A low δLi lower crustal component: Evidence from an alkalic intraplate volcanic series (Chaîne des Puys, French Massif Central)     

Cdric Hamelin  Hans-Michael Seitz  Jean-Alix Barrat  Laure Dosso  Ren C. Maury  Marc Chaussidon 《Chemical Geology》2009,266(3-4):205-217

The intraplate volcanic suite of the Chaîne des Puys (French Massif Central) shows a complete petrologic range, from alkali basalts to trachytes. The significant variations of trace elements and radiogenic isotopes along the series strongly support the occurrence of crustal assimilation associated with fractional crystallization (AFC). The least contaminated basalts are clearly related to a HIMU-type reservoir (²⁰⁶Pb/²⁰⁴Pb > 19.6; ⁸⁷Sr/⁸⁶Sr < 0.7037; ε_Nd > + 4). The behavior of radiogenic isotopes suggests that the most likely crustal contaminants are meta-sediments located in the lower crust.The Li isotopic compositions of the lavas range from high δ⁷Li (> + 7‰) in basalts to lighter values in more evolved lavas (down to δ⁷Li ≈ 0‰). The mantle component, expressed in the least evolved lavas, has a heavy Li isotopic signature, in good agreement with previous δ⁷Li measurements of OIB lavas with HIMU affinities. The evolution of Li isotopic compositions throughout the volcanic series is in agreement with the AFC model suggested by the Sr–Nd–Pb isotopic systems. Although the behavior of Li isotopes during assimilation processes is currently poorly constrained, our calculations suggest that at least a portion of the lower crust beneath the Chaîne des Puys is characterized by a light Li isotopic composition (δ⁷Li < − 5‰).  相似文献   

Mapping waterholes and testing for aridity using a remote sensing water index in a southern African semi-arid wildlife area     

Zorodzai Dzinotizei  Amon Murwira  Fadzai M. Zengeya  Laure Guerrini 《国际地球制图》2013,28(11):1268-1280

Abstract

Waterholes are a key resource that influences wildlife distribution in semi-arid ecosystems. Mapping waterholes can guide intervening decisions for supplementing water resources and managing wildlife distribution patterns. Although remote sensing provides a key to mapping distribution of waterholes, efficiency of existing remotely sensed methods for detecting waterholes have to be evaluated and even new ones developed. In this study, we evaluated performance of the Modified Normalized Difference Water Index (MNDWI) and Superfine Water Index (SWI) at selected optimum thresholds. Kappa results indicated that MNDWI detects waterholes better than SWI. We further validated MNDWI detected waterholes by testing response of waterhole area to temporal rainfall variability and waterhole persistence to spatial rainfall variability. Extent of MNDWI-detected waterholes varied in relation to temporal rainfall variability (p < 0.05). Waterhole persistence was not associated with spatial rainfall variability which could be explained by differences in waterhole types or low spatial rainfall variability.  相似文献   

Climate change and warm‐water species at the north‐western boundary of the Mediterranean Sea          下载免费PDF全文

Valeriano Parravicini  Luisa Mangialajo  Laure Mousseau  Andrea Peirano  Carla Morri  Monica Montefalcone  Patrice Francour  Michel Kulbicki  Carlo Nike Bianchi 《Marine Ecology》2015,36(4):897-909

The effects of global change are particularly serious in areas where range shifts of species are physically constrained such as the Ligurian Sea, which is one of the coldest sectors of the Mediterranean. In this basin, historical information on water temperature (from the sea surface down to 75 m depth) dates back to the 1950s. Early studies also recorded warm‐water species occurrence. Thanks to these data we provide the first detailed characterization of water temperature variation from 1958 up to 2010 in the layer 0–75 m depth. We coupled this analysis with the available information on rocky reef epibenthic communities (literature review from 1955 to 1964 and field data from 1980 to 2010). The analysis of water temperature revealed several patterns of variation: a cooling phase from 1958 to 1980, a phase of rapid warming from 1980 to 1990 and a phase of slower warming from 1990 to 2010. Inter‐annual variation in temperature increased over the entire period for the water layer down to 20 m. Warm‐water native and alien species richness increased during the warming phases. Literature estimates suggest a decrease in warm‐water native species richness during the cooling phase. The analysis of quantitative data collected in the early 1990s and late 2000s indicated a decrease in the cover of warm‐water native species on shallow rocky reefs and an increase in deeper waters. We argue that increased inter‐annual variation in water temperature may disadvantage native warm‐water species in shallow waters. Our results indicate that the effect of temperature rises in cold, constrained basins may be more complex than the simple prediction of species changing their geographical range according to their thermal limits.  相似文献   

