Toward an improved understanding of the global biogeochemical cycle of mercury

Mercury (Hg) is a potent neurotoxin, has both natural and anthropogenic sources to the environment, and is globally dispersed. Humans have been using Hg since antiquity and continue its use in large quantities, mobilizing Hg from stable long-lived geologic reservoirs to actively cycling surface terrestrial and aquatic ecosystems. Human activities, such as mining and coal combustion, have perturbed the natural biogeochemical cycle of Hg. However, the distribution of natural versus anthropogenic Hg in the environment today and the extent of anthropogenic perturbation (i.e., enrichment) are uncertain. Previous model estimates of anthropogenic enrichment have been limited by a lack of information about historical emissions, examined only near-term effects, or have not accounted for the full coupling between biogeochemical reservoirs. Presented here is a framework that integrates recently available historical emission inventories and overcomes these barriers, providing an improved quantitative understanding of global Hg cycling.;This dissertation aims to advance our understanding of the global biogeochemical cycle of Hg by synthesizing observations together with state-of-the-science global Hg models. The objectives of this work are: (1) Develop an empirical relationship for gas-particle partitioning of atmospheric Hg and quantify the impact on global Hg deposition; (2) quantify the present-day enrichment of Hg levels in the ocean, atmosphere, and terrestrial ecosystems resulting from all-time anthropogenic emissions; and (3) explore the impact of riverine discharges of Hg on the marine environment and the biogeochemical implications of burial of riverine Hg in ocean margin sediments.;The first dissertation chapter concludes that atmospheric Hg partitions between gas and particle-phases as a function of temperature and that inclusion of this process improves our ability to simulate observed deposition. In the second chapter, global anthropogenic enrichment is shown to be larger than previously estimated. It is also found that the legacy of past anthropogenic emissions plays a central role in influencing future trajectories of environmental Hg concentrations. Lastly, it is demonstrated that although coastal waters occupy only a few percent of the ocean surface, the effect of Hg burial in sediments at ocean margins propagates globally and affects anthropogenic Hg enrichment in all geochemical reservoirs.