Award: OCE-1736659

Anthropogenic inputs of mercury (Hg) to the atmosphere are one of the major sources of Hg to the biosphere. Additionally, deposition of Hg to the ocean is a major sink for atmospheric Hg, and the main source of ocean Hg input. However, Hg can be reduced from its ionic form (Hg(II)) to elemental Hg (Hg(0)) in ocean surface waters. As Hg(0) is present in the water as a dissolved gas, it can build up to supersaturated concentrations in the surface ocean, and Hg(0) can be lost back to the atmosphere. This exchange at the air-sea interface is the major input and export of Hg from the ocean, and thus factors that affect this exchange will impact the buildup of Hg in ocean waters, and also in the marine food chain, primarily in its organic form (methylmercury (MeHg)). Human exposure to elevated levels of MeHg from seafood consumption is a global human health concern and the levels of MeHg in seafood appear to be increasing due to human impacts, as well as the impacts of climate change. The current study therefore was aimed at investigating the exchange of Hg across the air-sea interface during the multi-investigator GEOTRACES GP15 research expedition in the Pacific Ocean from Alaska to Tahiti in fall 2018 to examine the controlling factors. Samples were collected continuously in the atmosphere and in surface waters during the cruise, and additional studies looked at the form of Hg in the air and water, and the processes that were affecting these levels. There was also an effort to determine the best methods for making these measurements as, even though Hg is a toxic compound, its levels in the air and water can be low and difficult to measure without contamination. The intellectual merit of the study was focused on better constraining the rate of exchange between the ocean and atmosphere while the broader impacts, beyond those associated with student education and development of scientific skills, we aimed at providing better data that can be used by others to make future predictions of the impact of humans and climate change on levels of MeHg in fish in the future. Last Modified: 10/22/2020 Submitted by: Robert P Mason