Ice Flow Impacts the Firn Structure of Greenland's Percolation Zone

• Main Author: Leone, Rosemary C
• Format: Thesis
• Language: unknown
• Published: University of Montana 2019
• Subjects: Firn; Greenland; Climate; Hydrology; Modeling; Glaciology; ice core; Ice Sheet
• Online Access: https://scholarworks.umt.edu/etd/11474; https://scholarworks.umt.edu/context/etd/article/12548/viewcontent/Leone_Rosemary_Thesis.pdf

One dimensional simulations of firn evolution neglect horizontal transport as the firn column moves down slope during burial. This approach is justifiable near Greenland's ice divide, where ice flow is near vertical, but fidelity is lost in the percolation zone where horizontal ice flow advects the firn column through climate gradients. We simulate firn evolution processes under advection conditions using a transient, thermo-mechanically coupled model for firn densification and heat transfer with various schemes for meltwater penetration and refreezing. The simulations isolate processes in synthetic runs and investigate an ice core site and four transects of Greenland’s percolation zone. The impacts of advection on the development of firn density, temperature, and stratigraphy of melt features are quantified, and two dimensional simulations are compared against a 1D baseline. The advection process tends to increase the pore close off depth, reduce the heat content, and decrease the frequency of melt features with depth, by emplacing firn sourced from higher locations under increasingly warm and melt-affected surface conditions. Pore close off and temperature are mainly impacted in the lowermost 20 km of the percolation zone, the impacts vary around the ice sheet but can change the firn’s air content by 10s of percent. Ice flow can also have a substantial impact on the stratigraphy of melt features in the firn column, independent of changing melt frequency, even in locations where the air content and firn temperature are relatively unaffected by advection. Thus, this effect should be quantified in order to correctly interpret temporal changes in ice cores in regards to climate.