| 1. |
- Bohlin, Madeleine, et al.
(författare)
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High-precision determination of lithium and magnesium isotopes utilising single column separation and multi-collector inductively coupled plasma mass spectrometry
- 2018
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Ingår i: Rapid Communications in Mass Spectrometry. - : Wiley. - 0951-4198 .- 1097-0231. ; 32:2, s. 93-104
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Tidskriftsartikel (refereegranskat)abstract
- Rationale Li and Mg isotopes are increasingly used as a combined tool within the geosciences. However, established methods require separate sample purification protocols utilising several column separation procedures. This study presents a single-step cation-exchange method for quantitative separation of trace levels of Li and Mg from multiple sample matrices.Methods The column method utilises the macro-porous AGMP-50 resin and a high-aspect ratio column, allowing quantitative separation of Li and Mg from natural waters, sediments, rocks and carbonate matrices following the same elution protocol. High-precision isotope determination was conducted by multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) on the Thermo Scientific NEPTUNE Plus fitted with 1013Ω amplifiers which allow accurate and precise measurements at ion beams <0.51 V.Results Sub-nanogram Li samples (0.3-0.5 ng) were regularly separated (yielding Mg masses of 1-70 μg) using the presented column method. The total sample consumption during isotopic analysis is <0.5 ng Li and <115 ng Mg with long-term external 2σ precisions of ±0.39‰ for δ7Li and ±0.07‰ for δ26Mg. The results for geological reference standards and seawater analysed by our method are in excellent agreement with published values despite the order of magnitude lower sample consumption. Conclusions The possibility of eluting small sample masses and the low analytical sample consumption make this method ideal for samples of limited mass or low Li concentration, such as foraminifera, mineral separates or dilute river waters.
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| 2. |
- Bohlin, Madeleine, et al.
(författare)
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The reactive transport of Li as a monitor of weathering processes in kinetically limited weathering regimes
- 2019
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 511, s. 233-243
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Tidskriftsartikel (refereegranskat)abstract
- Analytical solutions to reactive-transport equations describing the evolution of Li concentrations and isotopic ratios are presented for one-dimensional flow paths where reaction stoichiometry is constant along the flow path. These solutions are considered appropriate for chemical weathering in rapidly eroding catchments. The solutions may be described by two dimensionless numbers; 1) a Damköhler number describing the product of reaction rate and fluid residence time, and 2) a net partition coefficient which describes the fraction of Li re-precipitated in secondary minerals as the product of a fluid-secondary mineral partition coefficient and the mass fraction of secondary mineral precipitates. In settings where water entering flow paths is dilute, Li concentrations will increase along the flow path until they reach a limiting value determined by the net partition coefficient. Simultaneously, 7Li/6Li isotopic ratios will increase to a limiting value of the source rock ratio minus the secondary mineral-fluid Li-isotopic fractionation factor. Waters with Li-isotopic ratios in excess of this limiting value must have evolved with a change of reaction stoichiometry and/or partition coefficient along the flow path such that at some point net removal of Li to secondary minerals exceeds that supplied by dissolution of primary minerals. The modelling shows that the multiple controls on chemical weathering rates (temperature, rainfall, erosion rate, hydrology) cannot be inferred from Li concentration and isotopic ratio data alone, which only provide two independent constraints. Caution should be exercised in interpretation of oceanic Li records in terms of potential climatic variables. The model is illustrated by a set of Li concentration and isotopic ratio measurements on river waters and bed sands in the Alaknanda river basin which forms the headwaters of the Ganges. This illustrates how values of the Damköhler number and net partition coefficient can be used to trace weathering processes. Water samples from catchments with similar lithologies and climates scatter along contours of approximately constant net partition coefficient, reflecting similar reaction stoichiometries, but with more variable Damköhler numbers reflecting variations in flow path length, fluid flux and/or reaction rate. Samples from the lower, warmer and less rapidly eroding catchments have high 7Li/6Li isotopic ratios with lower Li concentrations and must reflect at least a two-stage weathering process where reaction stoichiometry and/or Li fluid-mineral partition coefficients change along the flow path so that net Li is removed in the later stages.
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| 3. |
- Gout, Thomas L., et al.
