And was there a mighty wind?

Readers will be familiar with the to-ing and fro-ing that surrounds the idea of Neoproterozoic Snowball Earth episodes from earlier issues of EPN.  The leading proponent and sturdy defender of the hypothesis, Paul Hoffman of Harvard University, re-enters the fray as co-author of a paper that builds on the idea that following global glaciation the climate became not only very warm but also violent (Allen, P.A. & Hoffman, P.F. 2005.  Extreme winds and waves in the aftermath of a Neoproterozoic glaciation.  Nature, v. 433, p. 123-127).  They document evidence from “cap carbonates” in northern Canada and Spitzbergen that succeed diamictites of “Marinoan” (~635 Ma) age, in the form of large-scale sedimentary structures.  Many of these are submarine ripples with amplitudes up to 40 cm, and forms that suggest they were produced by sea-bed motion due to surface waves, down to 200-400 m, far deeper than modern storm-wave base.  Central to their argument is hydrodynamic modelling of wind speeds that might have produced such large ripples, and their specific shapes – steep sided.  Being based on experiment and observation of modern sea-bed processes, the theory seems quite rigorous.  It retrodicts wave periods that are somewhat longer than those commonly seen in modern ocean storms.  From that they derive sustained wind speeds that exceed 70 km per hour across open oceans, extraordinary by modern ocean wind standards.

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