Control of early diagenesis on rare earth element cycling and enrichment in pelagic hydrothermal-influenced sediments

Hydrothermal plumes impact oceanic rare earth element and yttrium (REE + Y) cycling through Fe-Mn particle scavenging. However, REE + Y cycling and enrichment mechanisms in hydrothermal-influenced sediments remain poorly constrained. Here, we present geochemical data for seawater, pore water, and bioapatite from a hydrothermal-influenced region in the eastern South Pacific Ocean. Our results reveal that hydrothermal Fe-Mn oxides scavenge REE + Y from the water column (Nd burial flux: ∼206 pmol cm−2 yr−1) and then act as a source of benthic flux (Nd: 24 pmol cm−2 yr−1) during early diagenesis. Early diagenetic REE + Y release in metalliferous sediments mainly occurs at the sediment-seawater interface, with deep burial environments showing only sporadic and low-magnitude mobilization. This diagenetic flux dominates REE + Y enrichment in bioapatite, and radiogenic εNd signatures of bioapatite at the sediment-water interface provide direct evidence of pore-water processes.