Biologically induced mineralization of dypingite by cyanobacteria from an alkaline wetland near Atlin,British Columbia,Canada

Background  

This study provides experimental evidence for biologically induced precipitation of magnesium carbonates, specifically dypingite (Mg₅(CO₃)₄(OH)₂·5H₂O), by cyanobacteria from an alkaline wetland near Atlin, British Columbia. This wetland is part of a larger hydromagnesite (Mg₅(CO₃)₄(OH)₂·4H₂O) playa. Abiotic and biotic processes for magnesium carbonate precipitation in this environment are compared.     

Crystal field and covalency of octahedral chromium in natural [8](Mg1?xCax) 3[6] (Al0.67Cr0.33)2Si3O12 garnets from upper mantle rocks

In the course of a thorough study of the influences of the second coordination sphere on the crystal field parameters of the 3d ^N -ions and the character of 3d ^N –O bonds in oxygen based minerals, 19 natural Cr³⁺-bearing (Mg,Ca)-garnets from upper mantle rocks were analysed and studied by electronic absorption spectroscopy, EAS. The garnets had compositions with populations of the ^[8] X-sites by 0.881 ± 0.053 (Ca + Mg) and changing Ca-fractions in the range 0.020 ≤ w _Ca[8] ≤ 0.745, while the ^[6] Y-site fraction was constant with x _Cr³⁺ _[6] = 0.335 ± 0.023. The garnets had colours from deeply violet-red for low Ca-contents (up to x _Ca = 0.28), grey with 0.28 ≤ x _Ca ≤ 0.4 and green with 0.4 ≤ x _Ca. The crystal field parameter of octahedral Cr³⁺ 10Dq decreases strongly on increasing Ca-fraction from 17,850 cm⁻¹ at x _Ca[8] = 0.020 to 16,580 cm⁻¹ at x _Ca[8] = 0.745. The data could be fit with two model which do statistically not differ: (1) two linear functions with a discontinuity close to x _Ca[8] ≈ 0.3,

Ab initio study of the high-pressure behavior of CaSiO3 perovskite

Using density functional simulations, within the generalized gradient approximation and projector-augmented wave method, we study structures and energetics of CaSiO₃ perovskite in the pressure range of the Earths lower mantle (0–150 GPa). At zero Kelvin temperature the cubic CaSiO₃ perovskite structure is unstable in the whole pressure range, at low pressures the orthorhombic (Pnam) structure is preferred. At 14.2 GPa there is a phase transition to the tetragonal (I4/mcm) phase. The CaIrO₃-type structure is not stable for CaSiO₃. Our results also rule out the possibility of decomposition into oxides.

Kinetics of heterogeneous bubble nucleation in rhyolitic melts: implications for the number density of bubbles in volcanic conduits and for pumice textures

We performed decompression experiments to simulate the ascent of a phenocryst-bearing rhyolitic magma in a volcanic conduit. The starting materials were bubble-free rhyolites water-saturated at 200 MPa–800°C under oxidizing conditions: they contained 6.0 wt% dissolved H₂O and a dense population of hematite crystals (8.7 ± 2 × 10⁵ mm⁻³). Pressure was decreased from the saturation value to a final value ranging from 99 to 20 MPa, at constant temperature (800°C); the rate of decompression was either 1,000 or 27.8 kPa/s. In all experiments, we observed a single event of heterogeneous bubble nucleation beginning at a pressure P _N equal to 63 ± 3 MPa in the 1,000 kPa/s series, and to 69 ± 1 MPa in the 27.8 kPa/s series. Below P _N, the degree of water supersaturation in the liquid rapidly decreased to a few 0.1 wt%, the nucleation rate dropped, and the bubble number density (BND) stabilized to a value strongly sensitive to decompression rate: 80 mm⁻³ at 27.8 kPa/s vs. 5,900 mm⁻³ at 1,000 kPa/s. This behaviour is like the behavior formerly described in the case of homogeneous bubble nucleation in the rhyolite-H₂O system and in numerical simulations of vesiculation in ascending magmas. Similar degrees of water supersaturation were measured at 27.8 and 1,000 kPa/s, implying that a faster decompression rate does not result in a larger departure from equilibrium. Our experimental results imply that BNDs in acid to intermediate magmas ascending in volcanic conduits will depend on both the decompression rate and the number density of phenocrysts, especially the number density of magnetite microphenocrysts (1–100 mm⁻³), which is the only mineral species able to reduce significantly the degree of water supersaturation required for bubble nucleation. Very low BNDs (≈1 mm⁻³) are predicted in the case of effusive eruptions ( ≈ 0.1 kPa/s). High BNDs (up to 10⁷ mm⁻³) and bimodal bubble size distributions are expected in the case of explosive eruptions: (1) a relatively small number density of bubbles (1–100 mm⁻³) will first nucleate in the lower part of the conduit ( ≈ 10 kPa/s), either at high pressure on magnetite or at lower pressure on quartz and feldspar (or by homogeneous nucleation in the liquid) and (2) then, extreme decompression rates near the fragmentation level ( ≈ 10³ kPa/s) will trigger a major nucleation event leading to the multitude of small bubbles, typically a few micrometers to a few tens of micrometers in diameter, which characterizes most silicic pumices.     

