A Common Reference Material for Cadmium Isotope Studies – NIST SRM 3108

Research into natural mass‐dependent stable isotope fractionation of cadmium has rapidly expanded in the past few years. Methodologies are diverse with MC‐ICP‐MS favoured by all but one laboratory, which uses thermal ionisation mass spectrometry (TIMS). To quantify the isotope fractionation and correct for instrumental mass bias, double‐spike techniques, sample‐calibrator bracketing or element doping has been used. However, easy comparison between data sets has been hampered by the multitude of in‐house Cd solutions used as zero‐delta reference in different laboratories. The lack of a suitable isotopic reference material for Cd is detrimental for progress in the long term. We have conducted a comprehensive round‐robin assay of NIST SRM 3108 and the Cd isotope offsets to commonly used in‐house reference materials. Here, we advocate NIST SRM 3108 both as an isotope standard and the isotopic reference point for Cd and encourage its use as ‘zero‐delta’ in future studies. The purity of NIST SRM 3108 was evaluated regarding isobaric and polyatomic molecular interferences, and the levels of Zn, Pd and Sn found were not significant. The isotope ratio ¹¹⁴Cd/¹¹⁰Cd for NIST SRM 3108 lies within ～ 10 ppm Da^?1 of best estimates for the Bulk Silicate Earth and is validated for all measurement technologies currently in use.     

Arsenic in an alkaline AMD treatment sludge: Characterization and stability under prolonged anoxic conditions

Lime treatment of acid mine drainage (AMD) generates large volumes of neutralization sludge that are often stored under water covers. The sludge consists mainly of calcite, gypsum and a widespread ferrihydrite-like Fe phase with several associated species of metal(loid) contaminants. The long-term stability of metal(loid)s in this chemically ill-defined material remains unknown. In this study, the stability and speciation of As in AMD sludge subjected to prolonged anoxic conditions is determined. The total As concentration in the sludge is 300 mg kg⁻¹. In the laboratory, three distinct water cover treatments were imposed on the sludge to induce different redox conditions (100%N₂, 100%N₂ + glucose, 95%N₂:5%H₂). These treatments were compared against a control of oxidized, water-saturated sludge. Electron micro-probe (EMP) analysis and spatially resolved synchrotron X-ray fluorescence (SXRF) results indicate that As is dominantly associated with Fe in the sludge. In all treatments and throughout the experiment, measured concentrations of dissolved As were less than 5 μg L⁻¹. Dissolved Mn concentration in the N₂ + glucose treatment increased significantly compared to other treatments. Manganese and As K-edge X-ray absorption near edge structure spectroscopy (XANES) analyses showed that Mn was the redox-active element in the solid-phase, while As was stable. Arsenic(V) was still the dominant species in all water-covered sludges after 9 months of anoxic treatments. In contrast, Mn(IV) in the original sludge was partially reduced into Mn(II) in all water-covered sludges. The effect was most pronounced in the N₂ + glucose treatment, suggesting microbial reduction. Micro-scale SXRF and XANES analysis of the treated sludge showed that Mn(II) accumulated in areas already enriched in Fe and As. Overall, the study shows that AMD sludges remain stable under prolonged anoxic conditions. External sources of chemical reductants or soluble C were needed to induce lower redox state in the systems, and even under these imposed treatments, only weakly reducing conditions (Mn threshold) developed. The results suggest that As(V) in AMD sludge will remain stable under prolonged anoxic conditions as long as Mn(IV) is present and organic matter accumulation is negligible.     

Dislocations in CaTiO3 perovskite deformed at high-temperature: a transmission electron microscopy study

Dislocation configurations in natural single crystals of CaTiO₃ perovskite deformed in high-temperature creep were examined and characterized by transmission electron microscopy. Screw dislocations with Burgers vector [100]_pc and [011]_pc, dissociated on the $(01\bar 1)_{{\text{pc}}} $ plane, form rectangular networks with extended four-fold nodes in the shape of octagons, a configuration never observed in any of the previously investigated perovskites, except CaGeO₃. Screw dislocations with Burgers vector [101]_pc and $(\bar 101)_{{\text{pc}}} $ , on the (010)_pc plane, react to form a twist wall; the dislocations with Burgers vector [002] produced by the reaction decompose into two perfect dislocations [001]_pc. This results in a new configuration, never observed before, with three-fold nodes at the corners of rectangles. Both the octagonal extended nodes and the junctions decomposed into perfect dislocations are seen in samples deformed indifferently by slip on {100}_pc or {110}_pc planes, but they seem to appear only above 1520 K, in the cubic phase.     

