Final Report Summary - MERCURY ISOTOPES (Exploring the isotopic dimension of the global mercury cycle)
Mercury is a global pollutant that affects human health. Anthropogenic mercury emissions to the atmosphere outweigh natural volcanic emissions by at least a factor ten. Understanding the fate of mercury across the Earth's surface is important to develop appropriate environmental policies that aim at reducing anthropogenic Hg emissions. The ERC StG MERCURY ISOTOPES project explored the use of mercury stable isotope signatures in better understanding the global biogeochemical mercury cycle. Mercury has seven stable isotopes, whose proportions code for different mercury sources and transport pathways in the environment. By studying the mercury isotope signatures of anthropogenic activities and of different forms of mercury in the atmosphere we find that, contrary to common belief, atmospheric mercury deposition is dominated by gaseous absorption by plant leaves and not by rainfall. Consequently, the atmospheric life-time of mercury is shorter than current estimates, 4 months instead of 6. We use natural accumulation of peat deposits to assess historical atmospheric mercury deposition over the past ten thousand years and find that humans have perturbed the global mercury cycle to a far greater extent (20x) than previously thought (3x). Finally, in a particular focus on the Arctic Ocean marine ecosystem, we learn how sea ice and natural sunlight influence the formation and destruction of toxic forms of mercury in the ocean. We provide a new explanation for elevated mercury levels and exposure to Arctic biota by recognizing that marine methylmercury levels occur at much shallower depth than in other ocean basins. All together the MERCURY ISOTOPES project has shed new light on ill-known aspects of the global mercury cycle and will help improve mercury models and environmental policy assessments.