of prediction (0.035 mm.d(-1)) was slightly above the mean value of the growth (0.026 mm.d(-1)). . Amongst climate variables, we highlight the predominant role of water availability in determining seasonal variation in tree growth of neotropical forest trees and the need to include these relationships in forest simulators to test, in silico, the impact of different climate scenarios on the future dynamics of the rainforest.
ISSN: 1932-6203

hal-01268350
https://hal.archives-ouvertes.fr/hal-01268350
DOI : 10.1371/journal.pone.0034074
PRODINRA : 215438
PUBMED : 22506012

Résumé : The maritime economy includes the activities linked to the sea, namely: - Marine resource extraction: living resources and marine minerals, - Exploitation of marine space and of physical properties of marine waters (energy plants - using marine water as a heat sink, marine renewable energies, submarine cable laying, - maritime and coastal construction and public works, maritime transport, Navy), - Exploitation of seascapes (tourism, leisure, boating), - Resource processing (of living resources and oil & gas) - Manufacturing and service industries supplying the above exploitation activities: shipbuilding, ship repair and boat building and their suppliers, oil and gas services, financial services, - Public services: defence; State intervention at sea and public services to maritime activities and to seafarers; public and private activities contributing to the protection of marine and coastal environment; and public research. Since 1997, the French Marine Economic Data report, published by Ifremer, includes a set of key sectoral indicators used to value the economic significance of the French marine-related activities in terms of production and jobs, their role in the national economy, their weight in international competition and the importance of non-market public services. The analysis of the marine sectors is carried out mainly at national scale but regional indicators are also presented when they are available. The European dimension of the activities is also taken into account.

Droits : 2014 Ifremer
http://archimer.ifremer.fr/doc/00253/36455/34990.pdf
DOI:10.13155/36455
http://archimer.ifremer.fr/doc/00253/36455/

Éditeur(s) : EDP Sciences
Résumé : The present work was carried out on the hydroelectric reservoir Petit-Saut on the Sinnamary river in French Guiana. Measurements were performed during the wet and dry seasons along a longitudinal gradient, from upstream of the reservoir in two inflow rivers, to the Sinnamary estuary downstream of the dam. Gold extraction has led to a marked increase in suspended matter and total mercury (HgT) in one of the rivers. Dissolved monomethylmercury (MMHg) measured in surface waters were similar for both rivers: 0.03-0.05 ng l(-1) (1.0-1.7% of the dissolved HgT). These results indicate similar methylation efficiency and/or transfer of MMHg into the dissolved fraction of the water column, independently of the amounts of inorganic mercury transported. Dissolved MMHg concentrations in surface waters of the reservoir were similar to those in the rivers, but were more than 10 times higher in deep anoxic waters, up to 0.6 ng l(-1) (20 % of dissolved HgT). The MMHg concentration profiles in the water column suggest that methylation occurs mainly in anoxic waters and sediments in relation with the activity of sulfate reducing bacteria. Dissolved MMHg concentrations measured in the Sinnamary at the base of the dam were still high (0.5 - 0.6 ng l(-1); 20 to 35% of the dissolved HgT).
Journal de Physique IV (1155-4339) (EDP Sciences), 2003-05 , Vol. 107 , P. 327-331

Droits : EDP Sciences
http://archimer.ifremer.fr/doc/2003/publication-5283.pdf
DOI:10.1051/jp4:20030308
http://archimer.ifremer.fr/doc/00000/5283/

Éditeur(s) : HAL CCSD Elsevier
Résumé : Primary arc melts may form through fluxed or adiabatic decompression melting in the mantle wedge, or via a combination of both processes. Major limitations to our understanding of the formation of primary arc melts stem from the fact that most arc lavas are aggregated blends of individual magma batches, further modified by differentiation processes in the sub-arc mantle lithosphere and overlying crust. Primary melt generation is thus masked by these types of second-stage processes. Magma-hosted peridotites sampled as xenoliths in subduction zone magmas are possible remnants of sub-arc mantle and magma generation processes, but are rarely sampled in active arcs. Published studies have emphasised the predominantly harzburgitic lithologies with particularly high modal orthopyroxene in these xenoliths; the former characteristic reflects the refractory nature of these materials consequent to extensive melt depletion of a lherzolitic protolith whereas the latter feature requires additional explanation.Here we present major and minor element data for pristine, mantle-derived, lava-hosted spinel-bearing harzburgite and dunite xenoliths and associated primitive melts from the active Kamchatka and Bismarck arcs. We show that these peridotite suites, and other mantle xenoliths sampled in circum-Pacific arcs, are a distinctive peridotite type not found in other tectonic settings, and are melting residues from hydrous melting of silica-enriched mantle sources. We explore the ability of experimental studies allied with mantle melting parameterisations (pMELTS, Petrolog3) to reproduce the compositions of these arc peridotites, and present a protolith (‘hybrid mantle wedge’) composition that satisfies the available constraints. The composition of peridotite xenoliths recovered from erupted arc magmas plausibly requires their formation initially via interaction of slab-derived components with refractory mantle prior to or during the formation of primary arc melts. The liquid compositions extracted from these hybrid sources are higher in normative quartz and hypersthene (i.e., they have a more silica-saturated character) in comparison with basalts derived from prior melt-depleted asthenospheric mantle beneath ridges. These primary arc melts range from silica-rich picrite to boninite and high-Mg basaltic andesite along a residual spinel harzburgite cotectic. Silica enrichment in the mantle sources of arc-related, subalkaline picrite-boninite-andesite suites coupled with the amount of water and depth of melting, are important for the formation of medium-Fe (‘calc-alkaline’) andesite-dacite-rhyolite suites, key lithologies forming the continental crust.
ISSN: 0016-7037

