Isotopic fractionation of zinc in tektites     

Frederic Moynier  Pierre Beck  Fred Jourdan  Qing-Zhu Yin  Uwe Reimold  Christian Koeberl 《Earth and Planetary Science Letters》2009,277(3-4):482-489

Tektites are terrestrial natural glasses produced during a hypervelocity impact of an extraterrestrial projectile onto the Earth's surface. The similarity between the chemical and isotopic compositions of tektites and terrestrial upper continental crust implies that the tektites formed by fusion of such target rock. Tektites are among the driest rocks on Earth. Although volatilization at high temperature may have caused this extreme dryness, the exact mechanism of the water loss and the behavior of other volatile species during tektite formation are still debated. Volatilization can fractionate isotopes, therefore, comparing the isotope composition of volatile elements in tektites with that of their source rocks may help to understand the physical conditions during tektite formation.For this study, we have measured the Zn isotopic composition of 20 tektites from four different strewn fields. Almost all samples are enriched in heavy isotopes of Zn compared to the upper continental crust. On average, the different groups of tektites are isotopically distinct (listed from the isotopically lightest to the heaviest): Muong-Nong type indochinites (δ^66/64Zn = 0.61 ± 0.30‰); North American bediasites (δ^66/64Zn = 1.61 ± 0.49‰); Ivory Coast tektites (δ^66/64Zn = 1.66 ± 0.18‰); the Australasian tektites (others than the Muong Nong-type indochinites) (δ^66/64Zn = 1.84 ± 0.42‰); and Central European moldavites (δ^66/64Zn = 2.04 ± 0.19‰). These results are contrasted with a narrow range of δ^66/64Zn = 0–0.7‰ for a diverse spectrum of upper continental crust materials.The elemental abundance of Zn is negatively correlated with δ^66/64Zn, which may reflect that isotopic fractionation occurred by evaporation during the heating event upon tektite formation. Simple Rayleigh distillation predicts isotopic fractionations much larger than what is actually observed, therefore, such a model cannot account for the observed Zn isotope fractionation in tektites. We have developed a more realistic model of evaporation of Zn from a molten sphere: during its hypervelocity trajectory, the molten surface of the tektite will be entrained by viscous coupling with air that will then induce a velocity field inside the molten sphere. This velocity field induces significant radial chemical mixing within the tektite that accelerates the evaporation process. Our model, albeit parameter dependent, shows that both the isotopic composition and the chemical abundances measured in tektites can be produced by evaporation in a diffusion-limited regime.  相似文献   

Biochemical indicators for the bioavailability of organic carbon in ground water   总被引：1，自引：0，他引：1  

Chapelle FH  Bradley PM  Goode DJ  Tiedeman C  Lacombe PJ  Kaiser K  Benner R 《Ground water》2009,47(1):108-121

The bioavailability of total organic carbon (TOC) was examined in ground water from two hydrologically distinct aquifers using biochemical indicators widely employed in chemical oceanography. Concentrations of total hydrolyzable neutral sugars (THNS), total hydrolyzable amino acids (THAA), and carbon-normalized percentages of TOC present as THNS and THAA (referred to as "yields") were assessed as indicators of bioavailability. A shallow coastal plain aquifer in Kings Bay, Georgia, was characterized by relatively high concentrations (425 to 1492 μM; 5.1 to 17.9 mg/L) of TOC but relatively low THNS and THAA yields (∼0.2%–1.0%). These low yields are consistent with the highly biodegraded nature of TOC mobilized from relatively ancient (Pleistocene) sediments overlying the aquifer. In contrast, a shallow fractured rock aquifer in West Trenton, New Jersey, exhibited lower TOC concentrations (47 to 325 μM; 0.6 to 3.9 mg/L) but higher THNS and THAA yields (∼1% to 4%). These higher yields were consistent with the younger, and thus more bioavailable, TOC being mobilized from modern soils overlying the aquifer. Consistent with these apparent differences in TOC bioavailability, no significant correlation between TOC and dissolved inorganic carbon (DIC), a product of organic carbon mineralization, was observed at Kings Bay, whereas a strong correlation was observed at West Trenton. In contrast to TOC, THNS and THAA concentrations were observed to correlate with DIC at the Kings Bay site. These observations suggest that biochemical indicators such as THNS and THAA may provide information concerning the bioavailability of organic carbon present in ground water that is not available from TOC measurements alone.  相似文献   

Mesoscale slope current variability in the Gulf of Lions. Interpretation of in-situ measurements using a three-dimensional model     

