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31.
Virginie Chapon Laurie Piette Marie-Hélène Vesvres Frédéric Coppin Claire Le Marrec Richard Christen Nicolas Theodorakopoulos Laureline Février Sviatoslav Levchuk Arnaud Martin-Garin Catherine Berthomieu Claire Sergeant 《Applied Geochemistry》2012
The diversity of bacterial communities exposed to radioactive contamination in Chernobyl soils was examined by a combination of molecular and culture-based approaches. A set of six radioactive soil samples, exhibiting high levels of 137Cs contamination, were collected from the T22 trench. Three samples were also collected in nearby soils with low contamination. Complex bacterial community structures were observed in both highly and weakly contaminated samples, using a molecular approach targeting the 16S rRNA gene. However, the presence of specific populations within samples from highly contaminated soils could not be revealed by statistical analysis of the DGGE profiles. More than 200 culturable isolates, representative of dominant morphotypes, were grouped into 83 Operational Taxonomic Units (OTUs) and affiliated to Firmicutes, Actinobacteria, Alpha-, Beta-, Gamma-Proteobacteria and Bacteroïdetes. No specific pattern linked to contamination was observed for these culturable bacteria. The results show that both highly and weakly contaminated soils host a wide diversity of bacteria, suggesting that long term exposure to radionuclides does not lead to the extinction of bacterial diversity. 相似文献
32.
Franois De Vleeschouwer Virginie Renson Philippe Claeys Karin Nys Richard Bindler 《Geoarchaeology》2011,26(3):440-450
A wavelength‐dispersive X‐ray fluorescence (WD‐XRF) calibration is developed for small powdered samples (300mg) with the purpose of analyzing ceramic artifacts that might be available only in limited quantity. This is compared to a conventional calibration using a larger sample mass (2g). The comparison of elemental intensities obtained in both calibrations shows that the decrease in analyzed sample mass results in a linear decrease in measured intensity for the analyzed elements. This indicates that the small‐ and large‐sample calibrations are comparable. Moreover, the elemental contents of four ceramic sherds and two potential clay sources fall well within the range of the certified reference materials that are the basis of the calibration curves. The advantage with the analytical method presented here is that it is rapid and requires only a small amount of sample that can easily be re‐used for further analyses. This method has great potential in ceramic provenance studies. © 2011 Wiley Periodicals, Inc. 相似文献
33.
Virginie Guemas Francisco J. Doblas-Reyes Kristian Mogensen Sarah Keeley Yongming Tang 《Climate Dynamics》2014,43(9-10):2813-2829
Polar climate studies are severely hampered by the sparseness of the sea ice observations. We aim at filling this critical gap by producing two 5-member sea ice historical simulations strongly constrained by ocean and atmosphere observational data and covering the 1958–2006 and 1979–2012 periods. This is the first multi-member sea ice reconstruction covering more than 50 years. The obtained sea ice conditions are in reasonable agreement with the few available observations. These best estimates of sea ice conditions serve subsequently as initial sea ice conditions for a set of 28 3-year-long retrospective climate predictions. We compare it to a set in which the sea ice initial conditions are taken from a single-member sea ice historical simulation constrained by atmosphere observations only. We find an improved skill in predicting the Arctic sea ice area and Arctic near surface temperature but a slightly degraded skill in predicting the Antarctic sea ice area. We also obtain a larger spread between the members for the sea ice variables, thus more representative of the forecast error. 相似文献
34.
