Why not to Eavesdrop on Glaciers and Whales with Seafloor Seismology?

Dangerous and challenging access makes monitoring subaqueous parts of maritime and polar glaciers difficult. Nevertheless, these sensitive zones are essential in ice-ocean interactions and attract marine animals (e.g., seals and whales). Recently, we made several attempts to approach the calving front of a Greenlandic glacier to conduct direct observations. This effort included deploying an ocean-bottom seismometer next to the calving front. Our system stayed at a depth of ~250 m, where it continuously recorded seismicity (at 128 Hz), underwater sound (at 96 kHz), and temperature (1 sample per min) for more than two weeks. The experiment yielded several insights of glaciological, seismological, biological, and technological relevance. For example, we detected a seismic tremor proportional to the ice speed and reminiscent of a slow earthquake, recorded a glacial earthquake due to iceberg calving, and recognized the acoustic presence of narwhals. We also identified unusually deep sediments as a crucial feature for future deployments. We believe our approach is of broad interest and could be used in any marine or lacustrine setting where sea-ice and ice-mélange conditions allow.