20 search hits
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Proceedings of the International Conference of "Atmospheric Transport and chemistry in Forest Ecosystems" Castle of Thurnau, Germany Oct 5 to Oct 8, 2009
(2009)
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Johannes Lüers
Thomas Foken
- no abstract
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Jahresbericht 2008 zum Förderprojekt 01879, Untersuchung der Veränderung der Konzentration von Luftbeimengungen und Treibhausgasen im hohen Fichtelgebirge
(2009)
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Johannes Lüers
Thomas Foken
- keine Zusammenfassung
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Mesoscale Circulations and Energy and GaS Exchange Over the Tibetan Plateau Documentation of the Micrometeorological Experiment, Nam Tso, Tibet
(2009)
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Tobias Biermann
Wolfgang Babel
Johannes Olesch
Thomas Foken
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Carbon dynamics under natural and manipulated meteorological boundary conditions in a forest and a fen ecosystem
(2009)
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Jan Muhr
- Current climate models predict changes in the amount, intensity, frequency and type of precipitation within this century. These changes are likely to result in an increasing frequency of severe drought periods in summer, causing irregular and extreme drought stress in well-drained soils or a lowering of the water table in water-logged soils. Due to rising temperatures precipitation is more likely to occur as rain rather than snow, resulting in reduced snowpacks in winter. In some regions, this can lead to an increasing frequency of soil frost. In summary, changes in the global water cycle can significantly affect boundary conditions within soils. This thesis investigated the impact of extreme meteorological boundary conditions on CO2 fluxes in two ecosystems in South-eastern Germany. Using a combination of field site manipulation and laboratory experiments we investigated the effects of prolonged summer drought and soil frost on soil C dynamics in a Norway spruce forest. In a minerotrophic fen located nearby, the effect of water table lowering (as a result of summer drought) on ecosystem C dynamics was quantified. Additionally, soil C dynamics at both sites were modeled under current meteorological conditions. For the Norway spruce forest, modeling indicated that soil C turnover predominantly occurred within the organic horizons. During the last decades, the soil has acted as a small sink. The possibility of altered C dynamics at the site due to undocumented liming has to be considered when comparing results presented here to results from other sites. For the fen, modeling revealed that soil C turnover was dominated by processes occurring within the uppermost 15 cm of the peat and that root biomass was a very important soil C stock. Most important, modeling indicated that the fen was turned into a net C source during the last decades, presumably because of disturbance of the hydrological conditions. Results from this fen cannot be regarded as representative for undisturbed peatlands. Soil frost was induced at the forest site by removing the snowpack in the winter of 2005/2006. On the snow removal plots, soil frost occurred down to a depth of at least 15 cm and for several weeks, in contrast to the snow-covered control plots where no soil frost occurred. Soil C losses were significantly reduced not only during the soil frost period but also in the summer of 2006. This phenomenon could be explained by changes in the composition of the microbial community due to soil frost, primarily a reduction of fungal biomass. To investigate the effect of drought on soil C dynamics we experimentally induced prolonged drought at the forest-site by excluding throughfall with a transparent roof during the summers of 2006-2008. Additionally, undisturbed soil columns from the site were subjected to drought in the laboratory. In both experiments, drought reduced total soil C losses in comparison to C losses from a control. This reduction was mainly owed to decreased soil respiration rates during the actual drought period, but water repellency also hindered rewetting of the dry soil, thus further prolonging the period of reduced soil respiration rates. In the past, mobilization of stabilized C due to drying-wetting has been repeatedly discussed as a possibility to actually enhance soil C losses. In the studies presented here, no evidence for this assumption was found. Soil C mineralization rates were reduced during drought and recovery was slow, possibly delayed by water repellency and preferential flow. At the fen site we used two approaches: (i) Experimental lowering of water tables to measure resulting C fluxes in comparison to C fluxes under natural conditions (i.e. control plots), and (ii) repeated measurements under varying natural conditions to be able to later statistically identify the main drivers of CO2 fluxes. We included measurements of C uptake and respiration by aboveground vegetation, thus being able to study ecosystem rather than soil C dynamics at the fen site. In summary, the impact of the water table on CO2 fluxes in and out of the fen ecosystem was minimal. Soil respiration was not affected at all by the manipulative lowering of the water table from ca. 15 cm down to more than 60 cm, most likely due to low substrate quality in deeper peat. Measurements of the natural C dynamics indicate that water table could have an impact on soil respiration within the uppermost 0-15 cm of the soil, but predominantly low water tables during summer under current boundary conditions make it unlikely that further lowered water tables due to climate change will markedly affect soil respiration rates at this site. In summary, CO2 fluxes at the site are presumably very resilient towards an increasing frequency of summer drought resulting in lowering of the water table.
