Iron isotope fractionation between pyrite (FeS₂), hematite (Fe₂O₃) and siderite (FeCO₃): A first-principles density functional theory study     

Marc Blanchard  Franck Poitrasson  Michele Lazzeri  Etienne Balan 《Geochimica et cosmochimica acta》2009,73(21):6565-776

In addition to equilibrium isotopic fractionation factors experimentally derived, theoretical predictions are needed for interpreting isotopic compositions measured on natural samples because they allow exploring more easily a broader range of temperature and composition. For iron isotopes, only aqueous species were studied by first-principles methods and the combination of these data with those obtained by different methods for minerals leads to discrepancies between theoretical and experimental isotopic fractionation factors. In this paper, equilibrium iron isotope fractionation factors for the common minerals pyrite, hematite, and siderite were determined as a function of temperature, using first-principles methods based on the density functional theory (DFT). In these minerals belonging to the sulfide, oxide and carbonate class, iron is present under two different oxidation states and is involved in contrasted types of interatomic bonds. Equilibrium fractionation factors calculated between hematite and siderite compare well with the one estimated from experimental data (ln α⁵⁷Fe/⁵⁴Fe = 4.59 ± 0.30‰ and 5.46 ± 0.63‰ at 20 °C for theoretical and experimental data, respectively) while those for Fe(III)_aq-hematite and Fe(II)_aq-siderite are significantly higher that experimental values. This suggests that the absolute values of the reduced partition functions (β-factors) of aqueous species are not accurate enough to be combined with those calculated for minerals. When compared to previous predictions derived from Mössbauer or INRXS data [Polyakov V. B., Clayton R. N., Horita J. and Mineev S. D. (2007) Equilibrium iron isotope fractionation factors of minerals: reevaluation from the data of nuclear inelastic resonant X-ray scattering and Mössbauer spectroscopy. Geochim. Cosmochim. Acta71, 3833-3846], our iron β-factors are in good agreement for siderite and hematite while a discrepancy is observed for pyrite. However, the detailed investigation of the structural, electronic and vibrational properties of pyrite as well as the study of sulfur isotope fractionation between pyrite and two other sulfides (sphalerite and galena) indicate that DFT-derived β-factors of pyrite are as accurate as for hematite and siderite. We thus suggest that experimental vibrational density of states of pyrite should be re-examined.  相似文献   

Vertical distributions of chlorophyll in deep, warm monomictic lakes   总被引：1，自引：0，他引：1  

David P. Hamilton  Katherine R. O’Brien  Michele A. Burford  Justin D. Brookes  Chris G. McBride 《Aquatic Sciences - Research Across Boundaries》2010,72(3):295-307

The factors affecting vertical distributions of chlorophyll fluorescence were examined in four temperate, warm monomictic lakes. Each of the lakes (maximum depth >80 m) was sampled over 2 years at intervals from monthly to seasonal. Profiles were taken of chlorophyll fluorescence (as a proxy for algal biomass), temperature and irradiance, as well as integrated samples from the surface mixed layer for chlorophyll a (chl a) and nutrient concentrations in each lake. Depth profiles of chlorophyll fluorescence were also made along transects of the longest axis of each lake. Chlorophyll fluorescence maxima occurred at depths closely correlated with euphotic depth (r ² = 0.67, P < 0.01), which varied with nutrient status of the lakes. While seasonal thermal density stratification is a prerequisite for the existence of a deep chlorophyll maximum (DCM), our study provides evidence that the depth of light penetration largely dictates the DCM depth during stratification. Reduction in water clarity through eutrophication can cause a shift in phytoplankton distributions from a DCM in spring or summer to a surface chlorophyll maximum within the surface mixed layer when the depth of the euphotic zone (z _eu) is consistently shallower than the depth of the surface mixed layer (z _SML). Trophic status has a key role in determining vertical distributions of chlorophyll in the four lakes, but does not appear to disrupt the annual cycle of maximum chlorophyll in winter.  相似文献   

Biochemical and microbial features of shallow marine sediments along the Terra Nova Bay (Ross Sea,Antarctica)   总被引：1，自引：0，他引：1  

Franco Baldi  Davide Marchetto  Francesco Pini  Renato Fani  Luigi Michaud  Angelina Lo Giudice  Daniela Berto  Michele Giani 《Continental Shelf Research》2010

Shallow marine sediments were collected from seven stations (three of which located at Gerlache Inlet, two at Tethys Bay, one at Adelie Cove and one just beneath the Italian Research Base) along the Terra Nova Bay coast (Ross Sea, Antarctica). Their chemical, biochemical and microbiological properties were studied in order to provide further insights in the knowledge of this Antarctic benthic ecosystem. Overall, the organic carbon (OC) represented the major fraction of total carbon (TC) and displayed concentrations similar to or slightly lower than those previously measured in Antarctic bottom sediments. The biopolymeric carbon within OC ranged from 4.1% to 19.9% and showed a wide trophic range (65–834 μg g⁻¹ d.w.). Proteins (PRT) represented on average the main biochemical class contributing to labile organic carbon, followed by lipids (LIP) and carbohydrates (CHO). The activity of aminopeptidase, β-d-glucosidase, alkaline phosphatase and esterase was checked, giving the highest values at Tethys Bay and at the deepest water sediments. The principal component analysis, which was computed considering physical, chemical (elemental and biochemical sedimentary composition) and microbiological parameters (including bacterial abundance, ectoenzymatic activities, T-RFs richness and diversity indices), allowed to obtain two main clusters (“Tethys Bay” and “other stations”). Based on data obtained, two representative 16S rRNA clone libraries using samples from Tethys Bay and Gerlache Inlet were constructed. The sequences of 171 clones were compared to those available in public databases to determine their approximate phylogenetic affiliations. Both aerobic and anaerobic bacteria were disclosed, with the majority of them affiliated with the Gamma- and Deltaproteobacteria, Bacteroidetes and Acidobacteria. The occurrence of strictly anaerobic bacteria suggests that sediments might also undergo anoxic conditions that, in turn, could favor the accumulation of PRT in respect to CHO, assuming that fermentation of amino acids is slower than that of sugars from decomposing polysaccharides.  相似文献   

