Arctic Sea-Ice puts the Brakes on Mercury Release
24.01.2011 - Water & Oceans, Land & Geology, Flora & Fauna, Arctic
In a recent study published in the journal Nature Geoscience, a French-American team has underlined the role Arctic sea-ice plays in the mercury cycle. Sea-ice can influence the breakdown and transfer of toxic forms of mercury into the atmosphere by blocking sunlight. The role of climate in the mercury cycle and the release of mercury into the atmosphere could therefore be accentuated by the melting of Arctic sea-ice.
Mercury in its oxidized form is easily deposited in the snow and ice covering the Arctic. When the snow and ice melts, the mercury transforms into methylmercury (CH3Hg) through various physicochemical and biological processes. Living organisms up and down the food chain ingest this toxin; concentrations in animals at the top of the food chain can reach one million times higher than those measured in surface waters.
Over the past 20 years, however, mercury concentration monitoring programs in the Arctic have identified contrasting geographic and temporal trends. Researchers measured the isotopic signature of mercury in murre eggs from various Arctic and sub-Arctic locations, and found significant geographic variations. This anomaly appears to be closely related to sea-ice cover around murre colonies' egg laying sites. Measuring the quantity of this toxin, which can be destroyed by sunlight, the researchers came to the conclusion that sea-ice prevents the photochemical breakdown of methylmercury and limits exchanges of mercury between the Arctic Ocean and the atmosphere. The mercury cycle and climate change are thus closely related, and further sea-ice depletion will influence the mercury cycle.
