Low-oxygen settings strongly influence the cycling of trace metals across the water-column–sediment continuum, yet the processes that set the signals ultimately preserved in sediments remain difficult to disentangle. Sinking particles deliver trace metals scavenged in the water column, while early diagenesis can remobilise, erase, or enrich these signals at the seafloor — leaving the origin of sedimentary trace-metal records ambiguous. Manganese and iron oxides are central to this transfer, but their distinct roles have rarely been separated.
We combine reactive-transport modelling with water-column, pore-water and sediment observations from an eastern Pacific oxygen-deficient zone to examine how oxide scavenging and diagenesis together govern trace-metal transfer and preservation, using rare earth elements as a sensitive tracer of these processes. We find that the redox structure of the system drives contrasting behaviour of manganese and iron oxides, with consequences for how trace-metal signals are imparted to and retained in sediments. We discuss the implications for interpreting trace-metal and isotope proxies of past ocean redox, and for understanding sedimentary metal cycling more broadly.