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Geochemical Journal, Vol. 52 (No. 6), pp. e29-e38, 2018
doi:10.2343/geochemj.2.0545

EXPRESS LETTER

Organic complexation of zinc in a coastal hydrothermal area, Tachibana Bay, Nagasaki, Japan

Taejin Kim,1,2* Hajime Obata,1 Shigenobu Takeda,3 Kuo Hong Wong,1 Asami Suzuki Mashio1,4 and Toshitaka Gamo1

1Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan
2School of Earth and Environmental Sciences, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, Republic of Korea
3Graduate School of Fisheries and Environmental Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan
4College of Science and Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan

(Received August 23, 2018; Accepted October 22, 2018; Online published November 12, 2018)

Abstract: Distributions of trace metals (Mn, Fe, Cu, and Zn) and Zn chemical speciation were determined in Tachibana Bay to investigate the role of organic complexing ligands and sulfide on Zn in a coastal hydrothermal system. At the coastal area near Obama Hot Springs, dissolved sulfide was only detected in two bottom water samples in Stn. 6 (29.2 and 59.4 nM). At this coastal area, dissolved Mn and Fe concentrations were high and increased toward the bottom, whereas dissolved Cu and Zn concentrations generally decreased toward the bottom. The Zn complexing organic ligands (CL) and conditional stability constants (log KZnL,Zn2+) in Tachibana Bay ranged from 0.9 nM to 1.6 nM and from 9.9 to 10.3, respectively. The free sulfide concentration calculated from Zn chemical speciation was much lower than the measured dissolved sulfide concentrations. Although dissolved Zn mainly precipitate as sulfide in shallow hydrothermally active area, the organic complexation of Zn is important in the remaining dissolved Zn.
Key words: shallow hydrothermal system, Tachibana Bay, dissolved trace metals, zinc speciation, sulfide


*Corresponding author E-mail: tkim0206@snu.ac.kr


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