Fe–Mn Crust δ 98 Mo Decline Records Tectonic Forcing on Marine Oxide Sink Reduction During the Early Eocene–Early Oligocene

Abstract S, Tl, and W isotope records document pronounced early Eocene shifts in marine redox, yet the absence of a Mo isotope record obscures its progression. Here, we present ∼80 Myr Mo–Os–Be–Nd isotope profiles from a Northwest Pacific hydrogenetic Fe–Mn crust, revealing a systematic δ 98 Mo decline from −0.24‰ (early Eocene) to −0.83‰ (early Oligocene). This trend challenges the notion of Cenozoic Mo isotope stability and mainly reflects a reduced isotopic fractionation during marine Mo removal (ΔSW‐sink) from a contracted oxic sink. Coupled Mo–S–Tl–W isotope records suggest that this contraction was primarily driven by the tectonically forced loss of extensive shelf environments during the initial India–Asia collision. We establish Fe–Mn crust δ 98 Mo as a reliable proxy for global seawater redox evolution, demonstrating that multi‐proxy integration resolves tectonic controls on Earth's long‐term oxygenation history.