Gaël André  Pierre Garreau  Philippe Fraunie 《Continental Shelf Research》2009

The ECOLOPHY experiments aimed at investigating physical exchanges between coastal and open sea. They were carried out in June and December 2005 over the shelf-break in the North-eastern part of the Gulf of Lions (Northwestern Mediterranean Sea). This area is considered to be the generation zone for the eddy and meandering structures of the Northern Current (NC). The objective of the present work is to examine mesoscale variability of this coastal slope current in the light of available data. Numerical modeling is used to support the field data analysis. ADCP current measurements over a one-year period show that mesoscale activity is maximal in late winter, correlating with the seasonal variability of the NC and, also, partly with local winds. Measured currents exhibit mesoscale fluctuations with periods ranging from 3 to 30 days, in agreement with previous analyses. Fluctuations of periods longer than 10 days are found to be mainly oriented in the direction of the mean current, whereas more frequently observed high frequency fluctuations tend to be oriented cross-slope, suggesting a relationship with the NC mesoscale meandering. Moreover, trajectories of surdrift buoys launched in the NC vein exhibit mesoscale phenomena, such as current meanders or eddies and on-shelf intrusions. Numerical modeling provides a synoptic point of view and is used hereafter to support physical interpretation of punctual eulerian or lagrangian measurements. Therefore, modeled hydrodynamic fields are used to analyze surdrift buoy trajectories and computed vertically averaged current and Ertel potential vorticity provide a better understanding of these behaviors.  相似文献   

Recent occurrence of large jökulhlaups at Lake Tuborg,Ellesmere Island,Nunavut     

Ted Lewis  Pierre Francus  Raymond S. Bradley 《Journal of Paleolimnology》2009,41(3):491-506

The varved sediment record from glacially-fed Lake Tuborg, Ellesmere Island, Nunavut, shows that only three large jökulhlaups have occurred there in the last millennium: 2003, 1993, and 1960. Detailed analyses of sediment microstructure and particle size, combined with in-situ hydrometeorological and limnological process studies, allowed jökulhlaup facies identification and discrimination from deposits from other processes. Deposits from large jökulhlaups are anomalously thick, typically lack internal structure, have sharp bases, and fine upwards. The ice-dammed lake above Lake Tuborg (the source of the jökulhlaups) likely changed its drainage style in 1960, from ice-dam overtopping to ice-dam flotation and glacial tunnel enlargement by melt widening, which allowed the lake to drain completely and catastrophically. Complete drainage of ice-dammed lakes by ice-dam flotation is rare in the region is due to the pervasiveness of cold-based ice. Twentieth century warming is likely responsible for some combination of dam thinning, lake expansion and deepening, and changing the thermal regime at the base of the dam. Anomalously thick individual varves were periodically deposited beginning in the nineteenth century, and their thickness increased with time. This likely reflects a combination of increased ice dam overtopping, subaqueous slope failures, sediment availability and rising air temperature. The varve record presented here significantly correlates with a previous, shorter record from Lake Tuborg. However, generally weak correlations are found between the new varve time series, regional records of air temperature, and glacial melt from ice cores on the Agassiz Ice Cap. It is hypothesized that on short timescales, sedimentation at the coring location reflects a complex and varying integration of multiple hydroclimatic, geomorphic and limnologic influences.  相似文献   

Assessing the value of GODAE products in coastal and shelf seas     

Pierre De Mey  Roger Proctor 《Ocean Dynamics》2009,59(1):1-2

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Multiple Well-Shutdown Tests and Site-Scale Flow Simulation in Fractured Rocks     

Claire R. Tiedeman  Pierre J. Lacombe  Daniel J. Goode 《Ground water》2010,48(3):401-415

A new method was developed for conducting aquifer tests in fractured-rock flow systems that have a pump-and-treat (P&T) operation for containing and removing groundwater contaminants. The method involves temporary shutdown of individual pumps in wells of the P&T system. Conducting aquifer tests in this manner has several advantages, including (1) no additional contaminated water is withdrawn, and (2) hydraulic containment of contaminants remains largely intact because pumping continues at most wells. The well-shutdown test method was applied at the former Naval Air Warfare Center (NAWC), West Trenton, New Jersey, where a P&T operation is designed to contain and remove trichloroethene and its daughter products in the dipping fractured sedimentary rocks underlying the site. The detailed site-scale subsurface geologic stratigraphy, a three-dimensional MODFLOW model, and inverse methods in UCODE_2005 were used to analyze the shutdown tests. In the model, a deterministic method was used for representing the highly heterogeneous hydraulic conductivity distribution and simulations were conducted using an equivalent porous media method. This approach was very successful for simulating the shutdown tests, contrary to a common perception that flow in fractured rocks must be simulated using a stochastic or discrete fracture representation of heterogeneity. Use of inverse methods to simultaneously calibrate the model to the multiple shutdown tests was integral to the effectiveness of the approach.  相似文献   