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Iron oxidation in (Mg,Fe)0: Calibration of the Flank method on synthetic samples and applications on natural inclusions from lower mantle diamonds
(2009)
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Micaela Longo
- (Mg,Fe)O ferropericlase is the most common mineral found in diamonds originating in the lower mantle (more than 50% of occurrences). It is well known that the Fe3+ concentration in (Mg,Fe)O is sensitive to oxygen fugacity, even at high pressures. Therefore, the determination of Fe3+/Fetot in such inclusions provides a direct method for investigating lower mantle redox conditions during diamond formation. The goal of the present research is to calibrate the “flank method” by electron microprobe using synthetic (Mg,Fe)O, and then apply the method to determine in situ Fe3+/Fetot in ferropericlase inclusions from lower mantle diamonds. Up to now a calibration of the flank method is available only for garnets. Initially, the flank method was calibrated for garnets to test the reproducibility of the method on the Jeol XA-8200 electron microprobe in use at Bayerisches Geoinstitut. Results showed that for garnets a new calibration curve needs to be established at each working session. Then the flank method was calibrated for the Jeol XA-8200 electron microprobe in use at Bayerisches Geoinstitut for a homogeneous set of (Mg,Fe)O ferropericlase crystals over a wide range of composition (xFe = 2 to 60 at.%) and Fe3+/Fetot (1 to 15%). Samples were obtained by performing high pressure high temperature experiments in a multi anvil apparatus. In order to avoid compositional effects on flank method measurements, the high sample homogeneity was essential. Moreover, the determination of the Fe3+/Fetot ratio needed to be extremely accurate. For this purpose, a more accurate procedure for fitting the Mössbauer spectra of the final set of synthetic (Mg,Fe)O was adopted. The calibration curve determined is Fe2+ = 46.238 + 8.161 * ln (Fetot) - 137.01 * (Lbeta/Lalpha) + 85.57 * (Lbeta/Lalpha)2, for a Fe compositional range between 3 and 47 wt. %. A comparison of Fe3+/Fetot determined by flank method and values determined earlier by Mössbauer spectroscopy shows that results are generally consistent between the two different methods within the experimental errors. In contrast with garnet, the calibration curve established for ferropericlase does not need to be recalibrated at each microprobe session. Therefore, the calibration curve can be considered universal for the electron microprobe in use if the spectrometer adjustments remain identical with time. To explore applications of the flank method, a set of (Mg,Fe)O samples from diffusion studies was also investigated. Three (Mg,Fe)O crystals were measured by electron microprobe in order to test the sensitivity and accuracy of the flank method for small variations of bulk (Fetot)(wt%) as well as to measure Fe3+/Fetot along diffusion profiles. In the present work it is demonstrated how the flank method can be a powerful tool to measure small variations in Fe3+ content, with a spatial resolution of only few microns (2-3 µm) and a lower detection limit of Fetot of 3 wt%. Moreover, the measurement of Fe3+ content on the micron scale enables the study of the variation of oxygen fugacity conditions along diffusion gradients. A set of (Mg,Fe)O ferropericlase inclusions from ultra deep diamonds selected worldwide were analyzed by the flank method. The data set consists of eighteen (Mg,Fe)O ferropericlase samples from Juina, Brazil, Machado River, Brazil, and Ororoo, Australia. Inclusions are between 10 and 50 µm in size, therefore they are suitable to perform flank method measurements to determine Fe3+/Fetot. For the first time Fe3+/Fetot ratios were measured directly at the electron microprobe on inclusions of less than 50 µm in size. Results for the (Mg,Fe)O inclusions show good