Chlorine budget and partitioning during the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE)

The amount of chlorine in the stratosphere has a direct influence on the magnitude of chlorine-catalyzed ozone loss. A comprehensive suite of organic source gases of chlorine in the stratosphere was measured during the NASA Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE) campaign in the arctic winter of 2000. Measurements included chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halon 1211, solvents, methyl chloride, N2O, and CH4. Inorganic chlorine contributions from each compound were calculated using the organic chlorine measurements, mean age of air, tropospheric trends, and a method to account for mixing in the stratosphere. Total organic chlorine measured at tropospheric levels of N2O was on the order of 3500 ppt. Total calculated inorganic chlorine at a N2O mixing ratio of 50 ppb (corresponding to a mean age of 5.5 years) was on the order of 3400 ppt. CFCs were the largest contributors to total organic chlorine (55-70%) over the measured N2O range (50-315 ppb), followed by CH3Cl (15%), solvents (5-20%), and HCFCs (5-25%). CH3Cl contribution was consistently about 15% across the organic chlorine range. Contributions to total calculated inorganic chlorine at 50 ppb N2O were 58% from CFCs, 24% from solvents, 16% from CH3Cl, and 2% from HCFCs. Updates to fractional chlorine release values for each compound relative to CFC 11 were calculated from the SOLVE measurements. An average value of 0.58 was calculated for the fractional chlorine release of CFC 11 over the 3-4 year mean age range, which was lower than the previous value of 0.80. The fractional chlorine release values for HCFCs 141b and 142b relative to CFC 11 were significantly lower than previous calculations

Two-billion-year-old evaporites capture Earth's great oxidation

Funding sources: Simons Foundation (SCOL 339006 to C.L.B.), European Research Council (ERC Horizon 2020 grant 678812 to M.C.), Research Council of Norway (RCN Centres of Excellence funding scheme project 223259 to K.P. and A.L.), Estonian Science Agency (PUT696 to K.K., A.L., K.P., T.K.).Major changes in atmospheric and ocean chemistry occurred in the Paleoproterozoic Era (2.5–1.6 billion years ago). Increasing oxidation dramatically changed Earth’s surface, but few quantitative constraints exist on this important transition. This study describes the sedimentology, mineralogy, and geochemistry of a remarkably preserved two-billion-year-old and ~800 meter-thick evaporite succession from the Onega Basin in Russian Karelia. The deposit consists of a basal unit dominated by halite (~100 m) followed by anhydrite-magnesite (~500 m) and dolomite-magnesite (~200 m) dominated units. The evaporite minerals robustly constraint marine sulfate concentrations to at least 10 millimoles per kilogram of water, representing an oxidant reservoir equivalent to over 20% of the modern ocean-atmosphere oxidizing capacity. These results show that substantial amounts of surface oxidant accumulated during this critical transition in Earth’s oxygenation.PostprintPeer reviewe

The convective transport of active species in the tropics (Contrast) experiment

The Convective Transport of Active Species in the Tropics (CONTRAST) experiment was conducted from Guam (13.5degN, 144.8degE) during January-February 2014. Using the NSF/NCAR Gulfstream V research aircraft, the experiment investigated the photochemical environment over the tropical western Pacific (TWP) warm pool, a region of massive deep convection and the major pathway for air to enter the stratosphere during Northern Hemisphere (NH) winter. The new observations provide a wealth of information for quantifying the influence of convection on the vertical distributions of active species. The airborne in situ measurements up to 15-km altitude fill a significant gap by characterizing the abundance and altitude variation of a wide suite of trace gases. These measurements, together with observations of dynamical and microphysical parameters, provide significant new data for constraining and evaluating global chemistry climate models. Measurements include precursor and product gas species of reactive halogen compounds that impact ozone in the upper troposphere/lower stratosphere. High-accuracy, in situ measurements of ozone obtained during CONTRAST quantify ozone concentration profiles in the upper troposphere, where previous observations from balloon-borne ozonesondes were often near or below the limit of detection. CONTRAST was one of the three coordinated experiments to observe the TWP during January-February 2014. Together, CONTRAST, Airborne Tropical Tropopause Experiment (ATTREX), and Coordinated Airborne Studies in the Tropics (CAST), using complementary capabilities of the three aircraft platforms as well as ground-based instrumentation, provide a comprehensive quantification of the regional distribution and vertical structure of natural and pollutant trace gases in the TWP during NH winter, from the oceanic boundary to the lower stratosphere

