Isotopic composition of silicon in meteorites     

Carol Molinivelsko  Toshiko K. Mayeda  Robert N. Clayton   《Geochimica et cosmochimica acta》1986,50(12):2719-2726

Samples of bulk meteorites show only mass-dependent fractionation of silicon isotopes. No isotopic anomalies were found. The variation of the ratios ²⁹Si/²⁸Si and ³⁰Si/²⁸Si over the meteorite classes is small; 1%. per mass unit difference. The average Si isotopic composition for each class of meteorites is identical, within analytical uncertainties. This is quite unlike O, whose anomalous isotopic abundances in bulk samples differentiate among the classes of meteorites. The overlapping abundance ranges of Si isotopes among many classes of meteorites suggest closed-system behavior for this element prior to meteorite accretion and allow calculation of an average solar system Si isotope composition.  相似文献   

Pyrolysis-GC characterization of whole rock and kerogen-concentrate samples of immature Jurassic source rocks from NW-Germany     

Carol Arnosti  Peter J. Müller   《Organic Geochemistry》1987,11(6)

Nine rock samples from three Jurassic stratigraphic units of a shallow core from NW Germany were analyzed by pyrolysis-gas chromatography. The units contain a mixed Type-II/III kerogen (Dogger-α), a hydrogen-rich Type-II kerogen (Lias-), and a hydrogen-poor Type-III kerogen (Lias-δ). All of the kerogen was immature (R_o = 0.5%). Two sets of kerogen concentrates (“AD”: HCl/HF followed by a density separation, and “A”: only acid treatment) prepared from the rock samples were also analyzed to make a detailed comparison of the pyrolysates of rock and corresponding kerogen-concentrates.Hydrogen-index (HI) values of the kerogen concentrates prepared from organic-carbon poor rock were nearly 200% higher than HI values of the rock samples. Changes in HI were minimal for the samples containing Type-II kerogen. The A and AD samples from the C_org-poor rock yielded pyrolysates with n-alkane series of very different molecular lengths. Pyrograms of the rock samples had n-alkane series extending to n-C₁₄; the chromatograms of the A samples reached the n-C₁₄-nC₂₀ range. The AD samples from C_org-poor rock and all three sample types from the C_org-rich rock had n-alkane series up to n-C₂₉. The benzene/hexane and toluene/heptane ratios for the C_org-poor rock and A samples were far higher than for the AD samples, which had ratios similar to those of all three sample types from the C_org-rich rocks. These results indicate that choice of kerogen preparation method is critical when C_org-poor samples are analyzed.  相似文献   

Book reviews     

Carol Stoker  S. K. Sinha  David Pimentel 《Climatic change》1984,6(1):99-102

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The Geochemical Evolution of Riparian Ground Water in a Forested Piedmont Catchment   总被引：2，自引：0，他引：2  

Douglas A. Burns  L. Niel Plummer  Jeffrey J. McDonnell    Eurybiades Busenberg  Gerolamo C. Casile  Carol Kendall  Richard P. Hooper  James E. Freer  Norman E. Peters  Keith Beven  Peter Schlosser 《Ground water》2003,41(7):913-925

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Global financial stability,rapid transition to a low-carbon economy and social justice: can climate-related financial risk disclosure do it all?     

Carol Farbotko 《The Australian geographer》2019,50(3):273-278

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A perturbed parameter ensemble of HadGEM3-GC3.05 coupled model projections: part 1: selecting the parameter combinations     

Sexton  David M. H.  McSweeney  Carol F.  Rostron  John W.  Yamazaki  Kuniko  Booth  Ben B. B.  Murphy  James M.  Regayre  Leighton  Johnson  Jill S.  Karmalkar  Ambarish V. 《Climate Dynamics》2021,56(11):3395-3436