agreement with the theoretical trend described by the synthetic samples, which confirms high phase homogeneity for most of the samples. Flank method measurements show a large range of Fe3+/Fetot values for (Mg,Fe)O inclusions, which implies a large range of oxygen fugacities based on charge balance calculations. This large range of oxygen fugacities is similar to results for a suite of much larger inclusions from Kankan, Guinea, and São Luiz, Brazil, that were studied using Mössbauer spectroscopy. The variation of oxygen fugacity seems to be correlated to the geographical distribution of the inclusions studied, showing a redox gradient with more reducing conditions at Kankan, Guinea, and São Luiz, Brazil, and more oxidized in the case of Juina and Machado River, Brazil, and Eurelia, Australia. Such a correlation may be linked to the proto-pacific subduction mechanism, and the different ages combined with the geographic variation may indicate a difference in depth correlating with the large redox variation. Inclusions recovered from the same host diamond from Eurelia shows a strong redox gradient, which suggests a drastic change in the oxygen fugacity conditions during diamond growth. In order to provide information on the mechanisms able to control the redox conditions at lower mantle depths, a multi disciplinary study is suggested for further work.
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Direct Amino Acid Uptake by Plants related to Grassland Diversity - methodological and ecological Investigations
(2009)
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Leopold Sauheitl
- Uptake of intact amino acids by plants has been identified as an alternative nitrogen (N) source for plants in a number of ecosystems and soil types. Up to now it is assumed that this uptake strategy is of particular relevance in ecosystems with low mineral N (Nmin) contents due to insignificant microbial activity or due to poorly developed soils. However, it has also been discussed that amino acid uptake might enable plants to lower intracspecific competition for mineral N and shortcut the microbial mineralization of organic N in systems were competition is exceptionally high. The positive effect of plant diversity on plant productivity is known to induce conditions of intense N competition and thus amino acid uptake might explain how plant communities enable higher productive with increasing diversity. However, the ecological importance of organic N uptake has also been questioned due to the high competitive power of microbes in soils of the temperate zone and due to a number of flaws in the commonly used method to proof and quantify direct amino acid uptake. In this, dual labelled (13C and 15N) amino acids are injected into the soil and direct tracer uptake is quantified via bulk isotope measurement of 13C and 15N enrichment in plant tissues, which recently has been challenged to exclusively reflect direct amino acid uptake. The first objective therefore was to identify and reduce methodological influences on the direct amino acid uptake by plants. Thus the effect of changed amino acid concentrations on amino acid uptake was investigated by application of different tracer amounts. Next, the accuracy and precision of commonly used bulk isotope measurements were compared to compound specific measurements with respect to the determination of direct amino acid uptake. It was shown that the use of high tracer amounts accompanied by high Nmin release reduces direct amino acid uptake via plant internal down regulation of amino acid transporters. This corroborates the importance of minimizing tracer amounts and suggests that plants can actively increase amino acid uptake when N availability in soil is low. Bulk measurements turned out to overestimate direct amino acid uptake by a factor of up to six, as they were not able to separate uptake of intact tracer molecules from uptake of