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  • 1
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 29 October 2013, Vol.110(44), pp.17638-43
    Description: It is generally thought that the sulfate reduction metabolism is ancient and would have been established well before the Neoarchean. It is puzzling, therefore, that the sulfur isotope record of the Neoarchean is characterized by a signal of atmospheric mass-independent chemistry rather than a strong overprint by sulfate reducers. Here, we present a study of the four sulfur isotopes obtained using secondary ion MS that seeks to reconcile a number of features seen in the Neoarchean sulfur isotope record. We suggest that Neoarchean ocean basins had two coexisting, significantly sized sulfur pools and that the pathways forming pyrite precursors played an important role in establishing how the isotopic characteristics of each of these pools was transferred to the sedimentary rock record. One of these pools is suggested to be a soluble (sulfate) pool, and the other pool (atmospherically derived elemental sulfur) is suggested to be largely insoluble and unreactive until it reacts with hydrogen sulfide. We suggest that the relative contributions of these pools to the formation of pyrite depend on both the accumulation of the insoluble pool and the rate of sulfide production in the pyrite-forming environments. We also suggest that the existence of a significant nonsulfate pool of reactive sulfur has masked isotopic evidence for the widespread activity of sulfate reducers in the rock record.
    Keywords: Neoarchean Polysulfide Production Pathways ; Δ33s ; Δ36s ; Δ34s ; Geological Phenomena ; Iron -- Chemistry ; Sulfides -- Chemical Synthesis ; Sulfur Isotopes -- Chemistry
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 2
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 28 March 2017, Vol.114(13), pp.E2571-E2579
    Description: Emerging evidence suggests that atmospheric oxygen may have varied before rising irreversibly ∼2.4 billion years ago, during the Great Oxidation Event (GOE). Significantly, however, pre-GOE atmospheric aberrations toward more reducing conditions-featuring a methane-derived organic-haze-have recently been suggested, yet their occurrence, causes, and significance remain underexplored. To examine the role of haze formation in Earth's history, we targeted an episode of inferred haze development. Our redox-controlled (Fe-speciation) carbon- and sulfur-isotope record reveals sustained systematic stratigraphic covariance, precluding nonatmospheric explanations. Photochemical models corroborate this inference, showing ΔS/ΔS ratios are sensitive to the presence of haze. Exploiting existing age constraints, we estimate that organic haze developed rapidly, stabilizing within ∼0.3 ± 0.1 million years (Myr), and persisted for upward of ∼1.4 ± 0.4 Myr. Given these temporal constraints, and the elevated atmospheric CO concentrations in the Archean, the sustained methane fluxes necessary for haze formation can only be reconciled with a biological source. Correlative δC and total organic carbon measurements support the interpretation that atmospheric haze was a transient response of the biosphere to increased nutrient availability, with methane fluxes controlled by the relative availability of organic carbon and sulfate. Elevated atmospheric methane concentrations during haze episodes would have expedited planetary hydrogen loss, with a single episode of haze development providing up to 2.6-18 × 10 moles of O equivalents to the Earth system. Our findings suggest the Neoarchean likely represented a unique state of the Earth system where haze development played a pivotal role in planetary oxidation, hastening the contingent biological innovations that followed.
