The Principal Investigators will improve our understanding of the mass balance and ice dynamics of polythermal land-terminating glaciers using McCall Glacier in arctic Alaska as a primary field site. Specifically, they will try to better understand the processes of internal accumulation of ice within firn to better predict how climate change impacts glacier dynamics and volume change. This work follows five years of research by this team and 50 years of research within the long-term McCall Glacier research project.
Scientific Merit. Prior research has shown that the surface mass balance (SMB) of arctic glaciers in Alaska is increasingly negative, with late-summer snow lines ascending higher than the glacier elevations in the last several years. But traditional SMB measurements via stakes do not account for internal accumulation of ice by refreezing of meltwater within firn and crevasses, which in recent years would account for 100% of the annual accumulation since there was no surface accumulation. With mean annual air temperatures of roughly -10 degrees C in Alaska's arctic glaciers, there is no opportunity to capture as much as half the winter snow pack within the subsurface, and not accounting for this mass hampers our ability understand and predict change. With snow lines rising throughout the Arctic, the processes of internal accumulation are becoming increasingly important globally as formerly dry firn areas begin melting. The Principal Investigators will improve prediction rates of internal accumulation from weather conditions through intensive field studies. This information will be used to further improve Hock's mass balance models; then these can be used to reconstruct a complete mass balance record for the past 50 years using regional climate models as input and the past 15 years of field SMB and weather records as calibration. This cumulative record will be compared with volume change calculated using a 50 year map-comparison using a new topographic map made for this project. Hindcasts and forecasts of mass balance will then be used to drive Pattyn's finite difference thermo-mechanical flow-line model. In previous work with this model, they found that if the climate remains unchanged, all the glaciers within arctic Alaska would disappear within a few hundred years. However, through comparisons with speed and surface elevation time-series of the past 50 years, they believe the model's predicted response is slower than actual, as it is poorly constrained for rates of internal accumulation, ice temperatures, and ice fabrics. Based on this research, they will construct a time-series of volume loss from 1890 to 2100 using volume-area scaling for nearly all of the glaciers in the geographically-defined US Arctic.
Broader Impacts: This research will also extend and improve the existing 50-year record of McCall Glacier, which has intrinsic value to glaciology as the only such record in the US Arctic. This project will help support at least two graduate students and one post-doc, and will result in a series of professional papers, as well as popular press articles and public lectures using their expanding collections of repeat-photo pairs that qualitatively document ecological change in the Arctic to help explain the significance of our research.