Influence of temperature,composition, silica activity and oxygen fugacity on the H<Subscript>2</Subscript>O storage capacity of olivine at 8 GPa

Olivine crystals were grown in the presence of a hydrous silicate fluid during multi-anvil experiments at 8 GPa and 1,000–1,600°C. Experiments were conducted both in a simple system (FeO–MgO–SiO₂–H₂O) and in a more complex system containing additional elements (CaO–Na₂O–Al₂O₃–Cr₂O₃–TiO₂–FeO–MgO–SiO₂–H₂O). Silica activity was buffered by the presence of either pyroxene (high a _SiO2) or ferropericlase (low a _SiO2), and was buffered by the presence of Ni + NiO or Fe + FeO, or constrained by the presence of Fe₂O₃. Raman spectroscopy was used to identify pyroxene polymorphs in the run products. Clinoenstatite was present in the 1,000°C experiment, and enstatite in experiments at 1,400–1,520°C. The H₂O content of olivine was measured using secondary ion mass spectroscopy, and infrared spectroscopy was used to investigate the nature of hydrous defects. The H₂O storage capacity of olivine decreases with increasing temperature at 8 GPa. In contrast to previous experimental results at ≤2 GPa, no significant effect of varying oxygen fugacity is evident, but H₂O storage capacity is enhanced under conditions of low silica activity. No significant growth of low wavenumber (<3,400 cm⁻¹) peaks, generally associated with high at low pressure, was observed in the FTIR spectra of olivine from the high experiments. Our experiments show that previous high pressure H₂O storage capacity measurements for olivine synthesized under more oxidizing conditions than the Earth’s mantle are not likely to be compromised by the of the experiments. However, the considerable effect of temperature on H₂O storage capacity in olivine must be taken into account to avoid overestimation of the bulk upper mantle H₂O storage capacity.     

Geochemical detection of carbon dioxide in dilute aquifers

Background  

Carbon storage in deep saline reservoirs has the potential to lower the amount of CO₂ emitted to the atmosphere and to mitigate global warming. Leakage back to the atmosphere through abandoned wells and along faults would reduce the efficiency of carbon storage, possibly leading to health and ecological hazards at the ground surface, and possibly impacting water quality of near-surface dilute aquifers. We use static equilibrium and reactive transport simulations to test the hypothesis that perturbations in water chemistry associated with a CO₂ gas leak into dilute groundwater are important measures for the potential release of CO₂ to the atmosphere. Simulation parameters are constrained by groundwater chemistry, flow, and lithology from the High Plains aquifer. The High Plains aquifer is used to represent a typical sedimentary aquifer overlying a deep CO₂ storage reservoir. Specifically, we address the relationships between CO₂ flux, groundwater flow, detection time and distance. The CO₂ flux ranges from 10³ to 2 × 10⁶ t/yr (0.63 to 1250 t/m²/yr) to assess chemical perturbations resulting from relatively small leaks that may compromise long-term storage, water quality, and surface ecology, and larger leaks characteristic of short-term well failure.     