The Revised Brussels–Locarno Sunspot Number (1981 – 2015)     

Frédéric Clette  Laure Lefèvre  Marco Cagnotti  Sergio Cortesi  Andreas Bulling 《Solar physics》2016,291(9-10):2733-2761

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Detailed Analysis of Solar Data Related to Historical Extreme Geomagnetic Storms: 1868 – 2010     

Laure Lefèvre  Susanne Vennerstrøm  Mateja Dumbović  Bojan Vršnak  Davor Sudar  Rainer Arlt  Frédéric Clette  Norma Crosby 《Solar physics》2016,291(5):1483-1531

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Emergent geomorphic–vegetation interactions on a subalpine alluvial fan          下载免费PDF全文

Stuart N. Lane  Laure Borgeaud  Pascal Vittoz 《地球表面变化过程与地形》2016,41(1):72-86

Following perturbation, an ecosystem (flora, fauna, soil) should evolve as a function of time at a rate conditioned by external variables (relief, climate, geology). More recently, biogeomorphologists have focused upon the notion of co‐development of geomorphic processes with ecosystems over very short through to very long (evolutionary) timescales. Alpine environments have been a particular focus of this co‐development. However, work in this field has tended to adopt a simplified view of the relationship between perturbation and succession, including: how the landform and ecosystem itself conditions the impact of a perturbation to create a complex spatial response impact; and how perturbations are not simply ecosystem destroyers but can be a significant source of ecosystem resources. What this means is that at the within landform scale, there may well be a complex and dynamic topographic and sedimentological template that co‐develops with soil, flora and fauna. Here, we present and test a conceptual model of this template for a subalpine alluvial fan. We combine detailed floristic inventory with soil inventory, determination of edaphic variables and analysis of historical aerial imagery. Spatial variation in the probability of perturbation of sites on the fan surface was associated with down fan variability in the across‐fan distribution of fan ages, fan surface channel characteristics and fan surface sedimentology. Floristic survey confirmed that these edaphic factors distinguished site floristic richness and plant communities up until the point that the soil–vegetation system was sufficiently developed to sustain plant communities regardless of edaphic conditions. Thus, the primary explanatory variable was the estimated age of each site, which could be tied back into perturbation history and its spatial expression due to the geometry of the fan: distinct plant communities were emergent both across fan and down fan, a distribution maintained by the way in which the fan dissipates potentially perturbing events. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Microanalysis of carbon isotope composition in organic matter by secondary ion mass spectrometry     

Laure Sangély  Marc Chaussidon  Vincent Huault 《Chemical Geology》2005,223(4):179-195

