Uncertainty in adaptive capacity

The capacity to adapt is a critical element of the process of adaptation: it is the vector of resources that represent the asset base from which adaptation actions can be made. Adaptive capacity can in theory be identified and measured at various scales, from the individual to the nation. The assessment of uncertainty within such measures comes from the contested knowledge domain and theories surrounding the nature of the determinants of adaptive capacity and the human action of adaptation. While generic adaptive capacity at the national level, for example, is often postulated as being dependent on health, governance and political rights, and literacy, and economic well-being, the determinants of these variables at national levels are not widely understood. We outline the nature of this uncertainty for the major elements of adaptive capacity and illustrate these issues with the example of a social vulnerability index for countries in Africa. To cite this article: W.N. Adger, K. Vincent, C. R. Geoscience 337 (2005).     

Rôle de la végétation dans la protection contre l'érosion hydrique de surface

This paper is a review on the current knowledge concerning the role of vegetation in protection against surface hydric erosion. It first explains the mechanisms of vegetation action in relation to processes of erosion and sedimentation. Secondly, it presents the results of researches carried out on the efficiency of different vegetation structures and the significance of the rate of vegetation cover for combating gully erosion. To cite this article: F. Rey et al., C. R. Geoscience 336 (2004).     

Further absolute geomagnetic paleointensities from Baja California: evaluation of Pliocene and Early/Middle Pleistocene data

From a large collection (more than 300 oriented cores) of Baja California Mio-Pliocene volcanic units, sampled for magnetostratigraphy and tectonics, 46 samples were selected for Thellier paleointensity experiments because of their low viscosity index, stable remanent magnetization and close to reversible continuous thermomagnetic curves. 19 samples, coming from 4 individual basaltic lava flows, yielded reliable paleointensity estimates with the flow-mean virtual dipole moments (VDM) ranging from 3.6 to 6.2 ×10²² A m². Our results, although not numerous, are of high technical quality and comparable to other paleointensity data recently obtained on younger lava flows. The NRM fractions used for paleointensity determination range from 38 to 79% and the quality factors vary between 4.8 and 16.7, being normally greater than 5. The combination of Baja California data with the available comparable quality Plio-Plesitocene paleointensity results yields a mean VDM of 6.3 ×10²² A m², which is almost 80% of the present geomagnetic axial dipole. Reliable paleointensity results for the last 5 Ma are still scarce and of dissimilar quality, which makes it hard to draw any firm conclusions regarding the Pliocene and Early/Middle Pleistocene evolution of the geomagnetic field. To cite this article: J. Morales et al., C. R. Geoscience 335 (2003).     

Tenseurs de perméabilité équivalente d'un domaine hétérogène fini

In an earlier paper, it has been shown that for a heterogeneous block of finite size, under linear boundary pressure conditions, a symmetric and positive definite tensor, denoted here by ${\mathbf{K}}^{\mathrm{p}}$, exists, which relates the mean flux to the mean gradient of pressure in the block. In this paper, the conditions of constant boundary flux are first defined. Then it is shown that, under these conditions also, a symmetric and positive definite tensor, denoted ${\mathbf{K}}^{\mathrm{q}}$, exists, which relates the mean flux to the mean pressure gradient. It is then shown that ${\mathbf{K}}^{\mathrm{q}}$ and ${\mathbf{K}}^{\mathrm{p}}$ respectively give the equivalent permeability in the direction of mean gradient and of mean flux. The directional permeability values given by ${\mathbf{K}}^{\mathrm{q}}$ are shown to be smaller than ${\mathbf{K}}^{\mathrm{p}}$. To cite this article: A. Pouya, C. R. Geoscience 337 (2005).     

L'évolution séculaire des températures de surface de la mer Méditerranée (1856–2000)

The mean sea surface temperature anomalies (SSTA) of the Mediterranean Sea during the past 150 years (1856–2000) are analysed. The first empirical orthogonal function (EOF) of the covariance matrix of the SSTA explains more than 45% of the variance, suggesting that the temporal variation of the Mediterranean Sea is largely in phase over the whole basin. The mean variability of Mediterranean SSTA from 1856 to 2000 superposes a main irregular oscillation (period of 60–70 years and mean amplitude of 0.4–0.5 °C) and a weak long-term positive trend (equivalent to an increase of +0.1 °C per century). The last warm phase, which is strongest in the western basin, is not warmer than the decade 1935–1945 or the ending part of the 1960s. The mean temporal evolution of the North Hemisphere is close to the variation of the Mediterranean Sea, except that the long-term increase is more intense in the North Hemisphere. To cite this article: V. Moron, C. R. Geoscience 335 (2003).     