Experimental Study of Cement - Sandstone/Shale - Brine - CO2 Interactions

Background

Reactive-transport simulation is a tool that is being used to estimate long-term trapping of CO₂, and wellbore and cap rock integrity for geologic CO₂ storage. We reacted end member components of a heterolithic sandstone and shale unit that forms the upper section of the In Salah Gas Project carbon storage reservoir in Krechba, Algeria with supercritical CO₂, brine, and with/without cement at reservoir conditions to develop experimentally constrained geochemical models for use in reactive transport simulations.

Results

We observe marked changes in solution composition when CO₂ reacted with cement, sandstone, and shale components at reservoir conditions. The geochemical model for the reaction of sandstone and shale with CO₂ and brine is a simple one in which albite, chlorite, illite and carbonate minerals partially dissolve and boehmite, smectite, and amorphous silica precipitate. The geochemical model for the wellbore environment is also fairly simple, in which alkaline cements and rock react with CO₂-rich brines to form an Fe containing calcite, amorphous silica, smectite and boehmite or amorphous Al(OH)₃.

Conclusions

Our research shows that relatively simple geochemical models can describe the dominant reactions that are likely to occur when CO₂ is stored in deep saline aquifers sealed with overlying shale cap rocks, as well as the dominant reactions for cement carbonation at the wellbore interface.     

Heat capacity, entropy, and magnetic properties of jarosite-group compounds

Jarosite phases are common minerals in acidic, sulfate-rich environments. Here, we report heat capacities (C _p) and standard entropies (S°) for a number of jarosite samples. Most samples are close to the nominal composition AFe₃(SO₄)₂(OH)₆, where A = K, Na, Rb, and NH₄. One of the samples has a significant number of defects on the Fe sites and is called the defect jarosite; others are referred to as A-jarosite. The samples, their compositions, and the entropies at T = 298.15 K are:

Experimental Investigation into Hydraulic Fracture Network Propagation in Gas Shales Using CT Scanning Technology

Multistage fracturing of the horizontal well is recognized as the main stimulation technology for shale gas development. The hydraulic fracture geometry and stimulated reservoir volume (SRV) is interpreted by using the microseismic mapping technology. In this paper, we used a computerized tomography (CT) scanning technique to reveal the fracture geometry created in natural bedding-developed shale (cubic block of 30 cm × 30 cm × 30 cm) by laboratory fracturing. Experimental results show that partially opened bedding planes are helpful in increasing fracture complexity in shale. However, they tend to dominate fracture patterns for vertical stress difference Δσ _v  ≤ 6 MPa, which decreases the vertical fracture number, resulting in the minimum SRV. A uniformly distributed complex fracture network requires the induced hydraulic fractures that can connect the pre-existing fractures as well as pulverize the continuum rock mass. In typical shale with a narrow (<0.05 mm) and closed natural fracture system, it is likely to create complex fracture for horizontal stress difference Δσ _h  ≤ 6 MPa and simple transverse fracture for Δσ _h  ≥ 9 MPa. However, high naturally fractured shale with a wide open natural fracture system (>0.1 mm) does not agree with the rule that low Δσ _h is favorable for uniformly creating a complex fracture network in zone. In such case, a moderate Δσ _h from 3 to 6 MPa is favorable for both the growth of new hydraulic fractures and the activation of a natural fracture system. Shale bedding, natural fracture, and geostress are objective formation conditions that we cannot change; we can only maximize the fracture complexity by controlling the engineering design for fluid viscosity, flow rate, and well completion type. Variable flow rate fracturing with low-viscosity slickwater fluid of 2.5 mPa s was proved to be an effective treatment to improve the connectivity of induced hydraulic fracture with pre-existing fractures. Moreover, the simultaneous fracturing can effectively reduce the stress difference and increase the fracture number, making it possible to generate a large-scale complex fracture network, even for high Δσ _h from 6 MPa to 12 MPa.     

