Sedimentary molybdenum and uranium: Improving proxies for deoxygenation in coastal depositional environments

Sedimentary molybdenum (Mo) and uranium (U) enrichments are widely used to reconstruct changes in bottom water oxygen conditions aquatic environments. Until now, most studies using Mo U have focused on restricted suboxic-euxinic basins continental margin minimum zones (OMZs), leaving mildly reducing oxic (but eutrophic) coastal depositional environments vastly understudied. Currently, it is unknown: (1) what extent enrichment factors (Mo- U-EFs) can accurately sites experiencing mild deoxygenation, (2) degree secondary (depositional environmental) impact Mo- U-EFs. Here we investigate 18 with varying redox conditions, which define by means of five “redox bins”, ranging from persistently euxinic, a variety Our results demonstrate that U-EF-based proxies sedimentary contents be differentiate concentration among range modern This underpinned the contrasting EFs along gradient, shows substantial difference Mo-EFs between bins 3–5 (ir/regularly suboxic – ir/regularly dysoxic oxic) U-EFs 1–2 (persistently euxinic euxinic). Surprisingly, observe comparatively low proxy potential for deoxygenation (redox 3–5). Further, found bias Mo-and such an do not reliably reflect conditions. We limited sequestration sulfidic (i.e., “basin reservoir effect”, equilibrium FeMoS4), Fe/Mn-(oxy)(hydr)oxide “shuttling”, oxidative dissolution, sulfate methane transition zone sediment, sedimentation rate, local Al background