tracer fragments or inorganic carbon. At the same time compound specific isotope measurements proofed to be an accurate and precise tool to demonstrate and quantify uptake of intact amino acids. Using these optimized methods, the importance of amino acid uptake for the N-nutrition of plants with respect to changing plant diversity was investigated. The uptake of amino acids and mineral N by plants as well as the competition between plants and microbes for amino acid N was investigated in grassland communities with 1 to 16 grassland species. Microbes were superior competitors for amino acid derived nitrogen, irrespective of plant diversity and took up 54% of the applied amino acid N in average within 24 h. In contrast, plants only incorporated 2.7% of the applied N and were thus less effective by a factor of 20 in short term N acquisition than microbes. In addition, plant mineral N uptake decreased with increasing plant diversity while uptake of intact amino acids increased. Thus the contribution of amino acid uptake to the overall plant N nutrition increased from 1.5 to 7.0% in which amino acid uptake was mainly controlled by plant N concentration shoot biomass and rooting density while mineral N uptake was controlled by microbial competition. In detail amino acid uptake increased with decreasing plant N concentration while mineral N uptake decreased with increasing microbial abundance and microbial N uptake. Thus, the boosted importance of amino acid uptake for plant N nutrition has to be seen as a reaction on increased N competition with increasing plant diversity. Additionally, plant diversity stimulated microbial diversity which was most likely due to the bottom up effect of increased root exudation and litter input caused by increasing N competition and plant productivity, respectively. While the microbial community was dominated by bacteria (54.7%) the abundance of litter and soil organic matter decomposing gram positive bacteria and fungi as well as protozoan abundance increased with increasing plant diversity. Protozoa are known to stimulate turnover of bacteria which was indicated by higher tracer incorporation of this microbial group and an overall increase of deaminase activity with increasing plant diversity. As higher microbial turnover is associated with increased loss of microbial N to plants, we have to expect higher N availability for plants in the long term. The positive feedback of a plant-induced higher microbial turnover rate on N availability in soil together with an increased amino acids uptake might therefore be an important model to explain the positive effect of plant diversity on plant productivity.
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Atmospheric Distribution and Seasonality of Airborne Polyfluorinated Compounds: Spatial and Temporal Concentration Variations from Ship-and Land-Based Measurements in Northern Germany, the Atlantic Ocean, and Polar Regions
(2009)
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Annekatrin Dreyer
- Per- und polyfluorierte Verbindungen (PFC) sind vielfältig verwendete chemische Substanzen, die mittlerweile weltweit und in allen Umweltmedien nachgewiesen werden konnten. Einige PFC, vor allem Perfluorcarboxylate (PFCA) und Perfluorsulfonate (PFSA), sind persistent, bioakkumulativ und toxisch. Der atmosphärische Transport und Abbau von neutralen volatilen PFCA und PFSA Vorläufersubstanzen könnte die Existenz der persistenten perfluorierten Säuren in quellenfernen Gebieten erklären. Obwohl erste Einzelmessungen von volatilen PFC in Luftproben einen atmosphärischen Transport bestätigten, fehlen bisher Studien, die die Verbreitung dieser Verbindungen umfassend darstellen. Aus diesem Grund wurden räumliche und zeitliche Variationen von PFC-Konzentrationen untersucht. Um PFC in Luftproben im Ultraspurenbereich bestimmen zu können, wurde die analytische Methode optimiert. Schließlich wurden PFC in der