This is the first of two papers that describe the generation of a 25-member perturbed parameter ensemble (PPE) of high-resolution, global coupled simulations for the period 1900–2100, using CMIP5 historical and RCP8.5 emissions. Fifteen of these 25 coupled simulations now form a subset of the global projections provided for the UK Climate Projections 2018 (UKCP18). This first paper describes the selection of 25 variants (combinations of 47 parameters) using a set of cheap, coarser-resolution atmosphere-only simulations from a large sample of nearly 3000 variants. Retrospective 5-day weather forecasts run at climate resolution, and simulations of 2004–2009 with prescribed SST and sea ice are evaluated to filter out poor performance. We opted for a single design choice and sensitivity tests were done after the PPE was generated to demonstrate the effect of design choices on the filtering. Given our choice, only 38 of the parameter combinations were found to have acceptable performance at this stage. Idealised atmosphere-only simulations were then used to select the subset of 25 members that were as diverse as possible in terms of their CO₂ and aerosol forcing, and their response to warmer SSTs. Using our parallel set of atmosphere-only and coupled PPEs (the latter from paper 2), we show that local biases in the atmosphere-only experiments are generally informative about the biases in the coupled PPE. Biases in radiative fluxes and cloud amounts are strongly informative for most regions, whereas this is only true for a smaller fraction of the globe for precipitation and dynamical variables. Therefore, the cheap experiments are an affordable way to search for promising parameter combinations but have limitations.

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Ceres’ spectral link to carbonaceous chondrites—Analysis of the dark background materials          下载免费PDF全文

Michael Schäfer  Tanja Schäfer  Matthew R. M. Izawa  Edward A. Cloutis  Stefan E. Schröder  Thomas Roatsch  Frank Preusker  Katrin Stephan  Klaus‐Dieter Matz  Carol A. Raymond  Christopher T. Russell 《Meteoritics & planetary science》2018,53(9):1925-1945

Ceres’ surface has commonly been linked with carbonaceous chondrites (CCs) by ground‐based telescopic observations, because of its low albedo, flat to red‐sloped spectra in the visible and near‐infrared (VIS/NIR) wavelength region, and the absence of distinct absorption bands, though no currently known meteorites provide complete spectral matches to Ceres. Spatially resolved data of the Dawn Framing Camera (FC) reveal a generally dark surface covered with bright spots exhibiting reflectance values several times higher than Ceres’ background. In this work, we investigated FC data from High Altitude Mapping Orbit (HAMO) and Ceres eXtended Juling (CXJ) orbit (~140 m/pixel) for global spectral variations. We found that the cerean surface mainly differs by spectral slope over the whole FC wavelength region (0.4–1.0 μm). Areas exhibiting slopes ?1 constitute only ~3% of the cerean surface and mainly occur in the bright material in and around young craters, whereas slopes ≥?10% μm^?1 occur on more than 90% of the cerean surface; the latter being denoted as Ceres’ background material in this work. FC and Visible and Infrared Spectrometer (VIR) spectra of this background material were compared to the suite of CCs spectrally investigated so far regarding their VIS/NIR region and 2.7 μm absorption, as well as their reflectance at 0.653 μm. This resulted in a good match to heated CI Ivuna (heated to 200–300 °C) and a better match for CM1 meteorites, especially Moapa Valley. This possibly indicates that the alteration of CM2 to CM1 took place on Ceres.  相似文献   

Fluoride-Selective Electrode as a Tool to Evaluate the Degradation of PFAS in Groundwater: A Bench-Scale Investigation     

Janice Stonebridge  Rachel Baldwin  Neil R. Thomson  Carol Ptacek 《Ground Water Monitoring & Remediation》2020,40(2):73-80

Fluoride (F⁻) concentration in groundwater can be used as an independent measure of the degradation of per- and polyfluoroalkyl substances (PFAS) at contaminated sites. This study assessed the impact of the groundwater matrix, oxidizing reagents, quenching agent, and sample handling procedures (filtration) on determinations of F⁻. F⁻ was quantified using a fluoride-selective electrode (FSE) using matrix spike recovery (acceptable range 75 to 125%) and electrode slope performance (ideal range −54 to −60 mV). For the unaltered aqueous matrices considered (ultrapure water, ultrapure water with sodium chloride, and simulated groundwater), matrix spike recoveries were greater than 93% and acceptable electrode slopes (−59.5 ± 0.2 mV) were obtained. Matrix spike recoveries and electrode slopes when persulfate or permanganate was added were 87 and 93%, and −58.4 ± 1.3 and −47.3 ± 2.2 mV, respectively. Therefore, quantifying F⁻ in matrices containing permanganate should involve use of either a matrix-matched calibration curve or the method of standard additions due to the low electrode slope. The addition of ascorbic acid as a quenching agent resulted in a decrease in matrix spike recoveries to <74% and suggests alternate quenching procedures should be used if an FSE is employed to measure F⁻. Removal of sediments by filtration prior to the addition of the fluoride spike led to improved matrix spike recoveries (>96%), which were otherwise underestimated using the FSE in the presence of sediments. While the FSE may be a quick and portable tool, its significant limitations need to be fully understood before it can be used to quantify the production of F⁻ resulting from the potential degradation of PFAS at field sites.  相似文献   

