bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evolution of the microstructure and crystallographic orientation during shell growth in Psilunio littoralis and Nautilus belauensis
Authors: Alvarez-Lloret P. , Rodriguez-Navarro A. B. , Checa A. G. 
Published: August 2008

AbstractThin sections of shells from different species of mollusc have been analysed by X-ray synchrotron diffraction using the BM16 at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. A sequence of 2-D X-ray diffraction patterns were acquired in transmission mode at regular intervals across the shell thickness. From the 2D patterns, 2θ- and χ-scans were calculatedan d analysed. We studied the evolution of the shell microstructures by analysing several parameters from calculated scans: (1) the intensity of the most intense aragonite reflections in the calculated 2θ scans; (2) the crystallinity calculated from the full width at half maximum values of the main reflections in those scans; and (3) the degree of orientation of crystals, measured from the angular width (in angle) of the arches displayed in the Debye-Scherrer rings which appeared in the 2D diffraction patterns. The determined parameters displayed sharp changes at the transitions between microstructurally distinct shell layers indicating that the microstructural switch occurred very rapidly and was precisely controlled.
Applications of time-resolved synchrotron X-ray diffraction to cation exchange, crystal growth and biomineralization reactions
Authors: Heaney P. J. , Post J. E. , Fischer T. B. , Hummer D. R. , Lopano C. L. , Wall A. J. 
Published: August 2008

AbstractAdvances in the design of environmental reaction cells and in the collection of X-ray diffraction data are transforming our ability to study mineral-fluid interactions. The resulting increase in time resolution now allows for the determination of rate laws for mineral reactions that are coupled to atomic-scale changes in crystal structure. Here we address the extension of time-resolved synchrotron diffraction techniques to four areas of critical importance to the cycling of metals in soils: (1) cation exchange; (2) biomineralization; (3) stable isotope fractionation during redox reactions; and (4) nucleation and growth of nanoscale oxyhydroxides.
Reduction of antimony by nano-particulate magnetite and mackinawite
Authors: Kirsch R. , Scheinost A. C. , Rossberg A. , Banerjee D. , Charlet L. 
Published: August 2008

AbstractThe speciation of antimony is strongly influenced by its oxidation state (V, III, 0, —III). Redox processes under anaerobic groundwater conditions may therefore greatly alter the environmental behaviour of Sb. Employing X-ray absorption and photoelectron spectroscopy, we show here that Sb(V) is reduced to Sb(III) by magnetite and mackinawite, two ubiquitous Fe(II)-containing minerals, while Sb(III) is not reduced further. At the surface of magnetite, Sb(III) forms a highly symmetrical sorption complex at the position otherwise occupied by tetrahedral Fe(III). The Sb(V) reduction increases with pH, and at pH values >6.5 Sb(V) is completely reduced to Sb(III) within 30 days. In contrast, at the mackinawite surface, Sb(V) is completely reduced across a wide pH range and within 1 h. The Sb(V) reduction proceeds solely by oxidation of surface Fe(II), while the oxidation state of sulphide is conserved. Independent of whether Sb(V) or Sb(III) was added, an amorphous or nano-particulate SbS3-like solid formed.
Weathering, soil formation and initial ecosystem evolution on a glacier forefield: a case study from the Damma Glacier, Switzerland
Authors: Bernasconi S. M. ,   Biglink Project Members
Published: August 2008

AbstractThe understanding of biogeochemical processes at the interface between geosphere, hydrosphere and biosphere is of paramount importance for many questions related to global climate and environmental change at very different time and spatial scales. In addition, soils are the principal resource for food production and the understanding of soil formation processes and biological interactions within soils is indispensable for the development of sustainable land-use strategies. In this contribution we present a research initiative, the multidisciplinary ‘BigLink’ Project, aiming at a better understanding of the links between weathering, soil formation and ecosystem evolution and how these biosphere-geosphere interactions are influenced (and themselves influence) climate and environmental change.
The first environmental science experiments on the new microfocus spectroscopy beamline at Diamond
Authors: Mosselmans J. F. W. , Quinn P. D. , Roque Rosell J. , Atkinson K. D. , Dent A. J. , Cavill S. I. , Hodson M. E. , Kirk C. A. , Schofield P. F. 
Published: August 2008

