Air-Sea Exchange of Mercury
Investigations of Hg in the near surface marine atmosphere in rainwater and in seawater have been conducted in open ocean regions of the tropical Pacific and the northwest Atlantic Oceans. Extensive studies of Hg in the atmosphere at the Sea-Air Exchange Program (SEAREX) tower facility at the Enewetak Atoll, Marshall Islands, were completed during 1979 while the southern hemisphere counterpart will be conducted at American Samoa in 1981. During 1979–1980 complementary work was conducted in the coastal marine environment of Long Island Sound. The distribution and chemical composition of atmospheric Hg have been examined using both Au and Ag amalgamation as selective trapping agents. Mercury analyses were conducted by a two-stage Au amalgamation flameless atomic absorption technique (4% precision @ 0.5 ng). Mercury determinations in seawater and in rainwater were made by the Au amalgamation procedure after reduction and aeration.
Most of the near surface atmospheric Hg species over both the open ocean and coastal regions studied are in the vapor phase (>99%). Similar concentrations of Hg were found in the air over the open ocean sites in the northern hemisphere (~1.5 ng m−3) while smaller concentrations of Hg were observed in the southern hemisphere (~1.0 ng m−3). Increases in gaseous Hg concentrations in the atmosphere, suggestive of Hg evasion from the sea surface, were observed in the central equatorial Pacific Ocean. At Long Island Sound the gaseous Hg concentrations are about twice the concentrations from oligotrophic oceanic areas, and a significant amount of Hg is in the organic form. The concentrations of Hg in open ocean rains are quite low (~10 pmol 1−1) and reactive Hg concentrations in surface waters are correspondingly small (~3 pmol 1−1).
These observations and the cycling of Hg between the atmosphere and ocean satisfy an air-sea exchange model which treats atmospheric Hg as a trace gas.
KeywordsOpen Ocean Marshall Island Marine Atmosphere Washout Ratio Enewetak Atoll
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