Evidence of air-snow mercury exchange recorded in the snowpack at Dome Fuji, Antarctica

摘要

Measuring the mercury content in shallow Antarctic snow pits is useful for understanding the mercury dynamics of the Antarctic Plateau and the global mercury cycle and for interpreting ice core data. We determined the total mercury concentration (HgT) in snow samples successively collected at 5 cm intervals from two 4m deep snow pits at Dome Fuji. The measured mercury concentration varied between 0.32 (the detection limit) and 2.93 pg g-1 (n = 160) with depth and was lower than that of summertime surface snow that was sampled simultaneously. This finding is consistent with previous observations that a bidirectional exchange of mercury between the snowpack and the atmosphere led to an increase in HgT in the surface snow during the summer. However, the contribution of the air-snow Hg exchange to the net Hg sequestration was offset by the intense re-emission of deposited mercury over the past ~50 years. Our results demonstrate that the Antarctic Plateau snowpack is a temporary reservoir of mercury rather than a permanent sink.