Methylmercury photodegradation influenced by sea ice cover in Arctic marine ecosystems
David Point, J E. Sonke, Russell D. Day, David G. Roseneau, Keith A. Hobson, Stacy S. Vander-Pol, Amanda J. Moors, Rebecca S. Pugh, Olivier F. Donard, Paul R. Becker
Despite two decades of research on mercury in northern environments, we do not fully understand the high levels of this pollutant in Arctic Biota. The presumption that global anthropogenic mercury emissions and Arctic atmospheric mercury depletion events may influence Arctic biota mercury levels fails to explain both spatial and temporal trends in mercury in biota across the Arctic. Here we present geographical variations of mercury stable isotopic composition in seabird eggs that were collected at colonies in the North Pacific Ocean, the Bering Sea and the Western Arctic Ocean. Both mass dependent and mass independent mercury isotope variations are observed. Mass dependent fractionation varies with food web structure and mass independent fractionation varies with geographical latitude. We suggest that the latitudinal sea ice gradient drives the mass-independent variations by controlling mercury photochemistry in Arctic surface waters. We suggest that these variations may be useful in estimating marine photochemical methylmercury degradation. We believe 33 that the anticipated loss of Arctic sea ice during the 21st century as a result of greenhouse warming will significantly intensify the photochemical degradation of methylmercury in northern surface waters.