Open AccessEnhanced trace element mobilization by Earth’s ice sheets
Author(s) -
Jon Hawkings,
Mark L. Skidmore,
Jemma L. Wadham,
John C. Priscu,
Peter L. Morton,
Jade Hatton,
Christopher B. Gardner,
Tyler J. Kohler,
Marek Stibal,
Elizabeth Bagshaw,
August Steigmeyer,
Joel Barker,
John E. Dore,
W. Berry Lyons,
Martyn Tranter,
Robert G. M. Spencer
Publication year - 2020
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.2014378117
Subject(s) - meltwater , weathering , trace element , greenland ice sheet , ice sheet , geology , environmental chemistry , biogeochemical cycle , antarctic ice sheet , seawater , glacier , geochemistry , environmental science , earth science , oceanography , sea ice , chemistry , cryosphere , geomorphology
Trace elements sustain biological productivity, yet the significance of trace element mobilization and export in subglacial runoff from ice sheets is poorly constrained at present. Here, we present size-fractionated (0.02, 0.22, and 0.45 µm) concentrations of trace elements in subglacial waters from the Greenland Ice Sheet (GrIS) and the Antarctic Ice Sheet (AIS). Concentrations of immobile trace elements (e.g., Al, Fe, Ti) far exceed global riverine and open ocean mean values and highlight the importance of subglacial aluminosilicate mineral weathering and lack of retention of these species in sediments. Concentrations are higher from the AIS than the GrIS, highlighting the geochemical consequences of prolonged water residence times and hydrological isolation that characterize the former. The enrichment of trace elements (e.g., Co, Fe, Mn, and Zn) in subglacial meltwaters compared with seawater and typical riverine systems, together with the likely sensitivity to future ice sheet melting, suggests that their export in glacial runoff is likely to be important for biological productivity. For example, our dissolved Fe concentration (20,900 nM) and associated flux values (1.4 Gmol y -1 ) from AIS to the Fe-deplete Southern Ocean exceed most previous estimates by an order of magnitude. The ultimate fate of these micronutrients will depend on the reactivity of the dominant colloidal size fraction (likely controlled by nanoparticulate Al and Fe oxyhydroxide minerals) and estuarine processing. We contend that ice sheets create highly geochemically reactive particulates in subglacial environments, which play a key role in trace elemental cycles, with potentially important consequences for global carbon cycling.