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Δ34S18O systematics of modern sulfate

In this study, 34 S- 18 O clumping in sulfate are newly used to constrain the sulfur and oxygen cycling. Quantitative conversion from sulfate sample into SO 2 F 2 is conducted by the reaction with BaSO 4 and F 2 at 280 ℃ for 3 h in a nickel reaction vessel. The produced SO 2 F 2 was purified and measured by high-mass-resolution mass spectrometer (MAT253 ULTRA). The fluorination method was applied to measure seawater, river water and hot spring water to elucidate the Δ 34 S 18 O systematics of modern sulfate. First, several seawater sulfate samples show constant Δ 34 S 18 O value, which is indistinguishable from that of the international sulfate standard NBS127 (modern marine evaporite). This suggests that Δ 34 S 18 O of gypsum/anhydrite could preserve seawater signature after precipitation. River water sulfate found to exhibit high Δ 34 S 18 O value up to +4.5‰ relative to seawater sulfate ( Δ 34 S 18 O = 0‰ by definition). The high Δ 34 S 18 O could be a distinctive signature for sulfate derived from oxidative weathering. On the other hand, sulfate in hot spring water always shows low Δ 34 S 18 O value from –1.0‰ to –0.5‰, which may reflect high temperature hydrothermal origin. These results suggest that the 34 S- 18 O clumping in seawater sulfate is modified from the river input potentially through microbial sulfate reduction and/or hydrothermal activity. In summary, the Δ 34 S 18 O of marine sulfate deposit could be useful to trace biogeochemical evolution of seawater.