Award: OCE-2023046

Intellectual Merit. This project significantly advanced our understanding of dimethylmercury (DMHg), a naturally occurring form of mercury, and its role in the global mercury cycle. DMHg, a relative of the neurotoxic monomethylmercury, often dominates in deep ocean waters but was poorly understood due in part to a lack of reliable analytical methods. Also traditional sampling techniques often lack the ability to track changes over time, making it difficult to study how DMHg is formed and broken down in seawater. To address these gaps, the project developed new, highly accurate methods for measuring DMHg. These were applied alongside innovative sampling strategies, such as tracking water parcels over time and establishing a long-term sampling program at the Scripps Pier in California. After over four years of weekly sampling, we discovered seasonal patterns in mercury levels influenced by rainfall, wave activity, and biological processes like phytoplankton growth. By studying upwelled water masses, we found that DMHg breaks down in surface waters and serves as a major source of monomethylmercury in the California Current System. This challenges prior assumptions about the sources of monomethylmercury in upwelling regions and highlights DMHg’s critical role in mercury cycling.

Broader Impacts. Mercury pollution poses significant risks to human health and marine ecosystems through its conversion into monomethylmercury, the neurotoxic form that accumulates in fish and enters the food chain. Human activities have disrupted the global mercury cycle, leading to increased monomethylmercury levels in seafood. International efforts aim to reduce mercury pollution, but a deeper understanding of the mercury cycle is essential to assess the effectiveness of these actions. This project identified a previously underestimated source of monomethylmercury in regions where it bioaccumulates in marine food webs. The findings provide essential insights for environmental monitoring and policy development, particularly in areas where mercury pollution poses significant risks. The project also supported the professional development of graduate students, contributing to three published manuscripts and several in progress. Students presented their findings at conferences, trained peers in advanced sampling techniques, and gained valuable research experience that will shape their careers.

This project expanded our knowledge of DMHg in marine systems, developed tools to improve mercury research, and supported the training of future environmental scientists. These findings will inform research and policies aimed at mitigating mercury’s harmful effects on ecosystems and human health.

Last Modified: 01/13/2025
Modified by: Amina B Schartup