Marine oxygen production and open water supported an active nitrogen cycle during the Marinoan Snowball Earth

Benjamin W Johnson,Colin Goldblatt,Simon W Poulton

doi:10.1038/s41467-017-01453-z

Benjamin W Johnson, Colin Goldblatt + Show 1 more

Open Access

https://doi.org/10.1038/s41467-017-01453-z

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Abstract

The Neoproterozoic Earth was punctuated by two low-latitude Snowball Earth glaciations. Models permit oceans with either total ice cover or substantial areas of open water. Total ice cover would make an anoxic ocean likely, and would be a formidable barrier to biologic survival. However, there are no direct data constraining either the redox state of the ocean or marine biological productivity during the glacials. Here we present iron-speciation, redox-sensitive trace element, and nitrogen isotope data from a Neoproterozoic (Marinoan) glacial episode. Iron-speciation indicates deeper waters were anoxic and Fe-rich, while trace element concentrations indicate surface waters were in contact with an oxygenated atmosphere. Furthermore, synglacial sedimentary nitrogen is isotopically heavier than the modern atmosphere, requiring a biologic cycle with nitrogen fixation, nitrification and denitrification. Our results indicate significant regions of open marine water and active biologic productivity throughout one of the harshest glaciations in Earth history.

Highlights

The Neoproterozoic Earth was punctuated by two low-latitude Snowball Earth glaciations
It was initially postulated that a “hard Snowball Earth” with sea ice hundreds of metres thick covered the ocean during low-latitude glaciation[1,4]
By normalizing trace elements (TE) to non-redox sensitive elements with similar geochemistry (i.e., Sc, Zr) and comparing with a detrital proxy (Al), we show that variations in detrital input, as indicated by Al, cannot fully explain these data (Fig. 3)