Articles | Volume 12, issue 3
The Cryosphere, 12, 955–970, 2018
The Cryosphere, 12, 955–970, 2018

Research article 21 Mar 2018

Research article | 21 Mar 2018

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

Matthew G. Cooper1, Laurence C. Smith1, Asa K. Rennermalm2, Clément Miège3, Lincoln H. Pitcher1, Jonathan C. Ryan1,4, Kang Yang5,6, and Sarah W. Cooley1,7 Matthew G. Cooper et al.
  • 1Department of Geography, University of California-Los Angeles, CA 90095, USA
  • 2Department of Geography, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA
  • 3Department of Geography, University of Utah, Salt Lake City, UT, USA
  • 4Institute at Brown for Environment and Society, Brown University, Providence, RI, USA
  • 5School of Geographical and Oceanographic Sciences, Nanjing University, Nanjing 210023, China
  • 6Joint Center for Global Change Studies, Beijing 100875, China
  • 7Dept. of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA

Abstract. 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 km2 supraglacial catchment yields 0.009–0.012 km3 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.

Short summary
We present measurements of ice density that show the melting bare-ice surface of the Greenland ice sheet study site is porous and saturated with meltwater. The data suggest up to 18 cm of meltwater is temporarily stored within porous, low-density ice. The findings imply meltwater drainage off the ice sheet surface is delayed and that the surface mass balance of the ice sheet during summer cannot be estimated solely from ice surface elevation change measurements.