(författare)
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Diffusive processes in aqueous glass dissolution
- 2019
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Ingår i: npj Materials Degradation. - : Springer Science and Business Media LLC. - 2397-2106. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- High level nuclear waste is often immobilised in a borosilicate glass for disposal. However, this glass corrodes in contact with aqueous solutions. To predict radionuclide releases from wasteforms, their dissolution mechanisms must be understood. Understanding glass dissolution mechanisms presents a challenge across numerous other disciplines and many glass dissolution models still remain conflicted. Here we show that diffusion was a significant process during the later stages of dissolution of a simplified waste glass but was not evidenced during the initial stages of dissolution. The absence of measurable isotopic fractionation in solution initially supports models of congruent dissolution. However, the solution becoming isotopically lighter at later times evidences diffusive isotopic fractionation and opposes models that exclude diffusive transport as a significant mechanism. The periodically sampled isotopic methodologies outlined here provide an additional dimension with which to understand glass dissolution mechanisms beyond the usual measurement of solution concentrations and, post-process, nano-scale analysis of the altered glass.
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| 4. |
- Gout, Thomas L., et al.
(författare)
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Temperature dependent lithium isotope fractionation during glass dissolution
- 2021
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier. - 0016-7037 .- 1872-9533. ; 313, s. 133-154
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the mechanisms by which borosilicate glasses corrode in contact with aqueous solutions remains a challenge to the safety case for the geological disposal of vitrified high-level nuclear waste. Here, lithium isotope fingerprinting techniques were applied to the leachates of a simulant Magnox waste glass to probe the mechanisms of aqueous corrosion at both short and long timescales (6 hours to 464 days). Experiments took place at 40 and 90 degrees C to assess the consistency of the dissolution mechanisms across a range of commonly employed temperatures and the legitimacy of applying higher temperature experimental datasets to understand glass corrosion within a disposal facility at lower temperatures. Two competing release mechanisms were observed for lithium (diffusion and hydrolysis), and the relative proportions of these mechanisms changed through time. Leachates initially had lower delta(7) Li values than the pristine glass (-2.7 parts per thousand at 40 degrees C and 1.1 parts per thousand at 90 degrees C relative to the pristine glass) at both temperatures due to lithium leaching incongruently through diffusive processes. The greater offset between solution and solid at lower temperatures indicates a larger rate of diffusion (incongruent dissolution) relative to the rate of hydrolysis (congruent dissolution) at lower temperatures. The fraction of lithium released through diffusion relative to the fraction of lithium released through hydrolysis then increased at both temperatures with time up to 126 days, increasing from 0.47 and 0.22 at 6 hours to 0.66 and 0.41 at 126 days at 40 and 90 degrees C respectively. Subsequently, the fractions of lithium released through diffusion sharply decreased to 0.36 at 40 degrees C and 0.22 at 90 degrees C after 464 days, consistent with network hydrolysis coupled with secondary phase precipitation later controlling the long-term release of Li at both temperatures. Throughout the duration of the experiments (464 days) the delta(7) Li values in solution increased to 9.0 parts per thousand at 40 degrees C and 10.0 parts per thousand at 90 degrees C due to the formation of talc and montmorillonite phases at 40 degrees C and additional smectite phases at 90 degrees C. Further, no evidence for the formation of a diffusive barrier to the transport of Li within the alteration layers became apparent during the later stages of dissolution at either temperature. However, the fraction of lithium leached through diffusion was still significant throughout all stages of dissolution. Lithium isotope ratios in solution were correlated with the transition from a system which was increasingly dominated by lithium diffusion as the dissolution rate slowed to one which was controlled by hydrolysis coupled with secondary phase precipitation at long durations. Alongside elemental ratios in solution, these results were consistent with the same set of mechanisms governing dissolution across the temperature range studied.
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| 5. |
- Jackson, Illiam S. C., 1986-, et al.
