222 research outputs found
Nickel Isotope Variations in Terrestrial Silicate Rocks and Geological Reference Materials Measured by MC-ICP-MS
International audienceAlthough initial studies have demonstrated the applicability of Ni isotopes for cosmochemistry and as a potential biosignature, the Ni isotope composition of terrestrial igneous and sedimentary rocks, and ore deposits remains poorly known. Our contribution is fourfold: (a) to detail an analytical procedure for Ni isotope determination, (b) to determine the Ni isotope composition of various geological reference materials, (c) to assess the isotope composition of the Bulk Silicate Earth relative to the Ni isotope reference material NIST SRM 986 and (d) to report the range of mass-dependent Ni isotope fractionations in magmatic rocks and ore deposits. After purification through a two-stage chromatography procedure, Ni isotope ratios were measured by MC-ICP-MS and were corrected for instrumental mass bias using a double-spike correction method. Measurement precision (two standard error of the mean) was between 0.02 and 0.04â°, and intermediate measurement precision for NIST SRM 986 was 0.05â° (2s). Igneous- and mantle-derived rocks displayed a restricted range of ÎŽ60/58Ni values between â0.13 and +0.16â°, suggesting an average BSE composition of +0.05â°. Manganese nodules (Nod A1; P1), shale (SDO-1), coal (CLB-1) and a metal-contaminated soil (NIST SRM 2711) showed positive values ranging between +0.14 and +1.06â°, whereas komatiite-hosted Ni-rich sulfides varied from â0.10 to â1.03â°
Multiple sulphur and iron isotope composition of detrital pyrite in Archaean sedimentary rocks : a new tool for provenance analysis
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 286 (2009): 436-445, doi:10.1016/j.epsl.2009.07.008.Multiple S (ÎŽ34S and ÎŽ33S) and Fe (ÎŽ56Fe) isotope analyses of rounded pyrite grains from 3.1 to 2.6 Ga conglomerates of southern Africa indicate their detrital origin, which supports anoxic surface conditions in the Archaean. Rounded pyrites from Meso- to Neoarchaean gold and uranium-bearing strata of South Africa are derived from both crustal and sedimentary sources, the latter being characterised by non-mass dependent fractionation of S isotopes (Î33S as negative as -1.35â°) and large range of Fe isotope values (ÎŽ56Fe between -1.1 and 1.2â°). Most sediment-sourced pyrite grains are likely derived from sulphide nodules in marine organic matter-rich shales, sedimentary exhalites and volcanogenic massive sulphide deposits. Some sedimentary pyrite grains may have been derived from in situ sulphidised Fe-oxides, prior to their incorporation into the conglomerates, as indicated by unusually high positive ÎŽ56Fe values. Sedimentary sulphides without significant non-mass dependent fractionation of S isotopes were also present in the source of some conglomerates. The abundance in these rocks of detrital pyrite unstable in the oxygenated atmosphere may suggest factors other than high pO2 as the cause for the absence of significant non-mass dependent fractionation processes in the 3.2 â 2.7 Ga atmosphere. Rounded pyrites from the ca. 2.6 Ga conglomerates of the Belingwe greenstone belt in Zimbabwe have strongly fractionated ÎŽ34S, Î33S and ÎŽ56Fe values, the source of which can be traced back to black shale-hosted massive sulphides in the underlying strata. The study demonstrates the utility of combined multiple S and Fe isotope analysis for provenance reconstruction of Archaean sedimentary successions.AH acknowledges support by NAI International Collaboration Grant and NRF grant
FA2005040400027. AB participation was supported by NSF grant EAR-937 05-45484, NAI
award No. NNA04CC09A, and NSERC 938 Discovery grant. Rouxel's contribution was
supported by NSF OCE-0622982
Integrated Fe- and S-isotope study of seafloor hydrothermal vents at East Pacific Rise 9â10°N
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Chemical Geology 252 (2008): 214-227, doi:10.1016/j.chemgeo.2008.03.009.In this study, we report on coupled Fe- and S-isotope systematics of hydrothermal fluids and
sulfide deposits from the East Pacific Rise at 9-10°N to better constrain processes affecting Fe-
