Now showing items 1-20 of 38

    • Anaerobic Methane Oxidation in Metalliferous Hydrothermal Sediments: Influence on Carbon Flux and Decoupling from Sulfate Reduction 

      Wankel, Scott D.; Adams, Melissa Marie; Johnston, David T; Hansel, Colleen; Joye, Samantha B.; Girguis, Peter R. (Wiley-Blackwell, 2012)
      The anaerobic oxidation of methane (AOM) is a globally significant sink that regulates methane flux from sediments into the oceans and atmosphere. Here we examine mesophilic to thermophilic AOM in hydrothermal sediments ...
    • Anoxygenic Photosynthesis Modulated Proterozoic Oxygen and Sustained Earth’s Middle Age 

      Johnston, David T; Wolfe-Simon, Felisa Lauren; Pearson, Ann; Knoll, Andrew Herbert (National Academy of Sciences, 2009)
      Molecular oxygen (O2) began to accumulate in the atmosphere and surface ocean ca. 2,400 million years ago (Ma), but the persistent oxygenation of water masses throughout the oceans developed much later, perhaps beginning ...
    • Authigenic Carbonate and the History of the Global Carbon Cycle 

      Schrag, Daniel P.; Higgins, John A.; Macdonald, Francis Alexander; Johnston, David T (American Association for the Advancement of Science (AAAS), 2013)
      We present a framework for interpreting the carbon isotopic composition of sedimentary rocks, which in turn requires a fundamental reinterpretation of the carbon cycle and redox budgets over Earth's history. We propose ...
    • A Basin Redox Transect at the Dawn of Animal Life 

      Sperling, Erik A.; Halverson, Galen P.; Knoll, Andrew Herbert; Macdonald, Francis Alexander; Johnston, David T (Elsevier BV, 2013)
      Multiple eukaryotic clades make their first appearance in the fossil record between ~810 and 715 Ma. Molecular clock studies suggest that the origin of animal multicellularity may have been part of this broader eukaryotic ...
    • Biologically Induced Initiation of Neoproterozoic Snowball-Earth Events 

      Tziperman, Eli; Halevy, Itay; Johnston, David T; Knoll, Andrew Herbert; Schrag, Daniel P. (Proceedings of the National Academy of Sciences, 2011)
      The glaciations of the Neoproterozoic Era (1,000 to 542 MyBP) were preceded by dramatically light C isotopic excursions preserved in preglacial deposits. Standard explanations of these excursions involve remineralization ...
    • Calibrating the Cryogenian 

      Macdonald, Francis Alexander; Schmitz, Mark D.; Crowley, James L.; Roots, Charles F.; Jones, David S.; Maloof, Adam C.; Strauss, Justin Vincent; Cohen, Phoebe; Johnston, David T; Schrag, Daniel P. (American Association for the Advancement of Science (AAAS), 2010)
      The Neoproterozoic was an era of great environmental and biological change, but a paucity of direct and precise age constraints on strata from this time has prevented the complete integration of these records. We present ...
    • Clay Mineralogy, Organic Carbon Burial, and Redox Evolution in Proterozoic Oceans 

      Tosca, Nicholas J.; Johnston, David T; Mushegian, Alexandra Arcadievna; Rothman, Daniel H.; Summons, Roger E.; Knoll, Andrew Herbert (Elsevier, 2010)
      Clay minerals formed through chemical weathering have long been implicated in the burial of organic matter (OM), but because diagenesis and metamorphism commonly obscure the signature of weathering-derived clays in Precambrian ...
    • A Contemporary Microbially Maintained Subglacial Ferrous “Ocean” 

      Mikucki, Jill A.; Pearson, Ann; Schrag, Daniel P.; Johnston, David T; Turchyn, Alexandra V.; Farquhar, James; Anbar, Ariel D.; Priscu, John C.; Lee, Peter A. (American Association for the Advancement of Science, 2009)
      An active microbial assemblage cycles sulfur in a sulfate-rich, ancient marine brine beneath Taylor Glacier, an outlet glacier of the East Antarctic Ice Sheet, with Fe(III) serving as the terminal electron acceptor. ...
    • Determination and Application of the Equilibrium Oxygen Isotope Effect Between Water and Sulfite 

      Wankel, Scott D.; Bradley, Alexander S.; Eldridge, Daniel L.; Johnston, David T (Elsevier BV, 2014)
      The information encoded by the two stable isotope systems in sulfate (δ34SSO4 and δ18OSO4) has been widely applied to aid reconstructions of both modern and ancient environments. Interpretation of δ18OSO4 records has been ...
    • Development of in situ sulfur four-isotope analysis with multiple Faraday cup detectors by SIMS and application to pyrite grains in a Paleoproterozoic glaciogenic sandstone 

      Ushikubo, Takayuki; Williford, Kenneth H.; Farquhar, James; Johnston, David T; Van Kranendonk, Martin J.; Valley, John W. (Elsevier BV, 2014)
      An in situ sulfur four-isotope analysis technique with multiple Faraday cup detectors by ion microprobe was developed and applied to detrital pyrite grains in ~2.4 Ga glaciogenic sandstone from the Meteorite Bore Member ...
    • An Emerging Picture of Neoproterozoic Ocean Chemistry: Insights from the Chuar Group, Grand Canyon, USA 

