https://www.nature.com/articles/s41467-023-37172-x (open access)

Abstract

During the Marinoan Ice Age (ca. 654–635 Ma), one of the ‘Snowball Earth’ events in the Cryogenian Period, continental icesheets reached the tropical oceans. Oceanic refugia must have existed for aerobic marine eukaryotes to survive this event, as evidenced by benthic phototrophic macroalgae of the Songluo Biota preserved in black shales interbedded with glacial diamictites of the late Cryogenian Nantuo Formation in South China. However, the environmental conditions that allowed these organisms to thrive are poorly known. Here, we report carbon-nitrogen-iron geochemical data from the fossiliferous black shales and adjacent diamictites of the Nantuo Formation. Iron-speciation data document dysoxic-anoxic conditions in bottom waters, whereas nitrogen isotopes record aerobic nitrogen cycling perhaps in surface waters. These findings indicate that habitable open-ocean conditions were more extensive than previously thought, extending into mid-latitude coastal oceans and providing refugia for eukaryotic organisms during the waning stage of the Marinoan Ice Age.

On 4/4/23 15:40, erik simpson wrote:
> Here, we report carbon-nitrogen-iron geochemical data from the fossiliferous black shales and adjacent diamictites of the Nantuo Formation. Iron-speciation data document dysoxic-anoxic conditions in bottom waters, whereas nitrogen isotopes record aerobic nitrogen cycling perhaps in surface waters. These findings indicate that habitable open-ocean conditions were more extensive than previously thought, extending into mid-latitude coastal oceans and providing refugia for eukaryotic organisms during the waning stage of the Marinoan Ice Age.

that is a near rewrite of the textbooks for snowball earth

Related

https://pubmed.ncbi.nlm.nih.gov/33000514/

On Tuesday, April 4, 2023 at 2:54:28 PM UTC-7, Popping Mad wrote:
> On 4/4/23 15:40, erik simpson wrote:
> > Here, we report carbon-nitrogen-iron geochemical data from the fossiliferous black shales and adjacent diamictites of the Nantuo Formation. Iron-speciation data document dysoxic-anoxic conditions in bottom waters, whereas nitrogen isotopes record aerobic nitrogen cycling perhaps in surface waters. These findings indicate that habitable open-ocean conditions were more extensive than previously thought, extending into mid-latitude coastal oceans and providing refugia for eukaryotic organisms during the waning stage of the Marinoan Ice Age.
> that is a near rewrite of the textbooks for snowball earth
>
> Related
>
> https://pubmed.ncbi.nlm.nih.gov/33000514/

Related for sure, but that reference discussses the chemistry of deep, anoxic water and the
metabolism of bacteria involved with sulfer processing. Today's article focusses on the continuity of eukayryotic
algae in shallow oxygenated water in "refugia" found not only near the equator, but also at mid-latitides (30-40N).
See the authors' Fig 3 for a comparison of snow- or slush-ball models.