C43E-01
Investigating the Greenland firn aquifer near Helheim Glacier based on geophysical noninvasive methods and in situ measurements
Thursday, 17 December 2015: 13:40
3002 (Moscone West)
Clément Miège1, Lora Koenig2, Richard R Forster1, Olivia Leigh Miller1, Douglas Kip Solomon1, Anatoly Legchenko3, Nicholas C Schmerr4,5, Lynn Nicole Montgomery6 and Ludovic Brucker5, (1)University of Utah, Salt Lake City, UT, United States, (2)National Snow and Ice Data Center, Boulder, CO, United States, (3)LTHE Laboratoire d'étude des Transferts en Hydrologie et Environnement, Saint Martin d'Hères, France, (4)University of Maryland, College Park, MD, United States, (5)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (6)University of Maryland College Park, College Park, MD, United States
Abstract:
Prior to the onset of seasonal surface melt, widespread perennial aquifers are detected at an average depth of 22 m below the snow surface in the firn of the Greenland ice sheet from airborne radar data. With an elevation range of ~1200-2000 m, the aquifers are mainly located within the percolation zone of the southern and southeastern parts of the ice sheet, in high snow accumulation regions. The impact of the aquifer on Greenland ice sheet hydrology and the direct (or indirect) contribution to sea-level rise remain unconstrained and require further attention. Our study is located on the upper portion of Helheim Glacier in SE Greenland, ~50 km west of the glacier calving front. We first used repeated airborne radar data collected by CReSIS to infer the presence of the firn over the last two decades from missing bed echoes. For 1993-2008, the aquifer remained relatively stable, after 2008 it expanded to higher elevations, and after spring 2012, drainage of its lower-elevation portion is suspected. Based on these initial insights, recent fieldwork was carried out along the surveyed radar line, following an elevation gradient. Geophysical investigation includes seismic refraction and magnetic resonance soundings to complement the radar data and to provide constraints on the base of the aquifer, water volume, and the transition from water-saturated firn to ice. In addition, piezometers and data-logging stations were deployed at point locations to measure hydraulic conductivity, water table vertical fluctuations, and firn temperature. We report on the different techniques used, initial observations made, and present some preliminary interpretations. Water appears to flow laterally in a highly-permeable unconfined aquifer, topographically driven by ice-sheet surface undulations until water encounters local sinks like crevasses. The aquifer impacts on the ice sheet are numerous, including firn densification, alteration of the ice thermal state, and water from the aquifer could enter the englacial network system, which would affect ice dynamics and Greenland’s contribution to sea-level rise.
