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Abstract Title: Mercury Methylation Linked with Nitrification in Polar Marine Regions
Presenter Name: Marissa Despins
Company/Institution: Wright State University
Session: Mercury in Polar Ecosystems
Co-Authors: Marissa Despins,Robert Mason,Ana Aguilar-Islas,Chad Hammerschmidt,Silvia Newell

Abstract Information :

Methylmercury (MeHg) is a neurotoxin that bioaccumulates to potentially harmful concentrations in Arctic marine wildlife and in those that consume them. Monitoring and modeling MeHg bioaccumulation and biogeochemical cycling in the ocean requires understanding of the mechanisms behind mercury (Hg) methylation. The key functional gene for Hg methylation, hgcAB, is widely distributed throughout ocean basins and spans multiple microbial phyla. Multiple microbially-mediated anaerobic pathways for Hg methylation are known, but in the ocean, the majority of hgcA homologs have been found in oxic subsurface waters. In particular, microaerophilic Nitrospina, a genera of nitrite-oxidizing bacteria, that contains a hgcA-like sequence, has been proposed as a potentially important Hg methylator in upper ocean waters. The objective of this work was to examine the potential of nitrifiers as Hg methylators and quantify total Hg and MeHg across three Arctic Seas (the Gulf of Alaska, the Bering Sea and the Chukchi Sea) in regions where Nitrospina are likely present. In Spring 2021, samples for Hg analysis were obtained from all sites with a trace metal clean rosette. Hg methylation rates were quantified in concert with nitrification rates using on-board incubation experiments with Hg and NH4 stable isotope additions. A significant correlation between Hg methylation and nitrification was observed across all sites, with the strongest correlation in the Chukchi Sea. Nitrospina-specific hgcA-like genes were detected at all sites. This study linking Hg methylation and nitrification in oxic seawater furthers understanding of MeHg cycling in these high latitude waters and the ocean in general. Furthermore, these studies inform predictions of how climate and human interactions could influence MeHg concentrations in the Arctic region in the future.

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