Uranium, vanadium, and chromium in fish scales: A redox‐unrelated accumulation pathway in continental margin sediments

Abstract Enrichment patterns of the redox‐ and bio‐sensitive trace elements U, V, Cr, and Ni in margin sediments are essential for environmental reconstructions. However, their sedimentary accumulation pathways are not fully understood. While the accumulation of toxic trace elements like Cd, Hg, Pb, and Zn has been relatively well studied in fish scales, less is known about U, V, Cr, and Ni. To investigate the role of fish scales as trace elements sinks in marine sediments, we analyzed U, V, Cr, Ni, Ca, and P in fish scales from cores taken from the central and southern Namibian shelf, alongside the bulk sediment and lithogenic composition of the respective hinterlands. Fish scales from the central Namibian shelf showed significantly higher contents of U (up to 134 ppm), V (up to 196 ppm), and Cr (up to 97 ppm), 2–5 times higher than scales from the southern shelf. In contrast, Ni levels were low in all fish scales, and bulk sediment trace elements were similarly enriched in all cores. The central Namibian hinterland has a much higher lithogenic trace element background than the southern hinterland. Hence, it appears that local marine biology could provide a more direct reflection of terrestrial inputs than the sediment record. Our results indicate that fish uptake rather than diagenesis controls trace element accumulation in scales. Seasonal dust inputs, potentially amplified by mining, could make U, V, Cr, and Ni bioavailable, highlighting the importance of fish scales as sedimentary trace element sinks. This reveals a redox‐independent enrichment pathway that should be considered in organic‐rich shelf upwelling sediments.