April 10, 2013 Chas Jones and Phillip Wilson, Tanana River Groundwater Regimes University of Alaska Fairbanks, International Arctic Research Center (Chas Jones) and West Valley High School (Phillip Wilson)

Tanana River Groundwater Regimes

Chas Jones and Phillip Wilson, University of Alaska Fairbanks, International Arctic Research Center (Chas Jones) and West Valley High School (Phillip Wilson)

Connecting the dots. Permafrost, upwelling, and ice thickness

Chas Jones, PhD Candidate, University of Alaska Fairbanks, International Arctic Research Center

I modeled the thermal balance between groundwater upwelling and changing ice conditions in side channel sloughs of the Tanana River near Fairbanks, a region characterized by discontinuous permafrost. Studies have linked degrading permafrost to increased winter discharge in rivers due to increasing contributions from groundwater flow. In the winter, interior Alaskan rivers are fed almost entirely by groundwater, which also serves as an external source of heat energy to the system. In fact, portions of the river fed by groundwater springs remain ice-free or have dangerously thin ice throughout the winter despite air temperatures that dip below -40° C. These areas are particularly dangerous for people that utilize Alaskan rivers for wintertime travel.

I developed a model to explore how fluctuations in groundwater discharge act as a control on river ice thickness under changing atmospheric conditions. Specifically, the model examines how local and regional changes in groundwater flow affect ice dynamics (growth or thinning) in the context of two primary research questions: 1) What are the dominant factors in the interactions of air temperature, groundwater upwelling rates, groundwater temperature, snow cover, and ice thickness in controlling the seasonal ice dynamics on the Tanana River? 2) What are the rates of change in ice thickness resulting from observed and projected changes in these parameters? My results indicate that under a warming climate scenario, heat flux due to upwelling may degrade river ice at up to 20 mm/day. The ice melt potential is amplified by increased hydraulic gradient, hydraulic conductivity, groundwater upwelling, air temperature, groundwater temperature ice thickness, or snow depth. Increased air temperatures associated with climate change is expected to increase upwelling rates, decrease the temperature gradient, increase snow depths, and decrease ice thickness. My model indicates that potential ice melt rates may increase by up to 35% under an altered climate. These results may corroborate reports from rural Alaskans that hydrologic conditions have changed in recent decades in noticeable ways and suggest that changes associated with permafrost degradation may amplify some impacts in a warming climate.



Thermal Dynamics of Ice on the Tanana River during Mid-Winter
Phillip Wilson, West Valley High School

On the Tanana River during mid-winter, upwelling of ground water appears to be a factor resulting in the strange occurrence of ice degradation, as seen by ice-free portions of the river, even during very cold (-35°C) temperatures. Air temperature, water depth and snow cover may also contribute to this condition. I hypothesized that groundwater temperatures in shallow sloughs would be above freezing and that this warmth could in part be a cause of thinning/melting ice. My studies were conducted in two sloughs of the Tanana River near the Bonanza Creek LTER sites. Investigations included measurements of: 1) sediment/groundwater temperatures, 2) gradients in ice thinning near snow machine trails, and 3) how snowmachine trails change snow densities, affecting its thermal properties. I found that groundwater temperatures could be nearly +3°C, supporting the hypothesis that it gives off heat. New snow has low thermal conductivity, and as it piles up on top of the ice over winter, it insulates the ice from the air. Consequently, ice covered by fluffy, undisturbed snow holds in the heat better than packed snow, and has greater potential for melting. Consequently, established trails may have thicker ice for safer travel during winter on the Tanana River.