| 1. |
- Axelsson, Mikael D., et al.
(author)
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High spatial resolution analysis of ferromanganese concretions by LA-ICP-MS
- 2002
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In: Geochemical Transactions. - : Springer Science and Business Media LLC. - 1467-4866. ; 3:5, s. 40-47
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Journal article (peer-reviewed)abstract
- A procedure was developed for the determination of element distributions in cross-sections of ferromanganese concretions using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The effects of carrier flow rates, rf forward power, ablation energy, ablation spot size, repetition rate and number of shots per point on analyte intensity were studied. It is shown that different carrier gas flow rates are required in order to obtain maximum sensitivities for different groups of elements, thus complicating the optimisation of ICP parameters. On the contrary, LA parameters have very similar effects on almost all elements studied, thus providing a common optimum parameter set for the entire mass range. However, for selected LA parameters, the use of compromise conditions was necessary in order to compensate for relatively slow data acquisition by ICP-MS and maintain high spatial resolution without sacrificing the multielemental capabilities of the technique. Possible variations in ablation efficiency were corrected for mathematically using the sum of Fe and Mn intensities. Quantification by external calibration against matrix-matched standards was successfully used for more than 50 elements. These standards, in the form of pressed pellets (no binder), were prepared in-house using
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| 2. |
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| 3. |
- Holm, Nils G.
(author)
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Glasses as sources of condensed phosphates on the early earth
- 2014
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In: Geochemical Transactions. - : Springer Science and Business Media LLC. - 1467-4866. ; 15, s. 8-
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Research review (peer-reviewed)abstract
- Procedures for the analysis of phosphorus in geological material normally aims for the determination of the total amount of P expressed as orthophosphate (PO43-) or the differentiation between inorganic and organic P. This is probably due to analytical difficulties but also to the prevalent opinion that the chemistry of phosphorus in geological environments is almost entirely restricted to the mineral apatite. Because of the low solubility of apatite it is, therefore, commonly argued that little P was around for prebiotic chemistry and that pre-biological processes would essentially have had to do without this indispensable element unless it was provided by alternative sources or mechanisms (such as reduction and activation by lightning or delivery to Earth by celestial bodies). It is a paradox that the potential existence of reactive phosphorus compounds, such as the mineral schreibersite - iron phosphide, in geological material on Earth is seldom considered although we are aware of the existence of such compounds in meteorite material. The content of Al2O3 in rocks appears to be important for the speciation of phosphorus and for how strongly it binds to silicates. In general, low alumina seems to promote the existence of isolated charge-balanced phosphorus complexes.
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| 4. |
- Holm, Nils, 1948-, et al.
(author)
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Reduction of nitrogen compounds i oceanic basemet and its implications for HCN formation and abiotic organic synthesis
- 2009
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In: Geochemical Transactions. - : BioMed Central Ltd. - 1467-4866. ; 10:9
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Journal article (peer-reviewed)abstract
- Hydrogen cyanide is an excellent organic reagent and is central to most of the reaction pathways leading to abiotic formation of simple organic compounds containing nitrogen, such as amino acids, purines and pyrimidines. Reduced carbon and nitrogen precursor compounds for the synthesis of HCN may be formed under off-axis hydrothermal conditions in oceanic lithosphere in the presence of native Fe and Ni and are adsorbed on authigenic layer silicates and zeolites. The native metals as well as the molecular hydrogen reducing CO2 to CO/CH4 and NO3-/NO2- to NH3/NH4+ are a result of serpentinization of mafic rocks. Oceanic plates are conveyor belts of reduced carbon and nitrogen compounds from the off-axis hydrothermal environments to the subduction zones, where compaction, dehydration, desiccation and diagenetic reactions affect the organic precursors. CO/CH4 and NH3/NH4+ in fluids distilled out of layer silicates and zeolites in the subducting plate at an early stage of subduction will react upon heating and form HCN, which is then available for further organic reactions to, for instance, carbohydrates, nucleosides or even nucleotides, under alkaline conditions in hydrated mantle rocks of the overriding plate. Convergent margins in the initial phase of subduction must, therefore, be considered the most potent sites for prebiotic reactions on Earth. This means that origin of life processes are, perhaps, only possible on planets where some kind of plate tectonics occur.
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| 5. |
- Konn, Cécile, et al.
