Large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet

The Greenland Ice Sheet is currently not accounted for in Arctic mercury budgets, despite large and increasing annual runoff to the ocean and the socio-economic concerns of high mercury levels in Arctic organisms. Here we present concentrations of mercury in meltwaters from three glacial catchments on the southwestern margin of the Greenland Ice Sheet and evaluate the export of mercury to downstream fjords based on samples collected during summer ablation seasons. We show that concentrations of dissolved mercury are among the highest recorded in natural waters and mercury yields from these glacial catchments (521–3,300 mmol km−2 year−1) are two orders of magnitude higher than from Arctic rivers (4–20 mmol km−2 year−1). Fluxes of dissolved mercury from the southwestern region of Greenland are estimated to be globally significant (15.4–212 kmol year−1), accounting for about 10% of the estimated global riverine flux, and include export of bioaccumulating methylmercury (0.31–1.97 kmol year−1). High dissolved mercury concentrations (~20 pM inorganic mercury and ~2 pM methylmercury) were found to persist across salinity gradients of fjords. Mean particulate mercury concentrations were among the highest recorded in the literature (~51,000 pM), and dissolved mercury concentrations in runoff exceed reported surface snow and ice values. These results suggest a geological source of mercury at the ice sheet bed. The high concentrations of mercury and its large export to the downstream fjords have important implications for Arctic ecosystems, highlighting an urgent need to better understand mercury dynamics in ice sheet runoff under global warming

Environmental drivers of plant diversity of chalk grasslands in north-western France

International audienceIn Europe, chalk grasslands are considered as biodiversity hotspots, hosting rare species (e.g. orchid and endemic species). However, since the mid 20th century, this habitat is threatened by changes in agricultural practices, especially the decline of pastoralism and recent anthropogenic nitrogen inputs. In this national research project (‘SURPAS’ project, French Ministry for the Ecological Transition, UMS PatriNat, OFB), we aimed to identify the main factors driving plant composition and richness of these chalk grassland communities to update our knowledge and recommendations in terms of conservation measures. The study was carried out in Natura 2000 chalk grassland sites in the valley of Somme river, in north-western France. We performed botanical and habitat surveys (topography and soil measures, vegetation structure, composition and biomass, fodder quality) at two spatial scales, in 1x1 m and 4x4 m plots. Data were analyzed using multivariate analyses (CCA) and mixed models. Our main results showed that plant height, South exposure, litter thickness and woody species abundance drive composition and richness species, and that nitrogen inputs in the ecosystem, Brachypodium pinnatum dominance and tree colonization were currently the major threats to the conservation of the diversity of chalk grasslands

Datasets for "Large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet", Version 3

Geochemical measurements and hydrochemical datasets linked to the publication "Large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet" in Nature Geoscience. Presented are (1) data for mercury concentrations in glacial meltwater outflows from the Greenland Ice Sheet taken in 2012, 2015 and 2018, (2) data for mercury concentrations in fjord waters from Nuup Kangerlua, Ameralik Fjord and Søndre Strømfjord, and (3) all associated hydrochemical data presented in the manuscript. For additional details (analytical techniques, precision, accuracy and limits of detection) please refer to the methodology in the publication. This third version has additional riverine data added the the 2012 dataset