Frequent Millennial-Scale Oceanic Redox Oscillations Recorded by Negative Pyrite Δ33S: Implications for Phanerozoic Extinctions

Phanerozoic extinctions may have been influenced by oceanic redox oscillations, as indicated by mixing-induced negative pyrite Δ³³S (Δ³³S_py). However, the frequencies, intensities, and timescales of these oscillations remain elusive. Here, we measured stratigraphic Δ³³S_py from the currently anoxic Cariaco Basin, spanning ∼0.6 million years. Our results reveal two distinct patterns of negative Δ³³S_py that are linked to specific redox oscillations, potentially analogous to patterns recorded during Phanerozoic extinctions. During Marine Isotope Stage 1–2 and 9–10, bottom water experienced redox oscillations on a timescale of 10,000 years, resulting in slightly negative Δ³³S_py (−0.03‰). In contrast, during the period of 160–200 kyr BP, bottom water underwent frequent redox oscillations on millennial- and centennial-timescales, leading to significantly more negative Δ³³S_py values (−0.09‰). We highlight that similarly frequent oceanic redox fluctuations may have contributed to the end-Guadalupian extinction, when notably negative Δ³³S_py values akin to those observed in our study were prevalent.