Abstract
The severe “Snowball Earth” glaciations proposed to have existed during the Cryogenian period (720 to 635 million years ago) coincided with the breakup of one supercontinent and assembly of another. Whereas the presence of extensive continental ice sheets predicts a tidally energetic Snowball ocean due to the reduced ocean depth, the supercontinent palaeogeography predicts weak tides because the surrounding ocean is too large to host tidal resonances. Here we show, using an established numerical global tidal model and paleogeographic reconstructions, that the Cryogenian ocean hosted diminished tidal amplitudes and associated energy dissipation rates, reaching 10–50% of today’s rates, during the Snowball glaciations. We argue that the near-absence of Cryogenian tidal processes may have been one contributor to the prolonged glaciations if these were near-global. These results also constrain lunar distance and orbital evolution throughout the Cryogenian, and highlight that simulations of past oceans should include explicit tidally driven mixing processes.
Highlights
The severe “Snowball Earth” glaciations proposed to have existed during the Cryogenian period (720 to 635 million years ago) coincided with the breakup of one supercontinent and assembly of another
It has been suggested that the Earth experienced near-global severe glaciations during the Cryogenian period (720–635 Ma), events which earned the nickname “Snowball Earth”[1,2]
We propose that a second factor, ocean tides, influenced the duration of Cryogenian Snowball glaciations
Summary
The severe “Snowball Earth” glaciations proposed to have existed during the Cryogenian period (720 to 635 million years ago) coincided with the breakup of one supercontinent and assembly of another. I.e., the loss of tidal energy due to boundary friction and tidal conversion (the generation of internal tidal waves), was added to the background flow, the stratification could break down further[13] This scenario predicts negligible tidal conversion (i.e., the generation of an internal tide), and tidal dissipation would be limited to the frictional boundary layer near the sea floor and underneath the ice. It has been suggested that tides in the vicinity of the Laurentide ice sheet during the last deglaciation probably contributed to its rapid collapse[14]. Weak tides would reduce under-ice mixing rates, which could prolong the duration of a Snowball glaciation, with farreaching consequences for the Earth system
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