# Biologically Induced Initiation of Neoproterozoic Snowball-Earth Events

 Title: Biologically Induced Initiation of Neoproterozoic Snowball-Earth Events Author: Tziperman, Eli; Halevy, Itay; Johnston, David T; Knoll, Andrew Herbert; Schrag, Daniel P. Note: Order does not necessarily reflect citation order of authors. Citation: Tziperman, Eli, Itay Halevy, David T. Johnston, Andrew Herbert Knoll, and Daniel P. Schrag. 2011. “Biologically Induced Initiation of Neoproterozoic Snowball-Earth Events.” Proceedings of the National Academy of Sciences 108 (37) (September 13): 15091–15096. doi:10.1073/pnas.1016361108. http://dx.doi.org/10.1073/pnas.1016361108. Full Text & Related Files: Tziperman-biologically-induced.pdf (2.518Mb; PDF) Abstract: 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. Published Version: doi:10.1073/pnas.1016361108 Terms of Use: This article is made available under the terms and conditions applicable to Other Posted Material, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#LAA Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:11895420 Downloads of this work: