Glaciers cover approximately 10% of land surface, but are rarely considered active components of global biogeochemical cycles. Research over the past two decades has revealed that active and widespread hydrological systems are present at the bed of the Antarctic and Greenlandic Ice Sheets. This has driven recent concern in the biogeochemistry of subglacial environments. The ocean waters surrounding the ice sheets harbour highly productive, ecologically and economically important waters. Only recently has an ice sheet influence, via the export of nutrients, been considered. A high-resolution hydrological dataset and dissolved and particulate geochemical record, from multiple ablation seasons of two contrasting Greenland Ice Sheet catchments were collected. These were used to infer subglacial biogeochemical weathering processes, and associated nutrient cycling. Estimates of glacial bioessential nutrient fluxes to downstream environments revealed the potential for significant export of iron and phosphorus to the near-coastal euphotic zone. Labile particulate nutrient species dominate total nutrient export due to the high concentrations of extremely fine-grained and highly reactive suspended sediments in meltwaters. Meltwater filterable iron and phosphorus concentrations were found to be temporally variable over an ablation season due to an evolving subglacial meltwater source coupled with evolution of subglacial drainage. More remote regions of the subglacial environment are progressively flushed over the course of an ablation season, releasing waters rich in nutrients compared to major ions. "Outburst events", driven by the drainage of supraglacial lakes into the subglacial environment, were found to be an especially important mechanism in driving pulses of stored, nutrient rich meltwaters downstream. It is demonstrated that dissolved macronutrient (nitrogen, phosphorus and silica) and solute export from the Greenland Ice Sheet are annually dynamic, with significantly higher fluxes in warmer melt years. This is likely to be driven through more exhaustive basal flushing by supraglacial meltwaters, and by progressively more efficient linking of remote regions of the subglacial environment with downstream drainage. Changes in nutrient export from the Greenland Ice Sheet with enhanced melting under future climate warming scenarios are therefore likely.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:685353 |
| Date | January 2015 |
| Creators | Hawkings, Jonathan R. |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.0019 seconds