Heliocentric evolution of the degradation of polyoxymethylene: Application to the origin of the formaldehyde (H2CO) extended source in Comet C/1995 O1 (Hale-Bopp)

The H₂CO production rates measured in Comet C/1995 O1 (Hale-Bopp) from radio wavelength observations [Biver, N., and 22 colleagues, 2002a. Earth Moon Planets 90, 5-14] showed a steep increase with decreasing heliocentric distance. We studied the heliocentric evolution of the degradation of polyoxymethylene (formaldehyde polymers: (CH₂O)_n, also called POM) into gaseous H₂CO. POM decomposition can indeed explain the H₂CO density profile measured in situ by Giotto spacecraft in the coma of Comet 1P/Halley, which is not compatible with direct release from the nucleus [Cottin, H., Bénilan, Y., Gazeau, M.-C., Raulin, F., 2004. Icarus 167, 397-416]. We show that the H₂CO production curve measured in Comet C/1995 O1 (Hale-Bopp) can be accurately reproduced by this mechanism with a few percents by mass of solid POM in grains. The steep heliocentric evolution is explained by the thermal degradation of POM at distances less than 3.5 AU. This study demonstrates that refractory organics present in cometary dust can significantly contribute to the composition of the gaseous coma. POM, or POM-like polymers, might be present in cometary grains. Other molecules, like CO and HNC, might also be produced by a similar process.     

Determination of deployment specific chemical uptake rates for SPMD and PDMS using a passive flow monitor

Passive sampling techniques facilitate the time-integrated measurement of pollutant concentrations through the use of a selective receiving phase. Accurate quantification using passive sampling devices rely on the implementation of methods that will negate the effects of environmental factors (flow, temperature, etc.) or that will allow the calculation of the chemical specific rates of uptake (R(s)) into the passive sampler employed. We have applied an in situ calibration technique based on the dissolution of gypsum to measure the average water velocity to which a sampler has been exposed. We demonstrate that the loss of gypsum from the passive flow monitor (PFM) can be applied to predict changes in R(s) dependent on flow when using the absorbent SPMD (semipermeable membrane device) and PDMS (polydimethyl siloxan) passive samplers. The application of the PFM will enhance the accuracy of measurements made when calculating and reporting environmental pollutant concentrations using a passive sampling device.     

Toward a unified model of Altaids geodynamics: Insight from the Palaeozoic polycyclic evolution of West Junggar (NW China)

The Altaid tectonic collage extends over Central Asia, exposing numerous accretionary orogens that can account for the Palaeozoic continental crust growth. A pluridisciplinary approach, using geochronological, geochemical, structural and palaeomagnetic tools was carried out to unravel the architecture and the evolution of West Junggar(Northwestern China), a segment of the Altaid Collage. A polycyclic geodynamic evolution is inferred and includes:(1) an Early Palaeozoic cycle, characterized by the closure of two oceanic basins bounded by island-arc systems;(2) an Early Devonian subduction jamming resulting in a minor-scale collision documented by thrusting, syntectonic sedimentation and subsequent crutal thinning associated with alkaline magmatism;(3) a Late Palaeozoic cycle, driven by the evolution of two opposite subduction zones developed upon the Early Palaeozoic basement. Detailed structural analysis and paleomagnetic data provide constraints for the late evolution of Junggar in the frame of the development of the Late Palaeozoic Kazakh orocline, which led to oblique subduction and transpression in the West Junggar accretionary complex. Progressive buckling of the Kazakh orocline further resulted in Late Carboniferous to Permian wrench tectonics, and lateral displacement of lithotectonic units. Block rotations that continued after the Late Triassic are due to diachronous intraplate reactivation. This scenario mirrors the Palaeozoic geodynamics of the Altaid Collage. Multiple Early Palaeozoic collisions of intra-oceanic arcs and micro continents have contributed to the formation of the Kazakhstan Microcontinent. Since the Late Palaeozoic, subductions formed around this microcontinent and the final oblique closure of oceanic domains resulted in the transcurrent collage of Tarim and Siberia cratons. Palaeozoic strike-slip faults were later reactivated during Mesozoic intracontinental tectonics.     

A preliminary investigation of strong-motion data from the French Antilles

Strong-motion networks have been operating in the Caribbean region since the 1970s, however, until the mid-1990s only a few analogue stations were operational and the quantity of data recorded was very low. Since the mid-1990s, digital accelerometric networks have been established on islands within the region. At present there are thought to be about 160 stations operating in this region with a handful on Cuba, 65 on the French Antilles (mainly Guadeloupe and Martinique), eight on Jamaica, 78 on Puerto Rico (plus others on adjacent islands) and four on Trinidad.After briefly summarising the available data from the Caribbean islands, this article is mainly concerned with analysing the data that has been recorded by the networks operating on the French Antilles in terms of their distribution with respect to magnitude, source-to-site distance, focal depth and event type; site effects at certain stations; and also with respect to their predictability by ground motion estimation equations developed using data from different regions of the world. More than 300 good quality triaxial acceleration time-histories have been recorded on Guadeloupe and Martinique at a large number of stations from earthquakes with magnitudes larger than 4.8, however, most of the records are from considerable source-to-site distances. From the data available it is found that many of the commonly-used ground motion estimation equations for shallow crustal earthquakes poorly estimate the observed ground motions on the two islands; ground motions on Guadeloupe and Martinique have smaller amplitudes and are more variable than expected. This difference could be due to regional dependence of ground motions because of, for example, differing tectonics or crustal structures or because the ground motions so far recorded are, in general, from smaller earthquakes and greater distances than the range of applicability of the investigated equations.     