    Keywords: Neoarchean ; Hydrogen Loss ; Organic Haze ; Planetary Oxidation ; Sulfur Mass-Independent Fractionation ; Earth (Planet) ; Atmosphere -- Chemistry ; Oxygen -- Analysis
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 3
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 25 November 2014, Vol.111(47), pp.16760-5
    Description: We used circular chromatin conformation capture (4C) to identify a physical contact in human pancreatic islets between the region near the insulin (INS) promoter and the ANO1 gene, lying 68 Mb away on human chromosome 11, which encodes a Ca(2+)-dependent chloride ion channel. In response to glucose, this contact was strengthened and ANO1 expression increased, whereas inhibition of INS gene transcription by INS promoter targeting siRNA decreased ANO1 expression, revealing a regulatory effect of INS promoter on ANO1 expression. Knockdown of ANO1 expression caused decreased insulin secretion in human islets, establishing a physical proximity-dependent feedback loop involving INS transcription, ANO1 expression, and insulin secretion. To explore a possible role of ANO1 in insulin metabolism, we carried out experiments in Ano1(+/-) mice. We observed reduced serum insulin levels and insulin-to-glucose ratios in high-fat diet-fed Ano1(+/-) mice relative to Ano1(+/+) mice fed the same diet. Our results show that determination of long-range contacts within the nucleus can be used to detect novel and physiologically relevant mechanisms. They also show that networks of long-range physical contacts are important to the regulation of insulin metabolism.
    Keywords: Chloride Channel ; Diabetes ; Insulin Secretion ; Promoter Regions, Genetic ; Chloride Channels -- Physiology ; Insulin -- Genetics ; Neoplasm Proteins -- Physiology
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 4
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 13 August 2013, Vol.110(33), pp.13534-9
    Description: Increased serum levels of IL-15 are reported in type 1 diabetes (T1D). Here we report elevated serum soluble IL-15Rα levels in human T1D. To investigate the role of IL-15/IL-15Rα in the pathogenesis of T1D, we generated double transgenic mice with pancreatic β-cell expression of IL-15 and IL-15Rα. The mice developed hyperglycemia, marked mononuclear cell infiltration, β-cell destruction, and anti-insulin autoantibodies that mimic early human T1D. The diabetes in this model was reversed by inhibiting IL-15 signaling with anti-IL2/IL15Rβ (anti-CD122), which blocks IL-15 transpresentation. Furthermore, the diabetes could be reversed by administration of the Janus kinase 2/3 inhibitor tofacitinib, which blocks IL-15 signaling. In an alternative diabetes model, nonobese diabetic mice, IL15/IL-15Rα expression was increased in islet cells in the prediabetic stage, and inhibition of IL-15 signaling with anti-CD122 at the prediabetic stage delayed diabetes development. In support of the view that these observations reflect the conditions in humans, we demonstrated pancreatic islet expression of both IL-15 and IL-15Rα in human T1D. Taken together our data suggest that disordered IL-15 and IL-15Rα may be involved in T1D pathogenesis and the IL-15/IL15Rα system and its signaling pathway may be rational therapeutic targets for early T1D.
    Keywords: Disease Models, Animal ; Diabetes Mellitus, Type 1 -- Etiology ; Insulin-Secreting Cells -- Metabolism ; Interleukin-15 -- Metabolism ; Interleukin-15 Receptor Alpha Subunit -- Metabolism ; Signal Transduction -- Drug Effects
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 5
    Language: English
