Characterization of marine seismic survey inter-pulse sound field in an Arctic shallow-water environment

In this study, we analyzed continuous acoustic recordings collected from a bottom-mounted hydrophone deployed in coastal shallow waters of the U.S. Beaufort Sea during a marine seismic survey in the summer of 2012. Two quantitative methods were developed to compare the inter-pulse sound field, defined as the acoustic field between two consecutive airgun pulses, with the ambient noise level. Results show that during periods when seismic airguns were active, inter-pulse sound field could exceed ambient noise levels by as much as 9 dB. Kolmogorov-Smirnov two-sample tests between inter-pulse sound levels and ambient noise levels showed significant differences in median SPLs. Spectral analysis of inter-pulse sound fiend in one-third-octave bands in relation with known and hypothetical marine mammal hearing sensitivities indicates potential acoustic masking during a seismic survey, even for animals at relative far distances from a survey vessel. Degrees of acoustic masking are related to frequency-depended hearing sensitivities of marine mammals. For the endangered bowhead whales, which are most sensitive to low-frequency sounds, acoustic masking is expected to be most severe as most energy from seismic airgun pulses is below 500 Hz. These results underscore the need for further research on reverberant field of marine seismic surveys and its potential impacts on marine animals.