(author)
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Characterisation of dissolved organic compounds in hydrothermal fluids by stir bar sorption extraction – gas chromatography – mass spectrometry : Case study: the Rainbow field (36°N, Mid-Atlantic Ridge)
- 2012
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In: Geochemical Transactions. - : Springer Science and Business Media LLC. - 1467-4866. ; 13
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Journal article (peer-reviewed)abstract
- The analysis of the dissolved organic fraction of hydrothermal fluids has been considered a real challenge due to sampling difficulties, complexity of the matrix, numerous interferences and the assumed ppb concentration levels. The present study shows, in a qualitative approach, that Stir Bar Sorptive Extraction (SBSE) followed by Thermal Desorption – Gas Chromatography – Mass Spectrometry (TD-GC-MS) is suitable for extraction of small sample volumes and detection of a wide range of volatile and semivolatile organic compounds dissolved in hydrothermal fluids. In a case study, the technique was successfully applied to fluids from the Rainbow ultramafic-hosted hydrothermal field located at 36°14’N on the Mid-Atlantic Ridge (MAR). We show that n-alkanes, mono- and poly- aromatic hydrocarbons as well as fatty acids can be easily identified and their retention times determined. Our results demonstrate the excellent repeatability of the method as well as the possibility of storing stir bars for at least three years without significant changes in the composition of the recovered organic matter. A preliminary comparative investigation of the organic composition of the Rainbow fluids showed the great potential of the method to be used for assessing intrafield variations and carrying out time series studies. All together our results demonstrate that SBSE-TD-GC-MS analyses of hydrothermal fluids will make important contributions to the understanding of geochemical processes, geomicrobiological interactions and formation of mineral deposits
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| 6. |
- Lindgren, Paula, et al.
(author)
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A demonstration of an affinity between pyrite and organic matter in a hydrothermal setting
- 2011
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In: Geochemical Transactions. - : Springer Science and Business Media LLC. - 1467-4866. ; 12, s. 3-
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Journal article (peer-reviewed)abstract
- One of the key-principles of the iron-sulphur world theory is to bring organic molecules close enough to interact with each other, using the surface of pyrite as a substrate in a hydrothermal setting. The present paper explores the relationship of pyrite and organic matter in a hydrothermal setting from the geological record; in hydrothermal calcite veins from Carboniferous limestones in central Ireland. Here, the organic matter is accumulated as coatings around, and through, pyrite grains. Most of the pyrite grains are euhedral-subhedral crystals, ranging in size from ca 0.1-0.5 mm in diameter, and they are scattered throughout the matrix of the vein calcite. The organic matter was deposited from a hydrothermal fluid at a temperature of at least 200 degrees C, and gives a Raman signature of disordered carbon. This study points to an example from a hydrothermal setting in the geological record, demonstrating that pyrite can have a high potential for the concentration and accumulation of organic materials.
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| 7. |
- Neubeck, Anna, et al.
(author)
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Formation of H(2) and CH(4) by weathering of olivine at temperatures between 30 and 70 degrees C
- 2011
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In: Geochemical Transactions. - : BioMed Central / Chemistry Central. - 1467-4866. ; 12:6
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Journal article (peer-reviewed)abstract
- Hydrocarbons such as CH(4) are known to be formed through the Fischer-Tropsch or Sabatier type reactions in hydrothermal systems usually at temperatures above 100 degrees C. Weathering of olivine is sometimes suggested to account for abiotic formation of CH(4) through its redox lowering and water splitting properties. Knowledge about the CH(4) and H(2) formation processes at low temperatures is important for the research about the origin and cause of early Earth and Martian CH(4) and for CO(2) sequestration. We have conducted a series of low temperature, long-term weathering experiments in which we have tested the CH(4) and H(2) formation potential of forsteritic olivine. The results show low temperature CH(4) production that is probably influenced by chromite and magnetite as catalysts. Extensive analyses of a potential CH(4) source trapped in the crystal structure of the olivine showed no signs of incorporated CH(4). Also, the available sources of organic carbon were not enough to support the total amount of CH(4) detected in our experiments. There was also a linear relationship between silica release into solution and the net CH(4) accumulation into the incubation bottle headspaces suggesting that CH(4) formation under these conditions could be a qualitative indicator of olivine dissolution. less thanbrgreater than less thanbrgreater thanIt is likely that minerals such as magnetite, chromite and other metal-rich minerals found on the olivine surface catalyze the formation of CH(4), because of the low temperature of the system. This may expand the range of environments plausible for abiotic CH(4) formation both on Earth and on other terrestrial bodies.
