Le Hir,G., Donnadieu,Y., Godderis(eの頭に´),Y., Pierrehumbert,R.T., Halverson,G.P., Macouin,M., Nedelec(最初と二番目のeの頭に´),A. and Ramstein,G.(2009): The snowball Earth aftermath: Exploring the limits of continental weathering processes. Earth and Planetary Science Letters, 277, 453-463.

『雪玉地球直後:大陸風化過程の限界を調べる』


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 dolostone, we show that continental weathering alone does not supply enough cations during the snowball melting phase to account for their observed volume.

Keywords: snowball Earth; greenhouse; cap dolostones; weathering; modelling』

1. Introduction
2. The climate of the snowball aftermath
 2.1. Climate model description and simulation design
 2.2. Post snowball Earth climate: runoff and water cycle behaviour
3. Continental weathering during the supergreenhouse climate
 3.1. Description of the continental weathering model
 3.2. Design of the WITCH simulations
 3.3. Weathering rates in a supergreenhouse environment
4. Duration of the post-snowball supergreenhouse climate
5. The deglaciation and the cap dolostone deposition, a model-data discussion
6. Conclusion
Acknowledgments
References


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