The northern hemisphere's permafrost regions have been concealing a really unpleasant surprise: mercury. A lot of mercury. Nearly twice as much mercury as the rest of the planet's natural mercury combined.
Researchers from the US Geological Survey studied core samples from the Alaskan permafrost, and their estimates show 793 million kilograms of mercury have been trapped in the northern hemisphere's permafrost since the last Ice Age.
This finding has grave implications if the permafrost melts away.