Abstract The GWAVA (Global Water AVailability Assessment) model for indicating human water security has been extended with a newly developed module for calculating pollutant concentrations. This module is first described and then illustrated by being used to model nitrogen, phosphorus and organic matter concentrations. The module uses solely input variables that are likely to be available for future scenarios, making it possible to apply the module to such scenarios. The module first calculates pollutant loading from land to rivers, lakes and wetlands by considering drivers such as agriculture, industry and sewage treatment. Calculated loadings are subsequently converted to concentrations by considering aquatic processes, such as dilution, downstream transport, evaporation, human water abstraction and biophysical loss processes. Aquatic biodiversity is indicated to be at risk if modelled pollutant concentrations exceed certain water quality standards. This is indicated to be the case in about 35% of the European area, especially where lakes and wetlands are abundant. Human water security is indicated to be at risk where human water demands cannot be fulfilled during drought events. This is found to be the case in about 10% of the European area, especially in Mediterranean, arid and densely-populated areas. Modelled spatial variation in concentrations matches well with existing knowledge, and the temporal variability of concentrations is modelled reasonably well in some river basins. Therefore, we conclude that the updated GWAVA model can be used for indicating changes in human water security and aquatic biodiversity across Europe. Editor Z.W. Kundzewicz Citation Dumont, E., Williams, R., Keller, V., Voss, A., and Tattari, S., 2012. Modelling indicators of water security, water pollution and aquatic biodiversity in Europe. Hydrological Sciences Journal, 57 (7), 1378–1403. 相似文献
35.
Fabien Gibert Irène Xuéref-Rémy Lilian Joly Martina Schmidt Juan Cuesta Kenneth J. Davis Michel Ramonet Pierre H. Flamant Bertrand Parvitte Virginie Zéninari 《Boundary-Layer Meteorology》2008,128(3):381-401
A network of remote and in-situ sensors was deployed in a Paris suburb in order to evaluate the mesoscale evolution of the
daily cycle of CO2 and related tracers in the atmospheric boundary layer (ABL) and its relation to ABL dynamics and nearby natural and anthropogenic
sources and sinks. A 2-μm heterodyne Doppler differential absorption lidar, which combines measurements of, (1) structure
of the atmosphere, (2) radial velocity, and (3) CO2 differential absorption was a particularly unique element of the observational array. We analyse the differences in the diurnal
cycle of CO, CO2, lidar reflectivity (a proxy for aerosol content) and H2O using the lidar, airborne measurements in the free troposphere and ground-based measurements made at two sites located few
kilometres apart. We demonstrate that vertical mixing dominates the early morning drawdown of CO and aerosol content trapped
in the former nocturnal layer but not the H2O and CO2 mixing ratio variations. Surface fluxes, vertical mixing and advection all contribute to the ABL CO2 mixing ratio decrease during the morning transition, with the relative importance depending on the rate and timing of ABL
rise. We also show evidence that when the ABL is stable, small-scale (0.1-km vertical and 1-km horizontal) gradients of CO2 and CO are large. The results illustrate the complexity of inferring surface fluxes of CO2 from atmospheric budgets in the stable boundary layer. 相似文献
36.
Most state-of-the art global coupled models simulate a weakening of the Atlantic meridional overturning circulation (MOC)
in climate change scenarios but the mechanisms leading to this weakening are still being debated. The third version of the
CNRM (Centre National de Recherches Météorologiques) global atmosphere-ocean-sea ice coupled model (CNRM-CM3) was used to
conduct climate change experiments for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4).
The analysis of the A1B scenario experiment shows that global warming leads to a slowdown of North Atlantic deep ocean convection
and thermohaline circulation south of Iceland. This slowdown is triggered by a freshening of the Arctic Ocean and an increase
in freshwater outflow through Fram Strait. Sea ice melting in the Barents Sea induces a local amplification of the surface
warming, which enhances the cyclonic atmospheric circulation around Spitzberg. This anti-clockwise circulation forces an increase
in Fram Strait outflow and a simultaneous increase in ocean transport of warm waters toward the Barents Sea, favouring further
sea ice melting and surface warming in the Barents Sea. Additionally, the retreat of sea ice allows more deep water formation
north of Iceland and the thermohaline circulation strengthens there. The transport of warm and saline waters toward the Barents
Sea is further enhanced, which constitutes a second positive feedback. 相似文献
37.