Natural minerals and divided solids: methodology for understanding surface phenomena related to industrial uses and environmental problems

This introductory paper aims at presenting the series of articles in this special issue of Comptes Rendus Geoscience devoted to the study and use of natural minerals. The research methodology that can be applied to the investigation of surface phenomena related to adsorption, exchange and retention onto the surface of natural minerals and divided solids is presented. A special focus is given to the retention of surfactant molecules, in view of their considerable importance in numerous industrial fields, such as, for instance, mineral flotation and enhanced oil recovery. Throughout this introductory paper, the relevance of this research approach to the field of geosciences is stressed by listing various applications where it can provide conclusive answers, especially for environmentally related issues. To cite this article: J.-M. Cases, C. R. Geoscience 334 (2002) 585–596.     

Les paléoenvironnements éocènes à crinoïdes pédonculés des marnes de Miretrain (Angoumé, SW France) : interprétations paléobathymétriques

A well-diversified fauna of stalked crinoids was found in the Eocene series exposed in the quarry of Miretrain at Angoumé (Landes, southwestern Aquitaine, northern edge of the Tercis diapir structure). The most frequent taxa belong to the genera Isselicrinus and Conocrinus. Adaptive stalk characters related to depth in the pentacrinid genus Isselicrinus allow us to document the bathymetric zonation of stalked crinoids during the Eocene. Both stalked crinoids, benthic foraminifera and additional organisms give convergent information on palaeodepths throughout the progradation of sedimentary bathyal slope between the two major tectonic events providing Pyrenean foreland shortening. The depth changes from more than 700 m (maybe about 1000 m) at the base of the series (Middle Lutetian) to about 50 m at the top (Late Bartonian). To cite this article: M. Roux et al., C. R. Geoscience 338 (2006).     

Atténuation de l'intensité macrosismique pour la France métropolitaine : importance de l'intensité épicentrale

The main result of this work is to show that macroseismic intensity decay with distance strongly depends on the epicentral intensity. An attenuation law that takes this parameter into account is proposed for Metropolitan France, from the analysis of SISFRANCE macroseismic database. Such a model significantly reduces the difference between observed and theoretical intensities. A map of the attenuation variations is also set up for Metropolitan France. No major site effects are observed, but at a broad scale, young Alpine regions display a stronger attenuation than old Hercynian regions. To cite this article: P. Arroucau et al., C. R. Geoscience 338 (2006).     

Optimisation de la quantification des flux de matière en suspension d'un cours d'eau alpin : l'Isère à Grenoble (France)

This study seeks to determine suspended-matter flux of the Isère at Grenoble, one of the most important rivers of the northern French Alps. Since 1994, and especially 1996, systematic samplings of the left bank make it possible to follow in one point the variations of suspended particles and matter (SPM) of this river. But from a single measurement, sometimes not very representative of the whole observable concentrations within the section, it remains still difficult to estimate precisely the SPM flux. The results of this study show in particular the successive appearance of several turbidity gradients, whose occurrence is explained mainly by the hydrological and hydro-sedimentary dynamics of this river. The estimate of these gradients thus makes it possible to extrapolate specific measurements more easily and consequently to daily define the quantities of suspended matter exported by the Isère. Since 1996, the results show a very high flow, specific of the Isère at Grenoble, variable between 124 and more than 460 t km^?2 yr^?1. To cite this article: D. Dumas, C. R. Geoscience 336 (2004).     

Étude expérimentale de la réactivité du CO2 supercritique vis-à-vis de phases minérales pures. Implications pour la séquestration géologique de CO2

Carbon dioxide sequestration in deep aquifers and depleted oilfields is a potential technical solution for reducing green-house gas release to the atmosphere: the gas containment relies on several trapping mechanisms (supercritical CO₂, CO_2(sc), dissolution together with slow water flows, mineral trapping) and on a low permeability cap-rock to prevent CO_2(sc), which is less dense than the formation water, from leaking upwards. A leakproof cap-rock is thus essential to ensure the sequestration efficiency. It is also crucial for safety assessment to identify and assess potential alteration processes that may damage the cap-rock properties: chemical alteration, fracture reactivation, degradation of injection borehole seals, etc. The reactivity of the host-rock minerals with the supercritical CO₂ fluid is one of the potential mechanisms, but it is altogether unknown. Reactivity tests have been carried out under such conditions, consisting of batch reactions between pure minerals and anhydrous supercritical CO₂, or a two-phase CO₂/H₂O fluid at 200?°C and 105/160 bar. After 45 to 60 days, evidence of appreciable mineral-fluid reactivity was identified, including in the water-free experiments. For the mixed H₂O/CO₂ experiments, portlandite was totally transformed into calcite; anorthite displayed many dissolution patterns associated with calcite, aragonite, tridymite and smectite precipitations. For the anhydrous CO₂ experiments, portlandite was totally carbonated to form calcite and aragonite; anorthite also displayed surface alteration patterns with secondary precipitation of fibrous calcite. To cite this article: O. Regnault et al., C. R. Geoscience 337 (2005).     