Adaptation of prestack migration to multi-offset ground-penetrating radar (GPR) data

In adapting the prestack migration technique used in seismic imaging to the inversion of ground‐penetrating radar (GPR) from time‐ to depth‐sections, we show that the theoretical integral formulation of the inversion can be applied to electromagnetic problems, albeit with three assumptions. The first two assumptions concern the electromagnetic characteristics of the medium, primarily that the medium must be perfectly resistive and non‐dispersive, and the third concerns the antennae radiation pattern, which is taken to be 2D. The application of this adaptation of the inversion method is confirmed by migrating actual GPR measurements acquired on the test site of the Laboratoire Central des Ponts et Chaussées. The results show good agreement with the geometry of the structures in the medium and confirm that the possible departure from the assumption of a purely resistive medium has no visible effect on the information concerning the geometry of scattering and reflecting structures. The field experiments also show that prestack migration processing is sufficiently robust with regard to the assumption of a non‐dispersive medium. The assumption of a 2D antennae radiation pattern, however, produces artefacts that could be significant for laterally heterogeneous media. Nevertheless, where the medium is not highly laterally heterogeneous, the migration gives a clear image of the scattering potential due to the geometry of structural contrasts in the medium; the scatterers are well focused from diffraction hyperbolae and well localized. Spatial geometry has limited dimensional accuracy and positions are located with a maximum error equal to the minimum wavelength of the signal bandpass. Objects smaller than one wavelength can nevertheless be detected and well focused if their dielectric contrasts are sufficiently high, as in the case of iron or water in gneiss gravels. Furthermore, the suitability of multi‐offset protocols to estimate the electromagnetic propagating velocity and to decrease the non‐coherent noise level of measurements is confirmed. Our velocity estimation is based on the semblance calculation of multi‐offset migrated images, and we confirmed the relevance of this quantification method using numerical data. The signal‐to‐noise ratio is improved by summing multi‐offset results after the addition of random noise on measurements. Thus the adaptation of prestack migration to multi‐offset radar measurements significantly improves the resolution of the scattering potential of the medium. Limitations associated with the methods used here suggest that 3D algorithms should be applied to strongly laterally heterogeneous media and further studies concerning the waveform inversion are necessary to obtain information about the electric nature of the medium.     

Impact of climate change on the hydrogeology of two basins in northern France

This study presents an analysis of climate-change impacts on the water resources of two basins located in northern France, by integrating four sources of uncertainty: climate modelling, hydrological modelling, downscaling methods, and emission scenarios. The analysis focused on the evolution of the water budget, the river discharges and piezometric heads. Seven hydrological models were used, from lumped rainfall-discharge to distributed hydrogeological models, and led to quite different estimates of the water-balance components. One of the hydrological models, CLSM, was found to be unable to simulate the increased water stress and was, thus, considered as an outlier even though it gave fair results for the present day compared to observations. Although there were large differences in the results between the models, there was a marked tendency towards a decrease of the water resource in the rivers and aquifers (on average in 2050 about ?14 % and ?2.5 m, respectively), associated with global warming and a reduction in annual precipitation (on average in 2050 +2.1 K and ?3 %, respectively). The uncertainty associated to climate models was shown to clearly dominate, while the three others were about the same order of magnitude and 3–4 times lower. In terms of impact, the results found in this work are rather different from those obtained in a previous study, even though two of the hydrological models and one of the climate models were used in both studies. This emphasizes the need for a survey of the climatic-change impact on the water resource.     

Rossby wave interactions with Mediterranean and subtropical latitudes

The downstream influence of a Rossby wave on weather conditions in the Mediterranean and North Africa is studied. The objective is to gain a better understanding of the atmospheric processes in these regions and to improve their quantification. The emphasis is placed on high-impact weather events to improve numerical forecasts and warnings about these hazardous weather phenomena. For this purpose, 4 days from 5 to 8 February 1997 are used to investigate both a Mediterranean low and a subtropical African convective situation. Sensitivity studies, using a potential vorticity inversion tool associated with the French atmospheric model ARPEGE, are presented. The Mediterranean surface low under study is shown to be associated with the mid-latitude upper level potential vorticity anomaly, itself associated with a Rossby wave. A subtropical convective cell is shown to be related to upward vertical motions associated with a cut-off low; this cut-off low coming from a mid-latitude Rossby wave.