hal-01553520
https://hal.archives-ouvertes.fr/hal-01553520
DOI : 10.1016/j.gca.2016.09.030

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Despite many studies, our understanding of silica precipitation from natural waters remains limited, in particular for geothermal waters. Here we present a detailed study on the kinetics of silica polymerization as a function of fluid temperature and pH using high-temperature (250-260 °C) seawater-derived geothermal fluids as those discharged from the Bouillante geothermal site.We monitored the on-site decrease in monomeric silica concentration(initial SiO2 concentration of about 600 mg/l)with time using the molybdenum blue spectrophotometric method on samples of separated water collected from the high-pressure separator at 167 °C and cooled to 25, 50, 75, and 90 °C and for pH values ranging from 5 to 8. During all these experiments, only silica polymerization was observed, with the formation of colloidal particles in suspension in the solutions. No scaling of amorphous silica was formed. The collected data were after modeled in order to determine the useful kinetic parameters for predicting and preventing amorphous silica precipitation in the production wells during fluid exploitation in the specific context of Bouillante. Results under the investigated experimental conditions show that the kinetics of silica precipitation is affected more strongly by pH than by temperature change. The reaction in the acidic Bouillante solution begins with a transition period that significantly decreases the kinetics of silica polymerization. Modeling the experimental data indicates that the silica polymerization up to the state of equilibrium is characterized by a 2nd-order kinetic law relative to dissolved silica; this could indicate that the polymerization is controlled mainly by the formation of dimers. However, the first hour of the experiments is better characterized by a 4th-order kinetic law, suggesting more complex polymerization reactions in the initial stage with the formation of nanocolloidal particles containing 3 to 4 monomers. In both cases, the corresponding kinetics rate constant k is linearly dependent on pH for pH between 5 and 7. The activation energy Ea for the overall reaction, calculated using the Arrhenius equation under the considered pH and temperature conditions, ranges between 41±9.8 and 54±9.6 kJ/mol. To complete this work, the colloid particles formed at the end of the kinetics experiments were extracted and analyzed by SEM and TEM microscopy, X-ray Diffraction and the BET method. Results show that the size of the colloids increase and their specific surface decrease with increasing pH and are thus dependent on pH. Globally, our work provides a reliable database for understanding silica polymerization kinetics in natural geothermal brines or geologic waters characterized by a near neutral pH and moderate dissolved silica concentrations.
ISSN: 0009-2541

hal-01403092
https://hal-brgm.archives-ouvertes.fr/hal-01403092
DOI : 10.1016/j.chemgeo.2016.08.031

