Influence of biological productivity on silver and redox-sensitive trace metal accumulation in Southern Ocean surface sediments, Pacific sector

• Productivity and redox proxies were measured in Southern Ocean surface sediments.
• All proxy fluxes except Mo increase within the opal belt.
• Elevated opal belt Ag and Cd fluxes imply biogenic particle delivery.
• Zonal Ag fluxes follow surface productivity patterns.

Accurate interpretation of paleoproductivity proxies in the Southern Ocean requires “ground truthing” these proxies. Here the concentrations of total Ba, organic carbon (Corg), and biogenic silica (Sibio), along with other redox-sensitive trace metals (Cd, Re, and Mo), are compared with the distribution of silver (Ag) in core top sediments from the Pacific sector of the Southern Ocean. Conventional thinking holds that enrichment of trace metals should be muted or absent in Southern Ocean sediments despite high export of Corg from surface waters because deposition under well-oxygenated bottom waters inhibits accumulation of reduced metal phases. While our data support this prediction, detectable preserved vertical fluxes of Ag, Cd, and Re exist beneath the opal belt and faithfully record surface productivity patterns. Therefore we suggest Ag fluxes into Southern Ocean sediments occur via biodetritus associated with high export production rather than accumulation by redox-driven diagenetic processes. Sedimentary Ag concentrations are likely altered at the seafloor by biogenic particle remineralization due to high bottom water O2. Nevertheless, zonal Ag fluxes are similar to surface productivity patterns, highlighting the potential of Ag to serve as a proxy for diatom export production.