Meltwater Penetration Through Temperate Ice Layers in the Percolation Zone at DYE‐2, Greenland Ice Sheet. Issue 15 (6th August 2020)

• Record Type: Journal Article
• Authors: Samimi, Samira; Marshall, Shawn J.; MacFerrin, Michael
• Is Part Of: Geophysical research letters. Volume 47:Issue 15(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-08-06
• Subjects: Greenland Ice Sheet -- firn -- meltwater retention -- TDR -- firn hydrology; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL089211
• Languages: English
• ISSNs: 0094-8276

Abstract

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. Plain Language Summary: Meltwater that percolates below the surface of the Greenland Ice Sheet is difficult to track; some of it contributes to runoff, mass loss, and sea level rise, but some meltwater refreezes and is retained within the system. Greenland has a large firn area, where multiyear snow that has not yet transitioned to glacial ice has pore space that can retain meltwater. To improve understanding of hydrological and mass balance processes in polar firn, we excavated two firn pits in the Greenland Ice Sheet accumulation area in spring, 2016, and instrumented these pits with thermistors and time domain reflectometry (TDR) sensors, connected to continuously recording dataloggers. These sensors allowed us to directly track the coupled thermal and hydrological evolution in the firn through the summer melt season. We recorded nearly identical conditions at each site, with evidence of meltwater infiltration to a depth of between 1.8 and 2.1 m and a wetting front that was thermally controlled, that is, coincided with the melting front. This included meltwater penetration through numerous ice layers, including layers up to 12 cm thick. All of this meltwater refroze. Our results indicate that ice layers do not necessarily act as impermeable barriers to meltwater percolation and retention. Key Points: Time domain reflectometry probes give direct measurements of meltwater infiltration in firn at DYE‐2 on the southwest Greenland Ice Sheet We document meltwater penetration through ice layers up to 12 cm thick in temperate firn The wetting front and melting front developed in tandem, indicating coupled hydrological and thermodynamic controls on meltwater infiltration depth