AbstractSynchrotron based μ-XRF, μ-XAS and μ-XRD have made a major impact in the field of environmental science in the last ten years. One of the first seven ‘day one’ beamlines on the Diamond Light Source is a microfocus spectroscopy beamline, beamline I18. Here the current status of the beamline and the opportunities it presents in the field of environmental science are described, with results from two of the first experiments also included. The first is based on the use of bonemeal to remediate soil. We used Zn K-edge and Pb L3-edge spectroscopy to characterize the speciation of these two elements on a soil after bonemeal treatment. The results are compared with bulk measurements taken on the whole soil and standard materials. The second experiment described here is a study of the speciation and association of Ni in a laterite from Moa Bay, Cuba. Here the differences in the Ni speciation associated with Mn oxides are examined and compared with Fe oxides phases.
Microscopy and spectroscopy with X-rays for studies in the environmental sciences
Authors: Thieme J. , Gleber S.-C. , Guttmann P. , Prietzel J. , McNulty I. , Coates J. 
Published: August 2008

AbstractX-ray spectromicroscopy is a powerful tool for addressing key questions in the environmental sciences due to its high spectral and spatial resolution. It has been used successfully for material research, biology and environmental studies, e.g. in the form of μ-X-ray fluorescence and spectromicroscopy with a spatial resolution of <100 nm. With the combination of high-resolution microscopy and spectroscopy it is possible to determine elemental composition as well as chemical speciation, and also identify trace elements to nm-resolution. Samples from soils and groundwater aquifers have been imaged to visualize the appearance of structures on the nm- and μm-scale. The effectof changing chemical conditions in an aqueous environment on the appearance of these structures has been imaged and evaluated. Clay dispersions, microhabitats and morphological effects of biologically-induced redox changes of humic substances have been imaged tomographically, conveying a detailed threedimensional presentation of the specimen structure. Using the spectromicroscopy potential, the distribution of organic and inorganic components, as well as different inorganic components, has been studied. Spectra were analysed for major chemical constituents and were used, for example, to assess differentsulphur species in an entire soil profile.
Transformation of ferrihydrite to hematite: anin situinvestigation on the kinetics and mechanisms
Authors: Vu H. P. , Shaw S. , Benning L. G. 
Published: August 2008

AbstractThe kinetics and mechanisms of the transformation of 2-line ferrihydrite (FH) to hematite (HM), in the presence of Pb at elevated temperatures and high pH condition, were elucidated using synchrotron-based,in situenergy dispersive X-ray diffraction (EDXRD). The time-resolved diffraction data indicated that HM crystallization occurred via a two-stage process. Based on the EDXRD data, combined with high-resolution electron microscopic images, an aqueous-aided 2D growth mechanism is proposed for both HM crystallization stages.
Biological control over the formation and storage of amorphous calcium carbonate by earthworms
Authors: Briones M. J. I. , López E. , Méndez J. , Rodríguez J. B. , Gago-Duport L. 
Published: August 2008

AbstractThe earthworm calciferous gland produces a concentrated suspension of calcium carbonate and in certain species precipitates as concretions of CaCO3, which then enter the soil. Here we investigated the initial stages of CaCO3 formation in the earthworm Lumbricus friendi by means of Fourier transform infrared and electron microscopy techniques (field-emission scanning electron microscopy, transmission electron microscopy, high resolution electron microscopy and selected area electron diffraction). In addition, comparisons between the IR spectra of the water-dissolved carbonic anhydrase (CA) and the glandular secretion (‘milky fluid’) were performed in order to investigate the mechanisms involved in CaCO3 precipitation. Our results strongly suggest that carbonation starts with the dissolved CO2, which is transformed via deprotonation to HCO3-, then to CO32- and finally to amorphous calcium carbonate (ACC). While ACC stabilization takes place under the biological control, further transformation stages leading to calcite concretions seem to be inorganically driven by an Ostwald ripening process.
Distribution of sulphated polysaccharides within calcareous biominerals suggests a widely shared two-step crystallization process for the microstructural growth units
Authors: Cuif J. P. , Dauphin Y. , Farre B. , Nehrke G. , Nouet J. , Salomé M. 
Published: August 2008

