"The contamination of the Arctic with mercury is of increasing concern and yet our knowledge of mercury biogeochemistry in this environment is rudimentary. We know that mercury reaches the Arctic from sources in lower latitudes by long distance atmospheric transport of elemental mercury and that it is deposited as inorganic mercury following oxidation in the atmosphere, most notably during atmospheric mercury depletion events. We also know that the Arctic food chain is contaminated with the neurotoxic substance methylmercury and that people whose subsistence depends on indigenous sources of food have elevated body burdens of mercury. Little is known on how the mercury that reaches the Arctic by atmospheric deposition of inorganic mercury accumulates in the food chain as methylmercury. The bioaccumulation of methylmercury directly depends on mercury biogeochemistry whose understanding has resulted in improved environmental management in many temperate ecosystems. Information that will lead to models of mercury biogeochemistry in polar-regions is being collected mostly focusing on the atmosphere-surface-deposition-evasion part of the cycle. Microbial redox transformations as well as conversions between methylated and inorganic forms of mercury have a significant role in the mercury cycle and presence and activities of microorganisms in polar-regions have been documented. We therefore propose to examine three modes of microbial interactions with mercury that are known to impact mercury geochemistry. These are: 1. Mercury redox transformations in various environmental matrices 2. Mercury methylation in snowpack where some of the atmospherically deposited mercury accumulates, in coastal lagoons, and in coastal marine sediments 3. The interaction of microbes in sea ice with the toxic concentrations of mercury in brine and their potential to reduce inorganic to elemental mercury as a detoxification mechanism"