Concentration and stable isotope composition of Hg in deep-sea sediment from the Nankai Trough

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Concentrations (n = 60) and stable isotope compositions (n = 10) of mercury (Hg) were determined for sediments as deep as 2200 m below the seafloor at ODP (Ocean Drilling Program) and IODP (International Ocean Discovery Program) Site 0002C in the forearc Kumano Basin, Nankai Trough. Concentrations of Hg varied within the range of 30–240 μg/kg, except for three samples of trench-fill sediment from the accretionary prism in which Hg concentrations were 330–820 μg/kg. Range of the studied Hg concentration is similar to those of modern subareal and marine sediments. Stable isotope values were close to those of volcanogenic and hydrothermal materials: –0.26 to –0.83‰ for δ²⁰²Hg. No mass-independent fractionation was observed, as Δ¹⁹⁹Hg was almost zero (range within 0.03 to 0.1). These results suggest that the Hg originated from volcanogenic or hydrothermal detrital materials and is being accreted and/or subducted with the oceanic plate.