『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