AbstractSynchrotron-based XANES characterization of sulphated sulphur combined with atomic force microscopy and transmission electron microscopy (imaging and diffraction) allow insights into the crystallization of the calcareous units produced by invertebrates. As a result of a series of converging data, reticulate crystallization of the amorphous Ca-carbonate molecules conveyed to the micron-thick growth layer by the sumicrometric organo-mineral units seems a reasonable hypothesis, providing us with a method of explaining the multiple and taxonomy-linked ‘vital effects’ which have long been recognized among the calcareous biocrystals.
The nanostructural unity of Mollusc shells
Authors: Dauphin Y. 
Published: August 2008

AbstractCalcite and aragonite shell layers of the main classes of Molluscs are composed of monocrystalline units (prisms, tablets, laths or fibres). Scanning electron and atomic force microscopy studies show these units are composed of small round granules with a thin cortex (amorphous calcium carbonate and/or organic matrix). These granules are organo-mineral composites. A comparison of the size and shape of the granules in different taxa (Mollusca, Brachiopoda) suggests a possible relationship with taxonomy and/or phylogeny.
Biocalcification by Emiliania huxleyi in batch culture experiments
Authors: de Bodt C. , Harlay J. , Chou L. 
Published: August 2008

AbstractCoccolithophores, among which Emiliania huxleyi is the most abundant and widespread species, are considered the most productive calcifying organism on earth. The export of organic carbon and calcification are the main drivers of the biological CO2 pump and are expected to change with oceanic acidification. Coccolithophores are further known to produce transparent exopolymer particles (TEP) that promote particle aggregation. As a result, the TEP and biogenic calcium carbonate (CaCO3) contribute to the export of carbon from the surface ocean to deep waters. In this context, we followed the development and the decline of E. huxleyi using batch experiments with monospecific cultures. We studied the link between different processes such as photosynthesis, calcification and the production of TEP. The onset of calcification was delayed in relation to photosynthesis. The timing and the general feature of the dynamics of calcification were closely related to the saturation state of seawater with respect to calcite, Ωcal. The production of TEP was enhanced after the decline of phytoplankton growth. After nutrient exhaustion, particulate organic carbon (POC) concentration increased linearly with increasing TEP concentration, suggesting that TEP contributes to the POC increase. The production of CaCO3 is also strongly correlated with that of TEP, suggesting that calcification may be considered as a source of TEP precursors.
Terrestrial plant-Si and environmental changes
Authors: Meunier J. D. , Guntzer F. , Kirman S. , Keller C. 
Published: August 2008

AbstractThe importance of silica in terrestrial land plants has been recognized since the middle of the 19th century with applications in agronomy and palaeovegetation reconstruction. In this presentation, we will review the latest advances in our understanding of phytolith formation and present a few examples of applications in the field of global environmental changes.
Exploring the role of ions and amino acids in directing the growth of minerals from solution
Authors: Piana S. , Jones F. , Taylor Z. , Raiteri P. , Gale J. D. 
Published: August 2008

AbstractThe influence of both sulphate ions and aspartic acid on directing the growth of baryte has been explored using computer simulation. Both species are found to significantly reduce the activation free-energy to growth under appropriate conditions, with the influence of sulphate being surface specific. This offers the potential for a new approach to morphology control without inhibition that may have implications for biomineralization.
Dehydration behaviour of the Ca(SO4,HPO4).2H2O solid solution
Authors: Pinto A. J. , Jimenez A. , Prieto M. 
Published: August 2008

AbstractGypsum (CaSO4·2H2O) and brushite (CaHPO4·2H2O) are minerals with similar structures, despite not being isostructural. They both belong to the monoclinic system, but crystallize in different space groups. It is known that, to some extent, phosphate and sulphate groups can substitute for each other within the structure of these minerals. In the present work, the dehydration behaviour of experimentally produced Ca(SO4,HPO4)·2H2O solid solutions is assessed from thermogravimetrical (TG and DTG) and differential scanning calorimetry (DSC) analyses. For the applied experimental conditions it was not possible to obtain homogenous precipitates with compositions within 0.27 < XBr < 0.53, where XBr is the brushite mole fraction. The results reveal that the dehydration behaviour of solid solutions with compositions within the 0 < XBr < 0.27 interval tend to approach the dehydration process of pure gypsum. On the other hand, solid solutions with compositions within 0.53 < XBr < 1 involve higher dehydration temperatures than the brushite end-member, in a two-step process.
How to make ‘stable’ ACC: protocol and preliminary structural characterization
Authors: Rodriguez-Blanco J. D. , Shaw S. , Benning L. G. 
Published: August 2008