(författare)
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Genetic assimilation in the fossil record: phenotypic plasticity and later accommodation in Cambrian arthropods
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Genetic assimilation is a hypothesised process in which an initially plastic developmental phenotypic response of an organism to the environment is fixed genetically, i.e. assimilated into its genome 1,2. One central prediction of genetic assimilation is that “phenotypic accommodation can precede, rather than follow, genetic change, in adaptive evolution”3. Here we test this prediction in the fossil record. Agnostus pisiformis, a Cambrian Series 3 trilobite-like arthropod, has been shown to exhibit subtly different patterns of pygidial morphological variation across coeval assemblages4, varying chiefly in the degree to which the axial lobe dominates the pygidium. We demonstrate that this morphological variation as well as that of the slightly younger closely related Homagnostus obesus is significantly correlated with geochemical indicators of dysoxia/euxinia and thus stressed environments5-7. In addition, the variances of high and low-stress assemblages also differ significantly, suggesting that the morphological variability of the different assemblages is induced by environmental stress and can be understood as a reaction norm8. We include in our analysis the younger relative Trilobagnostus holmi and interpret its morphology, which has a strongly reduced variance, as representing a more canalized9 or stabilized1 stage of the assimilation process. Thus our data contain all stages of adaptation via phenotypic plasticity and genetic assimilation10 and support the main predictions of the ‘Extended Evolutionary Synthesis’3.
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| 6. |
- Neubeck, Anna, et al.
(författare)
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Ni isotope fractionation during coprecipitation of Fe(III)(oxyhydr)oxides in Si solutions
- 2021
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Ingår i: Chemie der Erde. - : Elsevier BV. - 0009-2819 .- 1611-5864. ; 81:1
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Tidskriftsartikel (refereegranskat)abstract
- The dramatic decline in aqueous Ni concentrations in the Archean oceans during the Great Oxygenation Event is evident in declining solid phase Ni concentrations in Banded Iron Formations (BIFs) at the time. Several experiments have been performed to identify the main removal mechanisms of Ni from seawater into BIFs, whereby adsorption of Ni onto ferrihydrites has shown to be an efficient process. Ni isotopic measurements have shown limited isotopic fraction during this process, however, most experiments have been conducted in simple solutions containing varying proportions of dissolved Fe and Ni as NO3 salts, as opposed to Cl salts which are dominant in seawater. Further, Archean oceans were, before the advent of siliceous eukaryotes, likely saturated with amorphous Si as seen in the interlayered chert layers within BIFs. Despite Si being shown to greatly affect the Ni elemental partitioning onto ferrihydrite solids, no studies have been made on the effects of Si on the Ni isotope fractionation. Here we report results of multiple coprecipitation experiments where ferrihydrite precipitated in mixed solutions with Ni and Si. Ni concentrations in the experiments ranged between 200 and 4000 nM for fixed concentrations of Si at either 0, 0.67 or 2.2 mM. The results show that Si at these concentrations has a limited effect on the Ni isotope fractionation during coprecipitation of ferrihydrite. At 0.67 mM, the saturation concentration of cristobalite, the isotopic fractionation factors between the precipitating solid and experimental fluid are identical to experiments not containing Si (0.34 +/- 0.17 parts per thousand). At 2.2 mM Si, and the saturation concentration of amorphous silica, however, the Ni isotopic composition of the ferrihydrite solids deviate to more negative values and show a larger variation than at low or no Si, and some samples show fractionation of up to 0.5 parts per thousand. Despite this seemingly more unstable fractionation behaviour, the combined results indicate that even at as high concentrations of Si as 2.2 mM, the delta Ni-60 values of the forming ferrihydrites does not change much. The results of our study implicate that Si may not be a major factor in fractionating stable Ni isotopes, which would make it easier to interpret future BIF record and reconstruct Archean ocean chemistry.
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| 7. |
- Slater, Ben, 1987-, et al.
