Passive measurements of marine seismic reflection surveys using Ocean Observatories Initiative hydrophones

The Ocean Observatories Initiative (OOI) provides continuous monitoring of acoustic fields at various locations in the northeast Pacific Ocean, among other types of data. The effects of marine seismic reflection surveys on the ambient soundscape in the vicinity of these hydrophones can be quantified by looking at OOI hydrophone data in conjunction with cruise documentation. Two seismic reflection surveys, MGL1905 and MGL2104, and measurements on three hydrophones at varying depths with 64 kHz sampling rates are considered. The seismic air guns are exhibited to raise the mean ambient sound by up to 30 dB over several one-third octave bands, where the impact varies significantly as a function of range, depth, and other factors. Effects can be observed hundreds of kilometers from the air gun arrays, and shots may be frequent enough that the ambient sound does not return to its pre-cruise background levels between shots. Although range is strongly correlated with these effects, metrics, such as sound exposure level or sound pressure level, can easily vary by 10 dB or more at the same range.