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Geophysical constraints on the properties of a subglacial lake in northwest Greenland

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.
