| Summary: | Global warming has led to significant increases in melt rates of the Greenland Ice Sheet (GrIS) and runoff since the beginning of 1990, and the GrIS is expected to be a major contributor to global sea level rise in the coming decades. Recent warming has resulted in longer summers and greater runoff , which also raises the possibility for enhanced solute and nutrient export from ice sheet to the ocean. Very recent studies have confirmed the influence of GrIS in dissolved organic matter (DOM), nutrient and sediment exports. However, very little is known about the underlying hydrological controls and the fate of these nutrients once it exists the glacier system and passes via large rivers systems through the proglacial zone to fjords. This PhD used multi-year hydro chemical and hydrological datasets from four GrIS catchments of contrasting size to study chemical weathering rates and yields of cations and total silica. These calculations demonstrated that GrIS is an important potential source of solute and nutrients to downstream environments with chemical yields comparable to those documented in some temperate river catchments (e.g. Mississippi and Nile Rivers). One of the reasons for such high chemical weathering rates in GrIS catchments is likely to be the flushing out of long-time stored subglacial waters or subglacial outburst events (SOEs) and the high flushing rates associated with high specific water discharge. These SOEs are believed to be triggered by the drainage of supraglacial lakes, and indeed, have the tendency to cause pulses of discharge, solute, and suspended sediment measured in bulk runoff at the ice margin. SOE hydrological and hydrochemical dynamics from 5 different melt years (2009-2015) were Leverett glacier are presented in the second part of this study, with the aim of improving the understanding of hydrological evolution at the bed of the ice sheet during these events. Hydrochemical dynamics provided a useful insight into hydrological processes during the SOEs. As previous studies have suggested, these data showed the tendency for lake drainage to flush out concentrated, long-term stored subglacial meltwater from the ice sheet bed. However, discrete chemical tracers also revealed the draw out of long residence time subglacial water following new channel development and the creation of low pressure axes during SOEs. This PhD also demonstrated then that once exported from the glacier system, bulk meltwaters have minimal chemical change as they travelled from the glacier subglacial portal to the fjord, even over 25 km. This likely reflects the fast transit of the meltwaters via major river systems in the proglacial zone. It suggests that the glacier is the main nutrient contributor to coastal, and that expansion of the proglacial zone with ice sheet retreat in land-terminating zones is unlikely to influence the macronutrient fluxes associated with glacial runoff export to the ocean.
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