Patterns of water chemistry and discharge in the glacier-fed Kennicott River, Alaska: evidence for subglacial water storage cycles

Runoff from the temperate Kennicott Glacier in the Wrangell Mountains, Alaska, displays distinctive oscillations in discharge, electrical conductivity, and solute concentrations during the summer melt season. In addition to daily fluctuations, the Kennicott River undergoes quasi-cyclic changes in discharge over 12- to 18-day periods probably linked to weather-induced variations in melt. Solute variations are lagged from discharge by several days; solute concentrations peak during falling discharge, and reach minima during rising discharge. We explore probable weathering reactions through mass balance analysis. The reactions responsible for most solute fluctuations are halite dissolution and H2CO3-driven calcite dissolution, while sulfide oxidation and associated calcite dissolution are significant but steady components of the solute flux. Halite dissolution is probably limited by the glacial abrasion rate. Calcite dissolution by carbonation co-varies directly with the calculated PCO2 of the runoff. This result is not expected in an environment that is poorly connected to the atmosphere; a possible explanation is that respiration by subglacial microbes produces CO2 at the glacier bed. The extent of sulfide oxidation is limited by availability of O2, and the lack of temporal variation in this reaction suggests that this limit operates in both the distributed system and subglacial conduits. All solute variations are consistent with changes in subglacial water storage and are therefore indicative of changing efficiency of subglacial drainage through time.