Changes in Zn speciation during soil formation from Zn-rich limestones     

Olivier Jacquat  Andreas Voegelin  Farid Juillot  Ruben Kretzschmar 《Geochimica et cosmochimica acta》2009,73(19):5554-5571

In order to better understand the long-term speciation and fractionation of Zn in soils, we investigated three soils naturally enriched in Zn (237–864 mg/kg Zn) from the weathering of Zn-rich limestones (40–207 mg/kg Zn) using extended X-ray absorption fine structure (EXAFS) spectroscopy and sequential extractions. The analysis of bulk EXAFS spectra by linear combination fitting (LCF) indicated that Zn in the oolitic limestones was mainly present as Zn-containing calcite (at site Dornach), Zn-containing goethite (Gurnigel) and Zn-containing goethite and sphalerite (Liestal). Correspondingly, extraction of the powdered rocks with 1 M NH₄-acetate at pH 6.0 mobilized only minor fractions of Zn from the Gurnigel and Liestal limestones (<30%), but most Zn from the Dornach rock (81%). In the Dornach soil, part of the Zn released from the dissolving limestone was subsequently incorporated into pedogenic hydroxy-interlayered vermiculite (Zn-HIV, 30%) and Zn-containing kaolinite (30%) and adsorbed or complexed by soil organic and inorganic components (40%). The Gurnigel and Liestal soils contained substantial amounts of Zn-containing goethite (50%) stemming from the parent rock, smaller amounts (20%) of Zn-containing kaolinite (and possibly Zn-HIV), as well as adsorbed or complexed Zn-species (30%). In the soil from Liestal, sphalerite was only found in trace amounts, indicating its dissolution during soil formation. In sequential extractions, large percentages of Zn (55–85%) were extracted in recalcitrant extraction steps, confirming that Zn-HIV, Zn-containing kaolinite and Zn-containing goethite are highly resistant to weathering. These Zn-bearing phases thus represent long-term hosts for Zn in soils over thousands of years. The capability of these phases to immobilize Zn in heavily contaminated soils may however be limited by their uptake capacity (especially HIV and kaolinite) or their abundance in soil.  相似文献   

Arsenite sequestration at the surface of nano-Fe(OH)₂, ferrous-carbonate hydroxide, and green-rust after bioreduction of arsenic-sorbed lepidocrocite by Shewanella putrefaciens     

Georges Ona-Nguema  Guillaume Morin  Yuheng Wang  Farid Juillot  Giuliana Aquilanti  Christian Ruby  François Guyot  Gordon E. Brown Jr. 《Geochimica et cosmochimica acta》2009,73(5):1359-1446

X-ray Absorption Fine Structure (XAFS) spectroscopy was used in combination with high resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), X-ray energy dispersive spectroscopy (XEDS), X-ray powder diffraction, and Mössbauer spectroscopy to obtain detailed information on arsenic and iron speciation in the products of anaerobic reduction of pure and As(V)- or As(III)-adsorbed lepidocrocite (γ-FeOOH) by Shewanella putrefaciens ATCC 12099. We found that this strain of S. putrefaciens is capable of using Fe(III) in lepidocrocite and As(V) in solution or adsorbed on lepidocrocite surfaces as electron acceptors. Bioreduction of lepidocrocite in the absence of arsenic resulted in the formation of hydroxycarbonate green rust 1 [Fe^II₄Fe^III₂(OH)₁₂CO₃: GR1(CO₃)], which completely converted into ferrous-carbonate hydroxide (Fe^II₂(OH)₂CO₃: FCH) over nine months. This study thus provides the first evidence of bacterial reduction of stoichiometric GR1(CO₃) into FCH. Bioreduction of As(III)-adsorbed lepidocrocite also led to the formation of GR1(CO₃) prior to formation of FCH, but the presence of As(III) slows down this transformation, leading to the co-occurrence of both phases after 22-month of aging. At the end of this experiment, As(III) was found to be adsorbed on the surfaces of GR1(CO₃) and FCH. After five months, bioreduction of As(V)-bearing lepidocrocite led directly to the formation of FCH in association with nanometer-sized particles of a minor As-rich Fe(OH)₂ phase, with no evidence for green rust formation. In this five-month experiment, As(V) was fully converted to As(III), which was dominantly sorbed at the surface of the Fe(OH)₂ nanoparticles as oligomers binding to the edges of Fe(OH)₆ octahedra at the edges of the octahedral layers of Fe(OH)₂. These multinuclear As(III) surface complexes are characterized by As-As pairs at a distance of 3.32 ± 0.02 Å and by As-Fe pairs at a distance of 3.50 ± 0.02 Å and represent a new type of As(III) surface complex. Chemical analyses show that the majority of As(III) produced in the experiments with As present is associated with iron-bearing hydroxycarbonate or hydroxide solids, reinforcing the idea that, at least under some circumstances, bacterial reduction can promote As(III) sequestration instead of mobilizing it into solution.  相似文献   

