The ice core samples from the Upper Fremont Glacier indicated that levels of mercury increased dramatically during the industrial revolution and have decreased significantly since the mid-1980s. It is believed that the decrease in mercury deposition since the 1980s coincides with the passage of the Clean Air Act.
The decline in mercury deposition since the 1980s is linked to the passage of the Clean Air Act, which aimed to reduce air pollution. This reduction in mercury levels can be observed through ice core samples from the Upper Fremont Glacier.