Exploitation de la fracturation d’un massif par la karstification : exemple du Causse de l’Hortus (Hérault,France)

Résumé

Le Causse de l’Hortus est un massif particulièrement adapté à l’étude de la fracturation et de ses interdépendances avec la karstification. La réalisation en cours d’une monographie hydrogéologique et spéléologique du massif ainsi que l’existence de plus de 20 km de galeries explorées appartenant aux réseaux actifs, permettent d’apporter des données nouvelles face aux précédentes études réalisées dans ce domaine. La confrontation des directions de fracturation visibles sur les photographies aériennes avec les directions réellement exploitées par les réseaux karstiques sur l’ensemble du Causse a permis de mettre en évidence le rôle des fractures majeures et l’influence du gradient hydraulique sur l’exploitation du spectre de fractures. En fin de compte, la mise en évidence des relations existant entre les failles décrochantes dextres et les émergences temporaires de type « boulidou » permet d’aboutir à des applications concrètes tant sur le plan spéléologique que sur le plan hydrogéologique. L’étude de ces « boulidous » apporte également de nouvelles informations sur la structuration verticale du karst. © Elsevier, Paris     

Multixenobiotic resistance, acetyl-choline esterase activity and total oxyradical scavenging capacity of the Arctic spider crab, Hyasaraneus, following exposure to bisphenol A, tetra bromo diphenyl ether and diallyl phthalate

The Arctic has become a sink for persistent organic pollutants (POPs) originating from lower latitudes, and relatively high levels have been found in different biota. Recent studies have identified detrimental effects on wildlife including endocrine disruption, impairment of enzyme activity, and reduced immune function. The Arctic spider crab, Hyas araneus, shown interesting potential for its use as sentinel organism in polar ecosystems. This study investigated the effect of 2,2',4,4'-tetra bromo diphenyl ether (BPDE), bisphenol A (BPA), and diallyl phthalte (DPA) on H. araneus in a three weeks exposure study. Expression of multixenibiotic resistance (MXR) proteins has been studied using the C219 monoclonal antibody which allows identifying an immunoreactive protein of 40 kDa in the digestive gland while no such protein could be observed in the gills. Expression of this protein was increased by exposure to DPA (+75%; p<0.05, n=10). All compounds significantly affected muscle acetylcholine esterase (AChE) activity (p<0.05, n=10) with 50 microg/L DPA having the strongest effect by lowering the value to 37% of control. The total oxyradical scavenging capacity measured in the digestive gland toward peroxyl, hydroxyl and peroxynitrite was also significantly reduced indicating a decreased resistance to oxidative stress generated by DPA (p<0.05, n=5). These results thus suggest the potential detrimental effects of DPA even at concentration as low as 50 microg/L on H. araneus.     

Expression of the Early Toarcian negative carbon-isotope excursion in separated carbonate microfractions (Jurassic,Paris Basin)

The causes of the pronounced negative excursion in carbon-isotope values that was recorded during the Early Toarcian Oceanic Anoxic Event (T-OAE) are still under debate, particularly with regard to the local versus global pattern of the excursion, and the extent to which recorded signals are under a diagenetic control. In this study we employ a novel microseparation technique in order to investigate the isotopic and mineralogical characteristics of different size fractions of the carbonate content from a Toarcian section recovered from the Sancerre–Couy borehole, southern Paris Basin. Beyond the recognition of a ? 6‰ δ¹³C excursion in the bulk carbonate content, our data also demonstrate that biogenic particles (such as coccoliths) and inorganic grains precipitated as early diagenetic phases (including dolomite) both record the excursion with the same magnitude. Although several black shales occur through the Paris Basin Toarcian section, it is only that associated with the onset of the OAE that coincides with a large negative carbon-isotope excursion. Taken together these observations indicate that during this event, the entire water column was characterized by homogeneous carbon-isotope values; such a pattern is incompatible with the idea that the negative excursion was generated simply through the upwelling of bottom waters enriched in re-mineralized organic carbon (cf. “the Küspert model”), since this would have required a strong vertical gradient in the water column. Additionally, the Paris Basin data show that the decrease in carbonate δ¹³C values during the OAE occurred in several discrete steps (each of some ? 2‰), as has previously been found for organic carbon substrates in other European sections. The stepped nature of the isotopic profile, which is part of a stratigraphic signature previously ascribed to Milankovitch forcing, is compatible with regular pulsed input of light carbon into the whole atmosphere–ocean system from a climatically sensitive source such as gas hydrate, or from thermal methanogenesis of organic-rich sediments in the Karoo–Ferrar large igneous province. Contrasts in the amplitude of the negative carbon-isotope excursion on a regional scale remain an important unexplained aspect of the Toarcian record.     