    In: Earth and Planetary Science Letters, March 15, 2013, Vol.366, p.17(10)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.epsl.2013.01.028 Byline: Florian Kurzweil (a)(b), Mark Claire (c), Christophe Thomazo (d), Marc Peters (e), Mark Hannington (f), Harald Strauss (a) Keywords: multiple sulfur isotopes; MIF-S; atmospheric oxygenation; late Archean; Great Oxidation Event Abstract: Mass-independently fractionated sulfur isotopes (MIF-S) provide strong evidence for an anoxic atmosphere during the Archean. Moreover, the temporal evolution of MIF-S shows increasing magnitudes between 2.7 and 2.5Ga until the start of the Great Oxidation Event (G.O.E.) at around 2.4Ga. The conclusion of a completely anoxic atmosphere up to the G.O.E. is in contrast to recent studies on redox-sensitive elements, which suggest slightly oxidizing conditions during continental weathering already several hundred million years prior to the G.O.E. In order to investigate this apparent inconsistency, we present multiple sulfur isotopes for 2.71Ga pyritic black shales derived from the Kidd Creek area, Ontario, Canada. These samples display high positive [DELTA].sup.33S values up to 3.8a[degrees] and the typical late Archean slope in [DELTA].sup.36S/[DELTA].sup.33S of -0.9. In contrast, the time period before (3.2-2.73Ga) is characterized by greatly attenuated MIF-S magnitudes and a slope in [DELTA].sup.36S/[DELTA].sup.33S of -1.5. We attribute the increase in [DELTA].sup.33S magnitude as well as the contemporaneous change in the slope of [DELTA].sup.36S/[DELTA].sup.33S to changes in the relative reaction rate of different MIF-S source reactions and changes in atmospheric sulfur exit channels. Both of these are dependent on atmospheric CH.sub.4:CO.sub.2 and O.sub.2 mixing ratios. We propose a distinct change in atmospheric composition at 2.7Ga resulting from increased fluxes of oxygen and methane as the best explanation for the observed Neoarchean MIF-S record. Our data and modeling results suggest that oxygenic photosynthesis was a major contributor to primary productivity 2.7 billion years ago. Author Affiliation: (a) Westfalische Wilhelms-Universitat Munster, Institut fur Geologie und Palaontologie, Munster, Germany (b) Eberhard Karls University of Tubingen, Institute of Geochemistry, Wilhelmstra[sz]e 56, 72076 Tubingen, Germany (c) School of Environmental Sciences, University of East Anglia, Norwich, Norfolk, United Kingdom (d) UMR/CNRS 5561 Biogeosciences, Universite de Bourgogne, Dijon, France (e) Laboratory of Resource Engineering and Remediation, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China (f) Department of Earth Sciences, University of Ottawa, Marion Hall, Ottawa ON, Canada Article History: Received 28 August 2012; Revised 11 January 2013; Accepted 21 January 2013 Article Note: (miscellaneous) Editor: B. Marty
    Keywords: Sulfur Compounds -- Analysis ; Sulfur -- Analysis ; Photosynthesis -- Analysis ; Plant Biochemistry -- Analysis
    ISSN: 0012-821X
    Source: Cengage Learning, Inc.
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  • 6
    In: Nature, 2017
    Description: The rise of oxygen on the early Earth (about 2.4 billion years ago) caused a reorganization of marine nutrient cycles, including that of nitrogen, which is important for controlling global primary productivity. However, current geochemical records lack the temporal resolution to address the nature and timing of the biogeochemical response to oxygenation directly. Here we couple records of ocean redox chemistry with nitrogen isotope (15N/14N) values from approximately 2.31-billion-year-old shales of the Rooihoogte and Timeball Hill formations in South Africa, deposited during the early stages of the first rise in atmospheric oxygen on the Earth (the Great Oxidation Event). Our data fill a gap of about 400 million years in the temporal 15N/14N record and provide evidence for the emergence of a pervasive aerobic marine nitrogen cycle. The interpretation of our nitrogen isotope data in the context of iron speciation and carbon isotope data suggests biogeochemical cycling across a dynamic redox boundary, with primary productivity fuelled by chemoautotrophic production and a nitrogen cycle dominated by nitrogen loss processes using newly available marine oxidants. This chemostratigraphic trend constrains the onset of widespread nitrate availability associated with ocean oxygenation. The rise of marine nitrate could have allowed for the rapid diversification and proliferation of nitrate-using cyanobacteria and, potentially, eukaryotic phytoplankton.
