Oceanic profiles of dissolved silver: precise measurements in the basins of western North Pacific, Sea of Okhotsk, and the Japan Sea

We present here the detailed vertical profiles of dissolved (<0.04 μm) Ag in the three different oceanic basins in the western margin of the North Pacific. Those profiles confirmed that Ag is strongly involved in the biogeochemical cycling of biological uptake in the surface water, particulate sinking, and regeneration in the deep sea. The vertical profiles of Ag best resemble those of dissolved Si, but in detail there are differences between the two. In the western North Pacific, dissolved Ag reaches a maximum at 2500-3000 m, which is deeper than that of dissolved Si (∼2000 m). This implies that Ag is regenerated more slowly than Si. The greater inter-oceanic variation of Ag over Si in the deep waters between the North Atlantic and North Pacific is consistent with this interpretation. The other two profiles from the Sea of Okhotsk and the Japan Sea fit well in this biogeochemical and oceanographic trend.

Our dissolved Ag concentrations (4.2-8.0 pmol/kg) in the surface waters are significantly higher than those reported previously for other locations, and it appears that the variability of Ag in the surface waters is greater than an order of magnitude. Although many factors are involved in controlling the Ag concentration in the surface waters, removal by biological uptake appears to be particularly important. Although there may be some indication of anthropogenic sources in the surface waters, it seems to be local, and the large-scale contamination of Ag in the ocean is not seen in our data.