Gaseous elemental mercury (Hg
0) is a globally distributedair toxin with a long atmospheric residence time. Anyprocess that reduces its atmospheric lifetime increasesits potential accumulation in the biosphere. Our data fromBarrow, AK, at 71
![](/images/entities/deg.gif)
N show that rapid, photochemicallydriven oxidation of boundary-layer Hg
0 after polar sunrise,probably by reactive halogens, creates a rapidly depositingspecies of oxidized gaseous mercury in the remote Arctictroposphere at concentrations in excess of 900 pg m
-3.This mercury accumulates in the snowpack during polarspring at an accelerated rate in a form that is bioavailableto bacteria and is released with snowmelt during thesummer emergence of the Arctic ecosystem. Evidencesuggests that this is a recent phenomenon that may beoccurring throughout the earth's polar regions.