High-frequency broadband active acoustic systems as a tool for high-latitude glacial fjord research

Abstract

High-frequency broadband scientific echosounders enable the monitoring of complex dynamics, via the rapid collection of high-resolution, near-synoptic observations of the water column and quantitative geophysical measurements. Here, we demonstrate the applicability and utility of broadband active acoustics systems to improve observational capabilities in high-latitude glaciated fjords. These isolated and challenging field locations are a critical environment, linking the terminal end of terrestrial ice fields to the broader ocean, undergoing complex changes due to accelerated high-latitude warming trends. Using broadband (160-240 kHz) acoustic data, collected in tandem with ground-truth measurements from a conductivity-temperature-depth (CTD) and microstructure probe, in Hornsund Fjord in southwest Svalbard, we address the following three topics: (1) variability in the thermohaline structure and mixing across different temporal and spatial scales, (2) identification and characterization of processes in play at dangerous glacier termini, and (3) remote estimation of dissipation rates associated with mixing. Through these analyses, we illustrate the potential of broadband echosounders as a reasonably priced, relatively straightforward addition to experimental field kits, well suited for field deployment in high-latitude fjords where observations are limited by the length of season and generally challenging conditions.