Low mercury concentrations in a Greenland glacial fjord attributed to oceanic sources

Abstract High mercury concentrations found in meltwater from the southwest Greenland Ice Sheet and surface waters of nearby fjords, including neurotoxic and bioaccumulative methylmercury (MeHg), have raised concerns about regional ecosystem and community health. We present full water column profiles of MeHg and total mercury (THg) from Sermilik Fjord, a large glacial fjord in southeast Greenland, fed by multiple marine-terminating glaciers. We measured THg concentrations of 0.23-1.1 pM and MeHg of 0.02-0.17 pM, similar to nearby coastal waters and 1-3 orders of magnitude lower than reported in southwest Greenland. We show that the dominant source of mercury species to the fjord is inflowing ocean waters from the continental shelf, while the exported glacially-modified waters are relatively depleted in inorganic mercury (Hg(II)). We deduce that Hg(II) is removed from the water column within the fjord, implying that the fjord is a net sink of oceanic mercury.