northern permafrost soils are the largest reservoir of mercury on the planet, storing nearly twice as much mercury as all other soils, the ocean and the atmosphere combined. Warmer air temperatures due to climate change could thaw much of the existing permafrost layer in the northern hemisphere. This thawing permafrost could release a large amount of mercury that could potentially affect ecosystems around the world. Mercury accumulates in aquatic and terrestrial food chains, and has harmful neurological and reproductive effects on animals. The study found approximately 793 gigagrams, or more than 15 million gallons, of mercury is frozen in northern permafrost soil. The study also found all frozen and unfrozen soil in northern permafrost regions contains a combined 1,656 gigagrams of mercury, making it the largest known reservoir of mercury on the planet.
— source American Geophysical Union | Feb 5, 2018