2017 Ablation Zone Photos
In July 2017 I spent 1 week at a field location in the ablation zone in the Issunguata Sermia catchment. This field site was where scientists from the University of Montana and University of Wyoming installed inclinometers and temperature sensors throughout the ice column in 9 boreholes. I helped to dismantle the field experiments and map the bed using ground penetrating radar.
2017 Ablation Zone Photos
In July 2017 I spent 1 week at a field location in the ablation zone in the Issunguata Sermia catchment. This field site was where scientists from the University of Montana and University of Wyoming installed inclinometers and temperature sensors throughout the ice column in 9 boreholes. I helped to dismantle the field experiments and map the bed using ground penetrating radar.
2017 Ablation Zone Photos
Firn microstructure influences ice layer formation in the shallow firn column in western Greenland
Poster Presentation - AGU 2021 Fall Meeting
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Abstract
Ice layers in polar firn serve as proxies for previous ice sheet summer surface temperatures and melt, while also reducing the ability for additional meltwater to vertically percolate deep into the firn column in the future. Therefore, determining the factors controlling ice layer formation will refine paleoclimate reconstructions relying on trends in melt feature percentages and will improve estimates of firn’s capacity to accept meltwater and buffer sea level rise in a warmer climate. Here, we show ice layer frequency in the top 10 m of seven firn cores collected in the western Greenland Ice Sheet percolation zone does not correspond to the climate gradient, which suggests a more complicated relationship between ice layer formation and climate. These cores were collected as part of the 2016-2017 Greenland Traverse for Accumulation and Climate Studies (GreenTrACS). We hypothesize microstructural changes within the firn column, such as grain size transitions resulting in variations in firn permeability, generate the discrepancy between ice layer frequency and the position of the cores along the climate gradient. We document ice core stratigraphy and grain size transitions as well as develop an ice layer classification scheme by digitally analyzing photographs detailing the top 10 m of the cores. These results can serve as validation for microstructural modeling of the firn column in western Greenland, which can improve estimates of past surface melt and inform future simulations of meltwater percolation and refreezing or firn aquifer formation.​​
Motivation
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As surface temperatures increase over Greenland in the future, more areas will be prone to melting. Understanding how microstructure affects ice layer formation and meltwater infiltration will assist in partitioning runoff, refreezing, and water storage components to refine rates of future sea level rise (Figure 1).
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Empirical evidence of microstructural controls on ice layer formation can be incorporated into existing firn models to update infiltration schemes.
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Ice layers and melt features have been used as proxies of past summer surface temperature and melt (e.g. Graeter et al., 2018). However, meltwater can infiltrate to depths greater than 1 year of snow/firn accumulation. Thus, increases in melt extent over time can only describe general periods of inicreased melt. Knowing how firn microstructure influences refreezing can help to refine the use of ice layers as paleoclimate proxies.
Fig 1. (Top) Map showing melt anomaly relative to the 1981 – 2010 average across the Greenland Ice Sheet during the unprecedented melt year of 2012. As temperatures continue to warm, melt extent is expected to continue to cover much of the accumulation zone. Map courtesy of NSIDC. (Bottom) The effects of future melt on current firn regions: some low elevation regions near the current equilibrium line will become runoff zones; thick ice layers will form in near-surface firn and generate shallow lateral runoff; refrozen meltwater will create discrete melt lenses that continues to allow for heterogeneous meltwater percolation into deep pore space; and the expansion of existing and formation of new firn aquifers that store liquid water beneath the ice sheet surface for years to decades. Current firn structure and future climate conditions will influence which scenario occurs in firn regions experiencing higher rates of future melt.