Luft auf Glasfaserfiltern (partikuläre Phase) und geeigneten Adsorbtionsmaterialien (Gasphase), hier Polyurethanschaum und XAD-2, angereichert. Neutrale volatile PFC wurden mit Aceton:Methyl-tert-butylether (1:1) extrahiert und mittels GC-MS detektiert. Perfluorierte Säuren wurden mit Methanol extrahiert und mit HPLC-MS/MS detektiert. Die optimierte Methode wurde angewendet, um Fluortelomeralkohole (FTOH), Fluortelomeracrylate (FTA), Perfluoralkylsulfonamide (FASA), and Perfluoralkyl-sulfonamidoethanole (FASE) in der Gas- und Partikelphase sowie PFCA und PFSA in der partikulären Phase zu bestimmen. Die Luftkonzentrationen von PFC wurden in Proben aus verschiedenen Probenahme-kampagnen der Jahre 2007 und 2008 bestimmt. Als Probenahmeplattformen dienten Dauermessstellen bei Hamburg (Deutschland) und verschiedene Forschungsschiffe, die in atlantischen und antarktischen Gewässern sowie der Nord- und Ostsee operierten. Die perfluorierten Säuren (PFCA, PFSA) wurden ausschließlich in geringen Konzentrationen in der partikulären Phase bestimmt. Die Gasphasenkonzentrationen ihrer neutralen volatilen Vorläufer (FTOH, FTA, FASA, FASE) bis zu zwei Größenordnungen höher und variierten zwischen ein und zwei Größenordnungen auf räumlicher und zeitlicher Ebene. PFC Summenkonzentrationen variierten zwischen 4.5 pg/m3 im antarktischen Ozean und 335 pg/m3 in Quellengebieten (marine Luft) und zwischen17 und 972 pg/m3 (permanente Stationen bei Hamburg). Mit durchschnittlich mehr als 80 % dominierten die FTOH das Substanzspektrum in der Gasphase. Perfluoroctylethanol (8:2 FTOH) war die Substanz, die in höchsten Konzentrationen vorgefunden wurde. Die Einzelstoffkonzentrationen in der partikulären Phase lagen meist unter 1 pg/m3. Während einer 14monatigen Probenahmekampagne an zwei Dauermessstationen bei Hamburg wurden die zeitlichen Variationen von PFC Konzentrationen untersucht. Die beobachteten starken Schwankungen über diesen Zeitraum verdeutlichten die limitierte Aussagekraft von Einzelmessungen. Der Konzentrationsverlauf war durch eine fluktuierende Grundlinie gekennzeichnet, die durch einzelne, unregelmäßig vorkommende Ereignisse stark erhöhter Konzentrationen unterbrochen wurde. Diese Ereignisse könnten durch lokale Quellen verursacht worden sein. Die Bereinigung der Zeitreihen von diesen Einzelereignissen führte zu weniger gestörten Konzentrationsverläufen, bei denen die PFC Konzentrationen im Sommer höher als die im Winter waren. Temperaturabhängige Emissionen von diffusen Quellen könnten für diesen Konzentrationsverlauf verantwortlich sein. Die Luftmassenherkunft hatte einen starken Einfluss auf die PFC Konzentrationen dieser Luftproben. Eine Trajektorienanalyse ließ auf westlich und südwestlich von Hamburg gelegene Quellenregionen mit hoher Bevölkerungs- und Industriedichte schließen. Trajektorien-, Korrelations- und Clusteranalysen von Luftproben aus der Deutschen Bucht bestätigten, dass Mittel- bis Langstreckentransport einen wichtigen Einfluss auf das detektierte PFC Niveau in Luftproben aus Norddeutschland und der Nordsee hat. PFC konnten in allen Luftproben von der Arktis bis zur Antarktis nachgewiesen werden, wobei ihre Konzentrationen von kontinentalen und küstennahen Regionen zur offenen See und von Mitteleuropa zu den Polen abnahmen. Die Einzelstoffkonzentrationen waren in der Nordhemisphäre höher als in der Südhemisphäre. Auf Grundlage der zeitlichen und räumlichen Konzentrationsvariationen konnten atmosphärische Verweilzeiten im Bereich von 20 bis 60 Tagen für die analysierten PFC berechnet werden. Die Ergebnisse dieser Arbeit liefern neue Erkenntnisse über atmosphärisch transportierte PFC. Sowohl die atmosphärischen Verweilzeiten als auch die festgestellte weltweite Verbreitung von PFC in der Luft bestätigen, dass diese Gruppe von Chemikalien von hauptsächlich nordhemisphärischen Quellenregionen über weite Strecken in entlegene Gebiete transportiert werden können.
