Sulfur isotopes track the global extent and dynamics of euxinia during Cretaceous Oceanic Anoxic Event 2

Oxygen in the atmosphere and ocean rose dramatically about 600 Mya, coinciding with the first proliferation of animals. However, numerous biotic events followed when oxygen concentrations in the younger ocean dipped episodically. The Cretaceous is famous for such episodes, and the most extensive of these oceanic anoxic events occurred 93.9 Mya. Our combined carbon- and sulfur-isotope data indicate that oxygen-free and hydrogen sulfide-rich waters extended across roughly 5% of the global ocean, compared to <<1% today, but with the likelihood that much broader regions were also oxygen challenged. These conditions must have impacted nutrient availability in the ocean and ultimately the spatial and temporal distribution of marine life across a major climatic perturbation.