The snowball Earth aftermath: Exploring the limits of continental weathering processes |
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| Authors: | Guillaume Le Hir Yannick Donnadieu Yves Goddéris Raymond T Pierrehumbert Galen P Halverson Mélina Macouin Anne Nédélec Gilles Ramstein |
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| Institution: | 1. LSCE, CNRS-CEA-UVSQ, Gif-sur-Yvette, France;2. LMTG, CNRS-Université de Toulouse, Observatoire Midi-Pyrénées, Toulouse, France;3. Dept of Geophysical Sciences, University of Chicago, Illinois, USA;4. School of Earth and Environmental Sciences, University of Adelaide, North Terrace, Adelaide, SA 5005, Australia;1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, 19 Beitucheng West Road, Chaoyang District, Beijing 100029, China;2. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China;3. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Wuhan), Wuhan 430074, China;4. Guizhou Academy of Geological Survey, Guiyang 550005, Guizhou, China;1. Department of Applied Geology, Institute of Geosciences and Exact Sciences, São Paulo State University (Unesp), Rio Claro, SP, Brazil;2. Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA;3. Department of Petrology and Metallogenesis, Institute of Geosciences and Exact Sciences, São Paulo State University (Unesp), Rio Claro, SP, Brazil;4. Institute of Geosciences, Federal University of Minas Gerais, Belo Horizonte, MG, Brazil;1. Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843, United States;2. Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093, United States;3. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, United States;4. Department of Geosciences, Princeton University, Princeton, NJ 08544, United States;1. State Key Laboratory of Biogeology and Environmental Geology, School of Earth Sciences, China University of Geosciences, Wuhan 430074, PR China;2. Department of Geosciences, Virginia Tech, Blacksburg, VA 24061, USA;3. Department of Earth and Planetary Sciences, Nagoya University, Nagoya 4648602, Japan;1. Princeton University, Guyot Hall, Princeton, NJ 08540, USA;2. University of California Santa Barbara, Department of Earth Sciences, Santa Barbara, CA 93106, USA;3. University of Victoria, School of Earth and Ocean Sciences, BCV8W 2Y2, Canada;4. University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen K, Denmark;5. The University of Tokyo, School of Science, Bunkyo-ku, Tokyo 113-0033, Japan;6. University of St Andrews, Irvine Building, St Andrews, United Kingdom;7. Dartmouth College, Fairchild Hall, Hanover, NH 03755, USA |
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| Abstract: | Carbonates capping Neoproterozoic glacial deposits contain peculiar sedimentological features and geochemical anomalies ascribed to extraordinary environmental conditions in the snowball Earth aftermath. It is commonly assumed that post-snowball climate dominated by CO2 partial pressures several hundred times greater than modern levels, would be characterized by extreme temperatures, a vigorous hydrological cycle, and associated high continental weathering rates. However, the climate in the aftermath of a global glaciation has never been rigorously modelled. Here, we use a hierarchy of numerical models, from an atmospheric general circulation model to a mechanistic model describing continental weathering processes, to explore characteristics of the Earth system during the supergreenhouse climate following a snowball glaciation. These models suggest that the hydrological cycle intensifies only moderately in response to the elevated greenhouse. Indeed, constraints imposed by the surface energy budget sharply limit global mean evaporation once the temperature has warmed sufficiently that the evaporation approaches the total absorbed solar radiation. Even at 400 times the present day pressure of atmospheric CO2, continental runoff is only 1.2 times the modern runoff. Under these conditions and accounting for the grinding of the continental surface by the ice sheet during the snowball event, the simulated maximum discharge of dissolved elements from continental weathering into the ocean is approximately 10 times greater than the modern flux. Consequently, it takes millions of years for the silicate weathering cycle to reduce post-snowball CO2 levels to background Neoproterozoic levels. Regarding the origin of the cap dolostones, we show that continental weathering alone does not supply enough cations during the snowball melting phase to account for their observed volume. |
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