Hydraulic Conductivity of a Firn Aquifer in Southeast Greenland

Olivia L Miller,Nicholas Schmerr,D Kip Solomon,Clément Miège,Richard R Forster,Anatoly Legchenko,Lora S Koenig,Ludovic Brucker,Lynn N Montgomery,Stefan R M Ligtenberg

doi:10.3389/feart.2017.00038

Abstract

Some regions of the Greenland ice sheet, where snow accumulation and melt rates are high, currently retain substantial volumes of liquid water within the firn pore space throughout the year. These firn aquifers, found between ~10-30 m below the snow surface, may significantly affect sea level rise by storing or draining surface meltwater. The hydraulic gradient and the hydraulic conductivity control flow of meltwater through the firn. Here we describe the hydraulic conductivity of the firn aquifer estimated from slug tests and aquifer tests at six sites located upstream of Helheim Glacier in southeastern Greenland. We conducted slug tests using a novel instrument, a piezometer with a heated tip that melts itself into the ice sheet. Hydraulic conductivity ranges between 2.5x10-5 and 1.1x10-3 m/s. The geometric mean of hydraulic conductivity of the aquifer is 2.7x10-4 m/s with a geometric standard deviation of 1.4 from both depth specific slug tests (analyzed using the Hvorslev method) and aquifer tests during the recovery period. Hydraulic conductivity is relatively consistent between boreholes and only decreases slightly with depth. The hydraulic conductivity of the firn aquifer is crucial for determining flow rates and patterns within the aquifer, which inform hydrologic models of the aquifer, its relation to the broader glacial hydrologic system, and its effect on sea level rise.

Highlights

Across the percolation zone of the southeast portion of the Greenland ice sheet, surface meltwater infiltrates to depth within the ice sheet, where it currently forms an extensive firn aquifer
The recovery data likely result in a more. These are the first hydraulic conductivity measurements of a firn aquifer in the southeastern Greenland ice sheet and these are the first depth specific slug tests conducted in a firn aquifer
We find relatively homogeneous hydraulic conductivity between measurement sites, and a slight decrease with depth

Summary

Introduction

Across the percolation zone of the southeast portion of the Greenland ice sheet, surface meltwater infiltrates to depth within the ice sheet, where it currently forms an extensive firn aquifer. Documented in 2011 (Forster et al, 2014), the aquifer has been identified and monitored with ground penetrating radar, airborne radar, and in situ measurements since (Koenig et al, 2014; Miège et al, 2016; Montgomery et al, this issue). Over the entire ice sheet, firn aquifers are estimated to cover an area between 20,000 and 70,000 km, with ∼50% of this total extent located in the southeastern portion of the ice sheet (Forster et al, 2014; Miège et al, 2016). Firn aquifers form in areas with a combination of high accumulation and high melt. Complete drainage of the aquifer could contribute up to 0.4 mm to sea level rise globally (Koenig et al, 2014)

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Conclusion