Estimation of grain size variability with micro X-ray fluorescence in laminated lacustrine sediments,Cape Bounty,Canadian High Arctic   总被引：4，自引：0，他引：4  

Stéphanie Cuven  Pierre Francus  Scott F. Lamoureux 《Journal of Paleolimnology》2010,44(3):803-817

Finely laminated sediment cores from two Arctic lakes were investigated using the Itrax™ Core Scanner that provides micro X-ray fluorescence (μ-XRF) measurements with a spatial resolution of 100 μm. We compared these chemical measurements with standard geochemical methods using, at the macroscopic scale, inductively coupled plasma–atomic emission spectrometry (ICP-AES) and, at the microscopic scale, energy dispersive spectroscopy (EDS). We also investigated the relationship between the chemical profiles and the grain size of sediments at macro-scale using laser particle-size analysis, and at microscopic scale, using thin section image analysis techniques. Results show a link between grain size and the relative abundance of several elements. Silicon and zirconium are associated with very coarse silt and sand deposits, K and Fe with clay-rich layers, and Ti with silty facies. Four sedimentary facies are characterised based on sedimentary structure and texture, and interpreted in terms of known seasonal hydroclimatic processes. We show that is possible to identify these sedimentary facies using μ-XRF element abundance or ratio variations. The K/Ti ratio is the best marker of the upper varve boundary, and it might be used for varve identification and counting of Cape Bounty sediments in future. More generally, this study demonstrates new applications for paleohydrological reconstructions from laminated sediments.  相似文献   

ERORUN-STAFOR: A collaborative observatory for the multidisciplinary study of the critical zone processes in a tropical volcanic watershed including a Tropical Montane Cloud Forest     

Alix Toulier  Jean-Lambert Join  Pierre Staménoff  Yoan Benoit  Geneviève Lebeau  Maxime Gautier  Caroline Gorge  Eric Gayer  Emmanuel Cordier  Victor Kbidi  Guillaume Payen  Magali David  Sophie Ferreira  François Bonnardot  Julien Bonnier  Stéphane Martel  Jimmy Gonthier  Emilie Roulleau  Jean-Pierre Cammas  Dominique Strasberg  Olivier Flores  Fabrice R. Fontaine  Thomas Giambelluca  Claudine Ah-Peng 《水文研究》2024,38(2):e15061

