Soundscape contributions of glacier ice blocks – Insights from laboratory measurements

Acoustic measurements in Arctic fjords and next to marine-terminating glaciers
show important contributions from glacier melting, and individual icebergs or growlers. As they melt, they release high-pressure gases and produce sounds at medium to high frequencies. Associated to fields of hundreds or thousands of melting growlers and ice blocks, they add significantly to the soundscape. A summer 2009 survey of Murchison Fjord and Hornsund Fjord (Svalbard) by Tegowski et al. (2010) show these contributions can, even in extremely calm weather (Sea State 0), be as loud as Sea State 4. To isolate individual contributions, a series of laboratory experiments have been conducted, using growlers of different sizes and freshness. In 2012, growlers collected in Svalbard and stored on R/V Horyzont II were measured a few months later in an anechoic tank at the Technical University of Gdansk in a variety of configurations, individually and in groups of colliding and scraping icebergs. A field survey in Svalbard, in summer 2014, was used to collect another series of growlers of different sizes, aspects (e.g. bubble contents, ice colours) and morphologies (from rough to rounder and partially melted). After collection, they were immediately measured in an ad hoc tank at the Polish Polar Station, until full melting of each growler. Both sets of experiments used similar setups, with high-sensitivity broadband hydrophones and high-frequency data acquisition (96-kHz sampling rates). The acoustic pressures and energies radiated over the lifetime of the growlers were measured by 0.1-second segments. Relative levels of individual transients and evolution over the lifetimes of the individual growlers, in different configurations and with different melting rates, have been
measured. These two sets of measurements can then be related to large fields of melting ice blocks, and compared to field measurements, quantifying the soundscape contributions at different frequency bands, and offering insights into ice dynamics and local conditions.