Nouvelles données sur le téphra de Sarliève et le téphra CF7, marqueurs chrono-stratigraphiques de Grande Limagne (Massif central,France)

A trachytic tephra, discovered in the ancient lake of Sarliève, ‘Grande Limagne’, has been dated using the thermoluminescence technique. The obtained age, 16±4 ka ($\text{2}\text{σ}$), is older than that of the trachytic volcanoes of the Cha??ne des Puys, the ashes of which have already been locally recognised in the region. Its analysis confirms its originality. In the course of the comparisons made to search for its spring, it appears that the wide-dispersion tephra CF7, beforehand correlated by hypothesis to the Puy de Clierzou, probably originates from the Kilian crater or the Puy de Vasset. To cite this article: D. Miallier et al., C. R. Geoscience 336 (2004).     

La prospection gravimétrique dans la modélisation d'un substratum sous formation sédimentaire : apport à l'hydrogéologie d'une zone semi-aride du Sud de Madagascar

A gravimetric survey has been carried out in a sedimentary basin, south of Madagascar, in order to define the bedrock morphology. The bedrock is made up of crystalline and volcanic rocks. The objective of the survey was to demonstrate whether a relationship could be established between bedrock morphology and groundwater mineralisation. Indeed, bedrock morphology has been successfully mapped and it is confirmed that most of the low mineralisation wells are located in areas where the slope of the bedrock is trending to the south-west, which ensures a higher hydraulic conductivity, i.e. a faster water flow, than in the other parts of the survey area. To cite this article: H. Rakoto et al., C. R. Geoscience 335 (2003).     

Les sondages électromagnétiques temporels comme outil de reconnaissance du gisement phosphaté de Sidi Chennane (Maroc) : apport à la résolution d'un problème d'exploitation

Exploitation of the phosphatic layers in Sidi Chennane deposit (Morocco) collides frequently with problems bound to the existence, in the phosphatic series, of sterile bodies qualified as derangements. Our study shows that these bodies, masked by the Quaternary cover can be mapped using the Time-Domain ElectroMagnetic Soundings method (TDEM). It is based on the acquisition and the interpretation of a series of tests carried out above a visible derangement in an old trench of exploitation and on 2500 TDEM soundings carried out in a virgin area of the deposit. The article concerns to the analysis of the results and of the proceeding for a possible large geophysics survey. To cite this article: A. Kchikach et al., C. R. Geoscience 338 (2006).     

In situ anaerobic degradation of petroleum alkanes in marine sediments: preliminary results

The degradation of acyclic petroleum hydrocarbons was studied during a 24-month experiment in Mediterranean coastal sediments (Gulf of Fos). Sediment cores entirely contaminated with oil (Arabian Light Crude Oil) were incubated in situ. The use of conservative tracers of sediment's particles reworking (luminophores) allowed the distinction of the reworked layer from the anoxic deeper sediments. Using the 17α,21βC₃₀ hopane (C₃₀H) as an inert internal reference, we could demonstrate that, after 24 months of experiment, acyclic petroleum hydrocarbons can be degraded under natural anaerobic conditions. The reactivity of individual alkanes appeared to depend on their chemical structure. To cite this article: D. Massias et al., C. R. Geoscience 335 (2003).To cite this article: D. Massias et al., C. R. Geoscience 335 (2003).     

Correlation of the Kimmeridgian succession of the Normandy coast,northern France with that of the Dorset-type area,southern England

The Kimmeridgian Stage is represented in the cliffs of the Dorset-type area and those in Normandy by richly fossiliferous marine mudstones and limestones. Taken together, these coastal exposures provide the only complete composite outcrop through this part of the Jurassic in the Sub-boreal Faunal Province. Detailed correlations between the two successions are presented here: these enable the Normandy-coast sections to be more accurately placed than previously within in their regional chronostratigraphical context. The Normandy succession is more completely exposed than that in Dorset, and is situated midway between Dorset and the Sub-Tethyan succession of the Berry region. It therefore offers a better prospect than any English section for inter-province correlation at this stratigraphical level. To cite this article: R. Gallois, C. R. Geoscience 337 (2005).     

