Meltwater storage in low-density near-surface bare ice in the Greenland ice sheet ablation zone

• Published in: The Cryosphere
• Main Authors: M. G. Cooper, L. C. Smith, A. K. Rennermalm, C. Miège, L. H. Pitcher, J. C. Ryan, K. Yang, S. W. Cooley
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2018
• Subjects: Environmental sciences; GE1-350; Geology; QE1-996.5; Greenland; Kangerlussuaq; Ice Sheet; The Cryosphere
• Online Access: https://doi.org/10.5194/tc-12-955-2018; https://doaj.org/article/6644dfc240bf4b8ba4b45789e6b4a0e4

We document the density and hydrologic properties of bare, ablating ice in a mid-elevation (1215 m a.s.l.) supraglacial internally drained catchment in the Kangerlussuaq sector of the western Greenland ice sheet. We find low-density (0.43–0.91 g cm −3 , μ = 0.69 g cm −3 ) ice to at least 1.1 m depth below the ice sheet surface. This near-surface, low-density ice consists of alternating layers of water-saturated, porous ice and clear solid ice lenses, overlain by a thin (< 0.5 m), even lower density (0.33–0.56 g cm −3 , μ = 0.45 g cm −3 ) unsaturated weathering crust. Ice density data from 10 shallow (0.9–1.1 m) ice cores along an 800 m transect suggest an average 14–18 cm of specific meltwater storage within this low-density ice. Water saturation of this ice is confirmed through measurable water levels (1–29 cm above hole bottoms, μ = 10 cm) in 84 % of cryoconite holes and rapid refilling of 83 % of 1 m drilled holes sampled along the transect. These findings are consistent with descriptions of shallow, depth-limited aquifers on the weathered surface of glaciers worldwide and confirm the potential for substantial transient meltwater storage within porous low-density ice on the Greenland ice sheet ablation zone surface. A conservative estimate for the ∼ 63 km 2 supraglacial catchment yields 0.009–0.012 km 3 of liquid meltwater storage in near-surface, porous ice. Further work is required to determine if these findings are representative of broader areas of the Greenland ice sheet ablation zone, and to assess the implications for sub-seasonal mass balance processes, surface lowering observations from airborne and satellite altimetry, and supraglacial runoff processes.