Meteorological influences on marine chemistry during the Cryogenian Sturtian glaciation

The Cryogenian Sturtian glaciation (717–660 Ma) represents the most extreme icehouse climate condition in Earth's history, during which the global ocean was completely frozen, known as the Snowball Earth event. It is widely accepted that such a global freeze could result in persistent anoxic and ferruginous marine conditions. Here, we report on a Sturtian-aged storm-prone shelf (ca. 678 Ma) in South China, characterized by dynamic fluctuations in marine redox conditions. We observe a sequence of transitions from euxinic (anoxic and H2S-enriched) to ferruginous (anoxic but iron-rich), and finally to oxic conditions on this shelf. The euxinic deposits frequently exhibit hummocky/swaley cross-bedding structures (HCS/SCS) and contain high levels of authigenic francolite. In contrast, the ferruginous interval displays rare occurrences of HCS/SCS and lower amounts of authigenic francolite. Conversely, the oxic deposits show no evidence of storm activity. These results suggest that the strong storm waves played a crucial role in facilitating the upwelling of phosphorus-enriched deep water, thereby creating favorable nutrient conditions that stimulated primary productivity and microbial sulfate reduction (MSR). These findings underscore the significant influence of local meteorological conditions, particularly storm activity, on marine redox changes. Furthermore, dynamic storm-induced currents combined with marine redox conditions indicate the presence of an unfrozen sea with active biogeochemical cycles during the Cryogenian Sturtian glaciation. This study confirms the complex interactions among meteorology, oceanography, and Earth's climate system during extreme glacial events. •The Huangdongzigou Formation demonstrates dynamic fluctuations in marine redox conditions.•Changes in marine redox are closely associated with the intensity of storm activities.•During the Cryogenian glaciation, unfrozen seas exhibited active biogeochemical cycles.