Atmospheric depletion of mercury over Antarctica during glacial periods.

Mercury is a globally dispersed toxic metal that affects even remote polar areas. During seasonal atmospheric mercury depletion events in polar areas, mercury is removed from the atmosphere(1,2) and subsequently deposited in the surface snows(3). However, it is unknown whether these events, which have been documented for the past two decades, have occurred in the past. Here we show that over the past 670,000 years, atmospheric mercury deposition in surface snows was greater during the coldest climatic stages, coincident with the highest atmospheric dust loads. A probable explanation for this increased scavenging is that the oxidation of gaseous mercury by sea-salt-derived halogens occurred in the cold atmosphere. The oxidized mercury compounds were then transferred to the abundant mineral dust particles and deposited on the snowpack, leading to the depletion of gaseous mercury in the Antarctic atmosphere. We conclude that polar regions acted as a mercury sink during the coldest climatic stages, and that substantial polar deposition of atmospheric mercury is therefore not an exclusively recent phenomenon.