Diurnal variation of electron density in Saturn’s ionosphere: Model comparisons with Saturn Electrostatic Discharge (SED) observations     

Luke Moore  Georg Fischer  Ingo Müller-Wodarg  Marina Galand  Michael Mendillo 《Icarus》2012,221(2):508-516

Using the Saturn Thermosphere Ionosphere Model (STIM), we present a study of the diurnal variation of electron density, with a focus on comparisons with peak electron densities (N_MAX) inferred from the low-frequency cutoff of radio emission due to lightning in the lower atmosphere, called Saturn Electrostatic Discharges (SEDs). It is demonstrated that photochemistry in Saturn’s ionosphere cannot reproduce the SED-inferred diurnal variation in N_MAX unless additional production and loss sources outside of the current best estimates are considered. Additional explanations of the SED-inferred diurnal variation of N_MAX are presented and analyzed, such as the possibility that the low-frequency cutoff seen in SEDs is due to the presence of sharp low-altitude layers of plasma, as frequently seen in radio occultation measurements. Finally, we outline the observational constraints that must be fulfilled by any candidate explanations of the SED-inferred diurnal variation of N_MAX.  相似文献   

Intermediate-mass black holes and ultraluminous X-ray sources in the Cartwheel ring galaxy     

M. Mapelli  B. Moore  L. Giordano  L. Mayer  M. Colpi  E. Ripamonti  S. Callegari 《Monthly notices of the Royal Astronomical Society》2008,383(1):230-246

Chandra and XMM–Newton observations of the Cartwheel galaxy show ∼17 bright X-ray sources  (≳5 × 10³⁸ erg s⁻¹)  , all within the gas-rich outer ring. We explore the hypothesis that these X-ray sources are powered by intermediate-mass black holes (IMBHs) accreting gas or undergoing mass transfer from a stellar companion. To this purpose, we run N -body/smoothed particle hydrodynamics simulations of the galaxy interaction which might have led to the formation of Cartwheel, tracking the dynamical evolution of two different IMBH populations: halo and disc IMBHs. Halo IMBHs cannot account for the observed X-ray sources, as only a few of them cross the outer ring. Instead, more than half of the disc IMBHs are pulled in the outer ring as a consequence of the galaxy collision. However, also in the case of disc IMBHs, accretion from surrounding gas clouds cannot account for the high luminosities of the observed sources. Finally, more than 500 disc IMBHs are required to produce ≲15 X-ray sources via mass transfer from very young stellar companions. Such number of IMBHs is very large and implies extreme assumptions. Thus, the hypothesis that all the observed X-ray sources in Cartwheel are associated with IMBHs is hardly consistent with our simulations, even if it is still possible that IMBHs account for the few (≲1–5) brightest ultraluminous X-ray sources.  相似文献   

Are ring galaxies the ancestors of giant low surface brightness galaxies?     

