Atmospheric Cycling and Air-Sea Exchange of Mercury in the South China Sea
Date Issued
2016
Date
2016
Author(s)
Chen, Wei-Chih
Abstract
Atmospheric cycling and air-sea exchange of mercury in the northern South China Sea (SCS) were investigated during 16 cruises of the SEATS (Southeast Asian Time-series Study) station between 2003 and 2007. The GEM (Gaseous elemental mercury, Hg0) and DEM (Dissolved elemental mercury) were measured all together on board ship during the cruise period. The GEM concentrations in spring, summer, autumn and winter averaged ca. 3.2 ± 0.6 ng m-3, 2.8 ± 0.4, 3.6 ± 0.6, and 4.5 ± 1.5, respectively. Additionally, seasonal DEM concentrations were 70 ± 40 fM, 160 ± 40, 120 ± 30, and 60 ± 30, respectively. Unlike the annual GEM pattern, the DEM concentrations were high in summer and low in winter. The opposite temporal trends between the GEM and DEM implied different controlling factors on those concentration variations. Source tracking through backward air trajectory of The HYSPLYT model demonstrated that the GEM concentrations were strongly influenced by seasonal monsoons. In winter, the prevailing northeast monsoon with terrigenous and anthropogenic pollutants resulted in high GEM concentrations. Instead, the summer southwest monsoon and inter-monsoon with less polluted air masses from the Indochina Peninsula and Indian Ocean and west Pacific Ocean resulted in low GEM levels. The DEM concentrations were highly correlated with sea water temperature (SST), showing high in summer and low in winter. The Q10 temperature coefficient calculation of DEM suggested that a seasonal change in DEM was mostly abiologically driven. Annually, the air-sea Hg0 exchange fluxes were estimated ca. 60 ± 160 pmol m-2 d-1, 580 ± 120, and 730 ± 210 in spring, summer and autumn, respectively, indicating that the SCS could be the source of Hg0 to the atmosphere in warm seasons. In winter, the SCS acted as a sink of atmospheric Hg0 (-180 ± 110 pmol m-2 d-1) due to low SST and high wind of the year, enhanced vertical mixing and elevated atmospheric Hg0. This is the first time we observed that ocean behaves as a sink of atmospheric Hg0 in low latitude marginal seas. Key words: South China Sea (SCS), Atmospheric cycling, Air-sea exchange, Gaseous elemental mercury (GEM) and Dissolved elemental mercury (DEM)
Subjects
South China Sea (SCS)
Atmospheric cycling
Air-sea exchange
Gaseous elemental mercury (GEM)
Dissolved elemental mercury (DEM)
Type
thesis
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