Application of passive hydroacoustics in the studies of sea-ice, icebergs and glaciers: Issues, approaches and future needs

Abstract

Arctic and Southern Oceans are extremely noisy places. Various geophysical and biological processes generate underwater sounds at different frequencies. Using spectral, wavelet and statistical analysis, it becomes possible to distinguish almost all individual phenomena. This allows the assessment of, among other things, the rainfall intensity, various characteristics of wind-generated waves, abundance of marine organisms and shipping traffic. These issues are now relatively well-understood. What is more, for such studies hydroacoustic methods have been widely used for many years and provided satisfactory results. In the last decades, however, more and more attention is paid to sea-ice processes and properties, calving events and drifting icebergs. Melting ice and retreating tidewater glaciers are also sources of underwater ambient noise. This becomes more and more noticeable due to the observed climate shifts. Dynamic nature of these phenomena and harsh conditions encountered during field measurements still limit the progress in this area of research. In spite of all, recent preliminary studies show the possibility of using passive acoustic methods for both analyzing calving events in the Arctic fjords and investigating the behavior of icebergs. It became possible, for instance, to identify and describe various stages of calving processes: Large rumbles, ice fractures, impacts on the water and iceberg oscillations. On the other hand, ambient noise related with freshwater outflows and sound propagation in the vicinity of glaciers are still unstudied. Moreover, underwater sounds associated with sea-ice processes occurring in small basins are also poorly understood, as well as their directivity and relationships with meteorological and oceanographic conditions. These topics require further investigation, which will enable the development of appropriate classification algorithms. For this purpose, new field experiments and methods of data analysis as well as state-of-the-art measuring devices are needed. A review of existing research articles concerning underwater cryogenic sounds is presented here, supplemented by a summary of the main gaps and suggested future needs. All papers are sorted thematically and chronologically, showing the historical development of hydroacoustic methods and approaches in this area.