Abstract
AbstractThe retention of meltwater in the accumulation area of the Greenland ice sheet and other Arctic ice masses buffers their contribution to sea level change. However, sustained warming also results in impermeable ice layers or ‘ice slabs’ that seal the underlying pore space. Here, we use a 1-D, physically based, high-resolution model to simulate the surface mass balance (SMB), percolation, refreezing, ice layer formation and runoff from across the high-elevation area of Devon Ice Cap, Canada, from 2001 to 2016. We vary the thickness of the ‘impermeable’ ice layer at which underlying firn becomes inaccessible to meltwater. Thick near-surface ice layers are established by an initial deep percolation, the formation of decimetre ice layers and the infilling of interleaving pore space. The cumulative SMB increases by 48% by varying impermeable layer thickness between 0.01 and 5 m. Within this range we identify narrower range (0.25–1 m) that can simulate both the temporal variability in SMB and the observed near-surface density structure. Across this range, cumulative SMB variation is limited to 6% and 45–49% of mass retention takes place within the annually replenished snowpack. Our results indicate cooler summers after intense mid-2000s warming have led to a partial replenishment of pore space.
Highlights
The Arctic is warming at twice the global mean leading to widespread ice mass loss, largely attributable to increased surface melt
surface mass balance (SMB) is relatively insensitive to a wide range of impermeable ice layer thicknesses, our results indicate that allowing very thick ice layers to be permeable to percolating meltwater leads to unrealistically positive SMB, evidenced by the Himp = 5 m runs having poor agreement with observations of both temporal and spatial patterns in SMB (Fig. 4)
We have reported the first systematic assessment of an impermeable layer thickness parameterisation in a 1-D snow and firn model, and assessed model performance using field SMB measurements, published Ground penetrating radar (GPR) profiles and measurements of near-surface bulk density
Summary
The Arctic is warming at twice the global mean leading to widespread ice mass loss, largely attributable to increased surface melt (e.g. van den Broeke and others, 2016). In the accumulation zone, meltwater can percolate into porous snow and firn. Meltwater may be retained as liquid water, but is more typically retained as infiltration ice, i.e. water that has percolated through the porous snowpack to refreeze as distinct high-density ice lenses or layers. Meltwater in the accumulation area that does not refreeze percolates to an impermeable horizon and migrates laterally, eventually entering the glacier hydrological system. In the warming Arctic, areas of previously dry snow are routinely experiencing melt and so elucidating processes controlling meltwater percolation, refreezing and runoff in an evolving stratigraphy is critical for improving projections of sea level rise
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