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
To constrain the relations between deformation and metasomatism in the subcratonic lithospheric mantle, we have analyzed the microstructures and crystal preferred orientations in 50 mantle xenoliths from the Kaapvaal craton. Water contents in olivine and pyroxenes were measured in 14 samples equilibrated at different depths. Coarse-granular microstructures recording deformation by dislocation creep followed by annealing predominate. Mylonitic (sheared) peridotites with partially or totally recrystallized microstructures are however common below 140 km. Refractory compositions predominate, but multiple metasomatic events resulted in orthopyroxene enrichment or secondary crystallization of clinopyroxene and phlogopite. Coherent orthopyroxene and olivine CPO in most coarse-grained peridotites implies in pre- to syn-kinematic orthopyroxene enrichment or epitaxial growth on primary orthopyroxene. Undeformed, interstitial orthopyroxene, clinopyroxene, and phlogopite with random orientations in coarse-grained peridotites record post-kinematic modal metasomatic events. Deformation of these phases in the sheared peridotites implies that mylonitization results from a later event, which affected locally the deep cratonic lithosphere. Olivine CPO recording dominant [100] glide predominate at all depths. Only two samples, equilibrated at ~ 3.3 GPa show olivine [001] and orthopyroxene [001] axes subparallel, suggesting dominant [001] glide. Water contents in olivine are maximum (150 wt. ppm H2O) in peridotites equilibrated at ~ 160 km depth. Peridotites equilibrated below 180 km depth are, in contrast, almost dry. Lack of correlation between olivine mg# and water content indicates that the high water contents in olivine record re-hydration after the extensive partial melting, which produced the cratonic root. The vertical variation in water contents in olivine observed in the Kaapvaal peridotites may result from hydrogen addition or loss during extraction by the kimberlites. Comparison with magnetotelluric electrical conductivity data suggests, however, that the observed vertical variation of water contents in olivine may be representative of the present-day state of the Kaapvaal mantle, implying that extensive metasomatism resulted in hydration of the cratonic mantle at intermediate depths. The annealed microstructures of Kaapvaal peridotites indicate however that this metasomatism was not followed by remobilization of the cratonic root.
ISSN: 0024-4937

hal-00750328
https://hal.archives-ouvertes.fr/hal-00750328
DOI : 10.1016/j.lithos.2012.05.001

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Banana has been a main agricultural product in the French West Indies (Guadeloupe and Martinique) since the 1960s. This crop requires the intensive use of pesticides to prevent attacks by insect pests. Chlorinated pesticides, such as hexachlorocyclohexane (HCH), chlordecone and dieldrin, were used until the beginning of the 1990s, resulting in a generalized diffuse contamination of the soil and water in the areas of banana production, hence the need to develop solutions for cleanup of the polluted sites. The aims of this work were (i) to assess lindane degradation in soil slurry microcosms treated with lindane at 10 mg/L and (ii) to detect the catabolic genes involved in the HCH degradation pathway. The soil slurry microcosm system showed a 40 % lindane degradation efficiency at the end of a 30-day experiment. Lower lindane removal was also detected in the abiotic controls, probably caused by pesticide adsorption to soil particles. Indeed, the lindane concentration decreased from 6000 to 1330 ng/mL and from 800 to 340 ng/mL for the biotic and abiotic soils, respectively. Nevertheless, some of the genes involved in the HCH degradation pathway were amplified by polymerase chain reaction (PCR) from crude deoxyribonucleic acid (DNA) extracted from the Guadeloupe agricultural soil, suggesting that HCH degradation is probably mediated by bacteria closely related to the family Sphingomonadaceae.
ISSN: 0944-1344

hal-01545905
https://hal.archives-ouvertes.fr/hal-01545905
DOI : 10.1007/s11356-015-5875-7