AbstractA reproducible and simple protocol to synthesize and stabilize the metastable CaCO3·nH2O phase termed amorphous calcium carbonate (ACC) was developed in order to allow the characterization of its structure at the nanoscale using high-resolution microscopy combined with Raman spectroscopy and X-ray diffraction. ‘Stable’ ACC consists of relatively smooth spherical particles, 50—200 nm in size, that have XRD and Raman patterns with no intense peaks or sharp bands, as expected from amorphous material. Furthermore, high-resolution imaging also supports this finding but in addition, beam-damage induced crystallization and the concomitant formation of locally ordered domains in the ACC spheres are discussed.
The size and polydispersity of silica nanoparticles under simulated hot spring conditions
Authors: Tobler D. J. , Benning L. G. , Knapp J. 
Published: August 2008

AbstractThe nucleation and growth of silica nanoparticles in supersaturated geothermal waters was simulated using a flow-through geothermal simulator system. The effect of silica concentration ([SiO2]), ionic strength (IS), temperature (T) and organic additives on the size and polydispersity of the forming silica nanoparticles was quantified. A decrease in temperature (58 to 33°C) and the addition of glucose restricted particle growth to sizes <20 nm, while varying [SiO2] or ISdid not affect the size (30—35 nm) and polydispersity (±9 nm) observed at 58°C. Conversely, the addition of xanthan gum induced the development of thin films that enhanced silica aggregation.
Simulations of monosaccharide on calcite surfaces
Authors: Yang M. , Harding J. , Stipp S. L. S. 
Published: August 2008

AbstractOrganic molecules control calcite growth byadsorbing preferentiallyonto particular surfaces of the crystal. Adsorption of a monosaccharide (-galactose) on various calcite surfaces has been simulated with molecular dynamics. The calculations of Z-density, mean square displacement (MSD) and adsorption energyindicate that the adsorption of monosaccharide on the acute-stepped calcite (31.8) surface is more favourable than that on the obtuse-stepped (31.16) surface, which suggests that monosaccharides maybe able to selectivelycover some surfaces, inhibit crystal growth on these surfaces, and as a result shape the calcite crystals as seen in biominerals, e.g. coccoliths.
Global sensitivity of weathering rates to atmospheric CO2 under the assumption of saturated river discharge
Authors: Arens S. , Kleidon A. 
Published: August 2008

AbstractThe sensitivity of the global river-borne flux of Ca2+ to atmospheric pCO2 was obtained from model simulations under the assumption of saturation of CaCO3. The response was subdivided into contributions from changes in runoff, temperature and partial CO2 pressure and these were then used to parameterize the different direct and indirect effects of a changing climate on carbonate weathering and equilibria. The parameterizations are comparable/compatible to those of Walker et al. (1981) for silicate weathering, but are taken directly from models demonstrating the potential of this approach in weathering studies.
Changes in the flux of Saharan dust to the East Mediterranean Sea since the last glacial maximum as observed through Sr-isotope geochemistry
Authors: Box M. R. , Krom M. D. , Cliff R. , Almogi-Labin A. , Bar-Matthews M. , Ayalon A. , Schillman B. , Paterne M. 
Published: August 2008

AbstractWe present a dust flux (g m-2yr-1) record for the East Mediterranean Sea constructed using 87Sr/86Sr ratio measurements on the fine fraction of carbonate-free sediment from core 9501 from the north Levantine basin. The Saharan dust flux profile shows a first order correspondence with Atlantic dust-flux records in showing: (1) small dust fluxes during the last glacial maximum, a dust pulse associated with the Heinrich 1 (H1) event; (2) a small peak corresponding with the younger dryas (YD); (3) a decrease during the African Humid Period (AHP); and (4) an abrupt return to dustier conditions between ~5.7—5.2 ky BP.
U-series constraints on aquifer groundwater residence time: the Adour-Garonne district case (southwest France)
Authors: Innocent C. , Négrel P. 
Published: August 2008

