Meltwater Penetration Through Temperate Ice Layers in the Percolation Zone at DYE‐2, Greenland Ice Sheet

Abstract

Meltwater retention in the firn layer of the Greenland Ice Sheet has the potential to buffer sea level rise due to ice sheet melt. The capacity of the firn layer to store meltwater is unclear, however, because refrozen ice layers can act as impermeable barriers to meltwater percolation, promoting runoff rather than retention. We present time domain reflectometry and thermistor data, which demonstrate that meltwater successfully penetrates ice layers up to 12 cm thick in the near‐surface firn at DYE‐2, Greenland. Our observations indicate that ice layers within polar firn can be permeable when summer warming and latent heat release from meltwater refreezing raise firn temperatures to the melting point. The extent and depth of refreezing, as determined by the coupled thermodynamic and hydrological evolution in the firn, are more important than the presence of ice layers in governing meltwater infiltration and retention at our study site.

Extreme melt season ice layers reduce firn permeability across Greenland

“…Together with the distinct character of the radar reflectors, these results suggest that the most prominent melt layer in northwest Greenland was the result of unprecedented melt production over otherwise cold firn, whereas, in the south, its formation was aided by vertical variability in firn density or microstructure 25,27 rather than sharp thermal gradients. These results also suggest that the lack of melt layer detections in the southern deep percolation zone may indicate a transition to deep, heterogeneous infiltration or meltwater penetration through temperate ice 28 that limits the formation of spatially coherent melt layers. This is consistent with the high radar-inferred density but low connectivity values we observe at the lower elevation boundary of our radar detections (Fig.…”

The firn meltwater Retention Model Intercomparison Project (RetMIP): evaluation of nine firn models at four weather station sites on the Greenland ice sheet

“…They also simulate meltwater refreezing and latent-heat release. All models simulate the retention of meltwater within a layer due to capillary suction, either explicitly (MeyerHewitt, CFM-Cr and CFM-KM) or, for all the other models, parameterized through the use of an irreducible water content (Coléou and Lesaffre, 1998;Schneider and Jansson, 2004). When meltwater cannot be transferred to the next layer or be retained within the layer by capillary suction, lateral runoff can occur according to model-specific rules ( Table 2).…”

“…If meltwater is conveyed to a model layer, the water is refrozen if sufficient pore space and cold content are available in the layer. Additional liquid water can be retained in a layer by capillary forces calculated after Schneider and Jansson (2004). This formulation does not allow for the formation of firn aquifers.…”

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“…The firn model is coupled with a surface energy balance model (Marshall, 2014;Ebrahimi and Marshall, 2016), with subsurface heat conduction calculated within the firn model. The coupled model system is described in Samimi and Marshall (2017) and Samimi et al (2020).…”

“…This relation roughly accounts for the effects of melting on liquid water content, rounding of snow grains, and increasing concentration of impurities, which collectively produce snow-albedo reductions over the summer melt season (Brock et al, 2000;Cuffey and Paterson, 2010). A value of 0.002 was used in this study, based on calibration at DYE-2 in the percolation zone of the Greenland Ice Sheet (Samimi et al, 2020). The calibration at DYE-2 is against long-term GC-Net automatic weather station data (Steffen and Box, 2001), and the value of b is about 40% larger than optimized values at mid-latitude mountain glacier sites where we have applied Eq.…”