The scientists measured mercury concentrations in permafrost cores from Alaska and estimated how much mercury has been trapped in permafrost north of the equator since the last Ice Age.
The study, published in the journal Geophysical Research Letters, revealed that 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.
"This discovery is a game-changer," said Paul Schuster, a hydrologist at the US Geological Survey in Boulder, Colorado and lead author of the new study.
"We've quantified a pool of mercury that had not been done previously, and the results have profound implications for better understanding the global mercury cycle," Schuster said.
The study found approximately 793 gigagrams, or more than 15 million gallons, of mercury is frozen in northern permafrost soil.
That is roughly 10 times the amount of all human-caused mercury emissions over the last 30 years, based on emissions estimates from 2016.
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.
This pool houses nearly twice as much mercury as soils outside of the northern permafrost region, the ocean and the atmosphere combined.
Mercury accumulates in aquatic and terrestrial food chains, and has harmful neurological and reproductive effects on animals.
"There would be no environmental problem if everything remained frozen, but we know the Earth is getting warmer," Schuster said.
"Although measurement of the rate of permafrost thaw was not part of this study, the thawing permafrost provides a potential for mercury to be released - that's just physics," Schuster explained.
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