This project will improve understanding of the global biogeochemical mercury cycle and its link to oceanic methylmercury, which bioaccumulates through the food chain and causes human health risks. It will use a global three-dimensional model (GEOS-Chem) driven by assimilated meteorological data and will include mechanistic representations of mercury speciation and transfer between the atmosphere and terrestrial and oceanic reservoirs. The model will improve on the existing version of GEOS-Chem, most notably through the incorporation of a detailed process-based terrestrial model. Although many processes are still uncertain, the work will develop a first capability to model how rapidly changes in anthropogenic mercury emissions are reflected by terrestrial inorganic mercury concentrations. The coupled land-atmosphere-ocean modeling framework will be evaluated and constrained using a large body of observational mercury data from the atmosphere (ships, aircraft, land sites), oceans (air-sea exchange, mercury speciation, correlations with environmental variables), and soils.
This research will provide a platform for future work examining (1) the potentially large impacts of climate change on the global mercury cycle, (2) the link between the global cycle of mercury and that of methylmercury, which is the bioavailable species that accumulates in food-webs. This will lead to a unique resource for the development of national and international policies targeted at reducing environmental mercury levels through control of anthropogenic emissions. The multiphase, three-dimensional modeling framework will have application to future modeling of other contaminants such as persistent organic pollutants. The project will train a graduate student in interdisciplinary environmental modeling.
This project focused on better understanding the sources and fate of mercury in the global environment. Mercury is a neurotoxin. Human exposure to mercury is mainly through consumption of ocean fish. Human influence on the global mercury cycle is mainly through coal combustion, mining, and (as demonstrated in this project) discard of commercial mercury-containing products. Mercury released to the environment cycles between different surface reservoirs (air, land, water). Our work provided a better understanding of this cycling and of the role of the atmosphere for global-scale mercury transport. Through development of global biogeochemical models and interpretation of observations, we constructed a new general understanding of the fate of mercury released in the environment. We proposed a new redox mechanism for atmospheric mercury with implications for the mechanism of mercury deposition. We showed that human influence in the present-day ocean is much larger than previously believed but that about half is from pre-1950 emissions. We showed that mercury used in commercial applications has made a major historical contribution to mercury in the global environment, and that the large decrease in commercial mercury use since 1970 helps to explain observed multi-decadal trends in environmental mercury. We identified a potentially dominant long-term sink for mercury from sediment formation at ocean margins following riverine discharge. We quantified the different time scales associated with mercury cycling between environmental reservoirs and concluded that it will take decades to centuries for reductions of mercury emissions to have an appreciable effect on oceanic loadings.
