Dissolved elemental mercury and dimethylmercury in continental shelf surface waters west of the Antarctic Peninsula

As part of a preliminary assessment of mercury (Hg) in the marine environment of the West Antarctic Peninsula (WAP), we mapped concentrations of dissolved elemental Hg (n = 2006) within the Palmer Long-Term Ecological Research (PAL-LTER) program sampling grid during the summer (January) of 2014. A limited set (n = 36) of dimethylmercury (DMHg) measurements were also made. Dissolved elemental Hg (DEM), a volatile form of Hg produced from the reduction of inorganic Hg(II) or monomethylmercury (MMHg), provides a measure of the concentrations and photochemical and biological reactivity of Hg in surface waters. The production of DMHg in the water column of marine systems has been linked to microbial and phytoplankton productivity. In January 2014, DEM varied from 20 fM in offshore areas to more than 250 fM within the WAP's inner continental shelf, corresponding to approximate equilibrium with the atmosphere at the more oceanic stations to up to 7-fold supersaturation near the coast. Similar to DEM, concentrations of DMHg were an order of magnitude higher within the inter-island straits of the WAP than further offshore. The spatial distributions of both forms of volatile Hg indicate a source of Hg substrate or higher rates of Hg reduction/methylation in the near-shore environment of the WAP than further offshore.