Influence of ice concentration and thickness on under-ice ambient noise levels in shallow coastal waters of Liaodong Bay, China

Abstract

Underwater noise levels may be strongly influenced by sea ice. This study presents systematic measurements of under-ice ambient noise levels in shallow (<30 m) coastal waters using passive acoustic technology. Acoustic data were collected at 6 sites with different ice concentration (two levels: incomplete and complete ice cover) and thickness (three levels: <10 cm, 10–20 cm and >20 cm) in Liaodong Bay, China. Wind (max = 5.3 m/s) and current (max = 0.3 m/s) conditions were very weak, making minimal contributions to under-ice noise in this study. Root-mean-squared broadband (20–10,000 Hz) noise levels (BNLs) and one-third-octave-band noise levels (TOLs) at 63, 125 and 2000 Hz were measured. Median BNLs of the 6 recording sites ranged from 104.5 to 129.1 dB re 1 μPa, and median TOLs at 63, 125 and 2000 Hz were between 76.5 and 118.0 dB re 1 μPa at the 6 sites. Generalized Linear Models were used to analyze broadband and three one-third-octave-band noise levels in different ice concentration and thickness levels. The results showed that, regardless of the ice thickness, the sites with incomplete ice concentration had higher BNLs and 63, 125 and 2000 Hz TOLs than the sites with complete ice concentration, and regardless of the ice concentration, both BNLs and all three TOLs decreased with increased ice thickness. This study provides baseline characterization of under-ice noise in shallow coastal waters and indicating that both ice concentration and thickness have significant influence on the under-ice noise levels. These findings are important for future studies investigating acoustic communication and noise pollution in shallow coastal waters with sea ice.