Fluid regime and diamond formation in the reduced mantle: Experimental constraints

The composition and potential diamond productivity of C–O–H fluids that could exist in the reduced regions of the Earth’s upper mantle and in the mantles of Uranus and Neptune were studied in experiments at 6.3 GPa and 1400–1600 °C and durations of 15–48 h. Hydrogen fugacity in the fluid phase was controlled by the Mo–MoO₂ or Fe–FeO buffers, using a specially modified double-capsule method. The oxygen fugacity in the samples was controlled by adding different amounts of water, stearic acid, anthracene, and docosane to a graphite charge. At high P–T conditions, the degree of decomposition of the heavy hydrocarbons added to the charge was 99.9%. The composition of the fluids coexisting with graphite/diamond in the buffered experiments varied from H₂O  H₂ > CH₄ (at fO₂ somewhat lower than the “water maximum”) to H₂ > CH₄ > (C₂H₄ + C₂H₆)>C₃H₈ (in C–H system). In the C–H system the maximum concentrations of major species in the synthesized fluid were: H₂ = 79 mol.% and CH₄ = 21 mol.%. The composition of the H₂-rich fluids, which were synthesized at 6.3 GPa and 1400–1600 °C for the first time, differs considerably from that of the ultra-reduced CH₄-rich fluids stable at 2.0–3.5 GPa and 1000–1300 °C. Thermodynamic calculations of the reduced C–O–H fluids at the P–T conditions of the experiments revealed CH₄-rich compositions (CH₄  H₂ > (C₂H₄ + C₂H₆)>C₃H₈), which however drastically differed from the synthesized compositions. The rates of diamond nucleation and growth in the experiments depended on the fluid composition. Diamond crystallization had a maximum intensity in the pure aqueous fluids, while in the H₂-rich fluids no diamond formation was observed. Only metastable graphite precipitated from the ultra-reduced fluids. The type of the initial hydrocarbon used for the fluid generation did not affect this process.     

Impact of Alkaline Earth Metals on Aqueous Speciation of Uranium(VI) and Sorption on Quartz

The effect of Mg-, Ca-, and Sr–Uranyl-Carbonato complexes with respect to sorption on quartz was studied by means of batch experiments with U(VI) concentration of 0.126 × 10⁻⁶ M in the presence and absence of Mg, Ca, and Sr (each 1 mM) at pH from 6.5 to 9. In the absence of alkaline earth elements, 90% of the U(VI) sorbed on the quartz surface at all pH. In the presence of Mg, Ca, and Sr, the sorption of U(VI) on quartz decreased to 50, 10, and 30%, respectively. Sorption kinetics of U(VI) on quartz is faster in the absence of alkaline earth elements and reached equilibrium after 12 h, whereas in the presence of Mg, Ca and Sr, the kinetics of U(VI) sorption on quartz is pH dependent and attained equilibrium after 24 h. Aqueous speciation calculations for alkaline earth uranyl carbonates were carried out by using PHREEQC with the Nuclear Energy Agency thermodynamic database (NEA_2007) by adding constants for MUO₂(CO₃)₃²⁻ and M₂UO₂(CO₃)₃⁰ (M = Ca, Mg, Sr). This study reveals that alkaline earth elements can have a significant effect on the aqueous speciation of U(VI) under neutral to alkaline pH conditions and subsequently sorption behavior and mobility of U(VI) in aqueous environments.     

The Effect of the CO32- to Ca2+ Ion activity ratio on calcite precipitation kinetics and Sr2+ partitioning

Background  

A proposed strategy for immobilizing trace metals in the subsurface is to stimulate calcium carbonate precipitation and incorporate contaminants by co-precipitation. Such an approach will require injecting chemical amendments into the subsurface to generate supersaturated conditions that promote mineral precipitation. However, the formation of reactant mixing zones will create gradients in both the saturation state and ion activity ratios (i.e., ). To better understand the effect of ion activity ratios on CaCO₃ precipitation kinetics and Sr²⁺ co-precipitation, experiments were conducted under constant composition conditions where the supersaturation state (Ω) for calcite was held constant at 9.4, but the ion activity ratio was varied between 0.0032 and 4.15.     