External controls on the distribution,fabrics and mineralization of modern microbial mats in a coastal hypersaline lagoon,Cayo Coco (Cuba)

Active, carbonate‐mineralizing microbial mats flourish in a tropical, highly evaporative, marine‐fed lagoonal network to the south of Cayo Coco Island (Cuba). Hypersaline conditions support the development of a complex sedimentary microbial ecosystem with diverse morphologies, a variable intensity of mineralization and a potential for preservation. In this study, the role of intrinsic (i.e. microbial) and extrinsic (i.e. physicochemical) controls on microbial mat development, mineralization and preservation was investigated. The network consists of lagoons, forming in the interdune depressions of a Pleistocene aeolian substratum; they developed due to a progressive increase in sea‐level since the Holocene. The hydrological budget in the Cayo Coco lagoonal network changes from west to east, increasing the salinity. This change progressively excludes grazers and increases the saturation index of carbonate minerals, favouring the development and mineralization of microbial mats in the easternmost lagoons. Detailed mapping of the easternmost lagoon shows four zones with different flooding regimes. The microbial activity in the mats was recorded using light–dark shifts in conjunction with microelectrode O₂ and HS^? profiles. High rates of O₂ production and consumption, in addition to substantial amounts of exopolymeric substances, are indicative of a potentially strong intrinsic control on mineralization. Seasonal, climate‐driven water fluctuations are key for mat development, mineralization, morphology and distribution. Microbial mats show no mineralization in the permanently submersed zone, and moderate mineralization in zones with alternating immersion and exposure. It is suggested that mineralization is also driven by water‐level fluctuations and evaporation. Mineralized mats are laminated and consist of alternating trapping and binding of grains and microbially induced magnesium calcite and dolomite precipitation. The macrofabrics of the mats evolve from early colonizing Flat mats to complex Cerebroid or Terrace structures. The macrofabrics are influenced by the hydrodynamic regime: wind‐driven waves inducing relief terraces in windward areas and flat morphologies on the leeward side of the lagoon. Other external drivers include: (i) storm events that either promote (for example, by bioclasts covering) or prevent (for example, by causing erosion) microbial mat preservation; and (ii) subsurface degassing, through mangrove roots and desiccation cracks covered by Flat mats (i.e. forming Hemispheroids and Cerebroidal structures). These findings provide in‐depth insights into understanding fossil microbialite morphologies that formed in lagoonal settings.     

A Compilation of Silicon,Rare Earth Element and Twenty‐One other Trace Element Concentrations in the Natural River Water Reference Material SLRS‐5 (NRC‐CNRC)

The natural river water certified reference material SLRS‐5 (NRC‐CNRC) was routinely analysed in this study for major and trace elements by ten French laboratories. Most of the measurements were made using ICP‐MS. Because no certified values are assigned by NRC‐CNRC for silicon and 35 trace element concentrations (rare earth elements, Ag, B, Bi, Cs, Ga, Ge, Li, Nb, P, Rb, Rh, Re, S, Sc, Sn, Th, Ti, Tl, W, Y and Zr), or for isotopic ratios, we provide a compilation of the concentrations and related uncertainties obtained by the participating laboratories. Strontium isotopic ratios are also given.     

Climate variability and trends in downscaled high-resolution simulations and projections over Metropolitan France

In order to fulfill the society demand for climate information at the spatial scale allowing impact studies, long-term high-resolution climate simulations are produced, over an area covering metropolitan France. One of the major goals of this article is to investigate whether such simulations appropriately simulate the spatial and temporal variability of the current climate, using two simulation chains. These start from the global IPSL-CM4 climate model, using two regional models (LMDz and MM5) at moderate resolution (15–20 km), followed with a statistical downscaling method in order to reach a target resolution of 8 km. The statistical downscaling technique includes a non-parametric method that corrects the distribution by using high-resolution analyses over France. First the uncorrected simulations are evaluated against a set of high-resolution analyses, with a focus on temperature and precipitation. Uncorrected downscaled temperatures suffer from a cold bias that is present in the global model as well. Precipitations biases have a season- and model-dependent behavior. Dynamical models overestimate rainfall but with different patterns and amplitude, but both have underestimations in the South-Eastern area (Cevennes mountains) in winter. A variance decomposition shows that uncorrected simulations fairly well capture observed variances from inter-annual to high-frequency intra-seasonal time scales. After correction, distributions match with analyses by construction, but it is shown that spatial coherence, persistence properties of warm, cold and dry episodes also match to a certain extent. Another aim of the article is to describe the changes for future climate obtained using these simulations under Scenario A1B. Results are presented on the changes between current and mid-term future (2021–2050) averages and variability over France. Interestingly, even though the same global climate model is used at the boundaries, regional climate change responses from the two models significantly differ.     

