Thawing permafrost could release massive amounts of toxic mercury
Mercury has its uses, but it's toxic to humans and animals and can pose a threat to the world's ecosystems. A new study has calculated there is more than 15 million gallons of the stuff sitting trapped in the permafrost north of the equator. That's around 10 times the mercury emissions produced by humans over the past 30 years and researchers from the American Geophysical Union are understandably concerned about the effects it could have.
Mercury becomes embedded in permafrost when the atmosphere binds with organic material in the soil, getting buried by sediment and freezing in permafrost where it can remain trapped for thousands of years. Only changes such as permafrost thaw, like that possible due to climate change, will release the mercury.
Over eight years, beginning in 2004, researchers drilled 13 permafrost soil cores from several Alaskan sites, and measured the mercury and carbon levels. Each site had varied soil types and were selected in an attempt to represent every part of the Northern Hemisphere as closely as possible.
"This discovery is a game-changer," says Paul Schuster, the lead author of the 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."
Permafrost makes up a large proportion of land above the equator and in this study the researchers found that it also holds the largest amount of mercury concentrations in the world. Calculations estimated approximately 793 gigagrams in frozen soil, and 1,656 gigagrams when combining both frozen and unfrozen soil. That's almost twice the amount found in the atmosphere, oceans and soils outside the northern permafrost region combined.
"Twenty-four percent of all the soil above the equator is permafrost, and it has this huge pool of locked-up mercury," says Schuster. "What happens if the permafrost thaws? How far will the mercury travel up the food chain? These are big-picture questions that we need to answer."
Scientists are still unsure how much of an effect thawed permafrost and the released mercury could have on food webs, the atmosphere or us. If it moves into waterways and gets taken up by microorganisms, it could be transformed into methylmercury, a toxic form of mercury that damages animals' motor functions and causes birth defects. This means local ecosystems and indigenous communities in the Northern Hemisphere face the prospect of methylmercury getting into their food supply.
"Rural communities in Alaska and other northern areas have a subsistence lifestyle, making them vulnerable to methylmercury contaminating their food supply," says Edda Mutter, science director for the Yukon River Inter-Tribal Watershed Council. "Food sources are important to the spiritual and cultural health of the natives, so this study has major health and economic implications for this region of the world."
But the risks aren't just restricted to local communities and ecosystems as Mercury can travel thousands of miles when released into the atmosphere.
"There would be no environmental problem if everything remained frozen, but we know the Earth is getting warmer," says Schuster.
Schuster says he is working on another study that models the effects of climate change on the release of mercury from permafrost and providing greater insights into the global mercury cycle.
This study was published in Geophysical Research Letters.
Source: American Geophysical Union