Sensitivity of high-resolution tropical cyclone intensity forecasts to surface flux parameterization

Surface flux parameterization schemes used in current dynamic models are primarily based upon measurements at low and moderate wind speeds. Recent studies show that these parameterization schemes may be incorrect at high wind speeds (e.g., tropical cyclone forecasts). Five high-resolution numerical model experiments are designed to assess the sensitivity of tropical cyclone intensity forecasts to changes in the surface flux parameterization. The sensitivity experiments are conducted by running 48 h forecasts of the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) for six selected tropical cyclones with individual modifications to surface flux calculation that include: (1) limiting the surface stress for wind speeds greater than 33 m s⁻¹, or 64 knots (kt); (2) computing the stress at the top of the model bottom grid layer (MBGL) by averaging results from surface layer similarity and turbulence mixing parameterization for wind speeds greater than 33 m s⁻¹; (3) increasing the roughness lengths for heat and moisture transfer by a factor of ten; (4) setting the roughness lengths for heat and moisture transfer to 1/10 of the momentum roughness length; and (5) cooling the sea surface temperature (SST) by a prescribed rate at high winds. Averaged responses for the six storms to these sensitivity tests show that: (i) the limit on surface stress at high winds significantly increases the cyclone intensity in 48 h forecasts; (ii) the averaged surface layer stress at high winds increases the cyclone intensity but to a much lesser degree than limiting the surface stress; (iii) large increases in the roughness lengths for heat and moisture transfer are needed to significantly impact the intensity forecast; (iv) the different roughness length formula for surface transfer coefficients notably increases C _h/C _d ratio from 0.59 to 0.79 for 25 m s⁻¹ and 0.41 to 0.75 for 50 m s⁻¹ that significantly increases the predicted cyclone intensity; and (v) cooling of the SST by −5.8°C in 48 h reduces the maximum surface wind speed by −32 kt, or 16.5 m s⁻¹, at 48 h forecast. These results suggest that a surface flux parameterization scheme suitable for tropical cyclone intensity forecast must correctly model the leveling-off character of surface stress and C _h/C _d ratio at high winds. All modifications to surface flux calculation have little influence on 48 h track forecasts, even though they may significantly impact the intensity forecasts.

FTIR microspectroscopy of Ediacaran phosphatized microfossils from the Doushantuo Formation,Weng'an,South China

Phosphatized microfossils from ca. 580 Ma from the Doushantuo Formation in the Weng'an region of South China were analyzed by Fourier transform infrared (FTIR) microspectroscopy for their chemical characterization. Two morpho-types of phosphatized embryo-like fossils (Megasphaera and Megaclonophycus) were analyzed, together with algal fossils. Transmission IR spectra of the microfossils have absorption bands of around 2960 cm^− 1 and 2925 cm^− 1, indicating the presence of aliphatic hydrocarbon (anti-symmetric aliphatic CH₃ and aliphatic CH₂), and have an additional band of around 1595 cm^− 1, probably derived from aromatic moieties (aromatic CC). In addition, IR microscopic mapping shows that aliphatic hydrocarbon and aromatics are distributed inside the embryo-like fossils. The embryo-like fossils appear to show three types of CH₃/CH₂ peak height ratios (R_3/2) and aromatic CC/CH₂ peak height ratios (R_CC/2 values): (1) high-R_3/2/low-R_CC/2 type (R_3/2 = ~ 0.2–1.0 and R_CC/2 ~ 0–2), (2) low-R_3/2/medium-R_CC/2 type (R_3/2 = ~ 0.2–0.6 and R_CC/2 = ~ 1–4); and (3) low-R_3/2/high-R_CC/2 type (R_3/2 = ~ 0.2–0.6 and R_CC/2 ~ 1–8). All three types are contained in both Megasphaera and Megaclonophycus. Raman spectra for the carbonaceous matter within the rock sample show a similar degree of thermal alteration, indicating that the organics were embedded in situ prior to thermal maturation. The IR spectroscopic differences might reflect differences in original organic compositions of microorganisms, and/or immediate post-mortem alteration. This suggests that the origins of phosphatized embryo-like fossils are more diverse than was previously recognized on the basis of their morphology. A comparison of R_3/2 and R_CC/2 values in the embryo-like fossils with those of the algal fossils and the extant microorganisms indicates the possible interpretation that some of the embryo-like fossils belong to animal embryo, others are algae, but none of them originate from bacteria.     

