Ice Core Perspective on Mercury Pollution during the Past 600 Years.

Past emissions of the toxic metal mercury (Hg) persist in the global environment, yet these emissions remain poorly constrained by existing data. Ice cores are high-resolution archives of atmospheric deposition that may provide crucial insight into past atmospheric Hg levels during recent and historical time. Here we present a record of total Hg (HgT) in an ice core from the pristine summit plateau (5340 m asl) of Mount Logan, Yukon, Canada, representing atmospheric deposition from AD 1410 to 1998. The Colonial Period (∼1603-1850) and North American "Gold Rush" (1850-1900) represent minor fractions (8% and 14%, respectively) of total anthropogenic Hg deposition in the record, with the majority (78%) occurring during the 20th Century. A period of maximum HgT fluxes from 1940 to 1975 coincides with estimates of enhanced anthropogenic Hg emissions from commercial sources, as well as with industrial emissions of other toxic metals. Rapid declines in HgT fluxes following peaks during the Gold Rush and the mid-20th Century indicate that atmospheric Hg deposition responds quickly to reductions in emissions. Increasing HgT fluxes from 1993 until the youngest samples in 1998 may reflect the resurgence of Hg emissions from unregulated coal burning and small-scale gold mining.