Calibrating Ice Core, Weather Station, and NASA MODIS Ice-Surface Temperature Records to Analyze Atmospheric Variability in the St. Elias, Yukon, Canada

The North Pacific is characterized by complicated atmospheric dynamics, which must be understood to predict the region's response to a warming climate. Glaciers in the St. Elias Mountains of Canada's Yukon present an opportunity to reconstruct past climate variability using ice cores. This study quantifies the relationships between meteorological data and ice core records in the St. Elias. Our focus sites are Icefield Divide (2,850 m elev.) and Eclipse Icefield (3,017 m elev.). In June 2018 our group extracted two ice cores (10 m and 20 m) from Divide. We processed the cores at 10 cm intervals in the field and analyzed them for stable water isotopes (δD and δ¹⁸O) using Picarro instrumentation. Our group has also collected and analyzed ice cores from Eclipse Icefield in 2017, 2016, and 2002. 20 m cores drilled at each location within the past two years show a larger range of isotope values at Divide (18.4 and 151.0 ‰ for δ¹⁸O and δD, respectively) than at Eclipse (15.0 and 120.9 ‰); however, the isotopic range at Divide decreases with depth and does not at Eclipse. In addition, a 400 MHz radar transect at Divide shows strong reflectance at 30 m depth. We interpret this as a firn aquifer, resulting in meltwater percolation that causes the isotope signal to deteriorate below the 2017/2018 snowpack ( 6 m depth). GPR data from Eclipse Icefield shows no evidence of an aquifer, indicating that the phenomenon may be restricted to sites in the St. Elias below 3,000 m elevation. This is not due to temperature differences: an automated weather station (AWS) at Divide has recorded a mean annual temperature of -10 °C, and Eclipse does not differ significantly given normal lapse rates. Presented results will examine variations in annual accumulation at the two sites that may account for the presence of the aquifer at Divide. Results will also include a comparison/calibration of the ice core data with instrumentally-observed air and ice-surface temperature data. This analysis includes data from the 2018 Divide cores, three Eclipse cores dating back to the beginning of the 15^th century, 2002-2018 AWS accumulation and air temperature data, and ice-surface temperatures recorded by NASA Moderate Resolution Imaging Spectroradiometer (MODIS) satellite sensors since the early 2000s.