Supraglacial biological niches as a solution to the Sturtian oxygenation problem

Understanding how climate and biology changed during and after Snowball Earth events - global glaciations which coincided with major shifts in the ocean-atmosphere state - is critical for understanding the evolution of life on Earth. New observations of the Neoproterozoic Sturtian glaciation pose challenges to the Snowball paradigm. Precision geochronology shows that the Sturtian lasted ~56 Myr, and the lack of sulfur-MIF signals observed indicates that the atmosphere remained oxygenated throughout. A source of O₂ is required to maintain an oxygenated atmosphere for ~56 Myr, but in the canonical Snowball scenario, primary production shuts down completely. Here, we model the carbon and oxygen cycles during the Snowball to investigate this challenge. We propose that photosynthesis in melt holes on the equatorial glacier surface was sufficiently productive to provide the missing O₂ source, and that accumulation of aeolian dust sustained these melt holes and supplied them with nutrients. We argue that primary production was limited by phosphorus availability and photosynthetically active surface area, and show that only a dust-supported supraglacial ecosystem could satisfy both conditions.