isotope fractionation in hydrothermal environments. We aim to address three fundamental
questions: (1) is there significant Fe isotope fractionation during sulfide precipitation? (2) Is there
significant variability of Fe-isotope composition of the hydrothermal fluids reflecting sulfide
precipitation in subsurface environments? (3) Are there any systematics between Fe- and S-
isotopes in sulfide minerals? The results show that chalcopyrite, precipitating in the interior wall
of a hydrothermal chimney displays a limited range of ÎŽ56Fe values and ÎŽ34S values, between â0.11 to â0.33â° and 2.2 to 2.6â° respectively. The ÎŽ56Fe values are, on average, slightly higher by
0.14â° relative to coeval vent fluid composition while ÎŽ34S values suggest significant S-isotope
fractionation (-0.6±0.2â°) during chalcopyrite precipitation. In contrast, systematically lower
ÎŽ56Fe and ÎŽ34S values relative to hydrothermal fluids, by up to 0.91â° and 2.0â° respectively, are
observed in pyrite and marcasite precipitating in the interior of active chimneys. These results
suggest isotope disequilibrium in both Fe- and S-isotopes due to S-isotopic exchange between
hydrothermal H2S and seawater SO42- followed by rapid formation of pyrite from FeS precursors,
thus preserving the effects of a strong kinetic Fe-isotope fractionation during FeS precipitation. In
contrast, ÎŽ56Fe and ÎŽ34S values of pyrite from inactive massive sulfides, which show evidence of
extensive late-stage reworking, are essentially similar to the hydrothermal fluids. Multiple stages
of remineralization of ancient chimney deposits at the seafloor appear to produce minimal Fe-isotope fractionation. Similar affects are indicated during subsurface sulfide precipitation as
demonstrated by the lack of systematic differences between ÎŽ56Fe values in both high-temperature, Fe-rich black smokers and lower temperature, Fe-depleted vents.Support for W. Bach and
K. Edwards was provided by NSF grant OCE-0241791 and support for O. Rouxel was provided
by funding from the WHOI Deep Ocean Exploration Institute and NSF grant OCE-0622982 and
OCE-0647948
Ăpuiser sa prĂ©sence : rapports amoureux et tĂ©lĂ©phonie mobile
Cet article examine les spĂ©cificitĂ©s des rapports amoureux actuels en tant que ceux-ci sont Ă©quipĂ©s par toute une sĂ©rie de technologies Ă mĂȘme dâorganiser concrĂštement le contenu des relations. Il en est ainsi du tĂ©lĂ©phone portable, qui sâest immiscĂ© dans le cĆur de la vie amoureuse. Aussi, au moyen dâune phĂ©nomĂ©nologie de la relation amoureuse, il sâagira dâexaminer les recompositions des rĂ©gimes prĂ©sentiels et relationnels engendrĂ©s par le tĂ©lĂ©phone portable. Ă partir dâun corpus de 4 974 messages instantanĂ©s Ă©changĂ©s par neuf couples distincts, le but est dâapprĂ©hender la fragilisation du mouvement vers autrui que pourrait entraĂźner lâutilisation de ces technologies, dont lâeffet essentiel est probablement dâorganiser une coprĂ©sence particuliĂšre des ĂȘtres.This article analyzes the recomposition of presential and relational regimes caused by the mobile phone in love relationships. We will discuss phenomenological specificities of in-love copresence before examining results that introduce the effects of âavailabilityâ raised by these devices. This analysis will be based on a corpus of 4,974 SMS exchanged by nine different couples. We will especially highlight the specificities of the âtechnical principleâ inherent to these devices. The analysis of this "short time technology" helps to discern a radicalization of the feeling of remotness to the other.in this âtechnologically equipped copresence.âEste artĂculo pretende analizar las especificidades de las relaciones amorosas en la actualidad, en la medida en que estas utilizan una serie de tecnologĂas, que incluso llegan a organizar el contenido de las relaciones. El mejor ejemplo es el telĂ©fono mĂłvil, que se ha situado en el centro de la vida amorosa. Mediante una fenomenologĂa de la relaciĂłn amorosa, se busca analizar las recomposiciones de los regĂmenes presenciales y relacionales generados por el telĂ©fono mĂłvil. Este anĂĄlisis se apoya en un corpus de 4974 mensajes de texto (SMS) intercambiados por 9 parejas distintas. De manera mĂĄs especĂfica se busca analizar la fragilizaciĂłn del movimiento hacia la otra persona que pudiera resultar de la utilizaciĂłn de estas tecnologĂas con probabilidad, el efecto esencial es el de organizar una co-presencia particular de las personas
