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

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.

The Detection of Seismicity on Icy Ocean Worlds by Single‐Station and Small‐Aperture Seismometer Arrays

“…(2013), and further characterized by Maguire et al. (2021), who estimate the depth of the lake at 10–15 m. This site falls within the Mesoproterozoic Thule basin terrane and Inglefield mobile belt of northwestern Greenland (Dawes, 2009). Only 14 events above M w 5.0 occurred during the deployment, with no events larger than a M w 5.9.…”

“…The Greenland location was also colder (−14°C to −2°C) than the Alaska site and in the accumulation area, which reduces surface activity such as melt runoff and moulins significantly, producing quieter power density function (Figure 1c). The northwest Greenland stations were situated near the ice divide with an ice thickness of ∼850 m (Maguire et al., 2021), of this thickness, the top 45 m is firn. The site is situated over a subglacial lake first identified by Palmer et al.…”

Greenland and Canadian Arctic ice temperature profiles

“…Several process-level studies of potential heat sources have been performed, which compare individual observed temperature profiles from local areas with temperature profiles modeled by a thermal, or themo-mechanical, ice flow model (Iken et al, 1993;Lüthi et al, 2002;Harrington et al, 2015;Lüthi et al, 2015;Meierbachtol et al, 2015;McDowell et al, 2021;Law et al, 2021;Maguire et al, 2021). Although these studies featured different local areas, the comparisons generally showed that models tend to underestimate englacial temperatures, and thus need to incorporate additional heat sources in order to reproduce observed ice temperature profiles.…”

Seismic Detection of Euroquakes Originating From Europa's Silicate Interior

“…The changes in temperature reduce the seismic quality factor (increasing attenuation) (Cammarano et al., 2006). For these reasons, seismic waves traveling in a thinner ice shell will likely have stronger ground motion at lower frequencies compared to a thicker ice shell (Maguire et al., 2021; Panning et al., 2018). It is worth noting that the ground motion will be dependent on frequency content, such that if surface waves have wavelengths greater than the thickness of the ice, the resulting ground motion will be drastically reduced due to interactions with the ocean.…”