Mercury is a Roman god, a lifeless planet, a former singer with Queen and a mystery enfolded in the fog of the coldest, most isolated coves of Canada.
Up in the Arctic, when the spring sun finally deigns to rise after abandoning the land for months, something unusual occurs. Compounds of the chemical element mercury — the furtive quicksilver that takes our temperature and lights our offices — suddenly vanish from the sky.
One moment, the air is tainted with mercury and flush with highly reactive low-level ozone, and the next instant, it is devoid of the two compounds. Like baseball, blackflies and income tax, this happens every spring. No one understands why mercury disappears or how it reassembles in the lower atmosphere when the weary sun sets in fall.
A leading Canadian scientist investigating the phenomenon, Jan Bottenheim of Environment Canada, calls it “amazing and mind-boggling,” and he has been poking around the mystery for more than 20 years.
If mercury were not a known and powerful neurotoxin, capable of seriously damaging the human nervous system, and if ozone were not a greenhouse gas and the instigator of chemical reactions with many human-caused pollutants, this subject might be merely academic. But when mercury vanishes from the air at Arctic sunrise, it has to go somewhere: onto the ice, onto the snow, into the sea, into the fish, into the seals and, perhaps, into the bodies of the people of Canada’s North. So there is an urgency to the search for answers.
That search is the main focus of the Ocean-Atmosphere-Sea Ice-Snowpack (OASIS) project, one of the studies under the International Polar Year umbrella. OASIS, which runs to 2011, sends intrepid scientists from Canada, Europe and the United States to the Arctic’s most desolate coastlines and out onto the open seas. There, they deploy remotelymonitored sleds, floating sampling stations, ship-based experiments and their own sense of wonder.
In 2008, OASIS-Canada scientists spent three months on the Canadian Coast Guard icebreaker CCGS Amundsen taking measurements, collected data from an ozone monitor aboard a French sailboat named Tara, which was left to drift with the Arctic currents, and launched the first of three planned high-tech buoys in the Beaufort Sea. No longer confined to taking measurements from shore, the researchers are now able to study bodies of water and ice from Alaska to Quebec and from Hudson Bay to the North Pole.
Their recording instruments are some the hardiest ever designed. Several have cute nicknames, such as a sled known as OOTI, for Out On The Ice, that relays data on atmospheric mercury via a wireless communications link. The floating ozone gauges are known as O-buoys.
If the recording instruments are hardy, so, too, are the researchers who venture north. OASIS-Canada investigator and atmospheric mercury specialist Alexandra (Sandy) Steffen has worked at Canadian Forces Station Alert 21 times. In her more comfortable office at the Toronto headquarters of Environment Canada, Steffen describes the research base at Alert, 800 kilometres from the North Pole, as “a beautiful lab to study. It’s spectacular. My sister lived in Africa, and she had what she called mal d’Afrique. I have mal d’Arctique.” At a computer station in the Toronto laboratory, Steffen shows off a graph of the suspect compounds’ mercurial rise and fall. It is a cardiogram of jagged peaks and plunging valleys that looks like the pulse of a beating world — a wealth of hard-won information from across the Arctic that has a story to tell.
That story began more than 20 years ago. The depletion of ozone in the atmosphere over the Arctic was first reported in scientific journals in 1986 by Bottenheim and his colleagues at Environment Canada, based on their observations at Alert. In 1998, Environment Canada’s William Schroeder reported his discovery that mercury depletion occurs simultaneously with ozone depletion.
Over the years, the Canadian scientists developed a greater understanding of the chemistry behind these occurrences. They now know, for example, that when ozone reacts with sea salt on frozen surfaces such as ice and snow, a form of bromine atom is produced. Bromine reacts with ozone and mercury in different ways.
“The reaction of bromine atoms with ozone leads to the destruction of ozone molecules, so ozone effectively disappears,” explains Bottenheim. “The reaction between bromine atoms and mercury does not lead to the destruction of mercury but, instead, leads to the production of a new molecule that includes the mercury and bromine atoms.” The chemical identity and properties change, but the mercury is not destroyed. Rather, it disappears, possibly migrating from the atmosphere to the snowpack and ocean. “There are liable to be other consequences we haven’t even scratched yet,” Bottenheim says.
For reasons that still puzzle Bottenheim, these phenomena are observed only in the spring. He speculates that first-year ice, as opposed to the permanent ice pack, is a particularly effective type of ice surface to drive the depletion chemistry. For one thing, “young” sea ice cover is more concentrated in sea salt, the source of bromine. For another, first-year ice features plenty of open leads that refreeze, which can then result in the promotion of frost flowers, whose ice crystals are thought to “scavenge” chemicals from the atmosphere.
If it is true that first-year ice is responsible for the chemical train of events, then mercury levels in the North may rise with the warming of the Arctic Ocean. Changes in the Arctic ecosystem drive climate changes elsewhere on Earth, which explains the urgency to understand where the mercury goes when spring arrives. So the work of OASIS continues, even in the early winter, when mercury and ozone re-form in the Arctic atmosphere, waiting for the pulse of virgin sunshine that will banish the lightless skies.