The accumulation of silver in marine sediments: A link to biogenic Ba and marine productivity

Abstract

The concentrations of Ag and a suite of redox‐sensitive trace metals (Re, Cd, and Mo) were measured in surface sediments from the Western Canadian, Mexican, Peruvian, and Chilean continental margins. In all regions, Ag content increases from ∼80 ng g−1 (i.e., lithogenic values) on the shelf up to as high as 1483 ng g−1 on the lower slope. However, the trend of increasing Ag with increasing water depth breaks down at deepwater sites (>2500 m) where only lithogenic concentrations are documented. Silver content does not correlate with the distributions of redox‐sensitive trace metals, suggesting that sedimentary redox conditions are not the primary control on Ag accumulation. Instead, a positive correlation between Ag and Ba in surface and near‐surface sediments suggests that Ag is scavenged by and delivered to the sediment with the organic particle flux. Scavenging probably results from the precipitation of Ag2S within the organic particles due to the development of anoxia and sulfate reduction. If this hypothesis is correct, then Ag has the potential to be a paleoproductivity proxy.