Date of Award
Fall 12-15-2023
Level of Access Assigned by Author
Open-Access Thesis
Language
English
Degree Name
Master of Science (MS)
Department
Quaternary and Climate Studies
Advisor
Seth Campbell
Second Committee Member
Kristin Schild
Third Committee Member
Peter Koons
Abstract
Glaciers are important freshwater resources which have far reaching impacts on a range of local to global systems and processes, including ecosystems and societies. As global climate continues to change, the response of glaciers has largely been reductions in ice mass and widespread retreat. A high degree of accumulation and ablation occurs in the near surface which is exposed to the atmosphere. The Juneau Icefield (JIF) has, up until the mid-2010s, historically responded climate change anomalously where its main drainage, Taku Glacier (here forward referred to its native name T’aakú Kwáan Sít’i), has been advancing while all other JIF outlet glaciers have been retreating for years.
In this thesis, I quantify and compare snow water equivalent (SWE) of the annual accumulation between 2012 (pre-retreat) and 2021 (during retreat) with repeated 400 MHz common-offset ground-penetrating radar (GPR) surveys across the southern portion of the Juneau Icefield which includes T’aakú Kwáan Sít’i and its main tributaries. Because these calculations require assumptions of radio wave velocity which depends on liquid water content and density, both properties that can vary spatially and temporally, I quantify this variability with ground-truthed measurements to determine bulk relative permittivity in the annual accumulation. From this, I determine the range of liquid water content in the snowpack. I additionally quantify the difference in firn thickness and volume across JIF over this time period from the same GPR dataset and begin to investigate the potential causes of this change.
The SWE in 2012 ranged between 42-688 cm water equivalent (cm w.e.) and in 2021 between 15-570 cm w.e. The depth-density relationship is relatively consistent across JIF, so I conclude that variability in liquid water content is the likely driver for variability in derived relative permittivity. Between 2012 and 2021, JIF experienced widespread firn thinning that resulted in an approximate reduction of firn volume by 51.3 percent. This difference in firn thickness was most highly correlated with marine proximity and elevation. From the investigation into glacier velocity, it is likely that the observed firn thinning was not due to dynamic thinning and was likely a result of increased ablation, decreased accumulation, or increased densification rates.
These decadal-scale observations have implications for the future health of JIF and for interpretations of GPR data in temperate glacier environments. First, such a drastic decrease in firn volume reduces the mass influx to glacier ice and its ability to store short-term melt water while also potentially increasing JIF’s susceptibility to contributing more to global sea-level rise. Second, the variability in relative permittivity across the study site suggests potential for high uncertainty in depth (30.5-54.1%) and SWE (32.2-56.2%) calculations due to spatial and, likely, temporal variability in liquid water content when using GPR to determine both variables in a temperate environment.
Recommended Citation
Mannello, Mikaila, "Spatial and Temporal Variability in Snow Properties and Firn Volume Across the Juneau Icefield in Southeast Alaska" (2023). Electronic Theses and Dissertations. 3891.
https://digitalcommons.library.umaine.edu/etd/3891