Stratospheric N2O5, CH4, and N2O profiles from IR solar occultation spectra

Stratospheric volume mixing ratio profiles of N₂O₅, CH₄, and N₂O have been retrieved from a set of 0.052 cm^–1 resolution (FWHM) solar occultation spectra recorded at sunrise during a balloon flight from Aire sur l'Adour, France (44° N latitude) on 12 October 1990. The N₂O₅ results have been derived from measurements of the integrated absorption by the 1246 cm^–1 band. Assuming a total intensity of 4.32×10^–17 cm^–1/molecule cm^–2 independent of temperature, the retrieved N₂O₅ volume mixing ratios in ppbv (parts per billion by volume, 10^–9), interpolated to 2 km height spacings, are 1.64±0.49 at 37.5 km, 1.92±0.56 at 35.5 km, 2.06±0.47 at 33.5 km, 1.95±0.42 at 31.5 km, 1.60±0.33 at 29.5 km, 1.26±0.28 at 27.5 km, and 0.85±0.20 at 25.5 km. Error bars indicate the estimated 1- uncertainty including the error in the total band intensity (±20% has been assumed). The retrieved profiles are compared with previous measurements and photochemical model results.Laboratoire associé aux Universités Pierre et Marie Curie et Paris Sud.     

Première datation UPb des orthogneiss œillés de la zone axiale de la Montagne noire (Sud du Massif central) : nouveaux témoins du magmatisme ordovicien dans la chaı̂ne Varisque

We present new U–Pb results on felsic Augen orthogneisses from the Axial Zone of the Montagne Noire (French Massif Central). The data indicate Ordovician ages, 456±3 and 450±6 Ma for two samples collected at ‘Pont-de-Larn’ and ‘Gorges d'Héric’, respectively. These ages are interpreted as the igneous emplacement age of the granitic protolith. To cite this article: F. Roger et al., C. R. Geoscience 336 (2004).     

Experimental study of arsenic speciation in vapor phase to 500°C: implications for As transport and fractionation in low-density crustal fluids and volcanic gases

The stoichiometry and stability of arsenic gaseous complexes were determined in the system As-H₂O ± NaCl ± HCl ± H₂S at temperatures up to 500°C and pressures up to 600 bar, from both measurements of As^(III) and As^(V) vapor-liquid and vapor-solid partitioning, and X-ray absorption fine structure (XAFS) spectroscopic study of As^(III)-bearing aqueous fluids. Vapor-aqueous solution partitioning for As^(III) was measured from 250 to 450°C at the saturated vapor pressure of the system (P_sat) with a special titanium reactor that allows in situ sampling of the vapor phase. The values of partition coefficients for arsenious acid (H₃AsO₃) between an aqueous solution (pure H₂O) and its saturated vapor (K = mAs_vapor /mAs_liquid) were found to be independent of As^(III) solution concentrations (up to ∼1 to 2 mol As/kg) and equal to 0.012 ± 0.003, 0.063 ± 0.023, and 0.145 ± 0.020 at 250, 300, and 350°C, respectively. These results are interpreted by the formation, in the vapor phase, of As(OH)₃(gas), similar to the aqueous As hydroxide complex dominant in the liquid phase. Arsenic chloride or sulfide gaseous complexes were found to be negligible in the presence of HCl or H₂S (up to ∼0.5 mol/kg of vapor). XAFS spectroscopic measurements carried out on As^(III)-H₂O (±NaCl) solutions up to 500°C demonstrate that the As(OH)₃ complex dominates As speciation both in dense H₂O-NaCl fluids and low-density supercritical vapor. Vapor-liquid partition coefficients for As^(III) measured in the H₂O-NaCl system up to 450°C are consistent with the As speciation derived from these spectroscopic measurements and can be described by a simple relationship as a function of the vapor-to-liquid density ratio and temperature. Arsenic^(III) partitioning between vapor and As-concentrated solutions (>2 mol As/kg) or As₂O₃ solid is consistent with the formation, in the vapor phase, of both As₄O₆ and As(OH)₃. Arsenic^(V) (arsenic acid, H₃AsO₄) vapor-liquid partitioning at 350°C for dilute aqueous solution was interpreted by the formation of AsO(OH)₃ in the vapor phase.The results obtained were combined with the corresponding properties for the aqueous As(III) hydroxide species to generate As(OH)₃(gas) thermodynamic parameters. Equilibrium calculations carried out by using these data indicate that As(OH)₃(gas) is by far the most dominant As complex in both volcanic gases and boiling hydrothermal systems. This species is likely to be responsible for the preferential partition of arsenic into the vapor phase as observed in fluid inclusions from high-temperature (400 to 700°C) Au-Cu (-Sn, -W) magmatic-hydrothermal ore deposits. The results of this study imply that hydrolysis and hydration could be also important for other metals and metalloids in the H₂O-vapor phase. These processes should be taken into account to accurately model element fractionation and chemical equilibria during magma degassing and fluid boiling.     

