Presenter: Hayden Johnson (Scripps Institution of Oceanography)

Description:
Ice sheets in Greenland and Antarctica have the potential to contribute dramatically to future sea level rise. Ice-ocean interactions at marine-terminating glaciers may influence feedback mechanisms such as marine ice sheet instability that contribute considerable uncertainty to projections. Knowledge of what is happening to these glaciers beneath the waterline is essential to improving our understanding of these processes, but is difficult to obtain, and is often limited to short-term active surveys. Passive acoustics presents a complimentary opportunity for long-term, high temporal resolution measurements of submarine melting at marine-terminating glaciers. Pressurized air bubbles in glacier ice radiate sound when the ice melts and they are released into the water. With sufficient knowledge of the properties of the ice, and sufficient understanding of the mechanisms of sound production, measurements of the underwater sound produced at the terminus of a glacier may be useful to quantify submarine melting. Here we present progress that has been made towards characterization of the sound produced by melting glacier ice, based on controlled melting experiments. The experiments were conducted with ice collected from Hornsund Fjord in Svalbard during a field campaign in the summer of 2019. We find that the acoustic energy radiated by the blocks of ice during melting is correlated with estimates of the total potential energy stored by the pressurized gas bubbles, which depends upon bubble pressure and volume. We discuss implications of this finding for understanding the depth dependence of the melting signal and for the broader usefulness of passive acoustic monitoring, as well as the limitations of the potential energy as a predictor of the source signal. Finally, we remark on the work that remains to be done in order to bring passive acoustic monitoring of submarine melting into the mainstream.