    Keywords: Sciences (General) ; Physics;
    ISSN: 0028-0836
    E-ISSN: 1476-4687
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  • 7
    Language: English
    In: Geochimica et Cosmochimica Acta, Sept 15, 2014, Vol.141, p.365(16)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.gca.2014.06.032 Byline: Mark W. Claire, James F. Kasting, Shawn D. Domagal-Goldman, Eva E. Stueken, Roger Buick, Victoria S. Meadows Abstract: Minor sulfur isotope anomalies indicate the absence of O.sub.2 from the Archean atmosphere. A rich dataset showing large variations in magnitude and sign of [DELTA].sup.33S and [DELTA].sup.36S, preserved in both sulfates and sulfides, suggests that further constraints on Archean atmospheric chemistry are possible. We review previous quantitative constraints on atmospheric [DELTA].sup.33S production, and suggest that a new approach is needed. We added sulfur species containing.sup.33S and.sup.34S to a 1-D photochemical model and describe the numerical methodology needed to ensure accurate prediction of the magnitude and sign of [DELTA].sup.33S produced by and deposited from the Archean atmosphere. This methodology can test multiple MIF-S formation mechanisms subject to a variety of proposed atmospheric compositions, yielding [DELTA].sup.33S predictions that can be compared to the rock record. We systematically test SO.sub.2 isotopologue absorption effects in SO.sub.2 photolysis (Danielache et al., 2008), one of the primary proposed mechanisms for [DELTA].sup.33S formation. We find that differential absorption through the Danielache et al. (2008) cross sections is capable of altering predicted [DELTA].sup.33S as a function of multiple atmospheric variables, including trace O.sub.2 concentration, total sulfur flux, CO.sub.2 content, and the presence of hydrocarbons, but find a limited role for OCS and H.sub.2S. Under all realistic conditions, the Danielache et al. (2008) cross sections yield [DELTA].sup.33S predictions at odds with the geologic record, implying that additional pathways for sulfur MIF formation exist and/or the cross sections have significant errors. The methodology presented here will allow for quantitative constraints on the Archean atmosphere beyond the absence of O.sub.2, as soon as additional experimental measurements of MIF-S producing processes become available. Article History: Received 18 April 2014; Accepted 28 June 2014 Article Note: (miscellaneous) Associate editor: Marc Norman
    Keywords: Atmospheric Chemistry -- Analysis ; Atmospheric Chemistry -- Models ; Photolysis -- Analysis ; Photolysis -- Models ; Sulfur -- Analysis ; Sulfur -- Models ; Sulfides -- Analysis ; Sulfides -- Models ; Sulfates -- Analysis ; Sulfates -- Models
    ISSN: 0016-7037
    Source: Cengage Learning, Inc.
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  • 8
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 September 2014, Vol.141, pp.365-380
    Description: Minor sulfur isotope anomalies indicate the absence of O from the Archean atmosphere. A rich dataset showing large variations in magnitude and sign of Δ S and Δ S, preserved in both sulfates and sulfides, suggests that further constraints on Archean atmospheric chemistry are possible. We review previous quantitative constraints on atmospheric Δ S production, and suggest that a new approach is needed. We added sulfur species containing S and S to a 1-D photochemical model and describe the numerical methodology needed to ensure accurate prediction of the magnitude and sign of Δ S produced by and deposited from the Archean atmosphere. This methodology can test multiple MIF-S formation mechanisms subject to a variety of proposed atmospheric compositions, yielding Δ S predictions that can be compared to the rock record. We systematically test SO isotopologue absorption effects in SO photolysis (Danielache et al., 2008), one of the primary proposed mechanisms for Δ S formation. We find that differential absorption through the Danielache et al. (2008) cross sections is capable of altering predicted Δ S as a function of multiple atmospheric variables, including trace O concentration, total sulfur flux, CO content, and the presence of hydrocarbons, but find a limited role for OCS and H S. Under all realistic conditions, the Danielache et al. (2008) cross sections yield Δ S predictions at odds with the geologic record, implying that additional pathways for sulfur MIF formation exist and/or the cross sections have significant errors. The methodology presented here will allow for quantitative constraints on the Archean atmosphere beyond the absence of O , as soon as additional experimental measurements of MIF-S producing processes become available.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 9
