Description: Glaciers and ice sheets export significant amounts of silicon (Si) to downstream ecosystems, impacting local and potentially global biogeochemical cycles. Recent studies have shown Si in Arctic glacial meltwaters to have an isotopically distinct signature when compared to non-glacial rivers. This is likely linked to subglacial weathering processes and mechanochemical reactions. However, there are currently no silicon isotope (d30Si) data available from meltwater streams in Antarctica, limiting the current inferences on global glacial silicon isotopic composition and its drivers. To address this gap, we present dissolved silicon (DSi), d30SiDSi, and major ion data from meltwater streams draining a polythermal glacier in the region of the West Antarctic Peninsula (WAP; King George Island) and a cold-based glacier in East Antarctica [Commonwealth Stream, McMurdo Dry Valleys (MDV)]. These data, alongside other global datasets, improve our understanding of how contrasting glacier thermal regime can impact upon Si cycling and therefore the d30SiDSi composition. We find a similar d30SiDSi composition between the two sites, with the streams on King George Island varying between -0.23 and C1.23h and the Commonwealth stream varying from -0.40 to C1.14h. However, meltwater streams in King George Island have higher DSi concentrations, and the two glacial systems exhibit opposite DSi–d30SiDSi trends. These contrasts likely result from differences in weathering processes, specifically the role of subglacial processes (King George Island) and, supraglacial processes followed by instream weathering in hyporheic zones (Commonwealth Stream). These findings are important when considering likely changes in nutrient fluxes from Antarctic glaciers under climatic warming scenarios and consequent shifts in glacial thermal regimes.

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.