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1.
Daniel Bernard Jamal El Khattabi Emilie Lefevre Hani Serhal Sabine Bastin-Lacherez Isam Shahrour 《Environmental Geology》2008,53(5):1129-1138
In the north of France, high registers of nickel are sometimes recorded within the chalk aquifer. In a confined context, the
presence of pyrite in the covering clays or in the marcasite nodules encrusted in the clay may constitute a natural source
of trace metals. With an objective of sanitary control, the limits of chemical contents regulating the quality of water destined
for human consumption have been lowered by the European Framework Directive in the field of water policy (2000/60/EC). As
a result, nickel limits have been reduced from 50 to 20 μg/l. The analyses, carried out on three water catchment fields in
our area of study, were centred on variable parameters (Eh, O2(d), pH, Conductivity, T°), major elements (SO4, NO3) and metals (Fe, Ni, Mn, Co). The acquired data enabled us to identify from one hand, the conditions which are presented
within the site, special thanks to the evolution of nitrate and iron contents and on the other hand, the natural origin (geological)
of nickel for two of the three sites studied based essentially on the evaluation of the Nickel/Cobalt ratio. Thus, on the
first site, the evolution of nickel content and nitrate content showed the influence of the phenomenon of denitrification
on the re-mobilisation of the nickel. Whereas on the second site, a high variation of total iron content and oxygen dissolved
in solution highlighted a particular phenomenon of oxidation of the pyrite through molecular oxygen. Finally, the correlation
with the sulphates clearly showed behaviour of the nickel, once released, that was entirely dependent on the phenomenon of
adsorption on the iron and manganese hydroxides. 相似文献
2.
The intermediate lavas of the Azores Archipelago are reinvestigated and compared with other lavas from oceanic islands. Using both published and new petrological data, it appears that the so-called andesites and latites are in fact hawaiites and tristanites. 相似文献
3.
The orogenic volcanic rocks of Erromango island are divided into a Quaternary theoleiitic group and an older Pliocene one showing calc-alkalic affinity. The microprobe mineralogy of these lavas agrees with this geochemical distinction and indicates a marked iron enrichment trend in the recent tholeiitic lavas, whereas titanomagnetite occurs as early formed phenocrysts (Al, Cr, Mg-rich) only in Pliocene basalts. Some Ni and Mg-rich olivine phenocrysts (Fo88) and unusual chemically zoned clinopyroxene megacrysts are described from Pliocene basic lavas and interpreted as deep-fractionated minerals. The large compositional range of these latter (diopside core to augite rim, through salite intermediate zone) leads us to discuss the physical conditions and the corresponding cation substitutions prevailing during their formation. Diopside cores crystallized at depths of about 20 km from a relatively ‘primitive’ melt. The formation of salite is considered to be the result of concomitant fractionation of Mg-rich phases and increase of fO2. An early stage of fractionation of Cr-bearing diopside + Ni-bearing olivine would account for the typical Cr and Ni depletion of Erromango lavas. 相似文献
4.
Sophie Szopa Y. Balkanski M. Schulz S. Bekki D. Cugnet A. Fortems-Cheiney S. Turquety A. Cozic C. Déandreis D. Hauglustaine A. Idelkadi J. Lathière F. Lefevre M. Marchand R. Vuolo N. Yan J.-L. Dufresne 《Climate Dynamics》2013,40(9-10):2223-2250
Global aerosol and ozone distributions and their associated radiative forcings were simulated between 1850 and 2100 following a recent historical emission dataset and under the representative concentration pathways (RCP) for the future. These simulations were used in an Earth System Model to account for the changes in both radiatively and chemically active compounds, when simulating the climate evolution. The past negative stratospheric ozone trends result in a negative climate forcing culminating at ?0.15 W m?2 in the 1990s. In the meantime, the tropospheric ozone burden increase generates a positive climate forcing peaking at 0.41 W m?2. The future evolution of ozone strongly depends on the RCP scenario considered. In RCP4.5 and RCP6.0, the evolution of both stratospheric and tropospheric ozone generate relatively weak radiative forcing changes until 2060–2070 followed by a relative 30 % decrease in radiative forcing by 2100. In contrast, RCP8.5 and RCP2.6 model projections exhibit strongly different ozone radiative forcing trajectories. In the RCP2.6 scenario, both effects (stratospheric ozone, a negative forcing, and tropospheric ozone, a positive forcing) decline towards 1950s values while they both get stronger in the RCP8.5 scenario. Over the twentieth century, the evolution of the total aerosol burden is characterized by a strong increase after World War II until the middle of the 1980s followed by a stabilization during the last decade due to the strong decrease in sulfates in OECD countries since the 1970s. The cooling effects reach their maximal values in 1980, with ?0.34 and ?0.28 W m?2 respectively for direct and indirect total radiative forcings. According to the RCP scenarios, the aerosol content, after peaking around 2010, is projected to decline strongly and monotonically during the twenty-first century for the RCP8.5, 4.5 and 2.6 scenarios. While for RCP6.0 the decline occurs later, after peaking around 2050. As a consequence the relative importance of the total cooling effect of aerosols becomes weaker throughout the twenty-first century compared with the positive forcing of greenhouse gases. Nevertheless, both surface ozone and aerosol content show very different regional features depending on the future scenario considered. Hence, in 2050, surface ozone changes vary between ?12 and +12 ppbv over Asia depending on the RCP projection, whereas the regional direct aerosol radiative forcing can locally exceed ?3 W m?2. 相似文献
5.
