Air–sea exchange of gaseous mercury in the tropical coast (Luhuitou fringing reef) of the South China Sea, the Hainan Island, China

Abstract

The air-sea exchange of gaseous mercury (mainly Hg(0)) in the tropical ocean is an important part of the global Hg biogeochemical cycle, but the related investigations are limited. In this study, we simultaneously measured Hg(0) concentrations in surface waters and overlaying air in the tropical coast (Luhuitou fringing reef) of the South China Sea (SCS), Hainan Island, China, for 13 days on January-February 2015. The purpose of this study was to explore the temporal variation of Hg(0) concentrations in air and surface waters, estimate the air-sea Hg(0) flux, and reveal their influencing factors in the tropical coastal environment. The mean concentrations (±SD) of Hg(0) in air and total Hg (THg) in waters were 2.34 ± 0.26 ng m −3 and 1.40 ± 0.48 ng L −1 , respectively. Both Hg(0) concentrations in waters (53.7 ± 18.8 pg L −1 ) and Hg(0)/THg ratios (3.8 %) in this study were significantly higher than those of the open water of the SCS in winter. Hg(0) in waters usually exhibited a clear diurnal variation with increased concentrations in daytime and decreased concentrations in nighttime, especially in cloudless days with low wind speed. Linear regression analysis suggested that Hg(0) concentrations in waters were positively and significantly correlated to the photosynthetically active radiation (PAR) (R 2 = 0.42, p < 0.001). Surface waters were always supersaturated with Hg(0) compared to air (the degree of saturation, 2.46 to 13.87), indicating that the surface water was one of the atmospheric Hg(0) sources. The air-sea Hg(0) fluxes were estimated to be 1.73 ± 1.25 ng m −2 h −1 with a large range between 0.01 and 6.06 ng m −2 h −1 . The high variation of Hg(0) fluxes was mainly attributed to the greatly temporal variation of wind speed.

Air–surface exchange of gaseous mercury over permafrost soil: an investigation at a high-altitude (4700 m a.s.l.) and remote site in the central Qinghai–Tibet Plateau

“…Due to the harsh environmental conditions and the unstable power supply, use of the commercial automatic Hg analyzer (such as Tekran 2537) to conduct field measurements of Hg(0) flux is challenging in the Beiluhe station. Therefore, air Hg(0) concentrations in the both inlet and outlet of the chamber were monitored manually by a gold trap simultaneously at 2-3 h intervals (Ci et al, 2016b). The air was pumped through gold trap using air pump (KNF Inc., Germany) with 0.50 L min −1 (0.03 m 3 h −1 ).…”

Spatial Differences and Influencing Factors of Dissolved Gaseous Mercury in the Yellow Sea and Bohai Sea in Spring

“…Higher THg concentrations appeared in the center of the South Yellow Sea, the Bohai Strait, south of Dalian Yalu River estuary. The average concentrations were higher than the Yellow Sea in summer ((1.69 ± 0.35) ng/L, Ci et al, 2011a) and the South China Sea in winter ((1.40 ± 0.48) ng/L, Ci et al, 2016). The concentrations of THg in the Yellow Sea and Bohai Sea was much higher than for other oceans and deep seas, such as the Mediterranean Sea ((0.24 ± 0.06) ng/L, Kotnik et al, 2007) and the Northern Pacific Ocean ((0.23 ± 0.17) ng/L, Laurier et al, 2004), reflecting the influence of land on the marginal sea of China.…”

“…The DGM concentrations in the South Yellow Sea were higher than those in the Mediterranean ((30.1 ± 24.1) pg/L) (Horvat et al, 2003). DGM in the Yellow Sea and Bohai Sea was lower than that in the South China Sea ((53.7 ± 18.8) pg/L, Ci et al, 2016), while it was higher than the concentrations in the Yellow Sea-Northwest Pacific ((39.6 ± 22.9) pg/L, Liu et al, 2017), and in the Baltic Sea (17.4 pg/L, Wängberg et al, 2001). In spring, DGM in the Yellow and Bohai Seas accounted for less than 2.2% of THg, far lower than for the Yellow Sea-Northwest Pacific surface seawater (8.06%, Liu et al, 2017) and for the Mediterranean Sea (20%, Kotnik et al, 2017) and for other open seas.…”

“…RHg is a type of mercury that can be directly reduced by stannous chloride and is mainly present in the form of Hg 2+ . There are different factors affecting DGM concentrations in the ocean and previous studies have suggested that photoreduction of Hg 2+ is the main method for Hg 0 production (Ahn et al, 2010;Ma et al, 2015;Ci et al, 2016) in seawater. Solar radiation and water temperature promote the formation of DGM 2017), and high concentration of dissolved organic carbon (DOC) and low pH can promote DGM production (Ahn et al, 2010).…”

A 1900‐year record of mercury (Hg) from the east continental shelf of Hainan Island, South China Sea

“…Due to the semi‐closed character of the sea, its marine sediments are well preserved and thus serve as ideal archives for studying oceanic histories during the Quaternary (Chen, Kissel, & Liu, ; Joachim & Hermann‐Rudolf, ; Wang et al, ; Wei et al, ). In addition, marine sediments in the South China Sea act as sinks for terrigenous debris (Liu et al, ; Wang, ), aeolian dust (Ci, Zhang, & Wang, ) and maritime biomass deposition (Hu, Peng, Jia, & Fang, ; Jia, Peng, Sheng, & Fu, ). The lithosphere, hydrosphere, atmosphere and biosphere interact with each other at the South China Sea (Zhou, Ding, & Wang, ).…”