Marine osmium‑uranium‑sulfur isotope evidence for the interaction of volcanism and ocean anoxia during the Middle Pleistocene in the tropical Western Pacific

Before the Quaternary, the Earth experienced a series of environmental perturbations. The causal links between large volcanic events, extreme climatic change, and ocean anoxia have been examined in the context of these perturbations. However, to date, the correlation between oceanic anoxia and large volcanic activity in the Pleistocene remains poorly constrained. Identifying the physical processes that can control changes to the marine osmium, uranium, and sulfur isotope ratios is critical to understanding how volcanic activity, climate changes, and ocean anoxia have coevolved throughout the Quaternary. In this study, we provide a continuous high-resolution marine record of 187Os/188Os from 1.31 Ma to 0.59 Ma, as well as uranium, sulfur and carbon isotope (δ238UCarb, δ34SCAS, and δ13C) data from carbonates collected from the International Ocean Discovery Program (IODP) site 363 to characterize the relationship between volcanic eruptions and the variations in the redox state of the oceans. The marine sediments in the studied core exhibited numerous prominent negative shifts in the isotopic ratios of osmium, implying that they were triggered by large volcanic events. Our δ238UCarb and δ34SCAS records also exhibit multiple negative shifts, suggesting a mantle-derived input during this period. Enhanced volcanic episodes can release large quantities of CO2, which can cause enhanced oceanic anoxia; hence, this study demonstrates that multiple oscillations in oceanic anoxia were driven by large volcanic eruptions during this stage.