An analytical procedure has been developed for the in situ measurement of carbon isotope composition of organic matter, with a spatial resolution of 20-30 μm, using a Cameca IMS 1270 ion microprobe. Instrumental mass fractionation (IMF) of carbon isotopes was observed to be independent of primary ion beam intensity and sputtering time, but did depend on vacuum conditions and on the chemical composition of the sample. To evaluate such “matrix effects”, a set of 9 standards representative of the natural chemical variability of organic matter was prepared, with H/C atomic ratios and organic carbon contents (C_org) ranging between 0.04 and 1.74 and between 41 and 100 wt.%, respectively. Under the analytical conditions tested, IMF was not found to be influenced by the presence of silicate mineral impurities in the organic matter, but variations in IMF up to 5‰ were observed over the set of standards with the magnitude of IMF negatively correlated to the H/C ratios of samples. Aliphaticity ratios determined using Fourier transform infrared microspectroscopy provided an in situ estimation of H/C ratios with a spatial resolution barely exceeding that of the ion microprobe and permit a correction for matrix effects with a standard error of ± 0.2‰ (1σ). Taking into account all sources of uncertainty, ion microprobe δ¹³C were accurately determined with a ± 0.7‰ (1σ) total uncertainty. The mechanism for the matrix effect of H/C ratios upon IMF is still to be determined but it is likely related to the difference in proportion of atomic vs. molecular carbon ions observed between samples of different H/C ratios.  相似文献   

Hydrocarbons in coastal sediments from the Mediterranean sea (Gulf of Fos area, France)   总被引：2，自引：0，他引：2  

Mille G  Asia L  Guiliano M  Malleret L  Doumenq P 《Marine pollution bulletin》2007,54(5):566-575

Sedimentary hydrocarbons have been studied quantitatively and qualitatively in 11 coastal stations located in the Gulf of Fos (French Mediterranean coast). Hydrocarbon levels ranged from 10 to 260 mg kg(-1) sed. dry weight. A new parameter "NAR" (Natural n-alkane ratio) is proposed to evaluate the contribution of terrestrial inputs of hydrocarbons in the sediments. The origins of hydrocarbons are multiple: terrestrial inputs, biogenic, pyrolytic (industry emissions mainly steel and iron industries, ship and road traffic). Generally, the main source of contamination is not petroleum. Several ratios between parent polycyclic aromatic hydrocarbons show that the sources of hydrocarbons in the sediments are generally much more pyrolytic than petrogenic.  相似文献   

Annual production of fish larvae and their prey in relation to size-fractionated primary production (Scotian Shelf, NW Atlantic)   总被引：4，自引：0，他引：4  

Mousseau  Laure; Fortier  Louis; Legendre  Louis 《ICES Journal of Marine Science》1998,55(1):44-57

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Water balance prediction in stormwater infiltration basins using 2-D modeling: An application to evaluate the clogging process     

Patrice Cannavo  Anaïs Coulon  Sylvain Charpentier  Béatrice Béchet  Laure Vidal-Beaudet 《国际泥沙研究》2018,33(4):371-384

Sustainable urban drainage systems are built along roads and in urban areas to collect urban runoff and avoid flooding, and to filter water pollutants. Sediment collected by runoff is deposited in the stormwater basin and progressively reduces water infiltration efficiency, leading to the clogging of the basin. To help stormwater basin managers and stakeholders better understand and predict clogging rates in order to elaborate maintenance plans and schedules, water transport prediction models are necessary. However,because of the heterogeneous sediment hydrodynamic properties inside the stormwater basin, a twodimensional(2-D) water flow model is required to predict water levels and possible overflow as accurately as possible. Saturated hydraulic conductivity(Ks) and sediment water retention curves were measured in the overall sediment layer of the stormwater basin, in addition to sediment layer thickness and organic matter content(11 sampling points). Sediment depth was used to predict organic matter(OM) content, and the OM was used to predict Ks. Water height in the basin was modeled with the HYDRUS-2 D model by taking into account the sediment hydrodynamic properties distribution. The HYDRUS-2 D model gave a satisfactory representation of the measured data. Scenarios of the hydraulic properties of stormwater basin sediment were tested over time, and hydraulic resistance, R, was calculated to assess the stormwater basin performance. Presently, after 20 years of functioning, the stormwater basin still ensures efficient water infiltration, but the first outflow(Hydraulic resistance,R 24 h)) is expected to appear in the next 5 years, and clogging(R 47 h) in the next 13 years. This 2-D water balance model makes it possible to integrate the hydrodynamic heterogeneity of a stormwater basin. It gives interesting perspectives to better predict 2-D/3-D contaminant transport.  相似文献