Tziperman, Eli and Halevy, Itay and Johnston, David T. and Knoll, Andrew H. and Schrag, Daniel P. (2011) Biologically induced initiation of Neoproterozoic snowball-Earth events. Proceedings of the National Academy of Sciences of the United States of America, 108 (37). pp. 15091-15096. ISSN 0027-8424 http://resolver.caltech.edu/CaltechAUTHORS:20110928-083841400
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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 of isotopically light organic matter and imply strong enhancement of atmospheric CO_2 greenhouse gas concentration, apparently inconsistent with the glaciations that followed. We examine a scenario in which the isotopic signal, as well as the global glaciation, result from enhanced export of organic matter from the upper ocean into anoxic subsurface waters and sediments. The organic matter undergoes anoxic remineralization at depth via either sulfate- or iron-reducing bacteria. In both cases, this can lead to changes in carbonate alkalinity and dissolved inorganic pool that efficiently lower the atmospheric CO_2 concentration, possibly plunging Earth into an ice age. This scenario predicts enhanced deposition of calcium carbonate, the formation of siderite, and an increase in ocean pH, all of which are consistent with recent observations. Late Neoproterozoic diversification of marine eukaryotes may have facilitated the episodic enhancement of export of organic matter from the upper ocean, by causing a greater proportion of organic matter to be partitioned as particulate aggregates that can sink more efficiently, via increased cell size, biomineralization or increased C:N of eukaryotic phytoplankton. The scenario explains isotopic excursions that are correlated or uncorrelated with snowball initiation, and suggests that increasing atmospheric oxygen concentrations and a progressive oxygenation of the subsurface ocean helped to prevent snowball glaciation on the Phanerozoic Earth.
|Additional Information:||© 2011 National Academy of Sciences. Edited by Timothy W. Lyons, University of California, Riverside, CA, and accepted by the Editorial Board July 12, 2011 (received for review November 11, 2010). Published online before print August 8, 2011. We thank Timothy Lyons, Chris Reinhard, and two anonymous reviewers for most constructive and helpful comments. We are grateful for helpful discussions and comments from Arren Bar-Even, Don Canfield, Hezi Gildor, Peter Huybers, Francis Macdonald, Ron Milo, and Aldo Shemesh. This work was supported by National Science Foundation Grant ATM-0902844 (to E.T.) and National Aeronautics and Space Administration Grant NNX07AV51 (to A.H.K. and D.T.J.). E.T. thanks the Weizmann Institute for its hospitality during parts of this work. Author contributions: E.T. designed research; E.T., I.H., D.T.J., A.H.K., and D.P.S. performed research; and E.T., I.H., D.T.J., A.H.K., and D.P.S. wrote the paper.|
|Subject Keywords:||carbon isotopes; CO_2|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||06 Oct 2011 18:19|
|Last Modified:||10 Aug 2012 23:03|
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