Vertical distribution of mercury in sediments from the East Pacific Rise

Abstract

Concentrations of mercury are often high in waters and sediments associated with volcanic hydrothermal systems, in both marine and terrestrial environments. Whereas the concentration of mercury in open ocean waters is reported to be in the range 0.002–0.05 µg 1⁻¹ (refs 1–4), significantly higher values of up to 1.4 µg l⁻¹ are reported in waters near, or having circulated through, areas of submarine hydrothermal activity^2,5. Mercury concentrations of up to 400 p.p.b. (parts per 10⁹) on a carbonate-free basis (CFB) have been measured in surface sediments on the East Pacific Rise crest, but concentrations decrease to <20 p.p.b. (CFB) on the peripheral seafloor⁶. Similar high concentrations from 160 to 890 p.p.b. (CFB) have been recorded in near-surface sediments from the median valley of the Mid-Atlantic Ridge⁷. We report here on the vertical variations of mercury in sediments from the East Pacific Rise, and suggest that increased concentrations are correlated with periods of increased submarine volcanic activity.