M. Mapelli  B. Moore  E. Ripamonti  L. Mayer  M. Colpi  L. Giordano 《Monthly notices of the Royal Astronomical Society》2008,383(3):1223-1231

We simulate the collisional formation of a ring galaxy and we integrate its evolution up to 1.5 Gyr after the interaction. About 100–200 Myr after the collision, the simulated galaxy is very similar to observed ring galaxies (e.g. Cartwheel). After this stage, the ring keeps expanding and fades. Approximately 0.5–1 Gyr after the interaction, the disc becomes very large (∼100 kpc) and flat. Such extended discs have been observed only in giant low surface brightness galaxies (GLSBs). We compare various properties of our simulated galaxies (surface brightness profile, morphology, H  i spectrum and rotation curve) with the observations of four well-known GLSBs (UGC 6614, Malin 1, Malin 2 and NGC 7589). The simulations match quite well the observations, suggesting that ring galaxies could be the progenitors of GLSBs. This result is crucial for the cold dark matter (CDM) model, as it was very difficult, so far, to explain the formation of GLSBs within the CDM scenario.  相似文献   

The Norma cluster (ACO 3627) – I. A dynamical analysis of the most massive cluster in the Great Attractor     

P. A. Woudt  R. C. Kraan-Korteweg  J. Lucey  A. P. Fairall  S. A. W. Moore 《Monthly notices of the Royal Astronomical Society》2008,383(2):445-457

A detailed dynamical analysis of the nearby rich Norma cluster (ACO 3627) is presented. From radial velocities of 296 cluster members, we find a mean velocity of 4871 ± 54 km s⁻¹ and a velocity dispersion of 925 km s⁻¹. The mean velocity of the E/S0 population (4979 ± 85 km s⁻¹) is offset with respect to that of the S/Irr population (4812 ± 70 km s⁻¹) by  Δ v = 164 km s⁻¹  in the cluster rest frame. This offset increases towards the core of the cluster. The E/S0 population is free of any detectable substructure and appears relaxed. Its shape is clearly elongated with a position angle that is aligned along the dominant large-scale structures in this region, the so-called Norma wall. The central cD galaxy has a very large peculiar velocity of 561 km s⁻¹ which is most probably related to an ongoing merger at the core of the cluster. The spiral/irregular galaxies reveal a large amount of substructure; two dynamically distinct subgroups within the overall spiral population have been identified, located along the Norma wall elongation. The dynamical mass of the Norma cluster within its Abell radius is  1–1.1 × 10¹⁵  h ⁻¹₇₃ M_⊙  . One of the cluster members, the spiral galaxy WKK 6176 which recently was observed to have a 70 kpc X-ray tail, reveals numerous striking low-brightness filaments pointing away from the cluster centre suggesting strong interaction with the intracluster medium.  相似文献   

A preliminary investigation of siliceous microfossil succession in late Quaternary sediments from Lake Baikal, Siberia     

M. L. Julius  E. F. Stoermer  S. M. Colman  T. C. Moore 《Journal of Paleolimnology》1997,18(2):189-206

Siliceous microfossil assemblage succession was analyzed in a 100 m sediment core from Lake Baikal, Siberia. The core was recovered from the lake's central basin at a water depth of 365 m. Microfossil abundance varied greatly within the intervals sampled, ranging from samples devoid of siliceous microfossils to samples with up to 3.49 × 10¹¹ microfossils g^-1 sediment. Fluctuations in abundance appear to reflect trends in the marine ¹⁸O record, with peak microfossil levels generally representing climate optima. Microfossil taxa present in sampled intervals changed considerably with core depth. Within each sample a small number of endemic diatom species dominated the assemblage. Changes in dominant endemic taxa between sampled intervals ranged from extirpation of some taxa, to shifts in quantitative abundance. Differences in microfossil composition and the association of variations in abundance with climate fluctuations suggest rapid speciation in response to major climatic excursions.  相似文献   

Production of methyl bromide and methyl chloride in laboratory cultures of marine phytoplankton II     

