The subglacial environment of the Greenland Ice Sheet (GrIS) is poorly understood, in terms of hydrology, water storage and biogeochemical processes. High temporal resolution biogeochemical sampling of bulk meltwaters at a typical, land-terminating outlet glacier of the GrIS was employed in order to infer processes at the ice sheet bed over three contrasting melt seasons. No high temporal resolution geochemical datasets previously existed for ice sheet environments, mainly due to inaccessibility. Bulk meltwaters comprised differing propOltions of waters originating from a widespread, distributed subglacial drainage system (these delayed flow waters being solute enriched due to prolonged residence times and high rock:water ratios in the contributing environments), and an efficient channelized system (dilute surface waters rapidly transmitted to the margin). Two-component chemical mixing models, in combination with MODIS satellite imagery, revealed that delayed flow was released continuously. However, higher volumes were released at times of subglacial outburst events when draining surface lakes interacted with the bed and expelled stored waters. Dissolution experiments and geochemical data indicated that these waters may have been stored at the bed over winter, or longer, and comprised one-third of delayed flow release in any given year (~O.02 km\ The geochemical data, in combination with 01 80 -H20 isotope data from bulk meltwaters and surface ice, were able to identify subglacial drainage system evolution and increasingly distant water sources contributing to bulk meltwaters. Enhanced silicate dissolution was observed compared to smaller valley glaciers, which may lead to enhanced CO2 sequestration compared to carbonate weathering' environments. Chemical weathering rates were lower than would be expected for a poly thermal ice mass, likely due to low reactivity bedrock. Ionic fluxes were higher in high melt years, which is a further indication of stored water release due to extensive basal flushing. Finally, isotopes of sulphate demonstrated that there are both oxic and anoxic conditions at the bed of the GrIS, with potential for highly anoxic sulphate reducing conditions in the interior.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:683692 |
| Date | January 2014 |
| Creators | Butler, Catriona Elizabeth Hamilton |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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