Glacial influence on the geochemistry of riverine iron fluxes to the Gulf of Alaska and effects of deglaciation
This paper is not subject to U.S. copyright. The definitive version was published in Geophysical Research Letters 38 (2011): L16605, doi:10.1029/2011GL048367.Riverine iron (Fe) derived from glacial weathering is a critical micronutrient source to ecosystems of the Gulf of Alaska (GoA). Here we demonstrate that the source and chemical nature of riverine Fe input to the GoA could change dramatically due to the widespread watershed deglaciation that is underway. We examine Fe size partitioning, speciation, and isotopic composition in tributaries of the Copper River which exemplify a long-term GoA watershed evolution from one strongly influenced by glacial weathering to a boreal-forested watershed. Iron fluxes from glacierized tributaries bear high suspended sediment and colloidal Fe loads of mixed valence silicate species, with low concentrations of dissolved Fe and dissolved organic carbon (DOC). Iron isotopic composition is indicative of mechanical weathering as the Fe source. Conversely, Fe fluxes from boreal-forested systems have higher dissolved Fe concentrations corresponding to higher DOC concentrations. Iron colloids and suspended sediment consist of Fe (hydr)oxides and organic complexes. These watersheds have an iron isotopic composition indicative of an internal chemical processing source. We predict that as the GoA watershed evolves due to deglaciation, so will the source, flux, and chemical nature of riverine Fe loads, which could have significant ramifications for Alaskan marine and freshwater ecosystems.We appreciate support from the USGS
CMGP, NCCWSC, and the Mendenhall Postdoctoral Program
Time-series analysis of two hydrothermal plumes at 9°50âČN East Pacific Rise reveals distinct, heterogeneous bacterial populations
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Geobiology 10 (2012): 178-192, doi:10.1111/j.1472-4669.2011.00315.xWe deployed sediment traps adjacent to two active hydrothermal vents at 9°50âN on the
East Pacific Rise (EPR) to assess variability in bacterial community structure associated with
plume particles on the time scale of weeks to months, to determine if an endemic population of
plume microbes exists, and to establish ecological relationships between bacterial populations
and vent chemistry. Automated rRNA intergenic spacer analysis (ARISA) indicated there are
separate communities at the two different vents and temporal community variations between
each vent. Correlation analysis between chemistry and microbiology indicated that shifts in the coarse particulate (>1 mm) Fe/(Fe+Mn+Al), Cu, V, Ca, Al, 232Th, and Ti as well as fine-grained
particulate (<1 mm) Fe/(Fe+Mn+Al), Fe, Ca and Co are reflected in shifts in microbial
populations. 16S rRNA clone libraries from each trap at three time points revealed a high
percentage of Epsilonproteobacteria clones and hyperthermophilic Aquificae. There is a shift
towards the end of the experiment to more Gammaproteobacteria and Alphaproteobacteria, many
of whom likely participate in Fe and S cycling. The particle attached plume environment is
genetically distinct from the surrounding seawater. While work to date in hydrothermal
environments has focused on determining the microbial communities on hydrothermal chimneys
and the basaltic lavas that form the surrounding seafloor, little comparable data exists on the
plume environment that physically and chemically connects them. By employing sediment traps
for a time series approach to sampling, we show that bacterial community composition on plume
particles changes on time scales much shorter than previously known.This work was supported by the NSF Marine
Geology and Geophysics program, the Science and Technology program, and the Gordon and
Betty Moore Foundation
Optical electron transfer through 2,7-diethynylfluorene spacers in mixed-valent complexes containing electron-rich "(η2-dppe)(η5-C5Me5)Fe" endgroups.