    Language: English
    In: Chemical Geology, Dec 20, 2013, Vol.362, p.26(9)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.chemgeo.2013.08.004 Byline: Kevin J. Zahnle, David C. Catling, Mark W. Claire Abstract: Oxygenic photosynthesis appears to be necessary for an oxygen-rich atmosphere like Earth's. But available geological and geochemical evidence suggest that at least 200Myr, and possibly more than 700Myr, elapsed between the advent of oxygenic photosynthesis and the establishment of an oxygen atmosphere. The interregnum implies that at least one other necessary condition for O.sub.2 needed to be met. Here we argue that the second condition was the oxidation of the surface and crust to the point where O.sub.2 became more stable than competing reduced gases such as CH.sub.4. The cause of Earth's surface oxidation would be the same cause as it is for other planets with oxidized surfaces: hydrogen escape to space. The duration of the interregnum would have been determined by the rate of hydrogen escape and by the size of the reduced reservoir that needed to be oxidized before O.sub.2 became favored. We suggest that continental growth has been influenced by hydrogen escape, and we speculate that, if there must be an external bias to biological evolution, hydrogen escape can be that bias. Article History: Received 23 January 2013; Revised 29 May 2013; Accepted 4 August 2013 Article Note: (footnote) [star] This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
    Keywords: Photosynthesis ; Hydrogen ; Plant Biochemistry
    ISSN: 0009-2541
    Source: Cengage Learning, Inc.
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  • 10
    In: Rapid Communications in Mass Spectrometry, 30 November 2018, Vol.32(22), pp.1949-1961
    Description: Byline: ,Mark W. Claire Rationale Triple oxygen isotopes (.sub.16O/.sub.17O/.sub.18O) in nitrate are a valuable tool to ascertain the pathways of nitrate formation in the atmosphere and the fate of nitrate in ecosystems. Here we present a new method for determining I.sub.17O values in nitrates, based on nitrate-water isotope equilibration (IE) and subsequent isotopic analysis of water using cavity ringdown laser spectroscopy (CRDS). Methods Nitrate oxygen (O-NO.sub.3.sub.-) is equilibrated with water oxygen (O-H.sub.2O) at low pH and 80[degrees]C. Subsequently, the I[acute accent].sub.17O and I[acute accent].sub.18O values of equilibrated water are determined by CRDS, scaled to V-SMOW and V-SLAP and calibrated against nitrate standards (USGS-34, USGS-35 and IAEA-NO3). We provide isotopic measurements of synthetic and natural nitrates and a direct inter-lab comparison with the classic method of thermal-decomposition of nitrate followed by isotope ratio mass spectrometry of O.sub.2 (TD-IRMS). Results For synthetic NaNO.sub.3, the precision (1SD) of the IE-CRDS method is 0.80/00 for I[acute accent].sub.17O values, 1.70/00 for I[acute accent].sub.18O values and 0.20/00 for I.sub.17O values when using an O-NO.sub.3.sub.-/O-H.sub.2O ratio greater than 0.0114 [+ or -] 0.0001 (e.g. 12 [MU]mol of NO.sub.3.sub.- in 50 [MU]L of acid solution). For natural samples, after purification of nitrates by column chemistry and reprecipitation as AgNO.sub.3, the precision is better than 1.80/00 for I[acute accent].sub.17O values, 3.20/00 for I[acute accent].sub.18O values and 10/00 for I.sub.17O values. IE-CRDS and TD-IRMS yield I.sub.17O values within the analytical errors of the two methods. Conclusions The IE-CRDS method for determining I.sub.17O values in nitrates utilizes a user-friendly and relatively cheaper benchtop analytical instrument, representing an alternative to IRMS-based methods for certain applications. Article Note: Present Address: F. Gazquez, Department of Biology and Geology, Universidad de Almeria, Carretera de Sacramento s.n, La Canada de San Urbano, Almeria 04120, Spain
    Keywords: Mass Spectrometry – Analysis ; Instruments (Equipment) – Analysis ; Nitrates – Analysis;
    ISSN: 0951-4198
    E-ISSN: 1097-0231
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