Evolution of Late Season Meltwater in Alpine and Arctic Glaciers: Sampling Strategies and Geochemical Observations

Abstract

The presence, configuration, and efficiency of subglacial hydrologic systems has important implications for both glacial dynamics and the chemistry of meltwaters. These networks may exist in configurations that range from poorly connected and unable to accommodate large volumes of water to fast flowing and highly competent in different regions of the glacial bed, simultaneously or in different seasons. Direct study of the configuration and development of these networks is difficult as they are obscured by ice, yet network configuration is important in glaciological research as it controls the spatial distribution and residence time of subglacial water. Subglacial network efficiency, or the ability of the network to quickly evacuate water, controls under-ice water-rock interaction time affecting chemical weathering reactions and thus solute type and concentration expressed in proglacial meltwaters. Previous research into the configuration of subglacial hydrologic networks is limited in both temporal and spatial resolution, as field research generally occurs during summer months and is limited to more easily accessible glaciers. This dissertation investigates seasonal changes in subglacial hydrologic networks as evidenced by changing meltwater chemistry in late-summer at both a Canadian alpine glacier and an outlet glacier from the Greenland Ice Sheet. I undertook multi-month field campaigns at each location, during which I collected samples and made in situ measurements to correlate changes in chemical constituents carried within melt to changes in seasonality, improving understanding of this understudied time in seasonal glacial development.

This dissertation uses laboratory experiments with sediment samples collected at glacial termini to evaluate the use of radon-222 (222Rn) activity concentrations, an intermediary in the uranium-238 (238U) decay chain, as a proxy for subglacial water residence time. These measurements are compared to in field 222Rn activity concentration measurements at sediment collection locations. Results show 222Rn activity concentration serves as a subglacial water residence time proxy but also reflects mineralogical sources of its parent isotope, radium-226 (226Ra). Field measurements of 222Rn activity concentrations as a proxy will be more robust and reliable if supported with laboratory leachate experiments with site-specific sediment samples, addressing likely lithological and sediment-size controls on 226Ra concentrations.

I undertook a three-month field study of the alpine Athabasca Glacier in the Canadian Rockies in August through October, 2014. Both in situ and elemental chemistry of pro-glacial meltwaters are investigated relative to water discharge fluxes, air temperatures, and precipitation events to see how the subglacial network responds to climatic and glacial variables during the late summer-early fall. Different chemical weathering rates in response to changes in weather reveal shifts in network configuration, indicating the subglacial environment is dynamic and very responsive to climate conditions. Methods used at the Athabasca Glacier were then applied to Kiattuut Sermiat, an outlet glacier from the Greenland Ice Sheet to investigate possible differences in hydrology between alpine and outlet glaciers. Although environmental conditions are dissimilar between locations, the Kiattuut Sermiat results suggest the possible existence of an interannual subglacial drainage system capable of evacuating waters sourced from significantly further up into the Greenland Ice Sheet concurrent with a well-organized subglacial network configuration. This dissertation presents new measurements of glacial chemistry from an understudied period in seasonal glacial evolution, with interpretations unique to each glacier investigated.