      Johnston, David T; Poulton, Simon W.; Dehler, Carol; Porter, Susannah; Husson, Jon; Canfield, Donald E.; Knoll, Andrew Herbert (Elsevier, 2009)
      Detailed iron, sulfur and carbon chemistry through the > 742 million year old ChuarGroup reveals a marine basin dominated by anoxic and ferrous iron-rich (ferruginous) bottom waters punctuated, late in the basin's development, ...
    • Explaining the Structure of the Archean Mass-Independent Sulfur Isotope Record 

      Halevy, I.; Johnston, David T; Schrag, Daniel P. (American Association for the Advancement of Science (AAAS), 2010)
      Sulfur isotopes in ancient sediments provide a record of past environmental conditions. The long–time-scale variability and apparent asymmetry in the magnitude of minor sulfur isotope fractionation in Archean sediments ...
    • Fractionation of multiple sulfur isotopes during phototrophic oxidation of sulfide and elemental sulfur by a green sulfur bacterium 

      Zerkle, Aubrey L.; Farquhar, James; Johnston, David T; Cox, Raymond P.; Canfield, Donald E. (Elsevier BV, 2009)
      We present multiple sulfur isotope measurements of sulfur compounds associated with the oxidation of H2S and S0 by the anoxygenic phototrophic S-oxidizing bacterium Chlorobium tepidum . Discrimination between 34S and 32S ...
    • Geobiology of the Late Paleoproterozoic Duck Creek Formation, Western Australia 

      Wilson, Jonathan P.; Fischer, Woodward W.; Johnston, David T; Knoll, Andrew Herbert; Grotzinger, John P.; Walter, Malcolm R.; McNaughton, Neal J.; Simon, Mel; Abelson, John; Schrag, Daniel P.; Summons, Roger; Allwood, Abigail; Andres, Miriam; Gammon, Crystal; Garvin, Jessica; Rashby, Sky; Schweizer, Maia; Watters, Wesley A. (Elsevier, 2010)
      The ca. 1.8 Ga Duck Creek Formation, Western Australia, preserves 1000 m of carbonates and minor iron formation that accumulated along a late Paleoproterozoic ocean margin. Two upward-deepening stratigraphic packages are ...
    • Imprints of Geodynamic Processes on the Paleoclimate Record 

      Austermann, Jacqueline (2016-05-18)
      In this thesis I investigate how solid Earth deformation associated with glacial isostatic adjustment and mantle convection impacted ice age climate. In particular, I discard approximations that treat the Earth's internal ...
    • Influence of sulfate reduction rates on the Phanerozoic sulfur isotope record 

      Leavitt, William Davie; Halevy, Itay; Bradley, Alexander S.; Johnston, David T (Proceedings of the National Academy of Sciences, 2013)
      Phanerozoic levels of atmospheric oxygen relate to the burial histories of organic carbon and pyrite sulfur. The sulfur cycle remains poorly constrained, however, leading to concomitant uncertainties in O2 budgets. Here ...
    • Key Factors Influencing Rates of Heterotrophic Sulfate Reduction in Active Seafloor Hydrothermal Massive Sulfide Deposits 

      Frank, Kiana L.; Rogers, Karyn L.; Rogers, Daniel R.; Johnston, David T.; Girguis, Peter R. (Frontiers Media S.A., 2015)
      Hydrothermal vents are thermally and geochemically dynamic habitats, and the organisms therein are subject to steep gradients in temperature and chemistry. To date, the influence of these environmental dynamics on microbial ...
    • Late Ediacaran Redox Stability and Metazoan Evolution 

      Knoll, Andrew Herbert; Johnston, David T; Poulton, S. W.; Goldberg, T.; Sergeev, V. N.; Podkovyrov, V.; Vorob’eva, N. G.; Bekker, A. (Elsevier, 2012)
      The Neoproterozoic arrival of animals fundamentally changed Earth's biological and geochemical trajectory. Since the early description of Ediacaran and Cambrian animal fossils, a vigorous debate has emerged about the drivers ...
    • Multiple Sulfur Isotope Applications in Diagenetic Models and Geochemical Proxy Records 

      Masterson, Andrew Laurence (2016-09-09)
      Many of the long-term geochemical fluxes influencing the surface sulfur cycle are microbially catalyzed and a substantial portion of active S cycling occurs in organic-rich continental margin sediments. Stable S isotopes ...
    • Multiple sulfur isotope constraints on the modern sulfur cycle 

      Tostevin, Rosalie; Turchyn, Alexandra V.; Farquhar, James; Johnston, David T; Eldridge, Daniel L.; Bishop, James K.B.; McIlvin, Matthew (Elsevier BV, 2014)
      We present 28 multiple sulfur isotope measurements of seawater sulfate \((δ^{34}S_{SO_{4}} and Δ^{33}S_{SO_4})\) from the modern ocean over a range of water depths and sites along the eastern margin of the Pacific Ocean. ...