Pyrite-induced hydroxyl radical formation and its effect on nucleic acids

Background  

Pyrite, the most abundant metal sulphide on Earth, is known to spontaneously form hydrogen peroxide when exposed to water. In this study the hypothesis that pyrite-induced hydrogen peroxide is transformed to hydroxyl radicals is tested.     

Very high CO2 cordierite from Norwegian Lapland: Mineralogy,petrology, and carbon isotopes

The most CO₂-rich cordierite thus far encountered in nature with about 2.2 wt.% CO₂ and 0.3 wt.% H₂O occurs as large poikiloblasts in a strange non-foliated reaction rock that dissects well-foliated granulites being part of the classical Lapland granulite area described by Eskola. The cordierite is optically positive with the highest optic angle 2V _x (106°) and birefringence (– = 0.017) ever measured on natural cordierites, but it is also optically very heterogeneous due to secondary loss of CO₂ along fractures and zones paralleling the fluid-bearing channels. Based on the optical properties of the degassed Lapland cordierite and on literature data a ternary diagram is given, which shows the variations of this cordierite in 2V _x and birefringence as a function of channel-filling with both CO₂ and H₂O.Following Losert (1971) the cordierite coexists with calcite, a thus far unique mineral assemblage that is probably only stable at very high CO₂ pressures. In the present case, the of the cordierite (0.75) indicates, on the basis of literature data, a coexisting fluid with >0.95.The carbon isotope composition ¹³C of CO₂ in cordierite lies near –7, that of the calcite is slightly lighter than about –9. Thus, at least for the CO₂ in cordierite, a deep-seated origin may be possible.Based on the geologic occurrence it is speculated that the cordierite-bearing reaction rock could perhaps represent an annealed channel of late degassing in the granulitic lower crust.     

A comparative study on the dissolution and solubility of hydroxylapatite and fluorapatite at 25 °C and 45 °C

Dissolution of the synthetic hydroxylapatite (HAP) and fluorapatite (FAP) in pure water was studied at 25 °C and 45 °C in a series of batch experiments. The XRD, FT-IR and SEM analyses indicated that the synthetic, microcrystalline HAP and FAP with apatite structure used in the experiments were found to have no obvious variation after dissolution except that the existence of OH groups in FT-IR spectra for FAP after 2880 h dissolution was observed. During the HAP dissolution (0–4320 h), the aqueous calcium and phosphate concentrations reached the maxima after 120 h and then decreased slowly with time. For the FAP dissolution in pure water, after a transient time of 1440 h (< 60 d), element concentrations and pH became constant suggesting attainment of a steady-state between the solution and solid. During early stages of the FAP dissolution reaction (< 72–120 h), mineral components were released in non-stoichiometric ratios with reacted solution ratios of dissolved Ca:P, Ca:F and P:F being lower than mineral stoichiometric ratios of Ca₅(PO₄)₃F, i.e., 1.67, 5.0 and 3.0, respectively. This indicated that F were preferentially released compared to Ca from the mineral structure. The mean K_sp values were calculated by using PHREEQC for HAP of 10^− 53.28 (10^− 53.02–10^− 53.51) and for FAP of 10^− 55.71 (10^− 55.18–10^− 56.13) at 25 °C, the free energies of formation ΔG_f^o[HAP] and ΔG_f^o[FAP] were calculated to be − 6282.82 kJ/mol and − 6415.87 kJ/mol, respectively.