Implementation of computer modelling of space framed structures

The algorithms for geometrical computer modelling of space framed structures are discussed in the paper. These algorithms are implemented by the authors in computer software. The software is based on geometrical analysis and visualization of selected types of structural systems based on unified prototypes and includes the feature of combining prototypes, thus creating complex spatial framed systems

Identifying global vs. basinal controls on Paleoproterozoic organic carbon and sulfur isotope records

Paleoproterozoic sedimentary successions are important archives of the redox evolution of Earth's atmosphere and oceans. Efforts to unravel the dynamics of our planet's early oxygenation from this archive rely on various geochemical proxies, including stable carbon and sulfur isotopes. However, ancient metasedimentary rocks often experienced early- and late-stage (bio)geochemical processes making it difficult to discern primary environmental signals from bulk-rock δ13Corg and δ34S values. Such complexity in carbon and sulfur isotope systematics contributes to uncertainty about the redox structure of Paleoproterozoic oceans. A currently popular idea is that, following the Great Oxidation Event, global changes led to low-oxygen environments and temporally fluctuating ocean redox conditions that lasted until the Neoproterozoic. The volcano-sedimentary rocks of the Onega Basin have figured prominently in this concept, particularly the exceptionally organic-rich rocks of the 1.98 Ga Zaonega Formation. However, a growing body of evidence shows that local depositional processes acted to form the δ13Corg and pyrite δ34S records of the Zaonega Formation, thus calling for careful assessment of the global significance of these isotope records. Placing new and existing organic carbon and sulfur isotope data from the Zaonega Formation into the context of basin history and by comparing those results with key Paleoproterozoic successions of the Francevillian Basin (Gabon), the Pechenga Greenstone Belt (NW Russia) and the Animikie Basin (Canada), we show that the stratigraphic δ13Corg and pyrite δ34S trends can be explained by local perturbations in biogeochemical carbon and sulfur cycling without requiring global drivers. Despite their temporal disparity, we also demonstrate that individual successions share certain geological traits (e.g. magmatic and/or tectonic activity, hydrocarbon generation, basin restriction) suggesting that their pyrite δ34S and δ13Corg trends were governed by common underlying mechanisms (e.g. similar basinal evolution and biogeochemical feedbacks) and are not necessarily unique to certain time intervals. We further show that pyrites in these successions that are most likely to capture ambient seawater sulfate isotopic composition have consistent δ34S values of 15–18‰, which hints at remarkable stability in the marine sulfur cycle over most of the Paleoproterozoic Era.</p

Comparing Measurement Approaches for Quantifying CO2 Flux from Downed Woody Debris with a Dynamic Chamber Method

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Mineral-templated growth of natural graphite films