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| 8. |
- Neubeck, Anna, et al.
(author)
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Formation of H2 and CH4 by weathering of olivine at temperatures between 30 and 70°C
- 2011
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In: Geochemical Transactions. - : Springer Science and Business Media LLC. - 1467-4866. ; 12:6
-
Journal article (peer-reviewed)abstract
- Hydrocarbons such as CH4 are known to be formed through the Fischer-Tropsch or Sabatier type reactions in hydrothermal systems usually at temperatures above 100°C. Weathering of olivine is sometimes suggested to account for abiotic formation of CH4 through its redox lowering and water splitting properties. Knowledge about the CH4 and H2 formation processes at low temperatures is important for the research about the origin and cause of early Earth and Martian CH4 and for CO2 sequestration. We have conducted a series of low temperature, long-term weathering experiments in which we have tested the CH4 and H2 formation potential of forsteritic olivine.The results show low temperature CH4 production that is probably influenced by chromite and magnetite as catalysts. Extensive analyses of a potential CH4 source trapped in the crystal structure of the olivine showed no signs of incorporated CH4. Also, the available sources of organic carbon were not enough to support the total amount of CH4 detected in our experiments. There was also a linear relationship between silica release into solution and the net CH4 accumulation into the incubation bottle headspaces suggesting that CH4 formation under these conditions could be a qualitative indicator of olivine dissolution.It is likely that minerals such as magnetite, chromite and other metal-rich minerals found on the olivine surface catalyze the formation of CH4, because of the low temperature of the system. This may expand the range of environments plausible for abiotic CH4 formation both on Earth and on other terrestrial bodies.
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| 9. |
- Ivarsson, Magnus, et al.
(author)
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Chromite oxidation by manganee oxides in subseafloor basalts and the presence of putative fossilized microorganisms
- 2011
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In: Geochemical Transactions. - : Springer Science and Business Media LLC. - 1467-4866. ; 12, s. 5-
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Journal article (peer-reviewed)abstract
- Chromite is a mineral with low solubility and is thus resistant to dissolution. The exception is when manganese oxides are available, since they are the only known naturally occurring oxidants for chromite. In the presence of Mn(IV) oxides, Cr(III) will oxidise to Cr(VI), which is more soluble than Cr(III), and thus easier to be removed. Here we report of chromite phenocrysts that are replaced by rhodochrosite (Mn(II) carbonate) in subseafloor basalts from the Koko Seamount, Pacific Ocean, that were drilled and collected during the Ocean Drilling Program (ODP) Leg 197. The mineral succession chromite-rhodochrosite-saponite in the phenocrysts is interpreted as the result of chromite oxidation by manganese oxides. Putative fossilized microorganisms are abundant in the rhodochrosite and we suggest that the oxidation of chromite has been mediated by microbial activity. It has previously been shown in soils and in laboratory experiments that chromium oxidation is indirectly mediated by microbial formation of manganese oxides. Here we suggest a similar process in subseafloor basalts.
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| 10. |
- Bie, Yiming, et al.
(author)
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Dynamic headway control for high-frequency bus line based on speed guidance and intersection signal adjustment
- 2020
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In: Computer-Aided Civil and Infrastructure Engineering. - : Wiley. - 1093-9687 .- 1467-8667. ; 35:1, s. 4-25
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Journal article (peer-reviewed)abstract
- Computer-Aided Civil and Infrastructure Engineering To prevent bus bunching, a dynamic headway control method in the V2I (vehicle to infrastructure) environment for a high-frequency route with bus lane is developed. Bus operating speed guidance on the mid-blocks and intersection signal adjustment are two main strategies in the proposed method. A forecasting model of bus travel time under the dynamic control method is developed. The objective function is set up by taking into account differences between actual bus headways and dispatching headways, and the scaling ratios of intersection cycle lengths. The optimization model is solved using genetic algorithm. The proposed method is applied to a real bus route in Meihekou city, China, and compared with the current control plan as well as holding strategy. Results show that the proposed method can reduce bus headway deviations in all investigating periods; negative impacts on cars can be limited by setting reasonable values for the parameters.
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