Antarctic polar plateau snow surface conversion of deposited oxidized mercury to gaseous elemental mercury with fractional long-term burial

Abstract

The role of the vast Antarctic polar plateau in the global mercury cycle was previously relatively unknown. Here, for the first time, mercury concentrations in snow and air, combined with vertical flux measurements at the South Pole (November-December 2003 and November 2005) have provided considerable insight into the cycling of this element through the Antarctic environment. These insights include observations showing atmospheric oxidized mercury depositing to the snow pack, subsequent photoreduction, and emissions of gaseous elemental mercury from the snow pack. Oxidized mercury (e.g., reactive gaseous mercury and fine particulate mercury) showed high concentrations (100-1000 pg m-3) in the near-surface air, with these concentrations strongly correlated with vertical mixing rates and showing rapid surface deposition. This suggests that the troposphere over Antarctica is enhanced in oxidized mercury, with mercury cycling between elemental and oxidized states, and between the atmosphere and snow pack. Based on these limited measurements at South Pole, we estimate that the Antarctic polar plateau could sequester as much as 60 metric tons of Hg annually. These data also suggest that there could be a seasonal cycling of atmospheric mercury oxidation, deposition, and re-emission via photoreduction of 490 metric tons annually. This cycling is restricted to the annual sunlit period and peaks 3-4 weeks after solar maximum. To our knowledge, these provisional values represent the first estimates of the mercury balance and cycling for the extensive Antarctic polar plateau. © 2007 Elsevier Ltd. All rights reserved.