High Precision Hf-W Isotopic Measurements in Meteoritic Material Using Negative Thermal Ionisation Mass Spectrometry (NTIMS)

This paper presents a two-stage anion-exchange procedure for tungsten extraction, an improved mass spectrometric procedure for tungsten analysis and a simplified chemical separation and TIMS procedure for the determination of Hf concentrations. The chemical separation of tungsten is based on its complexing properties with HF and H₂O₂. The blank level for a sample size of 300 mg is about 80 pg for tungsten. The procedure is designed for the high sensitivity of negative thermal ionisation mass spectrometry (NTIMS) provided by the use of Mg oxide as an emitter on Ir filaments. Tungsten can be readily measured with a high precision in various meteoritical material and especially in small W-poor silicate fractions. Samples containing as little as a few ng g^-1 tungsten can be analysed reliably with this method.     

Geodynamic significance of the Raspas Metamorphic Complex (SW Ecuador): geochemical and isotopic constraints

The Raspas Metamorphic Complex of southwestern Ecuador is regarded as the southernmost remnant of oceanic and continental terranes accreted in the latest Jurassic–Early Cretaceous. It consists of variably metamorphosed rock types. (1) Mafic and ultramafic rocks metamorphosed under high-pressure (HP) conditions (eclogite facies) show oceanic plateau affinities with flat REE chondrite-normalized patterns, Nd_{150 Ma} ranging from +4.6 to 9.8 and initial Pb isotopic ratios intermediate between MORB and OIB. (2) Sedimentary rocks metamorphosed under eclogitic conditions exhibit LREE enriched patterns, strong negative Eu anomalies, Rb, Nb, U, Th, Pb enrichments, low Nd_{150 Ma} values (from −6.4 to −9.5), and high initial ⁸⁷Sr/⁸⁶Sr and ^206,207,208Pb/²⁰⁴Pb isotopic ratios suggesting they were originally sediments derived from the erosion of an old continental crust. (3) Epidote-bearing amphibolites show N-MORB affinities with LREE depleted patterns, LILE, Zr, Hf and Th depletion, high Nd_{150 Ma} (>+10) and low initial Pb isotopic ratios.The present-day well defined internal structure of the Raspas Metamorphic Complex seems to be inconsistent with the formerly proposed interpretation of a “tectonic mélange”. The association of oceanic plateau rocks and continent-derived sediments both metamorphosed in HP conditions suggests that the thin edge of the oceanic plateau first entered the subduction zone and dragged sediments downward of the accretionary wedge along the Wadatti–Benioff zone. Subsequently, when its thickest part arrived into the subduction zone, the oceanic plateau jammed the subduction processes, due to its high buoyancy.In Ecuador and Colombia, the latest Jurassic–Early Cretaceous suture involves HP oceanic plateau rocks and N-MORB rocks metamorphosed under lower grades, suggesting a composite or polyphase nature for the latest Jurassic–Early Cretaceous accretionary event.     

