Mercury in Ancient Ice and Recent Snow from the Antarctic

Abstract

Atmospheric mobilization and depositional processes are major features of the global biogeochemical Hg cycle. The atmosphere is an important pathway for the introduction of Hg into marine and terrestrial aquatic systems. Current estimates for human-related Hg emissions to the atmosphere parallel natural fluxes (Fitzgerald, 1986; Nriagu, 1989; Nriagu and Pacyna, 1991). This large anthropogenic interference has increased Hg deposition regionally and globally. In addition, the impact of anthropogenic emissions is amplified because Hg and many of its compounds, while toxic, can be converted to more poisonous forms (i.e., monomethyl mercury) in aquatic systems (Fitzgerald and Clarkson, 1991; Beiger and Jernelöv, 1979). The present observed broad geographic incidence (e.g., USA, Canada, Sweden) of elevated Hg concentrations (as monomethyl mercury, MMHg) in piscivorous fish appears linked to human-related contemporary increases in Hg deposition (Lindqvist, 1991; Fitzgerald et al., 1991; Wiener et al, 1990). This is a serious international human health concern since fish and fish products are the largest source of MMHg in the human diet (Fitzgerald and Clarkson, 1991). Evidence for regional increases in atmospheric Hg deposition has been deduced from the Hg distribution in lake sediments (Rada et al, 1989; Björkland et al., 1984; Swain et al., 1992) and ombrotrophic bogs (Benoit et al., 1994; Madsen, 1981). On a larger spatial and temporal scale, however, hemispheric patterns of modern and historic deposition patterns are lacking. Such information is required to establish the extent of anthropogenic impact and to provide a foundation for future biogeochemical studies of Hg.