A preindustrial climate experiment was conducted with the third version of the CNRM global atmosphere–ocean–sea ice coupled
model (CNRM-CM3) for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4). This experiment is
used to investigate the main physical processes involved in the variability of the North Atlantic ocean convection and the
induced variability of the Atlantic meridional overturning circulation (MOC). Three ocean convection sites are simulated,
in the Labrador, Irminger and Greenland–Iceland–Norwegian (GIN) Seas in agreement with observations. A mechanism linking the
variability of the Arctic sea ice cover and convection in the GIN Seas is highlighted. Contrary to previous suggested mechanisms,
in CNRM-CM3 the latter is not modulated by the variability of freshwater export through Fram Strait. Instead, the variability
of convection is mainly driven by the variability of the sea ice edge position in the Greenland Sea. In this area, the surface
freshwater balance is dominated by the freshwater input due to the melting of sea ice. The ice edge position is modulated
either by northwestward geostrophic current anomalies or by an intensification of northerly winds. In the model, stronger
than average northerly winds force simultaneous intense convective events in the Irminger and GIN Seas. Convection interacts
with the thermohaline circulation on timescales of 5–10 years, which translates into MOC anomalies propagating southward from
the convection sites. 相似文献
38.
Michel Chouteau Stefka Krivochieva Ramiro Rodriguez Castillo Tomas Gonzalez Moran Virginie Jouanne 《Journal of Applied Geophysics》1994,31(1-4)
A tensor magnetotelluric test survey was carried out in the region of Santa Catarina, located in the Chalco sub-basin of the Mexico Basin. The objective was to define the stratification at depth with an emphasis on the geometry of the main aquifer of that region which is partially known from DC resistivity soundings and drilling. High-quality magnetotelluric soundings could be recorded in the immediate vicinity of large urban zones because the sub-surface is very conductive. Interpretation shows that the solid bedrock is located at a depth of at least 800 m to the south and 1300 m to the north; it could, however, be much deeper. Using complementary DC resistivity sounding and well-logging data, three main layers have been defined overlying the bedrock. These layers are, from surface to bottom, an unsaturated zone of sand, volcanic ash and clay about 10 m thick, followed by a very conductive (1.5 ohm·m) 200 m thick layer of sand and ash with intercalated clay, saturated with highly mineralized water, and finally a zone with resistivity increasing gradually to 60 ohm·m. The investigated deep aquifer constitutes most of this third layer. It consists of a sequence of sand, gravel, pyroclastites and mainly fractured basalts. MT resistivity soundings and magnetic transfer functions also indicate that a shallow resistive structure is dipping, from the northwest, into the lacustrine deposits of the basin. This geologic feature is likely to be highly permeable fractured basaltic flows, which provide a channel by which water contaminated by the Santa Catarina landfill may leak into the basin. 相似文献
39.
Summary We show that daily precipitation is characterized by a behaviour regulated by power laws. Both for the frequency distribution
of both event intensity and drought duration. In this respect, precipitation appears to follow self-organized criticality
laws, much as other geophysical phenomena such as avalanches and earthquakes. We use this feature to validate the simulation
of daily precipitation events in a multi-decadal regional climate model experiment for the European region. Our focus is on
the Italian peninsula and we show that both the model results and the station observations for daily precipitation intensity
and drought length follow power laws with comparable values of the relevant parameters. We suggest that complex systems theory
can provide useful tools for the validation of precipitation statistics in climate models. 相似文献
40.
Time-lapse resistivity investigations for imaging saltwater transport in glaciofluvial deposits 总被引:1,自引:1,他引:1
Five intersecting resistivity sections have been measured in glaciofluvial deposits hosting an aquifer of regional importance
situated along a heavy traffic highway in Sweden. The winter salt spreading has caused a regular salinity increase through
the years. For imaging the transport of saltwater in the aquifer, the sections were measured exactly in the same location
before and after winter, and interpreted using a time-lapse inverse procedure. Some auger drilling and RCPT data were available
for correlation. After winter, the resistivity had generally decreased under the water table and increased above it. The decrease
in resistivity in the saturated zone is interpreted as a plume of more saline groundwater created by de-icing salt from the
road. The increase in the upper layer can be explained by changes in temperature and soil moisture. The study shows that time-lapse
resistivity investigations has potential for imaging hydraulic pathways in complex hydrogeological environments. 相似文献