16 January 2014
By Christa Marshall
(Scientific American) – Cracks in sea ice are funneling additional mercury to the Arctic surface, raising concerns about the toxic element seeping into the food chain of the delicate ecosystem, according to a new study.
The research, published yesterday in Nature, finds that channels of open water in Arctic ice, known as leads, are stirring up air so that mercury is pumped from higher in the atmosphere to air close to the surface. Warming temperatures are increasing the amount of seasonal sea ice that melts every summer, which in turn helps create the leads, said study lead author Christopher Moore, an assistant research professor at the Desert Research Institute.
"As more and more of that seasonal sea ice is around as the Arctic changes, then there is the potential that this mechanism can occur over a larger and larger area," said Moore. Environment Canada, the Desert Research Institute and NASA jointly funded the research.
He emphasized that the new study does not definitively make conclusions that additional mercury is getting deposited on snow or ice or entering the food chain. Much more research is needed to outline what is ultimately happening in the region, the scientists said.
Yet the findings suggest that could happen as more mercury is hovering at the surface. When converted to a toxic form, mercury can enter the food chain, threatening the food supplies of native Arctic peoples dependent on marine animals and wildlife.
"There's a lot of people who rely on hunting and fishing, and of course, the main exposure of humans and wildlife to mercury is through consumption of fish," said Daniel Obrist, a research professor at the Desert Research Institute and co-author of the paper. "We know the Arctic is affected by mercury pollution." [more]
ABSTRACT: The ongoing regime shift of Arctic sea ice from perennial to seasonal ice is associated with more dynamic patterns of opening and closing sea-ice leads (large transient channels of open water in the ice)1, 2, 3, which may affect atmospheric and biogeochemical cycles in the Arctic4. Mercury and ozone are rapidly removed from the atmospheric boundary layer during depletion events in the Arctic5, 6, 7, caused by destruction of ozone along with oxidation of gaseous elemental mercury (Hg(0)) to oxidized mercury (Hg(ii)) in the atmosphere and its subsequent deposition to snow and ice5. Ozone depletion events can change the oxidative capacity of the air by affecting atmospheric hydroxyl radical chemistry8, whereas atmospheric mercury depletion events can increase the deposition of mercury to the Arctic6, 9, 10, 11, some of which can enter ecosystems during snowmelt12. Here we present near-surface measurements of atmospheric mercury and ozone from two Arctic field campaigns near Barrow, Alaska. We find that coastal depletion events are directly linked to sea-ice dynamics. A consolidated ice cover facilitates the depletion of Hg(0) and ozone, but these immediately recover to near-background concentrations in the upwind presence of open sea-ice leads. We attribute the rapid recoveries of Hg(0) and ozone to lead-initiated shallow convection in the stable Arctic boundary layer, which mixes Hg(0) and ozone from undepleted air masses aloft. This convective forcing provides additional Hg(0) to the surface layer at a time of active depletion chemistry, where it is subject to renewed oxidation. Future work will need to establish the degree to which large-scale changes in sea-ice dynamics across the Arctic alter ozone chemistry and mercury deposition in fragile Arctic ecosystems.