Satellite image of Bowdoin Glacier, with instrument locations, and bathymetry in front of the glacier with contour intervals of 25 m. Source: M. Minowa et al.

Global warming trends have accelerated glacial retreat as observed by calving and submarine melting trends. Accurate measurement of mass loss mechanisms has been challenging, as available methods that gauge volume based on satellite image analysis provide low temporal and spatial resolutions and do not allow continuous monitoring. An international research team demonstrated a more direct measurement method based on calving-generated tsunami signals recorded with a pressure sensor for estimating glacier calving flux.

An underwater pressure sensor capable of recording 20 measurements per second was placed in front of the Bowdoin Glacier, a calving glacier terminating at the head of Greenland’s Bowdoin Fjord. The sensor recorded calving-generated tsunami waves measuring 10 cm to 1 m high. The data was then compared with high-resolution images of the glacier front taken by unmanned aerial vehicles and with images from a time-lapse camera to determine a relationship between calving events and tsunami-wave properties.

A positive correlation between the volume of calving ice and wave amplitude was observed, and the analysis confirmed that the distance to calving events can be measured with a single pressure sensor from a frequency dispersion of water waves. The measurements were used to estimate the temporal and spatial distribution of icebergs that broke off during the study period, and the estimated volume of calving ice was also compared with the speed the glacier was flowing, the tides and air temperature fluctuations.

Calving volume was shown to be higher at sites where meltwater rises from the bottom of the glacier to the sea surface. The calving volume, or rate, was greater during periods of fast ice flow, high air temperature and at falling/low tide. A satellite image analysis showed calving events caused only 20% of the mass loss at the glacier front, suggesting 80% of the ice mass loss was caused by submarine melting.

The study conducted by researchers from Universidad Austral de Chile, Hokkaido University (Japan), ETH Zürich, University of Tokyo and Università di Firenze (Italy) is published in Earth and Planetary Science Letters.