Denis Michel Lefevre Dominique Thyssen Melilotus Jenkinson Ian R. Grégori Gérald 《中国海洋湖沼学报》2023,41(1):189-202
The short term (hourly scale) variability of heterotrophic prokaryote (HP) vertical distribution and respiratory activity, was investigated in the north-western (NW) Mediterranean Sea. HP vertical distribution was determined on board by flow cytometry analysis of seawater samples collected by series of CTD casts. Cell counts and viability were determined for all samples. HP respiratory rates were determined later in the laboratory from filtered seawater samples (23 dm3) from 300–1 150-m depth. The average cell viability was 94.8%±2.2% (n=240). There was no accumulation of dead cells, due to quick decay of damaged cells. In the epipelagic layer, three HP groups were distinguished, two (HNA1, HNA2) whose cells exhibited a high nucleic acid content and one (LNA) with low nucleic acid content cells. HNA2 was most populated at 50 m but not detected at 90 m and below, presumably aerobic anoxygenic photoheterotrophic bacteria (AAPs). The variability in HP abundance was mainly confined in the upper 80 m. A few secondary peaks of HP abundance were observed (80–150 m) in connection with abundance troughs in the surface layer. HP cells were continuously present in a wide layer around 500 m (mean 191×103 cells/cm3). Below this layer, HP abundance randomly exhibited peaks, coupled to respiratory rate peaks. The HP abundance and variability in the water column was suppressed during a strong wind event. The observed sporadic variability was tentatively interpreted through a pulsed carbon-export mechanism induced by the microorganism production of dissolved polysaccharides, followed by flocculation and rapid sinking. This mechanism would thus contribute to (i) preventing organic matter accumulation in the epipelagic layer, (ii) seeding the water column with live HP cells, and (iii) supplying the aphotic water column with fresh and labile organic matter. This important vertical flux mechanism needs further observations and modelling.
相似文献6.
7.
The content of uranium of andesitic rocks of southern Peru varies according to the distance from the Peru-Chile trench, as has been observed for other trace elements geochemically associated with K. The highest contents found in these rocks may exceed the estimated U content of the upper crust. This enrichment may be related to a variable degree of partial melting and/or crustal contamination of the same source material. 相似文献
8.
E. Robin C. Rabouille G. Martinez I. Lefevre J. L. Reyss P. van Beek C. Jeandel 《Marine Chemistry》2003,82(3-4):289-306
Barite (BaSO4) in marine sediments is considered as a proxy of surface ocean productivity and is widely used for paleo-productivity reconstructions. However, direct barite determination is not achieved by currently used methods, which rely on the measurement of total barium by inductively coupled plasma–mass spectrometry (ICP-MS) and instrumental neutron activation analysis (INAA) and correction from the allogenic Ba contribution. We report here on a technique that directly counts individual barite crystals using a scanning electron microscope (SEM) coupled to an energy dispersive spectrometer (EDS) equipped with an automated particle counting and classification (ACC) system. We show that barite–Ba concentrations can be deduced from the abundance, shape and size distributions of barite crystals with current precision and sensitivity as high as ±5 wt.% (2σ confidence limit) and 10 ppm, respectively. This technique, coupled with ICP-MS and INAA techniques for total Ba measurements, was applied to sediment samples from the tropical North Atlantic and the Central North Pacific oceans. Results show that: (1) barite and detrital aluminosilicates are the two main carriers of Ba in the investigated sediments; (2) calculated Ba/Al ratios range from 0.005 to 0.008 with an average value around 0.0066, in close agreement with previously reported values; (3) barite might not be the major source for released barium out of sediments and we suggest instead adsorbed barium as a potential source. 相似文献
9.
Comparison of wind and wave measurements and models in the Western Mediterranean Sea 总被引：2，自引：0，他引：2
Fabrice Ardhuin Luciana Bertotti Jean-Raymond Bidlot Luigi Cavaleri Valentina Filipetto Jean-Michel Lefevre Paul Wittmann 《Ocean Engineering》2007,34(3-4):526-541
We have hindcast the wind and wave conditions in the Mediterranean Sea for two one month periods. Four different meteorological models and three different wave models have been used. The results have been compared with satellite and buoy wind and wave observations.Several conclusions concerning both the instruments and the models have been derived. The quality of both wind and wave results has been assessed. Close to the coasts high resolution, nested wave models are required for sufficient reliability.A wave threshold analysis suggests a sufficient reliability only off the coast, with a substantial decrease for low wave heights. 相似文献
10.
In view of the construction of new sunspot-based activity indices and proxies, we conducted a comprehensive survey of all existing catalogs providing detailed parameters of photospheric features over long time intervals. Although there are a fair number of such catalogs, a global evaluation showed that they suffer from multiple limitations: finite or fragmented time coverage, limited temporal overlap between catalogs, and, more importantly, a mismatch in contents and conventions. Starting from the existing material, we demonstrate how the information from parallel catalogs can be merged to form a much more comprehensive record of sunspots and sunspot groups. To do this, we use the uniquely detailed Debrecen Photoheliographic Data (DPD), which is already a composite of several ground-based observatories and of SOHO data, and the USAF/Mount Wilson catalog from the Solar Observing Optical Network (SOON). We also outline our cross-identification method, which was needed to match the non-overlapping solar active-region nomenclature. This proved to be the most critical and subtle step when working with multiple catalogs. This effort, focused here first on the last two solar cycles, should lead to a better central database that collects all available sunspot group parameters to address future solar-cycle studies beyond the traditional sunspot-index time series [R i]. 相似文献