Award: OCE-2148407

Anthropogenic inputs of mercury (Hg) to the atmosphere are the major primary Hg source. Additionally, atmospheric deposition of Hg to the ocean is a major sink for atmospheric Hg, and the main source of ocean Hg input. In the ocean, Hg(II) is converted to methylmercury (MeHg) and the bioaccumulation of MeHg throughout the food web is concerning as human exposure to elevated concentrations of MeHg are an increasingly important impact on human health. Most people are exposed to MeHg primarily from seafood consumption and coastal regions such as the Gulf of Maine (GoM) are important for human exposure and are also being impacted by increasing temperatures and enhanced terrestrial inputs.  The exchange of Hg at the air-sea interface, primarily through evasion of elemental Hg (Hg(0)) and deposition of Hg(II), is the major input and output of Hg from the ocean, and thus factors that affect this exchange will impact the buildup of Hg in ocean waters, the amount of MeHg that is formed within the water column, and also its buildup in the marine food chain. The intellectual merit of current study therefore was aimed at investigating the inputs of Hg and MeHg from terrestrial sources and the atmosphere to the GoM compared to internal transformations of Hg forms through methylation, demethylation, and redox reactions, as well as their transport between the surface and deeper ocean waters. Samples were collected during four research cruises in the GoM and the Penobscot River estuary, which has been historically contaminated with Hg, and additional samples were collected upriver from land. The study was focused on better constraining the role of changing inputs of dissolved organic matter on the transport, transformation and bioaccumulation of Hg and MeHg, and the controlling factors. Additionally, the impact of the Penobscot River on Hg in the GoM was evaluated. Also, the pathways of MeHg formation and degradation and the uptake of MeHg into plankton at the base of the food chain was studied in detail. The studies showed that the formation of MeHg within the deeper waters of the GoM was a major source into this ecosystem and that gas exchange, sediment burial and transport offshore with ocean circulation were the major sinks for Hg (see attached figures). Two research papers have been published, and more are being written, detailing the results of this study and many presentations made at national and international conferences and meetings. The broader impacts of the study were associated with graduate student education and development of their scientific skills. Two MS students used findings from this study in their theses. An undergraduate and post-doc also participated in the cruises. Furthermore, the study design was aimed at providing more detailed data that can be used by others to make future predictions of the impact of humans and climate change on levels of MeHg in the GoM seafood, and that of other coastal ecosystems, in the future and the resultant impacts of this on humans and wildlife.    

Last Modified: 07/29/2026
Modified by: Robert P Mason