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 atmosphere1,2 and subsequently deposited in the surface snows3. 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. We suggest that this increased scavenging is caused by the low temperatures, which allowed the oxidation of gaseous mercury by sea-salt-derived halogens. The oxidized mercury compounds are then transferred onto the abundant mineral dust grains 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 atmospheric deposition of Hg is therefore not an exclusively recent phenomenon.