Quantifying calving flux from underwater noise of iceberg impact

Measuring ice discharge from marine-terminating glaciers is an important, but also challenging task. Here we investigate the possibility of quantifying iceberg flux with underwater noise from calving events. A relationship between the ice mass loss and impact noise associated with 169 subaerial calving events observed at Hans Glacier, Svalbard is explored through the combination of time-lapse photography and underwater acoustics. The iceberg kinetic energy at ocean impact was estimated from the images with error bounds, and all three major factors affecting the loss of acoustic energy generated by impact were also taken into account: (1) variability of the thermohaline structure in the bay, (2) complicated bathymetry along the propagation path, and (3) the contribution of the sound reflected from the underwater part of the glacier terminus. A robust correlation of 0.76 is found between the impact energy and the resulting underwater noise emission. The fraction of the kinetic energy of the falling ice block which is radiated as sound is of order of 10^-7. As we demonstrate, a simple power model can be used to quantify iceberg calving flux from the underwater noise, provided the calving inventory is large enough. The accuracy of the acoustic technique rapidly increases with the rising number of calving events analyzed, reaching 25 % for 25 ice blocks. New insight is needed on the physical mechanisms of sound production from iceberg calving to understand the variability in noise production observed between icebergs of similar mass and drop height.

[work funded by the Ministry of Science and Higher Education of Poland under ‘Mobility Plus’ program, grant 1621/MOB/V/2017, and US National Science Foundation, grant OPP-1748265]