Constraining the Properties of a Subglacial Lake in Northwest Greenland with Active Source Seismology

While the presence and nature of subglacial lakes in Antarctica have been studied for over 50 years, subglacial lakes in Greenland were only first discovered in the past decade, and little is understood about their properties or their origin. Using active source reflection seismology, we constrain the properties of a subglacial lake recently detected in northwest Greenland by ice penetrating radar (Palmer et al., 2013). The active source seismic experiment was conducted using a 4.5 kg hammer and metal plate as a source and recorded by a 24-channel 40 Hz geophone array. Reflected P-waves that are consistent with the depth of the lake (~800 m) and radar sounding are evident in the active source dataset. We perform amplitude-variation-with-angle (AVA) analysis on the P-wave reflections, comparing amplitudes from the first and second reflections of the base of the ice, to confirm the presence and depth of the water. At near-normal incidence angles, we find reflection coefficients with a mean of -0.39 ± 0.15, which is consistent with expected values for an ice-over-water interface. Using the average P-wave velocity in the ice of 3600 m/s, calculated from a normal-moveout velocity analysis, we use two-way reflection travel time to determine the depth of the lake surface to be at approximately 820 m. We also detect a second reflector below the lake surface, which we interpret as the lake bed, at a maximum depth of approximately 15 m below the base of the ice. Our results may provide new insights into the uncertain origins of subglacial lakes in Greenland.