Cracks in Arctic ice churn up mercury levels in the North
Atmospheric scientists have discovered a “pumping” process that is drawing mercury, a neurotoxin, into remote Arctic ecosystems.
They also warn that “profound changes” underway in the North have the potential to increase levels of the potent contaminant collecting at the top of the planet.
Giant cracks, or leads, in sea ice are driving the pumping or churning process that is pulling down mercury from higher in the atmosphere, they say. And the cracks have become much more widespread due to thinning of the sea ice across the Arctic Ocean.
“It’s all of a sudden a much more dynamic environment,” says Alexandra Steffen, a mercury specialist at Environment Canada and co- author of a report on the phenomenon published Wednesday in the journal Nature. It details how the more turbulent sea ice situation is altering and potentially increasing mercury deposition in the Arctic.
Steffen says it is just the latest evidence that climate change is altering the behaviour of priority pollutants in the North.
Another recent study by Environment Canada shows persistent organic pollutants trapped in the sea ice and sea water are on the move. “They were trapped in the sea ice and in the ocean, and you lift the lid and ‘ poof’ they come out,” Steffen said Wednesday.
Much attention is focused on the potential for shipping and resource extraction as the Arctic changes, but Steffen says people also need to be concerned with the contaminants “being driven through these natural processes that are being perhaps enhanced.”
The report in Nature describes how leads in the ice, which can stretch for hundreds of kilometres, create churning in the lower Arctic atmosphere as heat from open water is released into the frigid air.
“The atmospheric mixing created when thinner, seasonal sea ice opens to form leads is so strong that it pulls down mercury from a higher layer of the atmosphere to near the surface,” lead author Chris Moore, an atmospheric researcher at Nevada’s Desert Research Institute, says in a release.
Incinerators, coal- fired power plants, forest fires and volcanoes are leading sources of mercury. It has long been known the mercury wafts north in the atmosphere, where it can drop out of the atmosphere contaminating ecosystems thousands of kilometres from the source of emissions.
To get a better read on how mercury is behaving in the changing Arctic climate, the team from Environment Canada, NASA and Nevada set up camp for several weeks in 2009 and again in 2012 on the ice near Barrow, Alaska.
They fired up their generator to power their equipment and every two hours measured the level of mercury and other compounds in the air blowing across the Arctic Ocean. They also evacuated camp when curious polar bears got too close and the ice began to shift, says Steffen.
The measurements revealed that the level of mercury in the air varied markedly, almost disappearing for days and then rising dramatically. They then correlated the ups and downs with leads that opened in the ice and were visible in NASA satellite data.
The pumping process produced by the ice cracks pulls down mercury from a layer about 400 metres above the surface, says Moore.
Mercury is already a concern as wild game is a dietary mainstay for most people living in the Arctic. And the scientists suspect the increased thinning and cracking of the ice across much of the Arctic Ocean is depositing more mercury in northern ecosystems, but have yet to assess the loadings.
Steffen says more work is needed to find out if the mercury is being transformed into the biologically active form that can accumulate in ecosystems, wildlife and people.
The scientists plan to measure and compare current rates of deposition in different spots in the Arctic with the levels recorded by Environment Canada at Alert on the northern tip of Ellesmere Island.
It is longest running data set of atmospheric mercury in the Arctic — “a jewel that goes back to 1995, says Steffen, who will soon head to Ellesmere to continue the work.