| Summary: | The stability of the Greenland Ice Sheet is of critical interest to scientists and society at large in the context of future sea-level rise. The extent to which the Greenland Ice Sheet will lose mass and contribute to rising sea level in the coming decades depends on the discharge from glaciers at its edges and on the surface mass balance, which is the balance between snow accumulation and surface melt. Estimates of Greenland surface mass balance increasingly utilize climate reanalyses and high-resolution regional climate models to determine snow accumulation, surface melt and runoff/refreeze. These models show significant, and model-dependent, biases (differences from observations) along the steep edges of the Greenland Ice Sheet where the highest and most variable (in space and time) rates of accumulation and surface melt are observed. Thus, the edges of the Greenland Ice Sheet are in critical need of updated accumulation and melt data to validate models and improve mass balance estimates. The investigators propose a traverse in the Western Greenland percolation zone over two field seasons to develop continuous in-situ snow accumulation and firn density records using ground-based radar and shallow firn cores. The research objectives include: (1) determining the patterns, in time and space, of snow accumulation in Western Greenland over the past 20-40 years; (2) evaluating surface melt refreeze and englacial meltwater storage in the Western Greenland percolation zone over the past 20-40 years; and (3) quantifying the accumulation and surface melt biases of the most recent climate reanalysis models and their regional climate model counterparts. These data are radar echograms from the GreenTrACS multi-channel 500 MHz ground-penetrating radar operated in a multi-offset configuration. The multi-channel radar technique accurately and independently estimates density, depth, and annual snow accumulation -- between the Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) firn core and snow pit sites -- by horizon velocity analysis of common midpoint radar reflections from the snow and shallow firn.
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