| Summary: | Firn structure influences the fate and transport of meltwater generated in the accumulation zone of the Greenland Ice Sheet. Meltwater can be stored as refrozen ice layers within the firn column, but these features decrease future storage capacity as they act as impermeable barriers to deep infiltration. Observations of firn structure are necessary to validate firn model percolation schemes and predict future ice layer formation within the firn column for accurate ice sheet mass balance estimates. Here, we present grain size measurements and ice layer stratigraphy from seven firn cores collected in western Greenland during the 2016 Greenland Traverse for Accumulation and Climate Studies (GreenTrACS). We use the grain size data to count the number of grain size transitions within each firn core, and relate the number of grain size transitions, and particularly the number of fine-over-coarse grain size transitions to the total number of ice layers in each core. Unexpectedly, ice layers are strongly negatively correlated with all grain size transitions, and more specifically with fine-over-coarse grain transitions, which create capillary barriers that promote water ponding and ice layer formation. We suggest that these relationships are the final signature of capillary effects on vertical meltwater infiltration, as grain size transitions are overprinted during ice layer formation along stratigraphic horizons.
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