Simulation des changements climatiques au cours du XXIe siècle incluant l'ozone stratosphériqueSimulation of climate changes during the 21st century including stratospheric ozone

Two climate simulations of 150 years, performed with a coupled ocean/sea-ice/atmosphere model including stratospheric ozone, respectively with and without heterogeneous chemistry, simulate the tropospheric warming associated with an increase of the greenhouse effect of carbon dioxide and other trace gases since 1950 and their impact on sea–ice extent, as well as the stratospheric cooling and its impact on ozone concentration. The scenario with heterogeneous chemistry reproduces the formation of the ozone hole over the South Pole from the 1970s and its deepening until the present time, and shows that the ozone hole should progressively fill during the coming decades. To cite this article: J.-F. Royer et al., C. R. Geoscience 334 (2002) 147–154.     

Hyperspectral core logging for fire reconstruction studies

Lacustrine sediments contain a wide range of proxies that enable paleoenvironmental reconstructions. For instance, charcoal can be used to document past fire regime changes. In order to analyse high-temporal- and spatial-resolution records, however, it is necessary to develop fast, low-cost and high-stratigraphic-resolution methods. We developed a new paleo-fire proxy by studying a lacustrine core from the Esterel Massif, SE France, an area affected by two recent fire events, in AD 1987 and 2003. For this purpose, we searched for charcoal deposited and preserved in the lake sediments by combining a number of complementary methods, including: classic macrocharcoal tallying, scanning spectrophotometry, scanning hyperspectral imaging and high pressure liquid chromatography analyses. Macrocharcoal quantification is efficient, but time-consuming, and only provides intermediate-resolution data (cm scale). Spectrophotometry, used classically to quantify colour, is very fast, provides high-resolution data (4 mm) and is non-destructive (core preservation). Hyperspectral data have the same advantages as spectrophotometry, but offer higher spatial resolution (64-µm pixel size) and higher spectral resolution (6 nm) for core logging applications. The main result of this research is based on hyperspectral analysis at very high stratigraphic resolution using the I-band index. This index usually measures reflectance values at [660, 670 nm] corresponding to the trough in red reflectance produced by Chlorophyll a and its diagenetic products. This [660, 670 nm] reflectance trough, however, is also affected by the presence of altered organic matter and decreases with altered organic matter such as charcoal particles. Charcoal effect on the reflectance of Chlorophyll a and its diagenetic products is identified on first derivative spectra by a characteristic pattern around 675 nm, which is also in agreement with the Chlorophyll a concentrations measured by high-pressure liquid chromatography and charcoal particles. The I-band index is hence suitable for detecting burned organic matter, by quantifying the dilution of the chlorophyll signal by the charcoal signal. Thus, this adaptation of the I-band index can be applied in fire reconstruction studies.     

Asteroseismology and interferometry

Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research.     

Tracking the Settlement of North African Immigrants: speculations on the social and cultural impacts of a newly arrived immigrant group

In the past five years Australia has experienced a dramatic increase in the number of North African arrivals. The majority of North African arrivals for the past 4 years have arrived as humanitarian entrants. This migration stream reflected a shift in the regional focus of the humanitarian program towards Africa. The majority of North African arrivals since 2000–01 have been from Sudan. The States of New South Wales and Victoria received the highest proportions of these arrivals. Key issues, and important research topics for social scientists, are at least threefold. First, the domestic politics and international geopolitics of this humanitarian flow need critical analysis. Second, the suitability of settlement services needs to be assessed. Specifically, the effects and merit of privatising service provision to these refugees requires rigorous scholarly assessment. Finally, more needs to be known about the cultural adaptation of this group, especially youth. Research into the experiences of racism and, relatedly, the existence and appropriateness of anti-racism initiatives is required.