Mechanisms of Ice Core Stable Isotope Variability in the Upper Kaskawulsh-Donjek Region, St. Elias Mountains, Yukon, Canada

• Main Author: McConnell, Erin A
• Format: Text
• Language: unknown
• Published: DigitalCommons@UMaine 2019
• Subjects: alpine glacier; melt; atmospheric circulation; north pacific; firn; isotope signal; Atmospheric Sciences; Climate; Geochemistry; Glaciology; Meteorology; Arctic; Yukon; Canada; Pacific; glacier*; ice core
• Online Access: https://digitalcommons.library.umaine.edu/etd/3069; https://digitalcommons.library.umaine.edu/cgi/viewcontent.cgi?article=4143&context=etd

I use instrumental and ice core records to examine drivers of observed isotope variability in the Upper Kaskawulsh-Donjek (UKD) region of the St. Elias Mountains, Yukon, Canada over the time frame of instrument-proxy overlap (mid-1900s to present). One of the drivers of post-depositional isotope signal alteration is the vertical percolation of meltwater from the glacier surface through shallow layers of snow, which causes a reduction in the amplitude of the isotope signal recorded in ice cores. I examine isotope signal preservation in two sites in the St. Elias Mountains: Eclipse Icefield and Icefield Divide. These sites are relatively close (~30 km apart and 414 m elevation difference), yet display marked differences in melt amounts and isotope signal preservation related a ~1.8 °C increase in temperature along the downward altitudinal transect from Eclipse Icefield to Icefield Divide. The increase in melt and loss of isotope signal preservation in response to this relatively small temperature rise suggests that the isotope signal at Eclipse Icefield will begin to degrade by the mid-21st century if rapid Arctic warming continues as projected. However, temperatures in northwestern Canada have already exceeded those of the Holocene Thermal Maximum. This indicates that, given Eclipse Icefield’s lack of melt-related signal alteration at present, its ice may contain a complete and unaltered record of past regional climate variability through the Holocene— regardless of its ability to record climate variability in the near future. Extending this analysis to other ice core sites in the Arctic, I identify a meteorological threshold for melt-related signal alteration, characterized by high mean summer temperatures (approximately -1.5 °C and above) and low accumulation rates (less than ~1.2 m water-equivalent snowfall per year). In addition, I investigate mechanisms driving observed seasonality in the Eclipse Icefield isotope record using instrumental records and climate reanalysis products, which summarize broad-scale ...