AbstractU-series were investigated in groundwaters from two water bodies of the Eocene sands aquifer, southwest France. The 234U/238U activity ratios are always larger than the equilibrium value, some waters being highly enriched in 234U (as large as 13.5). In the southern water body, 234U/238U ratios correlate with 14C ages (with one exception). Such U isotopic signatures may allow the evaluation of the residence time of groundwaters within their aquifer using an open-system model based on U activity ratios and concentrations. It is suggested that the ‘oldest’ groundwaters from the southern water body are no older than 38 ky, whereas the maximum ‘age’ of groundwaters from the northern water body, though overall of the same order of magnitude, could be slightly younger (25 ky).
Chemostatic modes of the ocean-atmosphere-sediment system through Phanerozoic time
Authors: Mackenzie F. T. , Arvidson R. S. , Guidry M. 
Published: August 2008

AbstractThe essential state of the Phanerozoic ocean-atmosphere system with respect to major lithophile and organic components can be bounded by sedimentary observational data and relatively few model assumptions. The model assumptions are in turn sufficient to constrain and compute the remaining fluxes that result in a comprehensive model describing atmospheric and oceanic evolutionary history over the past 500 m.y. that is in accord with the sedimentary observational data. Two central themes emerge. First, there is a strong coupling of the state of various reservoirs throughout the entire system imposed mainly by negative physical, chemical and biological feedbacks. Second, there is a significant overprint of ‘physical’ processes, such as weathering, by biologically-mediated processes and ecosystem evolution. Ultimately, the Phanerozoic is characterized by two modes of seawater major-ion chemistry, pH and carbonate saturation state, and atmospheric CO2. Importantly, the transition between these two modes may result from the previous state of the system whose impacts lag by tens of millions of years. Thus, the instantaneous state of the system at any given point in time may reflect in part the ‘memory’ ofa previous period when fluxes and processes were not in balance. The modern-day problem of ocean acidification mainly reflects the fact that human activities of fossil fuel burning and land use changes are resulting in geologically rapid releases of CO2 to the atmosphere and its absorption by the surface ocean and does not reflect the longer term processes and feedbacks that led to the acidic oceans of the past.
Controlled biomineralization of magnetite (Fe3O4) by Magnetospirillum gryphiswaldense
Authors: Moisescu C. , Bonneville S. , Tobler D. , Ardelean I. , Benning L. G. 
Published: August 2008

AbstractResults from a study of the chemical composition and micro-structural characteristics of bacterial magnetosomes extracted from the magnetotactic bacterial strain Magnetospirillum gryphiswaldense are presented here. Using high-resolution transmission electron microscopy combined with selected-area electron diffraction and energy dispersive X-ray microanalysis, biogenic magnetite particles isolated from mature cultures were analysed for variations in crystallinity and particle size, as well as chain character and length. The analysed crystals showed a narrow size range (~14—67 nm) with an average diameter of 46±6.8 nm, cuboctahedral morphologies and typical Gamma type crystal size distributions. The magnetite particles exhibited a high chemical purity (exclusively Fe3O4) and the majority fall within the single-magnetic-domain range.
Variscite dissolution rates in aqueous solution: does variscite control the availability of phosphate in acidic natural waters?
Authors: Roncal-Herrero T. , Oelkers E. H. 
Published: August 2008

AbstractThe dissolution rates of natural well-crystallized variscite (AlPO4.2H2O) were measured from the evolution of aqueous Al and P concentrations in closed and mixed-flow through reactors at 25°C and from 1.5 to 9 pH. Measured dissolution rates decrease with increasing pH from 5.05x10-16 mol/cm2/s at pH = 1.51 to 4.92x10-17 mol/cm2/s at pH = 5.89 and then increase with increasing pH to 1.64x10-17 mol/cm2/s at pH = 8.99. Estimates of the time required to equilibrate a mildly acidic, initially Al- and P-free solution with variscite based on measured dissolution rates and solubility products suggests it takes no more than several weeks to equilibrate this mineral with soil pore fluids. This result suggests that variscite can buffer aqueous phosphate concentrations in a significant number of near surface environments.
Ethanol adsorption on the {104} calcite surface: preliminary observations with atomic force microscopy
Authors: Sand K. K. , Stipp S. L. S. , Hassenkam T. , Yang M. , Cooke D. , Makovicky E. 
Published: August 2008

AbstractPreliminary atomic force microscopy investigations of the {104} calcite surface cleaved in ethanol indicate a different surface behaviour than that of the {104} surface cleaved in air. The results are consistent with recent theoretical studies and suggest strong ordering of ethanol over the termination of the bulk calcite structure.