Abstract
Abstract. In this study, we report the results of an active-source seismology and ground-penetrating radar survey performed in northwestern Greenland at a site where the presence of a subglacial lake beneath the accumulation area has previously been proposed. Both seismic and radar results show a flat reflector approximately 830–845 m below the surface, with a seismic reflection coefficient of −0.43 ± 0.17, which is consistent with the acoustic impedance contrast between a layer of water and glacial ice. Additionally, in the seismic data we observe an intermittent lake bottom reflection arriving between 14–20 ms after the lake top reflection, corresponding to a lake depth of approximately 10–15 m. A strong coda following the lake top and lake bottom reflections is consistent with a package of lake bottom sediments although its thickness and material properties are uncertain. Finally, we use these results to conduct a first-order assessment of the lake origins using a one-dimensional thermal model and hydropotential modeling based on published surface and bed topography. Using these analyses, we narrow the lake origin hypotheses to either anomalously high geothermal flux or hypersalinity due to local ancient evaporite. Because the origins are still unclear, this site provides an intriguing opportunity for the first in situ sampling of a subglacial lake in Greenland, which could better constrain mechanisms of subglacial lake formation, evolution, and relative importance to glacial hydrology.
Highlights
There is mounting evidence that subglacial lake systems below the Antarctic and Greenland ice sheets play an important role in glacier dynamics and ice-sheet mass balance considerations
In order to confirm the presence of the subglacial lake and investigate its physical properties, we collected data using both active-source seismology and ground-penetrating radio-echo sounding (GPR)
We conducted an active-source seismic reflection and GPR survey in northwestern Greenland above a site that was previously identified as a possible subglacial lake
Summary
There is mounting evidence that subglacial lake systems below the Antarctic and Greenland ice sheets play an important role in glacier dynamics and ice-sheet mass balance considerations. In Antarctica, the presence of subglacial lakes is suspected to promote ice flow by reducing basal shear stress (e.g., Bell et al, 2007), and periodic drainage events have been linked to accelerated ice flow in outlet glaciers and ice streams (e.g., Stearns et al, 2008; Siegfried et al, 2016). In Greenland subglacial lake systems provide a reservoir for the storage of surface or basal meltwater and may be an important, but largely unknown, factor in global sea level change. R. Maguire et al.: Geophysical constraints on the properties of a subglacial lake
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