International audienceOrganic material in sediments is progressively altered during diagenesis and metamorphism, leading to the formation of kerogen and ultimately crystalline graphite. Bulk carbonaceous material in metamorphic terrains typically has attained an overall degree of structural order that is in line with peak metamorphic temperature. On a micron- to nano-scale, however, carbonaceous material can display strong structural variation. The main factor that drives this variation is the chemical and molecular heterogeneity of the precursor biologic material. Specific conditions during metamorphism, however, can also play a role in shaping the microstructure of carbonaceous material. Here we describe the structural variation of carbonaceous material in rocks of the 2.0 Ga Zaonega Formation, Karelia, Russia. Raman spectroscopy indicates that bulk carbonaceous matter in these rocks has experienced peak temperatures between 350 and 400 °C consistent with greenschist-facies metamorphism. On a nano-scale, however, a strong structural heterogeneity is observed. Transmission electron microscopy (TEM) reveals the occurrence of thin films of highly ordered graphitic carbon at mineral surfaces. These graphite films - consisting of 20-100 individual layers - completely envelop quartz crystals and occur on specific crystal surfaces of chlorite. It is proposed that minerals can act as templates for the parallel ordering of carbon crystallites causing enhanced graphitization within narrow zones at mineral surfaces. Alternatively, oriented organic precursor molecules could have been adsorbed onto charged mineral surfaces, leading to thin graphitic films during later metamorphic heating episodes. Overall the presented observations demonstrate that mineral surfaces can initiate and accelerate localized graphitization of sedimentary organic material during metamorphism, and therefore cause distinct nano-scale variation in structural order

Littérature et champ symbolique (essai pour une théorie de l'écriture actuelle en Afrique francophone)

L'objet premier de cette étude est de tenter "un essai pour une théorie de l'écriture littéraire actuelle en Afrique francophone". Accessoirement, il devait servir à redéfinir à travers une " autre " lecture du fait littéraire africain francophone, la nature et la fonction des littératures des pays dominés.Dans une perspective historiciste, il est apparu que la littérature africaine francophone dans son ensemble a pu se constituer depuis les années 1930 en un monde social " autonome " dont les propriétés générales reposent principalement sur les catégories culturelles dites " orales " et " traditionnelles ". D'un point de vue pratique, l'oralité et la tradition orale africaine loin d'être invariablement le prolongement de la proclamation d'une " âme nègre " demeurent essentiellement la " règle du jeu littéraire africain ". Objets d'enjeux et lieux de tension, l'oralité et la tradition orale servent aux écrivains du champ africain dans leur besoin de positionnement structural: aux pionniers (Césaire/Senghor) pour le maintien de leur statut de "dominants", aux prétendants (Pacéré/Zadi) pour leur prétention à la " classicité ". Stratégiquement porteurs et symboliquement riches en ressources, les items oraux et traditionnels subissent toutes sortes d'amplications, de grossissement et d'extrapolation (discours identitaires, manipulation de la racine et de la pureté, argument du sacré et du secret). En tout état de cause, l'acte littéraire en Afrique ou en francophonie , comme l'acte politique ou économique est un " acte calculé " dont la rationalité pour être saisie nécessite la parfaite connaissance de ce qu'il est convenu d'appeler suivant la terminologie bourdieusienne un " champ symbolique " et/ou le " champ littéraire africain "The first step of this study is to try an essay of a theory for the present litérary writing in the french-speaking communities of Africa . secondarily, the purpsose was to give another definition, through another reading of the african french-speaking literary fact, the nature and the function of the dominated contries literatures.In a historicity perspective, it appeared that the african french speaking literature, in its all, has been set-up since 1930 in an autonomous social word, which general copyrights are principally based on the cultural catégories, knows as the oral and traditional ones.On a pratical point of view, the oral way and the african oral tradition, far to invariably be the extension of the proclamation of a negro soul , are essentially the rule of the african literary game .Subjects of stakes and places of tensions, the oral way and the oral tradition are used by writers of the african field, in their need of structural setting up: the pioneers (Césaire/Senghor) for the maintaining of their dominant status ; the pretenders (Pacéré/Zadi) for their pretentiousness for the classicism . Strategically beneficial and symbolically rich of resources, the oral and the traditional items suffer from all kind of amplifications, of magnifications and extrapolations (speechs relating to the identity, manipulation of the roots and the purity, arguments of the sacred and secret ).In all case , the literary act in Africa or in the french-speaking communities, like the political or economical act is a calculated act that the rationality to be hold , needs a perfect knowledge of what has been agreed to call, following the Bourdieu's terminology a symbolic field and/or the african literary field .CERGY PONTOISE-BU Les Cerclades (951272104) / SudocSudocFranceF