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This chrat shows the level of atmospheric mercury deposition detected in ice cores from the Upper Fremont Glacier in Wyoming. Heightened deposition rates correspond to volcanic and anthropogenic events over the past 270 years. Preindustrial deposition rates can be conservatively extrapolated to present time (4 ng/L; in green) to illustrate the increase during the past 100 years (in red) and significant decreases in the past 15-20 years.
This image is in the public domain because it contains materials that originally came from the United States Geological Survey, an agency of the United States Department of Interior. For more information, see the official USGS copyright policy
Source: English Wikipedia, original upload 12 May 2005 by SEWilco
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