M. G. Scarratt  R. M. Moore 《Marine Chemistry》1998,59(3-4)

Methyl halides (monohalomethanes), especially methyl bromide, are known to contribute significantly to ozone destruction in the stratosphere. Budgets of natural and anthropogenic methyl bromide suggest that marine organisms may be the source of a significant proportion of the total global production. Since phytoplankton are abundant in surface waters, they are obvious candidates. Cultures of nine phytoplankton species were grown in CO₂-enriched, nitrate-limited medium in sealed glass vessels. Species tested include Chaetoceros calcitrans, Isochrysis sp., Porphyridium sp., Synechococcus sp., Phaeodactylum tricornutum, Tetraselmis sp., Prorocentrum sp., Emiliania huxleyi and Phaeocystis sp. Methyl bromide (CH₃Br) and methyl chloride (CH₃Cl) concentrations were determined by bubbling the cultures with high-purity air, cryotrapping the effluent and analyzing it on a gas chromatograph with an electron capture detector. The Phaeocystis sp. samples were monitored with GCMS. Cell population, bacterial population, Chl a, pH, and nitrate concentration were monitored for periods of at least two weeks. CH₃Cl was produced by all cultures. CH₃Br was absent in Tetraselmis sp. and Isochrysis sp. cultures, but present in all the others. Methyl iodide (CH₃I) was present in most cultures but could not be quantified due to analytical limitations. CH₃I and CH₃Br production was fastest in stationary phase and continued long after cell division had ceased. Axeic cultures of Phaeocystis sp. achieved almost identical production rates of CH₃Cl and CH₃Br as xenic cultures of the same species. Species from tropical waters had faster CH₃Cl and CH₃Br production rates than temperate species. Scaling the observed production rates using global standing stock estimates for Chl a and particulate nitrogen indicate that phytoplankton can account for only a fraction of the CH₃Cl and CH₃Br believed to be produced in the ocean. Calculations based on the estimated global biomass of Phaeocystis sp. and E. huxleyi blooms show that their contribution is insignificantly small.  相似文献   

Radiogenic Isotope Geology,by Alan P. Dickin,Cambridge University Press,Cambridge, UK, 1995 (paperback edition, 1997), $95.00 (U.S., cloth), ISBN 0 521 43151 4, $44.96 (U.S., paper), ISBN 0 521 59891 5     

Moore  Willard S. 《Mathematical Geosciences》1999,31(4):487-489

Mathematical Geosciences -  相似文献   

Pre‐drill Groundwater Geochemistry in the Karoo Basin,South Africa          下载免费PDF全文

Jennifer S. Harkness  Kelley Swana  William K. Eymold  Jodie Miller  Ricky Murray  Siep Talma  Colin J. Whyte  Myles T. Moore  Erica L. Maletic  Avner Vengosh  Thomas H. Darrah 《Ground water》2018,56(2):187-203

Enhanced production of unconventional hydrocarbons in the United States has driven interest in natural gas development globally, but simultaneously raised concerns regarding water quantity and quality impacts associated with hydrocarbon extraction. We conducted a pre‐development assessment of groundwater geochemistry in the critically water‐restricted Karoo Basin, South Africa. Twenty‐two springs and groundwater samples were analyzed for major dissolved ions, trace elements, water stable isotopes, strontium and boron isotopes, hydrocarbons and helium composition. The data revealed three end‐members: a deep, saline groundwater with a sodium‐chloride composition, an old, deep freshwater with a sodium‐bicarbonate‐chloride composition and a shallow, calcium‐bicarbonate freshwater. In a few cases, we identified direct mixing of the deep saline water and shallow groundwater. Stable water isotopes indicate that the shallow groundwater was controlled by evaporation in arid conditions, while the saline waters were diluted by apparently fossil meteoric water originated under wetter climatic conditions. These geochemical and isotopic data, in combination with elevated helium levels, suggest that exogenous fluids are the source of the saline groundwater and originated from remnant seawater prior to dilution by old meteoric water combined with further modification by water‐rock interactions. Samples with elevated methane concentrations (>14 ccSTP/kg) were strongly associated with the sodium‐chloride water located near dolerite intrusions, which likely provide a preferential pathway for vertical migration of deeply sourced hydrocarbon‐rich saline waters to the surface. This pre‐drill evaluation indicates that the natural migration of methane‐ and salt‐rich waters provides a source of geogenic contamination to shallow aquifers prior to shale gas development in the Karoo Basin.  相似文献