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Plant Species and Functional Diversity along Altitudinal Gradients, Southwest Ethiopian Highlands
(2009)
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Desalegn Wana Dalacho
- Understanding how biodiversity is organized across space and time has long been a central focus of ecologists and biogeographers. Altitudinal patterns of richness gradients are one of such striking patterns in the landscape. Despite its historical and ecological importance as a heuristic natural experimental site for development of ecological theories, the emergent patterns and mechanisms that structure them are poorly understood. This is partly because of the complex relationships of species to the environment and the choice of the response variable itself, i.e. using taxonomic richness as a metrics of diversity. This thesis, therefore, applies plant functional types (hereafter PFTs) approach to study the response of vegetation to environmental factors in the southwest Ethiopian highlands. It focuses on the classification of the vegetation into a few main plant functional response categories and relate them to environmental variables. For pattern identification and mechanistic explanations, a deconstructive approach of the taxonomic richness into its constituent components was used. Furthermore, the potential effects of land use/land cover change and global warming on the biodiversity of the study area was investigated. The results reveal that the application of plant functional types is a promising tool to understand vegetation-environment relationships. Local topographic attributes (altitude and slope) and soil properties found to structure the variance in the relative abundance of PFTs along environmental gradients. Moreover, specific response to drought favours the abundance of species with thorns/spines and tussocks in the lowlands as opposed to chilling which favours rosettes and rhizomes PFTs in the highlands. Concerning patterns of richness along altitudinal gradients, various structures of richness appear for total vascular plant species and growth forms. Woody plants, graminoids and climbers showed a uni-modal structure while ferns and herbs revealed an increasing pattern of richness along the altitudinal gradient. By contrast, total vascular plants species richness did not show any strong response to altitudinal gradients. Climate related water-energy dynamics, species area relationships due to the physical shape of the mountain, local topographic and soil conditions were found to be predominant factors structuring the observed richness in the study area. The threats to biodiversity loss due to land use/land cover change and global warming is eminent in the study area. Land conversion for agricultural purposes was a pervasive process that had a deleterious effect on the biodiversity of the study area. Population growth, socio-economic challenges (poverty) and government policy regimes drive land cover change processes. In addition, recent climate change poses a serious challenge to the biodiversity of the study area. The results of model predictions indicated that biodiversity of the study area will suffer severe consequences of lowland biotic attrition (i.e. the net loss of species richness in the tropical lowlands caused by altitudinal range shifts in the absence of new species arriving), range gap shifts and contraction, and extinction due to expected warming at the end of this century. The model also predicted that endangered and endemic species with restricted elevational ranges will disproportionately suffer from range contraction and extinction due to warming. In conclusion, the plant functional types approach was found to be an essential tool to reduce complexity of the vegetation of the study system and to elucidate vegetation-environment relationships. Moreover, the identification of emergent patterns and attributing them to mechanistic explanations are pre-requisites for conservation planning to save biodiversity of the study area. The study also evidenced that land use/land cover change and global warming will present strong threats to the loss of biodiversity in the study area. Salvaging biodiversity in the future requires the consideration of the effect of land use and climate change on vegetation responses. Consequently, nature conservation strategies and future reserve designs should take into account options of human assisted migration across fragmented landscapes and creating dispersal routes for species to track to new thermal niches.
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The evolution of Saharan dust input on Lanzarote (Canary Islands) – influenced by human activity in the Northwest Sahara during the early Holocene?
(2009)
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Hans von Suchodoletz
Hedi Oberhänsli
Dominik Faust
Markus Fuchs
Cécile Blanchet
Tobias Goldhammer
Ludwig Zöller
- An overall Holocene increase of Saharan dust input to the Canary Islands and to the North Canary Basin is accompanied by a strong coarsening of Saharan dust in loess-like sediments deposited on Lanzarote from ~7–8 ka. No similar coarsening events are indicated in investigations of the sedimentological record for the last 180 ka, a period showing several dramatic climate changes. Therefore a mobilisation of Holocene dust by anthropogenic activity in the northwest Sahara east of the Canary Islands is assumed. Although scarce archaeological data from the coastal area of that region does not point to strong anthropogenic activity during the early Holocene, a high density of unexplored archaeological remains is reported from the coastal hinterlands in the Western Sahara. Thus, the hypothesis of early anthropogenic activity cannot be excluded.