Scaling of the Vertical Spreading of a Plume of a Passive Tracer in a Rough-Wall Neutral Boundary Layer

The influence of surface roughness on the dispersion of a passive scalar in a rough wall turbulent boundary layer has been studied using wind-tunnel experiments. The surface roughness was varied using different sizes of roughness elements, and different spacings between the elements. Vertical profiles of average concentration were measured at different distances downwind of the source, and the vertical spread of the plume was computed by fitting a double Gaussian profile to the data. An estimate of the integral length scale is derived from the turbulence characteristics of the boundary layer and is then used to scale the measured values of plume spread. This scaling reduces the variability in the data, confirming the validity of the model for the Lagrangian integral time scale, but does not remove it entirely. The scaled plume spreading shows significant differences from predictions of theoretical models both in the near and in the far field. In the region immediately downwind of the source this is due to the influence of the wake of the injector for which we have developed a simple model. In the far field we explain that the differences are mainly due to the absence of large-scale motions. Finally, further downwind of the source the scaled values of plume spread fall into two distinct groups. It is suggested that the difference between the two groups may be related to the lack of dynamical similarity between the boundary-layer flows for varying surface roughness or to biased estimates of the plume spread.     

Carbonyl Sulphide (OCS) Variability with Latitude in the Atmosphere

Abstract

Carbonyl sulphide (OCS) is an important precursor of sulphate aerosols and consequently a key species in stratospheric ozone depletion. The SPectromètre InfraRouge d'Absorption à Lasers Embarqués (SPIRALE) and shortwave infrared (SWIR) balloon-borne instruments have flown in the tropics and in the polar Arctic, and ground-based measurements have been performed by the Qualité de l'Air (QualAir) Fourier Transform Spectrometer in Paris. Partial and total columns and vertical profiles have been obtained to study OCS variability with altitude, latitude, and season. The annual total column variation in Paris reveals a seasonal variation with a maximum in April–June and a minimum in November–January. Total column measurements above Paris and from SWIR balloon-borne instrument are compared with several MkIV measurements, several Network for the Detection of Atmospheric Composition Change (NDACC) stations, aircraft, ship, and balloon measurements to highlight the OCS total column decrease from tropical to polar latitudes. OCS high-resolution in situ vertical profiles have been measured for the first time in the altitude range between 14 and 30?km at tropical and polar latitudes. OCS profiles are compared with Atmospheric Chemistry Experiment (ACE) satellite measurements and show good agreement. Using the correlation between OCS and N₂O from SPIRALE, the OCS stratospheric lifetime has been accurately determined. We find a stratospheric lifetime of 68?±?20 years at polar latitudes and 58?±?14 years at tropical latitudes leading to a global stratospheric sink of 49?±?14?Gg?S?y^?1.     

A history of ENSO events since A.D. 1525: implications for future climate change

Reconstructions of past climate are important for providing a historical context for evaluating the nature of 20th century climate change. Here, a number of percentile-based palaeoclimate reconstructions were used to isolate signals of both phases of El Niño–Southern Oscillation (ENSO). A total of 92 (82) El Niño (La Niña) events were reconstructed since A.D. 1525. Significantly, we introduce the most comprehensive La Niña event record compiled to date. This annual record of ENSO events can now be used for independent verification of climate model simulations, reconstructions of ENSO indices and as a chronological control for archaeologists/social scientists interested in human responses to past climate events. Although extreme ENSO events are seen throughout the 478-year ENSO reconstruction, approximately 43% of extreme and 28% of all protracted ENSO events (i.e. both El Niño and La Niña phase) occur in the 20th century. The post-1940 period alone accounts for 30% of extreme ENSO years observed since A.D. 1525. These results suggest that ENSO may operate differently under natural (pre-industrial) and anthropogenic background states. As evidence of stresses on water supply, agriculture and natural ecosystems caused by climate change strengthens, studies into how ENSO will operate under global warming should be a global research priority.     

Investigating the Halogen Chemistry From High-Latitude Nighttime Stratospheric Measurements of OClO and NO2

Two cases of simultaneous nighttime measurements of NO₂ and OClO in the winter polar stratosphere are analyzed in order to test our present knowledge of halogen chemistry in the presence of high amount of NO₂ at low temperature. Comparisons with Lagrangian model calculations using several hypotheses are performed. First simulations, using the admitted constant rates of chemical reaction, strongly underestimate the measured OClO while the NO₂ profiles are correctly reproduced. If uncertainties in actinic fluxes calculations are taken into account, simulation results do not show a significant reduction of the underestimation. A better agreement can be achieved if the formation of unstable isomers of ClONO₂ and of BrONO₂ occurs in the cold conditions of the polar stratosphere. An approximate value of the branching ratios of the channels leading to ClONO₂ and ClOONO, and to BrONO₂ and BrOONO, necessary to reproduce both OClO and NO₂ is given and discussed.