Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hawkings, J. R., Linhoff, B. S., Wadham, J. L., Stibal, M., Lamborg, C. H., Carling, G. T., Lamarche-Gagnon, G., Kohler, T. J., Ward, R., Hendry, K. R., Falteisek, L., Kellerman, A. M., Cameron, K. A., Hatton, J. E., Tingey, S., Holt, A. D., Vinsova, P., Hofer, S., Bulinova, M., Větrovský, T., Meire, L., Spencer, R. G. M. Large subglacial source of mercury from the southwestern margin of the Greenland Ice Sheet. Nature Geoscience, 14, (2021): 496-502, https://doi.org/10.1038/s41561-021-00753-w.

Description: 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.

Description: This research is part of a European Commission Horizon 2020 Marie Skłodowska-Curie Actions fellowship ICICLES (grant agreement #793962) to J.R.H. Greenland terrestrial research campaigns were funded by a UK NERC standard grant (NE/I008845/1) and a Leverhulme Trust Research Grant (RPG-2016-439) to J.L.W., with additional support provided by a Royal Society Wolfson Merit Award to J.L.W. Additional funding came from Czech Science Foundation grants (GACR; 15-17346Y and 18-12630S) to M.S. Fjord fieldwork was supported by European Research Council grant ICY-LAB (grant agreement 678371) and Royal Society Enhancement Award (grant RGF\EA\181036) to K.R.H. L.M. was funded by research programme VENI (0.16.Veni.192.150, NWO). T.J.K. was supported by Charles University Research Centre program no. 204069. The authors thank the captain and crew of the RV Kisaq and staff at the Greenland Institute of Natural Resources for assistance during fjord fieldwork, and all those involved with fieldwork at Leverett Camp during the 2012 and 2015 field campaigns. M. Cooper is thanked for providing the geological overview file for Extended Data Fig. 1a, and K. Mankoff for help in generating the modelled GrIS discharge datasets. The authors also thank G. White in the geochemistry group at the National High Magnetic Field Geochemistry Laboratory, which is supported by NSF DMR-1644779 and the State of Florida, for analytical support.

Description: This data set includes temperature and salinity measurements from 2019 and 2020 in the fjords Ameralik and Godthåbsfjord in southwest Greenland. Seasonal measurements were made at 12 standard stations in Ameralik spaced between 3 and 13 km from one another (AM1-12) in May, July and September 2019. Longer term fjord sampling was also carried out at monthly intervals from March to December 2019 at selected stations (AM3, AM5, AM7, AM10, AM11 and AM12) and March 2020 at station AM5. There was no sea-ice present in Ameralik during sampling. Additionally, sampling was conducted at 13 standard stations in Godthåbsfjord (GF1-13) in May, July and September 2019. In May and July, sea-ice in the inner part of the fjord prevented sampling further in-fjord. Favourable ice conditions during the September campaign allowed the sampling of 4 further standard stations (GF14-17). Longer term fjord sampling in Godthåbsfjord was also carried out at monthly intervals from February to December 2019 at selected stations from GF5 and inwards. All sampling took place on research vessels operating in daytime: the Greenland RV Sanna (May cruise), the commercial Greenland vessels Polar Dive (July cruise) and Tulu (September cruise), and the Greenland Avataq (remaining monthly day trips). At every station depth profiles of conductivity, temperature and pressure were collected using a SeaBird SBE19plus CTD and averaged over 1 m vertical depth intervals. Sensors were calibrated annually by the manufacturer and salinity precision was typically within the range of 0.005-0.010. Temperature (ITS-90) and practical salinity is used. The data have been used to describe the seasonal hydrography of Ameralik, impacted by a land-terminating glacier only, and to compare Ameralik with Godthåbsfjord, which receives meltwater from both land- and marine-terminating fjords.

Description: This data set includes measurements from a weather station in the fjord Ameralik in southwest Greenland from 2019-01-01 to 2019-12-31. Air temperature, photosynthetically active radiation (PAR), wind speed, and wind direction were measured with 10 minute resolution using an Onset weather station located in the inner part of the fjord (64°13.42'N, 50°18.12'W). The data have been used to compliment a description of the seasonal hydrography of Ameralik.

Description: This data set includes temperature and salinity measurements from 2019 and 2020 in the fjord Ameralik in southwest Greenland. There was a SBE microcat (SBE 37-SMP, SeaBird) moored at a depth of ∼6 m located in the inner part of Ameralik measuring water temperature, salinity and pressure with 10 minute resolution. Sensors were calibrated annually by the manufacturer and salinity precision was typically within the range of 0.005-0.010. Temperature (ITS-90) and practical salinity is used. The data have been used to describe the seasonal hydrography of Ameralik, impacted by a land-terminating glacier only, and to compare Ameralik with Godthåbsfjord, which receives meltwater from both land- and marine-terminating fjords.

Description: This data set includes hydrographic and pore water and core incubation silicic acid concentration and isotope measurements, sediment Si-HCl and Si-Alk contents and isotope measurements, and pore water nutrient, major, and trace element concentrations measured in the fjords Ameralik Fjord and Nuup Kangerlua (Godhäbsfjord) in southwest Greenland. Data was collected during a research expedition, R/V Tulu 2019, in September 2019, as part of ERC funded (678371) project ICY-LAB (Isotope CYcling in the LABrador Sea) and Royal Society funded (RGF\EA\181036) project Biogeochemical Cycling in Greenlandic Fjords. Temperature and salinity data derived from CTD rosette casts were recorded at station AM10 in Ameralik Fjord and station GF-inlet in Nuup Kangerlua. Fjord water sampling was carried out at 2 stations (AM10 and AM12) in Ameralik Fjord and station GF-inlet in Nuup Kangerlua using Towfish and Niskin bottles for near surface and sub surface samples, respectively. For bottle samples, temperature and salinity were measured using an EXO3 Multiparameter Water Quality Sonde. Fjord sediments were collected by a large bore sediment corer (Aquatic Research Instruments) at station AM10a in Ameralik Fjord and station GF-inlet in Nuup Kangerlua. Pore waters were extracted from the sediment cores using Rhizon samplers and core incubation experiments were carried out following the methodology of Hammond et al. (2004, doi:10.4319/lom.2004.2.146). Sediment reactive silica was leached using a sequential extraction method from Michalopoulos and Aller (2004, doi:10.1016/j.gca.2003.07.018) and Pickering et al. (2020, doi:10.1029/2020GL087877).

Description: This hydrographic data set includes CTD and XCTD data from the long-term Hydrographic Fjord Program in Godthåbsfjord, Greenland, collected by Greenland Climate Research Centre, Greenland Institute of Natural Resources (GINR), Nuuk, Greenland. XCTDs were deployed from a helicopter close to a marine terminating outlet glacier. The CTDs in Godthåbsfjord were occupied at the edge of a dense ice field during small boat (Avataq) day trips to the inner part of the fjord. The CTDs outside Godthåbsfjord were obtained by RV Sanna and HDMS EJNAR MIKKELSEN in connection with GINR's annual monitoring program.