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First principles phase diagram calculations in group IV carbides and Mg2SiO4 liquid from Molecular Dynamics
(2009)
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Omar Adjaoud
- Atomistic simulations on stability and physical properties of Earth materials are playing an increasingly important role in high pressure mineralogy. Such computations can provide guidance for experimental studies and insight into underlying causes of observations, or explore conditions and properties that are inaccessible to experiments at the current time. A variety of approaches have been applied in such research, with density functional theory based methods having become a reliable tool in computational mineral sciences. Despite this progress there are interesting problems which density functional theory based methods are not able to tackle on a routine basis. These include computations of phase diagrams and transport properties in liquids. The sub-solidus phase diagrams of the binary systems TiC-ZrC, TiC-HfC, ZrC-HfC at ambient pressure are computed based on electronic structure and energy calculations within density functional theory. Formation energies for a large number of supercells with compositions of (M1,M2)C, M1, M2 = Ti, Zr, or Hf, are computed by a plane-wave pseudopotential method. The energies serve as a basis for fitting cluster expansion Hamiltonians that are used to explore the sub-solidus phase diagram, i.e. stability of ordered intermediate compounds and the degree of miscibility in the systems by Monte Carlo simulations. Hamiltonians can be fit to the formation energies of the cells directly or after taking into account vibrational free energy. As it is prohibitive to compute vibrational free energy for all configurations they are approximated by the transferable force constant scheme: nearest neighbor force constants are computed for the end-member crystals with imposed but varying lattice parameters. The resulting bond stiffness versus bond length relationships are applied to the superstructures, using the relaxed bond lengths and their chemical identities as predictor. Significant miscibility gaps were predicted for the binaries TiC-ZrC and HfC-TiC, with consolute temperature in excess of 2000 K, in good agreement with experiments. The system HfC-ZrC shows complete miscibility at room temperature. Approximately symmetric phase diagram for HfC-TiC and asymmetric phase diagrams for HfC-ZrC and TiC-ZrC were predicted. With the success of the method in the simple carbide systems similar computations can now be performed for geologically relevant mineral families. Mg2SiO4 liquid at high pressure is of central importance in our understanding of melts that occur in the deep Earth and in particular in the early history of our planet, when it was in a magma ocean stage. Due to high melting temperatures little is known experimentally about its high pressure thermodynamic and transport properties that govern magma ocean structure and dynamics. Molecular dynamics simulations now fill this gap. Currently, density functional theory based computations are restricted to a few hundred atoms and a few picoseconds. While such simulations allow for determination of thermodynamic properties, longer run durations and larger cells are necessary to obtain transport properties such as diffusivity and viscosity with sufficient precision. By contrast, semi-empirical pair potentials provide an efficient route to perform large-scale molecular dynamics simulations. They suffer, however, from the fact that the transferability of the potentials to different conditions is not guaranteed. The development of aspherical flexible potentials that are fit to density functional theory results bridge the gap between ab-initio methods and classical potentials. Comprehensive large-scale molecular dynamics simulations using the aspherical ionic model were performed on Mg2SiO4 melt to obtain thermodynamic properties as well as diffusivity and viscosity. The pressure-temperature range covered was 0-32 GPa and 2600-3200 K. The thermodynamic parameters agree well with density functional theory based results: the Grüneisen parameter $gamma$ was found to increase significantly with pressure. Diffusivity is predicted to decrease and viscosity to increase with pressure. Both transport properties were readily fit with closed Arrhenius expression. Independent estimates on diffusivity and viscosity allows an examination of their relation through the Eyring equation, often employed to compute viscosity from diffusivity data. The proportionality factor between them, the translation distance for a diffusion event $lambda$, is determined as $lambda$=18 AA at 0 GPa, and decreases with pressure. This is in good agreement with previous molecular dynamics simulations using classical potentials, but significantly larger than other estimates of $lambda$ based on experimental data that yield 2.8 AA $ < lambda < $ 5 AA. Combining the thermodynamic and viscosity fits a magma ocean adiabat and the associated viscosity profile were computed.