Éditeur(s) : HAL CCSD
Résumé : The heterogeneous nature and sometimes karstified carbonate environments has a direct impact on many environmental issues, such as coastal aquifers affected by saltwater intrusion. At the south of the island of Mallorca (Spain), the Llucmajor carbonate platform offers a privileged site for the study of such intrusions including the experimental site of Campos who meets the intrusion at shallow depth. The characterization of heterogeneous properties passes through a preliminary description of the properties of carbonate reservoirs, including those of the porosity. According to the wide range of sizes of heterogeneities from micrometer to hundreds of meters, the use of multiscale methods is required. This thesis focused on the determination of multiscale porosities from the microporosity to karstic porosity, and of relationships between observation scale changes of these properties. At the micron scale, high-resolution X-ray microtomography allows to extract the microporosity and the microporous network connectivity. At lower resolution (mm), X-ray tomography is also used to study the micro- and macro-porous network at the core scale which is already allocated to number of observations and measurements, including petrophysical. At the borehole scale, the wall images are used to identify the dissolved zones from centimeter macropores to plurimetric karstic cavities. At the larger scale, surface geophysics study the lateral extension of the karsts and heterogeneities. Finally, the porous structure of the studied site is integrated with its wide range of scales into the regional geology of the Llucmajor platform. Thus, the hydrogeophysical observatory set up on the site of Campos to monitor the spreading of salt water in the aquifer is integrated in its geological and petrophysical context, in order to refine the interpretation of its variations of salinity measurements during the time.
La nature hétérogène et parfois karstifiée des milieux carbonatés a un impact direct sur nombre de problématiques environnementales, comme celle des aquifères côtiers affectés par une intrusion d'eau salée. Au sud de l'ile de Majorque (Baléares, Espagne), la plate-forme carbonatée de Llucmajor offre un site privilégié pour l'étude de telles intrusions notamment avec le site expérimental de Campos, qui rencontre l'intrusion à faible profondeur. La caractérisation des propriétés hétérogènes du réservoir passe par une description préalable des propriétés des réservoirs carbonatés et notamment celle de la porosité. Au regard de la large gamme d'échelles d'hétérogénéités allant du micromètre à la centaine de mètre, l'utilisation de méthodes multi-échelles est nécessaire. Ce travail de thèse a porté sur la caractérisation multi-échelle de la porosité, allant de la microporosité à la porosité karstique, et l'établissement de relations entre les changements d'échelles d'observation de ces propriétés. A très petite échelle, la microtomographie haute-résolution à rayons X extrait à l'échelle du micron la microporosité et la connectivité des réseaux microporeux. A plus basse fréquence (celle du mm), la tomographie est également utilisée afin d'étudier le réseau micro- et macroporeux à l'échelle des carottes, à laquelle sont réalisées nombre d'observations et de mesures, notamment pétrophysiques. A l'échelle du puits, les images de paroi permettent d'identifier les zones de dissolution allant des macropores centimétriques aux cavités karstiques plurimétriques. A plus grande échelle, la géophysique de surface permet d'étudier l'extension latérale de ces karsts et hétérogénéités. Enfin, la structure poreuse du site étudié sur cette vaste gamme d'échelles est intégrée à la géologie régionale de la plate-forme de Llucmajor. Ainsi, l'observatoire installé sur le site pour surveiller la propagation de l'eau salée dans l'aquifère a pu être replacé dans son contexte géologique et pétrophysique, afin d'affiner l'interprétation de ses mesures de variations de salinité au cours du temps.
https://tel.archives-ouvertes.fr/tel-00633488

tel-00633488
https://tel.archives-ouvertes.fr/tel-00633488
https://tel.archives-ouvertes.fr/tel-00633488/document
https://tel.archives-ouvertes.fr/tel-00633488/file/TheseHebert.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : Nominally anhydrous minerals (NAMs) of Earth's mantle can contain hydrogen as atomic impurity in their crystal structures. This hydrogen substantially modifies many physical properties of Earth's mantle rocks. Also, the Earth's deep interior is made of rocks where minerals are separated by nanometer-scale interfaces call grain boundaries and interphase boundaries. These grain boundaries should carefully be considered as a potential hydrogen reservoir as well. I report here an experimental investigation of hydrogen diffusion through grain boundaries in olivine polycrystalline aggregates. Hot-press and diffusion experiments were performed using a gas-medium high-pressure vessel at a confining pressure of 300 MPa, over a temperature range of 1000-1200 degrees C. The diffusion assembly consisted of a dense polycrystalline cylinder of natural olivine from San Carlos (Arizona) mixed with olivine singles crystals of millimeter size. This mixture was couple with a talc cylinder. Ni capsule were used to buffer the oxygen fugacity at Ni-NiO level. Experiment durations varied from 3 min to 4 h. The presence of hydrogen in the sample was quantified using Fourier transform infrared spectroscopy. The calculation of the diffusion coefficients was based on the estimation of the length of polycrystalline solid affected by the diffusion of hydrogen. The absence or presence of hydrogen was recorded by the large olivines behaving here as "hydrogen sensor", which are implanted in the aggregate. The results indicate that effective hydrogen diffusivity which includes grain boundaries effect in olivine aggregate is barely one order of magnitude faster than hydrogen diffusion in an olivine single crystal with a diffusivity similar to 8.5x 10(-10) m(2) s(-1) 1000 degrees C and only twice faster similar to 2.1 x10(-9) m(2) s(-1) 1200 degrees C. Calculations of the diffusion data in relation to the Arrhenius Law, yield an activation energy of similar to 70 +/- 10 kJ mol(-l) . From these effective diffusivities and combined with published diffusion data for olivine single crystals, hydrogen diffusion in grain boundaries is extracted and yield diffusivities almost three order of magnitude faster (similar to 5 x 10(-6) m(2) s(-1) at 1200 degrees C) than in an olivine single crystal at the equivalent high temperature. On geological scales and for coarse-grain rocks, hydrogen diffusivity in grain boundaries is not fast enough to compete with lattice diffusion. The relative large grain size of mantle rocks will ensure a very limited hydrogen transport by effective diffusion, and a good conservation of water-rich zones in the Earth's mantle.
ISSN: 0012-821X

hal-00512821
https://hal.archives-ouvertes.fr/hal-00512821
DOI : 10.1016/j.epsl.2010.04.019