A User-Oriented Methodology for DInSAR Time Series Analysis and Interpretation: Landslides and Subsidence Case Studies     

Davide Notti  Fabiana Calò  Francesca Cigna  Michele Manunta  Gerardo Herrera  Matteo Berti  Claudia Meisina  Deodato Tapete  Francesco Zucca 《Pure and Applied Geophysics》2015,172(11):3081-3105

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Numerical modelling of centrifuge tests on tunnel–soil systems     

Glenda Abate  Maria Rossella Massimino  Michele Maugeri 《Bulletin of Earthquake Engineering》2015,13(7):1927-1951

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Erratum to: Influence of frequency content and amplitude of input motion in DSSI investigated by shaking table tests     

Giovanni Biondi  Maria Rossella Massimino  Michele Maugeri 《Bulletin of Earthquake Engineering》2015,13(6):1871-1871

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Application of direct displacement based design to long span bridges     

Gopal Adhikari  Lorenza Petrini  Gian Michele Calvi 《Bulletin of Earthquake Engineering》2010,8(4):897-919

The paper investigates the applicability of current direct displacement based seismic design (DDBD) procedure, developed by Priestley and his coworkers, for straight long span bridges under transverse seismic excitation synchronous to all supports. This category of bridges often possess some additional features such as massive tall piers, highly irregular distribution of mass and stiffness due to unequal superstructure spans and pier heights, large deformation capacity etc. that are absent in short-to-moderate span bridges for which DDBD has extensively been verified. It is shown that DDBD in its current form is unable to capture both displacement and base shear demand when compared with nonlinear dynamic analysis results. Accordingly, a simple mechanics based extension of the current procedure that takes into account the effect of pier mass while computing base shear demand as well as a modal combination rule for estimating displacement demand is proposed and validated using a series of parametric studies. The new procedure also allows engineer to allocate strength at the potential plastic hinge location in more general terms.  相似文献   

Deciphering the geologic memory of a Permian conglomerate of the Southern Alps by pebble <Emphasis Type="Italic">P</Emphasis>–<Emphasis Type="Italic">T</Emphasis> estimates     

M. Iole Spalla  Davide Zanoni  Guido Gosso  Michele Zucali 《International Journal of Earth Sciences》2009,98(1):203-226

The volcano–clastic sequence of Trompia Valley, which caps the Tre Valli Bresciane Variscan basement (TVB), comprises the Dosso dei Galli Conglomerate (DGC), the oldest deposit containing up to metre-sized metamorphic pebbles. This Lower Permian formation of the Trompia Basin was fed by the erosion products of the Variscan chain. We used microstructural and mineral chemical data on metamorphic pebbles of the DGC to infer a quantitative tectono-thermal evolution of the eroded pre-Permian basement and to compare them with those of TVB and the surrounding Southalpine basement units (tectono-metamorphic units = TMUs). Metapelitic and metaintrusive pebbles record a polyphase metamorphism with two metamorphic re-equilibrations: the first under epidote amphibolite facies (M1, ) and the second under greenschist facies (M2) conditions. Rock types and metamorphic data largely match those of TVB basement unit. The structural and metamorphic records in the pebbles are pre-Permian, and the conglomerate matrix is non-metamorphic. The DGC deposition age (283 ± 1–280.5 ± 2 Ma) constrains the minimal exhumation age of its basement source. The lack of staurolite bearing assemblages in metamorphic pebbles suggests that the DGC basement source was already exhumed to shallow structural levels (greenschist facies conditions) before the thermal equilibration consequent upon continental crust thickening induced by the Variscan collision.  相似文献   

BITS: a SMART indicator for soft-bottom, non-tidal lagoons     

Mistri M  Munari C 《Marine pollution bulletin》2008,56(3):587-599

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The Skin Effect of the Anelastic Earth     

Michele Caputo 《Pure and Applied Geophysics》1999,156(3):371-393

--Assuming that the rheology of the earth's crust is defined by stress-strain relations containing a memory mechanism, it is seen that the stress field and the maximum shear stress (mss), caused by elongated mountain ranges, are limited mostly to the crust. In a geological, relatively short time, where relaxation is reached, the mss assumes the depth distribution (2~x)exp(-2~x) where x is the depth h measured in units of wavelength w of the mountain range; the mss reaches its maximum value, of about 1/3 the surface load, at the depth x = 1/2~ (x = h/w). Contrary to the case of the perfectly elastic earth model, where the mss at the surface is about 0.25 the maximum surface load, in the case of the anelastic earth model the mss is asymptotically nil at the surface and for depths larger than w, the mss is less than 1.2% the maximum surface load. It is seen that the relaxation of the medium causes a rotation of the planes of the mss in a layer near the surface and that, in the case when the surface load is applied periodically, there is a phase shift between the surface load and the stress at depth which is less than four days when the period is one year; it is smaller for shorter periods. It is also seen that the creation of reservoirs lasting a finite time causes a small variation of the mss in the crust which, when the reservoir is removed, leaves a residual mss with maximum at the surface and decreasing exponentially with depth; for a load lasting one year it takes 250 days to reduce to 40% the stress at depth. As a consequence of the residual mss, caused by the load of the topography, after earthquakes the local mss will not drop to zero; this decreases the time required by tectonic forces to release the next earthquake and increases the rate of seismicity.  相似文献