(författare)
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Animal origins : The record from organic microfossils
- 2022
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Ingår i: Earth-Science Reviews. - : Elsevier. - 0012-8252 .- 1872-6828. ; 232
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Tidskriftsartikel (refereegranskat)abstract
- Accumulated records of organic microfossils span billions of years of Earth history. The majority of this record consists of prokaryotes plus eukaryotes of a protistan grade, yet this type of fossilisation is also capable of capturing the organically preserved remains of animals. Recently, it has become apparent that non-biomineralizing animal groups, otherwise known only from rare instances of exceptional fossilisation, can pre-serve in this fashion. Given this high taphonomic fidelity combined with the temporal continuity of organic microfossil preservation, it is clear this style of fossilisation has the potential to circumvent some of the major biases that afflict the current early animal fossil record. Despite this, there have been no attempts to survey recorded instances of animal-derived organic microfossils. We constructed a global database comprising 394 studies of organic microfossils covering 399 sedimentary rock formations spanning the Tonian-Cambrian Stage 5/Wuliuan Stage (1 Ga to 505 Ma). The database consolidates scattered reports and provides a first appraisal for how a record of metazoans emerges within the broader archives of organic microfossils. Scrutiny of the current record reveals that organic microfossils contain the oldest body fossil evidence for a number of key metazoan clades, including the Chaetognatha, Annelida, Priapulida, 'lobopods' and Panarthropoda, Crustacea, Ptero-branchia, and potentially even the Bilateria. Also detected among this record are the fossilised remains of por-iferans, chancelloriids, palaeoscolecids, loriciferans, bradoriids, trilobites, wiwaxiids, molluscs, hyoliths, brachiopods and chordates. Our data shows that metazoan-derived remains are relatively common constituents of palynological preparations from sediments of a Cambrian age or younger. Such metazoan remains are also detected in organic microfossil assemblages from several formations of late Ediacaran age, but are entirely absent from the large number of equivalent preparations from older sediments, throughout the Proterozoic. In this view, signs of animal diversification emerge as a unidirectional signal embedded within a deeper record of organic microfossils. We argue here that the absence of animal remains among the large number of equivalent studies from Tonian, Cryogenian and early Ediacaran strata weakens the case for the existence of a cryptic animal biosphere during the Tonian and Cryogenian.
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| 8. |
- Steiner, Zvi, et al.
(författare)
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Variability in the Concentration of Lithium in the Indo-Pacific Ocean
- 2022
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Ingår i: Global Biogeochemical Cycles. - : American Geophysical Union (AGU). - 0886-6236 .- 1944-9224. ; 36:6
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Tidskriftsartikel (refereegranskat)abstract
- Lithium has limited biological activity and can readily replace aluminium, magnesium and iron ions in aluminosilicates, making it a proxy for the inorganic silicate cycle and its potential link to the carbon cycle. Data from the North Pacific Ocean, tropical Indian Ocean, Southern Ocean and Red Sea suggest that salinity normalized dissolved lithium concentrations vary by up to 2%-3% in the Indo-Pacific Ocean. The highest lithium concentrations were measured in surface waters of remote North Pacific and Indian Ocean stations that receive relatively high fluxes of dust. The lowest dissolved lithium concentrations were measured just below the surface mixed layer of the stations with highest surface water concentrations, consistent with removal into freshly forming aluminium rich phases and manganese oxides. In the North Pacific, water from depths >2,000 m is slightly depleted in lithium compared to the initial composition of Antarctic Bottom Water, likely due to uptake of lithium by authigenically forming aluminosilicates. The results of this study suggest that the residence time of lithium in the ocean may be significantly shorter than calculated from riverine and hydrothermal fluxes.
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| 9. |
- Zhang, Wei, et al.
(författare)
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A rapid method of simultaneous chromatographic purification of Li and Mg for isotopic analyses using MC-ICP-MS
- 2022
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Ingår i: International Journal of Mass Spectrometry. - : Elsevier. - 1387-3806 .- 1873-2798. ; 480
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Tidskriftsartikel (refereegranskat)abstract
- Lithium (Li) and Magnesium (Mg) isotopes have been widely used as valuable tracers to study geological processes. In general, several column separation procedures have been used to separate Li and Mg. In this study, we present an optimized protocol for the rapid and simultaneous purification of Li and Mg, which significantly reduces the separation time, required reagent volume, and procedural blanks compared to previous methods. Samples with small amounts of Li (generally 5 ng Li yielding Mg masses of 1 -1200 mu g) were separated, with the corresponding yields of Li and Mg being nearly 100%. Lithium and Mg isotope analyses were performed using an MC-ICP-MS (Thermo Scientific NEPTUNE Plus) and only <0.2 ng Li and <150 ng Mg were consumed for each analysis. Matrix-doping experiments reveal that the matrix effect is negligible for the determination of Li and Mg isotopes from a wide array of geological samples using our protocol. The robustness of the protocol has been validated by replicated analyses of standard solutions and geological standards, which yield long-term external 2 sigma precision better than +/- 0.6 parts per thousand for delta Li-7 and +/- 0.08 parts per thousand for delta Mg-26. Lithium and Mg isotopic ratios of all reference materials measured in this study agreed well with previous data within uncertainties. The method developed in this study allows for the rapid and high-purity separation of Li and Mg and subsequent high-precision isotopic analyses of these elements. (C) 2022 Elsevier B.V. All rights reserved.
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