TERRAPUB Geochemical Journal

Geochemical Journal, Vol. 52, 2018

Mercury evasion fluxes from sea surfaces of the Tsushima Strait and Kuroshio Current in the East China Sea

Kohji Marumoto1,*, Akinori Takeuchi2, Shoko Imai1, Hitoshi Kodamatani3, and Noriyuki Suzuki4

1Environmental Chemistry Section, National Institute for Minamata Disease (NIMD), 4058-18, Hama, Minamata-shi, Kumamoto 867-0008, Japan
2Center for Environmental Measurement and Analysis, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba-shi, Ibaragi 305-8506, Japan
3Department of Earth and Environmental Sciences, Faculty of Science, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065, Japan
4Center for Health and Environmental Risk Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba-shi, Ibaragi 305-8506, Japan

(Received February 2, 2017; Accepted April 26, 2017)

Abstract: Re-emission of mercury (Hg), previously deposited in soils and oceans, plays an important role in the global Hg cycle. Mercury evasion from surrounding sea surfaces might be one of the main emission sources of atmospheric Hg in Japan. To obtain information on Hg cycling around the Japanese Islands, dissolved gaseous mercury (DGM) and Hg evasion fluxes from surface seawaters of the Tsushima Strait and East China Sea were investigated using a two-layer gas exchange model. The mean DGM concentrations in the Tsushima Strait are 22 ± 7 pg L-1 in October 2014 and 27 ± 6 pg L-1 in August 2015, suggesting slightly higher values in summer (P < 0.05, t-test). The DGM concentrations in the Kuroshio Current are lower than in the Tsushima Strait and Pacific Ocean. However, the DGM concentrations are supersaturated at all sites, except at the site with the highest atmospheric total gaseous Hg (TGM). This suggests that Hg is emitted from these sea surfaces into the atmosphere. The TGM concentrations are sometimes increased due to the long-range transport from the Asian continent and volcanic activities on the southern Kyushu Island. The DGM concentrations and %DGM of the total Hg in the Tsushima Strait are positively correlated with the solar radiation, indicating that the DGM is partly produced by photochemical formation from Hg(II) in the surface seawater. No positive relationships between the DGM and sunlight were observed in the Kuroshio Current. Given that most of the observations for the Kuroshio Current were made far from the land, at water depths > 200 m, the photochemical production of DGM is likely related to the distance from the coast and water depth, more specifically the inflow of terrestrial substances such as Fe and humic substances. The factors controlling the DGM variations differ at various sites, depending on the sea area and seasonal conditions. Based on the literature and results of this study, the Hg emissions of the East China Sea, including the Yellow Sea, are estimated to be 49 ± 17 t yr-1. This value is greater than the annual anthropogenic Hg emission from the Japanese Islands (18-34 t yr-1) but might be low compared with the outflow of Hg from the Asian continent.
Key words: Dissolved gaseous mercury; Evasion flux; Mercury cycling; East China Sea; Kuroshio Current

*Corresponding author E-mail: marumoto@nimd.go.jp

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