Now showing items 1-20 of 27

    • Abrupt Climate Shifts in Greenland Due to Displacements of the Sea Ice Edge 

      Li, Camille; Battisti, David S.; Schrag, Daniel P.; Tziperman, Eli (American Geophysical Union, 2005)
      An atmospheric circulation model is used to show that a reduction in sea ice extent in the North Atlantic produces a climatic response consistent with abrupt changes in temperature and snow accumulation recorded in Greenland ...
    • 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 ...
    • 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 ...
    • Clumped Isotope Measurements of Small Carbonate Samples Using a High-Efficiency Dual-Reservoir Technique 

      Petersen, Sierra Victoria; Schrag, Daniel P. (Wiley-Blackwell, 2014)
      Rationale: The measurement of multiply substituted isotopologues of CO2 derived from carbonate has allowed the reconstruction of paleotemperatures from a single phase (CaCO3), circumventing uncertainty inherent in other ...
    • Constraints on Global Carbon Cycling, Basin Formation, and Early Animal Evolution During the Neoproterozoic and Early Cambrian 

      Smith, Emily (2015-09-25)
      Within this dissertation, I document different time intervals during the Neoproterozoic through the early Cambrian (1000 – 525 Ma), one of the most dynamic and non-uniformitarian intervals in the history of the Earth. This ...
    • 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. ...
    • Dynamics of a Snowball Earth Ocean 

      Ashkenazy, Yosef; Gildor, Hezi; Losch, Martin; Macdonald, Francis Alexander; Schrag, Daniel P.; Tziperman, Eli (Nature Publishing Group, 2013)
      Geological evidence suggests that marine ice extended to the Equator at least twice during the Neoproterozoic era (about 750 to 635 million years ago), inspiring the Snowball Earth hypothesis that the Earth was globally ...
    • Early Neoproterozoic scale microfossils in the Lower Tindir Group of Alaska and the Yukon Territory 

      Macdonald, Francis Alexander; Cohen, Phoebe; Dudas, Francis Ő.; Schrag, Daniel P. (Geological Society of America, 2010)
      The Tindir Group is a <4-km-thick Neoproterozoic succession exposed in the Tatonduk inlier of east-central Alaska and the western Yukon Territory. The Tindir Group is informally divided into the Lower Tindir Group, which ...
    • Electrochemical Acceleration of Chemical Weathering as an Energetically Feasible Approach to Mitigating Anthropogenic Climate Change 

      Aziz, Michael; Schrag, Daniel; House, Christopher H.; House, Kurt Zenz (American Chemical Society, 2007)
      We describe an approach to CO<sub>2</sub> capture and storage from the atmosphere that involves enhancing the solubility of CO<sub>2</sub> in the ocean by a process equivalent to the natural silicate weathering reaction. ...
    • The energy penalty of post-combustion CO2 capture & storage and its implications for retrofitting the U.S. installed base 

      House, Kurt Zenz; Harvey, Charles F.; Aziz, Michael J.; Schrag, Daniel P. (Royal Society of Chemistry (RSC), 2009)
      A review of the literature has found a factor of 4 spread in the estimated values of the energy penalty for post-combustion capture and storage of CO2 from pulverized-coal (PC) fired power plants. We elucidate the cause ...
    • 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 ...
    • 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 ...
    • Isotopic Constraints on the Late Archean Carbon Cycle from the Transvaal Supergroup along the Western Margin of the Kaapvaal Craton, South Africa 

      Fischer, Woodward W.; Schroeder, Stefan; Lacassie, Juan P.; Beukes, Nicolas J.; Goldberg, Tatiana; Strauss, Harald; Horstmann, Uwe E.; Schrag, Daniel P.; Knoll, Andrew (Elsevier, 2009)
      Few existing studies illuminate the operation of the carbon cycle before the rise of atmospheric oxygen circa 2400 million years ago. Stable carbon isotopic measurements of shallow stromatolitic carbonates (~0 [parts per ...
    • Large Perturbations of the Carbon Cycle During Recovery from the End-Permian Extinction 

      Payne, Jonathan L.; Lehrmann, Daniel J.; Wei, Jiayong; Orchard, Michael J.; Schrag, Daniel; Knoll, Andrew (American Association for the Advancement of Science, 2004)
      High-resolution carbon isotope measurements of multiple stratigraphic sections in south China demonstrate that the pronounced carbon isotopic excursion at the Permian-Triassic boundary was not an isolated event but the ...
    • Neoproterozoic glaciation on a carbonate platform margin in Arctic Alaska and the origin of the North Slope subterrane 

      Macdonald, Francis Alexander; McClelland, William C.; Schrag, Daniel P.; Macdonald, Winston P. (Geological Society of America, 2009)
      The rotation model for the opening of the Canada Basin of the Arctic Ocean predicts stratigraphic links between the Alaskan North Slope and the Canadian Arctic islands. The Katakturuk Dolomite is a 2080-m-thick Neo protero ...
    • A New Mechanism for Dansgaard-Oeschger Cycles 

      Petersen, Sierra Victoria; Schrag, Daniel P.; Clark, P. U. (Wiley-Blackwell, 2013)
      [1] We present a new hypothesis to explain the millennial-scale temperature variability recorded in ice cores known as Dansgaard-Oeschger (DO) cycles. We propose that an ice shelf acted in concert with sea ice to set the ...
    • Phosphorus sources for phosphatic Cambrian carbonates 

      Creveling, J. R.; Johnston, David T; Poulton, S. W.; Kotrc, B.; Marz, C.; Schrag, Daniel P.; Knoll, Andrew Herbert (Geological Society of America, 2013)
      The fossilization of organic remains and shell material by calcium phosphate minerals provides an illuminating, but time-bounded, window into Ediacaran–Cambrian animal evolution. For reasons that remain unknown, phosphatic ...
    • Searching for an oxygenation event in the fossiliferous Ediacaran of northwestern Canada 

      Johnston, David T; Poulton, S.W.; Tosca, N.J.; O'Brien, T.; Halverson, G.P.; Schrag, Daniel P.; Macdonald, Francis Alexander (Elsevier BV, 2013)
      Late Neoproterozoic (Ediacaran) strata from northwestern Canada provide a thick and rich sedimentological record, preserving intercalated carbonates and shale extending from the ~ 635 million year old Marinoan glacial ...