Tropical volcanic islands are biodiversity hotspots where the Critical Zone (CZ) still remains poorly studied. In such steep topographic environments associated with extreme climatic events (cyclones), deployment and maintenance of monitoring equipment is highly challenging. While a few Critical Zone Observatories (CZOS) are located in tropical volcanic regions, none of them includes a Tropical Montane Cloud Forest (TMCF) at the watershed scale. We present here the dataset of the first observatory from the French network of critical zone observatories (OZCAR) located in an insular tropical and volcanic context, integrating a ‘Tropical Montane Cloud Forest’: The ERORUN-STAFOR observatory. This collaborative observatory is located in the northern part of La Réunion island (Indian Ocean) within the 45.0 km² watershed of Rivière des Pluies (i.e., Rainfall river) which hosts the TMCF of Plaines des Fougères, one of the best preserved natural habitats in La Réunion Island. Since 2014, the ERORUN-STAFOR monitoring in collaboration with local partners collected a multidisciplinary dataset with a constant improvement of the instrumentation over time. At the watershed scale and in its vicinity, the ERORUN-STAFOR observatory includes 10 measurement stations covering the upstream, midstream and downstream part of the watershed. The stations record a total of 48 different variables through continuous (sensors) or periodic (sampling) monitoring. The dataset consists of continuous time series variables related to (i) meteorology, including precipitation, air temperature, relative humidity, wind speed and direction, net radiation, atmospheric pressure, cloud water flux, irradiance, leaf wetness and soil temperature, (ii) hydrology, including water level and temperature, discharge and electrical conductivity (EC) of stream, (iii) hydrogeology, including (ground)water level, water temperature and EC in two piezometers and one horizontally drilled groundwater gallery completed by soil moisture measurements under the canopy. The dataset is completed by periodic time series variables related to (iv) hydrogeochemistry, including field parameters and water analysis results. The periodic sampling survey provides chemical and isotopic compositions of rainfall, groundwater, and stream water at different locations of this watershed. The ERORUN-STAFOR monitoring dataset extends from 2014 to 2022 with an acquisition frequency from 10 min to hourly for the sensor variables and from weekly to monthly frequency for the sampling. Despite the frequent maintenance of the monitoring sites, several data gaps exist due to the remote location of some sites and instrument destruction by cyclones. Preliminary results show that the Rivière des Pluies watershed is characterized by high annual precipitation (>3000 mm y⁻¹) and a fast hydrologic response to precipitation (≈2 h basin lag time). The long-term evolution of the deep groundwater recharge is mainly driven by the occurrence of cyclone events with a seasonal groundwater response. The water chemical results support existing hydrogeological conceptual models suggesting a deep infiltration of the upstream infiltrated rainfall. The TMCF of Plaine des Fougères shows a high water storage capacity (>2000% for the Bryophytes) that makes this one a significant input of water to groundwater recharge which still needs to be quantified. This observatory is a unique research site in an insular volcanic tropical environment offering three windows of observation for the study of critical zone processes through upstream-midstream-downstream measurements sites. This high-resolution dataset is valuable to assess the response of volcanic tropical watersheds and aquifers at both event and long-term scales (i.e., global change). It will also provide insights in the hydrogeological conceptual model of volcanic islands, including the significant role of the TMCFs in the recharge processes as well as the watershed hydrosedimentary responses to extreme climatic events and their respective evolution under changing climatic conditions. All data sets are available at https://doi.org/10.5281/zenodo.7983138 .  相似文献   

Effects of persistent organic pollutants on the thyroid function of the European sea bass (Dicentrarchus labrax) from the Aegean sea, is it an endocrine disruption?     

Schnitzler JG  Koutrakis E  Siebert U  Thomé JP  Das K 《Marine pollution bulletin》2008,56(10):1755-1764

We evaluated the alterations of organochlorinated compounds such as polychlorobiphenyls (PCB), dichloro-diphenyl-dichloroethylene (DDE) and dichloro-diphenyl-trichloroethane (DDT) on the thyroid in wild and cultured sea bass (Dicentrarchus labrax) at environmental concentrations. These compounds influence the endocrine system of many fish species and are qualified as endocrine disruptors. The thyroid seems to be a target organ. Two alteration endpoints: the thyroid histology and the muscular thyroid hormone concentrations, were used simultaneously.High concentrations in PCBs and DDT were detected in muscles, supporting the idea that the Mediterranean fauna could be more polluted than the Atlantic fauna. The high abundance of DDE indicates a progressive degradation of remnant DDT load and the absence of new inputs in this area. Aquaculture sea bass shows a significant higher amount of pollutants on fresh weight basis (especially PCBs) in their muscles compared to the wild sea bass. Those differences may be related mainly to the contaminations of diet.Thyroid parameters vary between wild and aquaculture sea bass, wild sea bass were characterized by higher follicle diameters, epithelial cell heights and muscular T₄ concentrations. A significant relationship between persistent organic pollutants (muscular PCBs and DDT concentration) and the different thyroid parameters (diameters of follicles, epithelial cell heights and muscular T₄ levels) could be observed, which support the hypothesis that these compounds have an adverse impact on thyroid morphometry and function.  相似文献   

L'extension à Madagascar du Néogène à l'Actuel: arguments structuraux et géophysiques     

Alain Piqu  Edgard Laville  Pierre Chotin  Jean Chorowicz  Solofo Rakotondraompiana  Catherine Thouin 《Journal of African Earth Sciences》1999,28(4):975-983

Field studies and observations from aerial photographs, remote sensing and numerical field models show that the Meso-Cenozoic and Recent sedimentary sequences of Madagascar are affected by normal faults. These faults, north-south, north-northeast-south-southwest and north-northwest-south-southwest trending, are responsible for the following morphological effects: scarps, block tilting and opening of faulted basins, the most important of which being the Lake Alaotra Basin. The general orientation of these brittle structures and some observations in the field show tha the horizontal maximum extension isroughly east-west directed. Other lines of evidence, seismic and gravimetric, confirm that Madagascar is presently submitted to a crustal and lithospheric extension, parallel to that in East Africa and the Mozambique Channel.  相似文献