Measurements of atmospheric mercury species at a coastal site in the Antarctic and over the south Atlantic Ocean during polar summer.

Mercury and many of its compounds behave exceptionally in the environment because of their volatility, capability for methylation, and subsequent biomagnification in contrast with most of the other heavy metals. Long-range atmospheric transport of elemental mercury, its transformation to more toxic methylmercury compounds, the ability of some to undergo photochemical reactions, and their bioaccumulation in the aquatic food chain have made it a subject of global research activities, even in polar regions. The first continuous high-time-resolution measurements of total gaseous mercury in the Antarctic covering a 12-month period were carried out at the German Antarctic research station Neumayer (70 degrees 39' S, 8 degrees 15' W) between January 2000 and February 2001. We recently reported that mercury depletion events (MDEs) occur in the Antarctic after polar sunrise, as was previously shown for Arctic sites. These events (MDEs) end suddenly during Antarctic summer. A possible explanation of this phenomenon is presented in this paper, showing that air masses originating from the sea-ice surface were a necessary prerequisite for the observations of depletion of atmospheric mercury at polar spring. Our extensive measurements at Neumayer of atmospheric mercury species during December 2000-February 2001 show that fast oxidation of gaseous elemental mercury leads to variable Hg0 concentrations during Antarctic summer, accompanied by elevated concentrations, up to more than 300 pg/m3, of reactive gaseous mercury. For the first time in the Southern Hemisphere, atmospheric mercury species measurements were also performed onboard of a research vessel, indicating the existence of homogeneous background concentrations over the south Atlantic Ocean. These new findings contain evidence for an enhanced oxidizing potential of the Antarctic atmosphere over the continent that needs to be considered for the interpretation of dynamic transformations of mercury during summertime.