Abstract During the early Cenozoic greenhouse period, counterintuitive contractions in tropical Pacific oxygen‐deficient zones have been linked to enhanced deep‐ocean ventilation, yet direct geological evidence remains limited. Here we present molybdenum (Mo) isotopic records from International Ocean Discovery Program Site U1509. Raman spectroscopy shows that Mn and Fe occur mainly as MnO 2 and Fe–Mn oxides. The δ 98 / 95 Mo values show a sustained negative shift from ∼1‰ to −2‰ between ∼59.5 and 50.5 Ma, and this trend is best explained by strengthened Mo adsorption onto Mn and Fe bearing oxides at the sediment–water interface. This mechanism provides a direct basis for interpreting the Mo isotope depletion, indicating prolonged bottom‐water oxygenation within early Cenozoic greenhouse conditions. At ∼50.5 Ma, a sharp decline in silicate εNd values and coeval rises in Ti, Zr, and Sc enrichment factors indicate intensified continental weathering that supplied isotopically light Mo. These results provide new constraints on early Cenozoic redox evolution.
Liu et al. (Sat,) studied this question.