The remote Arctic tundra may seem like the last place on Earth human pollution should be causing a problem – yet it's filled with mercury contamination. And that mercury leaks from the soil into rivers and ultimately the Arctic Ocean, contaminating the fish and other sea life that Native communities rely on for survival.
Now, in a new study, published Wednesday in the journal Nature, scientists have begun to outline how the mercury is getting into and moving through the landscape in the first place. And the short answer is: It's our fault it's there in the first place, and climate change could now make that even worse.
The study finds that the majority of the contamination in the Arctic tundra came from a gaseous form of elemental mercury, carried through the atmosphere from other parts of the world, where it was emitted to the atmosphere as a result of the burning of coal and other industrial activities.
Once it reaches the Arctic, the scientists believe the mercury is sucked up by plants – mainly in the summer, when snow cover is at its lowest and the tundra is at its greenest – in much the same way that vegetation pulls carbon dioxide out of the air. As the plants shed their leaves or die, the mercury moves into the soil and eventually may leach into rivers and waterways, which carry it into the Arctic Ocean.
And as climate change continues to heat up the Arctic, the scientists are concerned about the ways that the resulting landscape changes – which may include less sea ice, less snow and more vegetation – could affect the cycling of mercury through the ecosystem.
"This is really important in the sense of new work, because no one's really take a look at the Arctic tundra and the impact that it has on the mercury cycle," said Alexandra Steffen, an atmospheric mercury specialist with Environment Canada, who was not involved with the new research. And the work is likely to help scientists better understand the ways this mercury cycle may be affected by future climate change, she added.
"A huge amount of Canada and Russia is covered in this tundra, and it's melting," she told The Washington Post. "So to understand what's going on, where mercury is being housed, where it's coming from, will help us to understand what's going to happen when the tundra continues to melt."
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Scientists have known about the high levels of mercury pollution in the Arctic for a long time, said the new study's lead author Daniel Obrist, an atmospheric chemistry and environmental pollution expert at the University of Massachusetts Lowell. But the processes by which it was actually being deposited there have remained poorly understood. In the past, some scientists had theorized that the mercury pollution in the Arctic was reaching the landscape mainly through rain and snow, an idea that's been largely overturned by the new study.
"The question was really what's causing all that mercury presence and accumulation up there in the Arctic," Obrist said.
To investigate, Obrist and a team of colleagues from institutes in the United States and France spent two years collecting field data from the Alaska tundra, measuring mercury levels and conducting chemical analyses to determine what state the mercury was in and how it likely got out of the atmosphere.
They're still exploring some of the reasons the Arctic is such a mercury hot spot when it's so far removed from the industrial activities that release the pollution into the air. For one thing, once mercury is in the atmosphere, it's free to travel all over the world – it doesn't necessarily just stay in the spot where it was emitted. It can move out of the atmosphere and into plants and soil in other parts of the world just as it does in the Arctic, Obrist noted – but in places with more sun and higher temperatures, chemical reactions often cause it to move right back into the atmosphere, he said.
In the Arctic, on the other hand, conditions are a bit different. The new study suggests that a great deal of the mercury in the landscape is taken up by vegetation during a small portion of the year, when snow is melting and plants are growing. The vegetation has a relatively short window of time to flourish, and afterward it becomes covered up with snow and ice again for seven or eight months of the year. The result is that the mercury becomes more or less sequestered in the soil, without access to the sunlight and heat that might cause it to react and move back into the air.
"So we believe the Arctic really is an important depository for global mercury pollution," Obrist told The Post. "Once it reaches these Arctic soils, it's building up to high levels."
The scientists can't say for sure that their findings hold true all across the Arctic, since their study only focused on one region of the Alaskan tundra. But they suspect that similar processes are occurring all across the landscape.
Despite the growing concern about mercury contamination in the Arctic, there is some good news – research shows that global mercury emissions have been falling for the past two decades, meaning human efforts to curb the pollution are starting to work. And just a few years ago, nations around the world designed a global treaty called the Minamata Convention, which is an agreement to protect humans and the environment from mercury pollution. Some of its major points include banning new mercury mines, phasing out existing ones and cutting down on the use of mercury in other products and industrial processes.
Still, the future of the mercury that's already in the Arctic or will be deposited there in the future remains a concern as temperatures continue to climb. Vegetation, snow cover, sunlight and heat all play major roles in the way mercury moves through the atmosphere and the terrestrial earth, and climate change is already having a significant effect on all of them. Careful monitoring and continued investigation of the processes affecting the mercury cycle will be key to understanding how this contaminant may affect the ecosystem and the human communities that depend on it in the future.
"Temperatures in the Arctic are among the fastest rising ones, increasing at a rate about double what we see here in these areas farther south," Obrist said. " And given how much mercury we find now in these tundra soils, we have a concern that this may start to mobilize some of these mercury pools that reside in these tundra soils."
What will happen next, he said, remains unknown.
"Will it result in increased mobilization . . . into the ocean? We don't know, and that's a concern," he said.