The daily‐scale entrance dynamics of intermittently open/closed estuaries          下载免费PDF全文

Sarah Louise McSweeney  David M. Kennedy  Ian D. Rutherfurd 《地球表面变化过程与地形》2018,43(4):791-807

Intermittently open/closed estuaries (IOCE) are a dynamic form of estuary characterised by periodic entrance closure to the ocean. Entrance closure is a function of the relative balance between on and offshore sediment transport with closures occurring during periods of low fluvial discharge whereby the estuary ebb‐tidal prism is reduced. Although the broad scale processes of entrance closure are becoming better understood, there remains limited knowledge on channel morphodynamics during an individual closure event. In this study, the entrance dynamics of three IOCE on the coast of Victoria, Australia, were monitored over a daily timescale following both artificial and natural openings. The influence of changing marine and fluvial conditions on the relative sedimentation rate within the entrance channel was examined. IOCE in Victoria showed two distinct modes of entrance closure: (a) lateral accretion, whereby the estuary gradually closes by longshore drift‐driven spit growth during low river flows; and (b) vertical accretion, where the channel rapidly aggrades under high (> 2 m), near‐normal waves. During storms, when fluvial discharge and wave heights simultaneously increase, large swells will not always close the mouth due to an increase in the ebb‐tidal prism. The estuary water depth and the maximum channel dimensions following opening were not proportional to the opening duration, with this being a function of the wave and fluvial conditions occurring following lagoon drainage. Based on the findings of this work, implementing a successful artificial entrance opening is dependent on reduced onshore sedimentation rates which occur when wave energy is low (< 2 m Hs) relative to river flow. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Storage and Preservation of Artificial Sweeteners in Groundwater Samples          下载免费PDF全文

Emily M. Saurette  Laura G. Groza  David W. Blowes  Carol J. Ptacek 《Ground Water Monitoring & Remediation》2017,37(4):71-81

Compound‐specific standardized sampling and storage methods are not available for artificial sweeteners found in groundwater. This study aimed to understand: (1) the appropriate length of storage time for samples containing acesulfame (ACE), sucralose (SUC), saccharin (SAC), and cyclamate (CYC) in simulated groundwater (SGW); (2) conditions of their stability; and (3) which sampling materials are appropriate for sample collection. The evaluated storage conditions included acidification, headspace, exposure to light, and refrigeration; the evaluated sampling materials included steel, stainless steel, aluminum, polyvinyl chloride, polyamide (nylon), polypropylene (PharMed BPT?) tubing, styrene‐ethylene‐butylene co‐polymer (MasterFlex?) tubing, and polytetrafluoroethylene (Teflon?) tubing. All compounds evaluated were stable in storage at 4 °C for 241 d (8 months). Concentrations of artificial sweeteners were consistently within 60% to 120% of original concentrations, except ACE and SAC that were substantially lower under acidified conditions at 25 °C after 241 d. Artificial sweetener concentrations remained nearly constant while in contact with all sampling materials except steel. SEM and TEM images showed oxidation of steel occurred; moreover, removal of all artificial sweetener compounds from aqueous solution had occurred after 289 d. These results suggest artificial sweetener analyses conducted within 14 d of sample collection produce optimal results; however, longer storage times may be acceptable under certain conditions. The results also suggest concentrations of artificial sweeteners in SGW are not affected by contact with typical well casing, sampling, and storage materials, with the exception of steel. The findings from this study will improve the use of artificial sweeteners as tracers in environmental studies.  相似文献