Evolving Ice Fraction in the Shallow Firn Layer of Devon Ice Cap, Canada, between 2012 and 2022.

Firn can store glacial meltwater and delays contribution to sea level rise, but ice layers and ice slabs within the shallow firn layer can impede downward percolation of melt. Here we report firn conditions along a transect on southwest Devon Ice Cap, Nunavut, and explore its response to air temperature variability over a decadal period. We present results from two field campaigns; six shallow firn cores were extracted along the same transect in spring 2012 and 2022. At six different sites, the ice fraction has decreased over this 10-year period, and the content of firn increased. Between 2012 and 2022, the ice fraction of the firn layer decreased by 29.6% at the lowest elevation site (1400 m a.s.l.) and by 11% at the highest elevation site (1800 m a.s.l.). Despite higher annual positive degree day sum during 2012-2022 compared to 2002-2012, cooler summers in 2013, 2018 and 2021 resulted in less ice layers in the shallow firn layer. This demonstrates how the shallow firn layer can regenerate from several cooler years and highlights the nuanced response of Devon Ice Cap shallow firn layer to climate warming.