Polar Sunrise: Mercury in the Arctic
Nothing quite prepares you for it: the bleak expanse of snow and ice, temperatures so low they can freeze a sandwich mid-bite, frost flowers the size of small shrubs. Few people live in the Arctic Circle, and not many visit.
From late November to late January the sun never rises, and from mid-May to August it never sets. And yet this inhospitable region is chock full of life: single-celled algae, whales, seals, polar bears, human beings—disparate organisms that coexist in a fragile ecosystem that’s increasingly under assault by chemicals leached from the more populous world below.
“You can definitely see the effects of global warming way up there,” says Jerry Keeler, professor of environmental health sciences at the School of Public Health, who spent a week last March in Barrow, Alaska—the northernmost city in the western hemisphere—studying the pathways by which airborne contaminants make their way into the Arctic ecosystem. In collaboration with Joel Blum, professor of geological sciences at the University of Michigan, and researchers from the University of Alaska–Fairbanks and the United States Army Corps of Engineers Cold Regions Research and Engineering Laboratory in Fairbanks, Keeler was looking at mercury depletion events in the Arctic.
First documented by Canadian scientists in the late 1990s, mercury depletion events take place each spring during polar sunrise, when the sun first appears after weeks of winter darkness. Mercury is depleted from the air above the Arctic during this transitional period and winds up in the snow pack on sea as well as on land. From there the toxic chemical enters the food chain and works its way up. Researchers have found alarmingly high levels of mercury in the blood and tissues of polar bears, seals, and Inuit men, women, and children who call the Arctic Circle home.
Scientists suspect the process involves a set of complex atmospheric chemical reactions that require both sea ice and “leads” (pronounced LEEDS)—cracks in the sea ice caused by the first stirrings of spring in February and March. The open water in the leads releases chemical compounds such as bromine and chlorine, which then react with atmospheric mercury, effectively pulling it down to earth. Coal-burning power plants in more temperate climates are a major source of atmospheric mercury, which, like dozens of other chemicals spawned by the industrialized world, slowly but surely drifts north to the colder, more stable air of the Arctic, where it settles onto the earth’s surface and “builds up,” says Keeler.
“At this point we don’t know whether global warming is exacerbating the mercury problem we’re seeing or whether it’s been going on for a long time,” says Keeler. But he aims to find out. Funded by the National Science Foundation, the three-year study on which he’s collaborating may well influence how governments elsewhere in the world regulate power plants and other industries whose emissions are subject to regulations.
“We hope to better understand whether the polar sunrise and mercury depletion phenomenon is the primary reason that the arctic ecosystem is being contaminated at the rate it is,” Keeler says. “Is this something that would have happened in the Arctic anyway, and are rising global mercury emissions exacerbating the problem?”
To find out whether rising global mercury emissions are contributing to the growing contamination of the Arctic ecosystem, members of the project team are making detailed observations during mercury-depletion events and snowmelt, and are comparing and contrasting the fate of mercury on land to its fate at sea. Led by UM Professor Joel Blum, the team is also analyzing samples taken after the snow starts to melt from Arctic lakes, ice, tundra, and terrestrial and marine sediments in order to determine how much of the mercury that settles in the Arctic is converted to methyl mercury, the most toxic form of the chemical.
From March to June, as the Arctic Ocean gradually melts, researchers measure atmospheric pollutants released by “leads,” or cracks in the sea ice. Typically, scientists measure chemical compounds that concentrate in clouds ten feet above the surface of the lead. “The project team also take samples of snow all the way out in the leads, from the water, moving inland to see if we can see a dropoff in the concentration of mercury and halogens,” says Jerry Keeler.
During their March stay in Barrow, Keeler and his colleagues lived in dormitories and traveled by snowmobile to and from their research site at the edge of the Arctic Ocean. They hauled their equipment on sleds and boats. Inuit guides mapped out the ten-mile route, which changed frequently as the arctic ice moved. Guns were a necessity: polar bears are a real threat. So is the cold. Keeler and his team had to cover every inch of their skin, and they carried lunch inside their snow suits to keep it from freezing. (Originally a military base from which U.S. soldiers kept an eye on the Soviet Union, Barrow, Alaska, is now home to approximately 5,000 people, many of them scientists.)
Using kites, researchers collect chemical compounds from the Arctic’s atmosphere in Teflon bottles filled with liquid nitrogen. As Keeler points out, “You can’t use just any plastic, because it won’t withstand the cold.” During their March visit, he and his team packed dozens of samples in dry ice and flew them back to Ann Arbor for analysis in the University of Michigan’s clean labs.
Keeler (center) and the UM research team were assisted in March by Inuit guides Billy Adams (left) and Carl Kippi. The Inuit, whose diet is rich in fish, whale, and seal, are especially vulnerable to atmospheric contaminants from more temperate parts of the world, such as mercury, that find their way into the fragile Arctic ecosystem. Kippi told Keeler that during his grandfather’s lifetime, the ice along the shore at Barrow had dropped from a thickness of 200 feet to less than 100 feet. “They’re willing to help us because they very much want us to figure out why this is happening,” Keeler says of the Inuit guides. “Their way of life is changing drastically.” The ecosystem, Keeler adds, is “more than just a source of food to them— it’s an integral part of their culture.”
Article written by Leslie Stainton; photos provided by Jerry Keeler.
Additional photos are available in the PDF of this article as it appeared in the print version of Findings.
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