Large source of mercury from the western margin of the Greenland Ice Sheet

Abstract:

The Greenland Ice Sheet is largely ignored in Arctic budgets of the toxic element mercury. For example, no data exists for mercury concentrations or speciation from ice sheet meltwater rivers, despite large and increasing annual liquid water runoff fluxes to the surrounding oceans, and human health and economic concern of high mercury levels in Arctic marine organisms. Here we present inorganic- and methyl-mercury concentrations from subglacial runoff originating from the southwestern margin of the Greenland Ice Sheet from samples collected over multiple field campaigns from 2012-2018. We found globally elevated concentrations of inorganic mercury and the bioaccumulation neurotoxin methylmercury in all meltwater rivers sampled. Estimated dissolved mercury yields from three ice sheet catchments of contrasting size (100 – 3,200 km²) indicate high mercury mobility and regionally important denudation rates. Suspended particulate material mercury concentrations are among the highest found in the literature, implicating the importance of subglacial biogeochemical and physical weathering processes. The abundance of mercury reductase gene (merA) and the organomercurial lyase gene (merB) were quantified and provide evidence of subglacial microbial community adaptation to high mercury levels. We evaluate the possible fate of this ice sheet derived mercury in near coastal marine ecosystems with data collected from a fjord downstream of significant meltwater inputs. Our data highlights an urgent need to better understand regional differences in ice sheet runoff mercury concentrations and composition, and the consequences of increasing ice sheet meltwater discharge for Arctic ecosystems services.