Tracing Shifts in Subglacial Hydrochemistry Due to Changes in Drainage Configuration: Athabasca Glacier, Alberta, Canada

Abstract:

Differences in the hydrological and chemical composition of glacial outflow are controlled by seasonality, subglacial bedrock mineralogy, physical/chemical weathering processes, and water-rock interaction time. While the chemical progression from onset of melt to peak melt has been well studied at various glaciers, few studies exist that examine the hydrological and associated chemical changes as the subglacial drainage network evolves from peak flow back to winter basal flow conditions. Here we use traditional hydrological and chemical techniques to examine the changes in subglacial drainage network configuration with the onset of winter at the Athabasca Glacier, Alberta, Canada. This glacier is one of eight alpine glaciers draining the Columbia Icefield in the Canadian Rockies. The Athabasca Glacier is situated atop Middle Cambrian limestone and carbonate shale generating predominately a carbonate weathering regime, but exhibits some evidence of silicate weathering.

Analysis of major and trace element ratios, stable oxygen (δ¹⁸O) and hydrogen (δD) isotopic systems, and in-field chemical measurements (pH, electrical conductivity, total alkalinity), combined with discharge over a three-month period provides high-resolution insight into the change of subglacial hydrochemistry in this system. O-H isotopes over the course of the study show seasonal excursions, possibly indicating a change in meltwater source. Preliminary data reveal three possible shifts in subglacial dynamics suggesting shifts between carbonate and silicate weathering as expressed by relative cation contributions. These shifts may be reflective of different subglacial drainage configurations: higher silicate weathering rates, revealed by increased potassium concentrations in the end of season, could be generated by a shift to a more distributed drainage network and a longer water-rock interaction time.

Our results clearly indicate changes in elemental concentrations correlated with decreases in glacial discharge with the onset of winter. Future analysis of the O-H isotopic system and possible shifts in types of chemical weathering may provide further insight into the expected shift from a summertime connected drainage to a wintertime disconnected network.