Orbitally forced ice sheet fluctuations during the Marinoan Snowball Earth glaciation

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Two global glaciations occurred during the Neoproterozoic. Snowball Earth theory posits that these were terminated after millions of years of frigidity when initial warming from rising atmospheric CO₂ concentrations was amplified by the reduction of ice cover and hence a reduction in planetary albedo^{1, 2}. This scenario implies that most of the geological record of ice cover was deposited in a brief period of melt-back³. However, deposits in low palaeo-latitudes show evidence of glacial–interglacial cycles^{4, 5, 6}. Here we analyse the sedimentology and oxygen and sulphur isotopic signatures of Marinoan Snowball glaciation deposits from Svalbard, in the Norwegian High Arctic. The deposits preserve a record of oscillations in glacier extent and hydrologic conditions under uniformly high atmospheric CO₂ concentrations. We use simulations from a coupled three-dimensional ice sheet and atmospheric general circulation model to show that such oscillations can be explained by orbital forcing in the late stages of a Snowball glaciation. The simulations suggest that while atmospheric CO₂ concentrations were rising, but not yet at the threshold required for complete melt-back, the ice sheets would have been sensitive to orbital forcing. We conclude that a similar dynamic can potentially explain the complex successions observed at other localities.

 

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2502.html

 

Article

 

http://phys.org/news/2015-08-snowball-earth-period.html