Évaluation de la mobilité des métaux dans les sédiments fluviaux du bassin de la Vire (Normandie,France) par extractions simples ou séquentielles

This work compares the quantities of labile metals removed from the Vire River (Normandy) sediments by a sequential extraction procedure to those liberated by single leaches (Mg(NO₃)₂, HCl and EDTA). Compared to the other extractions, Mg(NO₃)₂ underestimated the mobility results. The sequential procedure was the most aggressive, except for Ca and Pb. The hypothetic correlation between quantities of an element removed by single leaches and its fractionation in the sediment according to the sequential procedure was not satisfying. Finally, it should be underlined that enrichments of Cd, Pb and Zn were noticed in the Vire sediments. To cite this article: L. Leleyter, F. Baraud, C. R. Geoscience 337 (2005).     

Premières datations directes de défrichements protohistoriques sur les chaumes secondaires des Vosges (Rossberg,Haut-Rhin). Approche pédoanthracologique

The age of the upland grasslands of the Vosges Mountains is still not well known. On the basis of the study of historical archives, it was assumed that the forest clearings, which led to grasslands establishment, were done by the monks who colonized the Vosges valleys between the 7th and the 8th centuries. Our pedo-anthracological study raises questions about this hypothesis, based on the discovery of Juniperus communis charcoal in soils from the 2nd or 1st century BC. This plant specie is characteristic of grasslands developing into fallows. The occurrence of Juniperus communis charcoals indicates that upland grasslands did exist at least 800 years earlier than it was expected before our study, i.e. at least since the late Iron Age. To cite this article: D. Schwartz et al., C. R. Geoscience 337 (2005).     

Neotectonics and seismic hazard assessment in Hengchun Peninsula,southern Taiwan

Neotectonic data may indicate whether stored elastic energy will be dissipated or released destructively. The Hengchun Peninsula of Taiwan is the southern extremity of the Central Range of Taiwan and thus an emergent part of the accretionary wedge resulting from subduction of Eurasia beneath the Philippine Sea plate at the Manila Trench. Radiocarbon dating of fossil shorelines on the peninsula shows that it has been uplifted at an average rate of 3.8 mm/yr during the Holocene. About $1/3$ of the uplift is due to deformation along the Hengchun reverse fault but, in contrast with the Chelungpu and other low angle reverse faults west of the Central Range, it accommodates strain principally by aseismic creep. To cite this article: C. Vita-Finzi, J.-C. Lin, C. R. Geoscience 337 (2005).     

Hydrogeological investigation in the Mekong Delta around Ho-Chi-Minh City (South Vietnam) by electric tomographyInvestigation hydrogéologique dans le delta du Mékong,autour de la ville de Ho-Chi-Minh (Sud-Vietnam), par tomographie électrique

In the Mekong Delta (South Vietnam), the agglomeration of Ho-Chi-Minh (HCM) City, with more than 5 million inhabitants, is confronted with a dramatic shortage of fresh water supply because of the pollution of several aquifers at different depths. The electric tomography, obtained by concurrent inversion of two complementary geoelectrical methods, the Vertical Electrical Sounding (VES) and the Magneto-Telluric Sounding (MTS), turned out to be very efficient to provide a complete electrical image of the underground from the surface until about 800 m depth. This methodology constitutes a very cheap guide for the evaluation of the quality of the groundwater resources in the vast alluvial plain of the Mekong Delta. To cite this article: V.N. Pham et al., C. R. Geoscience 334 (2002) 733–740.     

Enrichissement en uranium authigène dans les sédiments glaciaires de l'océan AustralEnrichments in authigenic uranium in glacial sediments of the Southern Ocean

Four sediment cores from the Polar frontal zone and the Antarctic zone in the Indian sector of the Southern Ocean present an increase of authigenic uranium during glacial periods. We show that this increase in uranium is due to a combination of (i) an increase in the lateral transport of organic matter, (ii) a decrease in the oxygen in deep waters, and (iii) a process of diagenesis. It appears that uranium concentration cannot be used as a proxy of palaeoproductivity in the Southern Ocean, as previously suggested by Kumar et al. in 1995. To cite this article: L. Dezileau et al., C. R. Geoscience 334 (2002) 1039–1046.