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Geochemical Journal, Vol. 49 (No. 4), pp. e1-e7, 2015
doi:10.2343/geochemj.2.0374

EXPRESS LETTER

Sulfides in oxic seawater over the submarine hydrothermal area of Kikai Caldera south of Kyushu Island, Japan

Noriko Nakayama*, Kotaro Shirai, Yuji Sano, Toshitaka Gamo and Hajime Obata

Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan

(Received December 19, 2014; Accepted May 29, 2015; Online published June 26, 2015)

Abstract: The concentration of total metal sulfide throughout a water column over a submarine hydrothermal vent in Kikai Caldera south of Kyushu Island, Japan, at ∼350 pmol/kg, was higher than that reported in previous studies, at <50 pmol/kg below the halocline. Seawater filtered at 0.2 μm pore size and unfiltered seawater exhibited almost identical metal sulfide concentrations throughout the water column, indicating that most metal sulfide existed in dissolved and particulate forms with diameters <0.2 μm. By using a mass balance calculation with the observed sulfide species of free and metal sulfides and carbonyl sulfide, we showed that ∼70% of the metal sulfide supplied from hydrothermal vents were contained in the water column beyond the halocline without undergoing oxidative loss even after mixing into overlying oxic seawater. Our findings clearly indicate that sulfide and trace metals emitted from hydrothermal vents form a stable metal-sulfide complex with diameters <0.2 μm. These results also strongly support the recently proposed theory such that metal-sulfide complexation/nanoparticles play an important role in the long-distance transportation of trace metals in the ocean.
Key words: dissolved sulfide, long distance transportation of trace metal, hydrothermal source, oxic seawater


*Corresponding author E-mail: noriko@aori.u-tokyo.ac.jp


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