The objective of this doctoral dissertation project is to reveal the natural and human controls on mercury deposition to northwestern North America. Human emissions of mercury, mostly from mining, smelting, and coal-burning, are currently rising, predominantly from Asia. The transport of mercury from Asia to northwestern North America may pose an emerging ecological and health hazard, contributing to already high levels of mercury in rivers and fish. However, in order to assess the impact of rising mercury pollution on the ecosystem, it is essential to also determine natural mercury levels through time, derived from volcanism, weathering, and forest fires. The Prospector Russell Col (PRCol) ice core, collected from the summit of Mt. Logan in the Yukon Territory of Canada in 2001 and 2002, is ideal for this study because of its location downwind from Asian pollution sources and its well-dated record spanning the past >17,000 years. This study will use clean sampling techniques and state-of-the-art analysis methods to measure mercury concentrations in the PRCol ice core at <1 to 100-year time scales. Mercury concentrations in this ice core will be compared to records of volcanic eruptions, forest fires, dust, and climate to determine the controls on natural changes in mercury levels. The impact of human mercury pollution on this region will be determined by comparing the concentrations of mercury deposited during the 20th century to concentrations deposited during the prior 17,000 years, before large-scale human mercury pollution. The influence of climate patterns such as El Nino on mercury transport and deposition will be investigated by comparing climate parameters and mercury concentrations during the 20th century.
Determining the magnitude and trend of recent mercury contamination is a fundamental step in addressing the global issue of mercury pollution in the environment. Results of this research will be disseminated through academic publications and conferences. An undergraduate research assistant will be trained to assist in this research and to complete a related sub-project. The PIs will do outreach at local middle schools about their research, combining it with discussions of careers in the geosciences. International collaboration will be established through close work between the PIs and the Canadian researchers who collected and have already done some analysis of data derived from the ice core. As a Doctoral Dissertation Research Improvement award, this project will provide support to enable a promising graduate student to establish an independent researchcareer.
The toxic metal mercury is globally distributed as it cycles between the land, ocean, and atmosphere. This cycling causes past mercury emissions to persist in the modern environment. However, the extent and timing of past mercury emissions are poorly constrained by existing data, and this uncertainty impacts model predictions of how the environment will respond to future reductions in mercury emissions. In this project, we reconstructed historical atmospheric mercury deposition in an ice core from Mount Logan, located near the border of Alaska and the Yukon Territory. The Mount Logan ice core was collected from the mountain’s summit (5300 meters above sea level) that is persistently below-freezing (average: -29 °C) and upwind of any regional mercury sources, making the site ideal for containing a signal from globally transported mercury. Over the course of the 2-year project, we developed and used clean methods to measure mercury concentrations in samples from the 186-meter-long Mount Logan ice core. Unexpectedly low mercury concentrations (less than one part per trillion) and suspected contamination in the deepest ice changed the focus of this project to a detailed analysis of the upper 128 meters of the ice core, representing atmospheric conditions from AD 1411 to 1998. This time period covers pre-anthropogenic baseline conditions (c. 1411 – c. 1561) as well as important periods of historical anthropogenic mercury use including Colonial Era gold and silver mining (c. 1570 – 1850), the "Gold Rush" (1850 – 1900), and Twentieth Century industrialization. Undergraduate female and male students assisted in the sampling and analysis of the ice core, which provided them with insight into scientific research. Overall, this work places much need empirical constraints on natural and anthropogenic mercury emissions. These constraints can improve the accuracy of global Hg models that are used to predict the environmental response to future mercury emissions scenarios. Accurate model predictions are crucially needed to evaluate the success of new policy aimed at reducing mercury emissions, namely the Minamata Convention on Mercury that is currently being ratified by 136 nations. The findings from this project were presented to a diverse audience of mercury scientists, modelers, and policy makers at the 11th International Conference on Mercury as a Global Pollutant, and a manuscript of the project is in preparation for a high-level scientific journal. The data set will become freely available to the public following publication, both through the publisher and the National Climatic Data Center.
