The fate and transport of metals, both those that are required by organisms as nutrients, such as iron and zinc, and those that are toxic, such as mercury and lead, in ocean waters has been a focus of research funded under the international GEOTRACES program. This research project collected mercury (Hg) and radioisotope samples during an international GEOTRACES research expedition in 2021 in the waters around Iceland, where both the water column and sediments were sampled in detail (see attached figure). The focus on this area was because these waters mix between the North Atlantic Ocean and the Arctic Ocean and the exchange of metals in the region between the two oceans, and between the sediment and water column, are poorly understood. The intellectual merit of the research related to the fact that this region is the confluence of two ocean basins and the study design was aimed at answering the question of whether the Arctic Ocean is a source of Hg and MeHg to the North Atlantic, as has been previously proposed, or a sink. The broader impact of the research relates to Hg, a toxic metal that bioaccumulates into the marine food web, primarily as methylmercury (MeHg). The heightened exposure of humans and wildlife to MeHg from seafood and marine mammal consumption is a global concern. Inorganic Hg is converted to MeHg in the water column and sediments and there is substantial addition or removal of both forms of Hg in this ocean region given the shallow waters around Iceland, and the elevated currents. Coastal inputs from Iceland and Greenland were also studied. The study used the concentration of naturally occurring radioisotopes (thorium and radium) to assess the extent of exchange at the sediment-water interface and the partitioning between dissolved and particulate Hg and MeHg in the water column. The results show that the sediment-water exchange is dynamic and not consistent across the area with some regions being a net sink for Hg to the sediments while other locations are a source of MeHg to the water column. Overall, the heightened degree of interaction complicates answering the question of nwhether the Arctic Ocean is a source of Hg and MeHg to the North Atlantic or a sink. Examination of the Hg data in conjunction with the other metals measured during the cruise by colleagues in Europe will allow for a more detailed assessment of this question. Results have been presented at international conferences and are being prepared for publication in the peer-reviewed literature. The research was carried out by a post-doctoral investigator who joined the expedition, and analyzed the samples collected for both Hg and radioisotopes, and gained substantial research experience, with the help from graduate students in the Mason research group.

Last Modified: 10/24/2023
Modified by: Robert P Mason