Australia: The Land Where Time Began

A biography of the Australian continent 

Marinoan Snowball Earth Glaciation – Ice Sheet Fluctuations that were Orbitally Forced

According to Benn et al. the Snowball Earth theory posits that during the Neoproterozoic there were 2 global glaciations that were terminated after periods of frigidity that lasted millions of years when rising carbon dioxide levels in the atmosphere led to initiation of warming when the reduction of ice cover amplified the warming and therefore reduced the planetary albedo (Hoffman & Schrag, 2002; Donnadieu, Goddéris & Le Hir, 2014). Most of the geological record of ice cover is implied by this scenario to have been deposited in a brief period of melt-back (Hoffman, 2011). Evidence of glacial-interglacial cycles is, however, shown by deposits at low palaeolatitudes (Allen & Etienne, 2008; Rieu et al., 2007; Le Heron, Busfield & Kamona, 2013). In this paper Benn et al. analyse the sedimentary and oxygen and sulphur isotopic signatures of Marinoan Snowball glaciation deposits present in Svalbard, the Norwegian High Arctic. A record of oscillations in the extent of glaciers and hydrologic conditions under carbon dioxide concentrations that are uniformly high. In their study Benn et al. used simulations from a coupled 3-D ice sheet and atmospheric general circulation model to show that orbital forcing can explain such oscillations in the late stages of a snowball glaciation. It is suggested by the simulations that as the concentrations of carbon dioxide were rising, though not yet at the threshold that was required for complete melt-back to take place, the ice sheets would have been sensitive to orbital forcing. The conclusion of Benn et al. is that the complex successions that are observed at other localities can potentially be explained by a similar dynamic.

Sources & Further reading

1. Benn, D. I., G. Le Hir, H. Bao, Y. Donnadieu, C. Dumas, E. J. Fleming, M. J. Hambrey, E. A. McMillan, M. S. Petronis, G. Ramstein, C. T. E. Stevenson, P. M. Wynn and I. J. Fairchild (2015). "Orbitally forced ice sheet fluctuations during the Marinoan Snowball Earth glaciation." Nature Geosci 8(9): 704-707.