The Intensity, Directionality, and Statistics of Underwater Noise From Melting Icebergs

Abstract

Freshwater fluxes from melting icebergs and glaciers are important contributors to both sea level rise and anomalies of seawater salinity in polar regions. However, the hazards encountered close to icebergs and glaciers make it difficult to quantify their melt rates directly, motivating the development of cryoacoustics as a remote sensing technique. Recent studies have shown a qualitative link between ice melting and the accompanying underwater noise, but the properties of this signal remain poorly understood.Here we examine the intensity, directionality, and temporal statistics of the underwater noise radiated by melting icebergs in Hornsund Fjord, Svalbard, using a three-element acoustic array. We present the first estimate of noise energy per unit area associated with iceberg melt and demonstrate its qualitative dependence on exposure to surface current. Finally, we show that the analysis of noise directionality and statistics makes it possible to distinguish iceberg melt from the glacier terminus melt. Plain Language SummaryRecent studies have demonstrated that impulsive underwater noise produced by tiny air bubbles released from melting glacier ice is a spectacular signal of the changing planet. A direct link between the melt rate and related noise would provide a first tool to study subsurface melting in a direct way. However, to make it possible, at first we need to better understand the properties of these sounds. To address this issue, we investigate intensity, directionality, and statistics of the melt noise. The results prove that icebergs can be automatically detected and tracked using several acoustic receivers immersed in water. Moreover, we provide the first estimate of acoustic energy produced by melting icebergs.

Monitoring Glacier Calving using Underwater Sound

“…First, we take advantage of the fact that submarine melting of glacier ice also generates underwater noise due to the impulsive release of pressurized air bubbles into the water (Urick, 1971;Deane et al, 2014;Pettit et al, 2015). Glowacki et al (2018) have demonstrated that the melt noise has an α-stable distribution. Importantly, the characteristic exponent of the α-stable distribution indicates proximity to a melting source.…”

Quantifying iceberg calving fluxes with underwater noise

“…Measurements are insensitive to lighting conditions such as fog; cloud coverage; and the polar night, humidity and intensity of precipitation. Moreover, acoustic signals recorded in glacial bays and fjords also contain signatures of ice melt associated with impulsive bubble release events (Urick, 1971;Tegowski et al, 2011;Deane et al, 2014;Pettit et al, 2015;Glowacki et al, 2018). While currently no quantitative models exist to estimate melt rates from underwater noise, the potential idea to simultaneously measure submarine melting and calving, two major processes acting at the glacier-ocean interface, is worth mentioning.…”

“…The number of beams was set to 2000, with launching angles ranging from −80 to 80 • with respect to the sea surface. Guided by previous geomorphological studies ( Görlich, 1986;Staszek and Moskalik, 2015), we assumed that the dominant sediment type in the study area is a clayey silt; density, sound speed and attenuation were taken to be 1.4 g cm −3 , 1530 m s −1 and 0.1 dB m −1 kHz −1 , respectively (Hamilton, 1970(Hamilton, , 1976. The absorption of sound in seawater is negligible for the low frequencies considered here (e.g., Ainslie and McColm, 1998).…”

Quantifying iceberg calving fluxes with underwater noise

“…Moreover, acoustic signals recorded in glacial bays and fjords also contain signatures of ice melt associated with impulsive bubble release events (Urick, 1971;Tegowski et al, 2011;Deane et al, 2014;Pettit et al, 2015;Glowacki et al, 2018).…”