International audienceWe report in this communication the study of the intramolecular electron transfer through a 2,7-diethynylfluorenyl spacer in the Fe(II)/Fe(III) mixed-valent (MV) complex [(η(2)-dppe)(η(5)-C(5)Me(5))FeCâĄC(2,7-C(21)H(24))CâĄCFe(η(5)-C(5)Me(5))(η(2)-dppe)][PF(6)] (1[PF(6)]). The complex is generated in situ by comproportionation from its homovalent dinuclear Fe(II) and Fe(III) parents (1 and 1[PF(6)](2)). It is shown that electronic delocalization is much more effective through a 2,7-fluorenyl than through a 4,4'-biphenyl bridging unit
Nickel and Chromium Stable Isotopic Composition of Ureilites: Implications for the Earth's Core Formation and Differentiation of the Ureilite Parent Body
We report the first Ni and Cr stable isotope data for ureilite meteorites that are the mantle residue of a carbon-rich differentiated planet. Ureilites have similar Ni stable isotope compositions as chondrites, suggesting that the core-mantle differentiation of ureilite parent body (UPB) did not fractionate Ni isotopes. Since the size of Earth is potentially larger than that of UPB; with diameter >690 km), resulting in higher temperatures at the core-mantle boundary of Earth, it can be predicted that the terrestrial core formation may not directly cause Ni stable isotope fractionation. On the other hand, we also report high-precision Cr stable isotope composition of ureilites, including one ureilitic trachyandesite (ALM-A) that is enriched in lighter Cr stable isotopes relative to the main-group ureilites, which suggests that the partial melting occurred on UPB. The globally heavy Cr in the UPB compared to chondrites can be caused by sulfur-rich core formation processes
The isotope composition of inorganic Germanium in seawater and deep sea sponges
Although dissolved concentrations of germanium (Ge) and silicon (Si) in modern seawater are tightly correlated, uncertainties still exist in the modern marine Ge cycle. Germanium stable isotope systematics in marine systems should provide additional constraints on marine Ge sources and sinks, however the low concentration of Ge in seawater presents an analytical challenge for isotopic measurement. Here, we present a new method of pre-concentration of inorganic Ge from seawater which was applied to measure three Ge isotope profiles in the Southern Ocean and deep seawater from the Atlantic and Pacific Oceans. Germanium isotopic measurements were performed on Ge amounts as low as 2.6 ng using a double-spike approach and a hydride generation system coupled to a MC-ICP-MS. Germanium was co-precipitated with iron hydroxide and then purified through anion-exchange chromatography. Results for the deep (i.e. > 1000 m depth) Pacific Ocean off Hawaii (nearby Loihi Seamount) and the deep Atlantic off Bermuda (BATS station) showed nearly identical ÎŽ74/70Ge values at 3.19 ± 0.31 â° (2SD, n = 9) and 2.93 ± 0.10 â° (2SD, n = 2), respectively. Vertical distributions of Ge concentration and isotope composition in the deep Southern Ocean for water depth > 1300 m yielded an average ÎŽ74/70Ge = 3.13 ± 0.25 â° (2SD, n = 14) and Ge/Si = 0.80 ± 0.09 ÎŒmol/mol (2SD, n = 12). Significant variations in ÎŽ74/70Ge, from 2.62 to 3.71 â°, were measured in the first 1000 m in one station of the Southern Ocean near Sars Seamount in the Drake Passage, with the heaviest values measured in surface waters. Isotope fractionation by diatoms during opal biomineralization may explain the enrichment in heavy isotopes for both Ge and Si in surface seawater. However, examination of both oceanographic parameters and ÎŽ74/70Ge values suggest also that water mass mixing and potential contribution of shelf-derived Ge also could contribute to the variations. Combining these results with new Ge isotope data for deep-sea sponges sampled nearby allowed us to determine a Ge isotope fractionation factor of -0.87 ± 0.37 â° (2SD, n = 12) during Ge uptake by sponges. Although Ge has long been considered as a geochemical twin of Si, this work underpins fundamental differences in their isotopic behaviors both during biomineralization processes and in their oceanic distributions. This suggests that combined with Si isotopes, Ge isotopes hold significant promise as a complementary proxy for delineating biological versus source effects in the evolution of the marine silicon cycle through time
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