Loudest industrial ocean noise pollution

The loudest industrial sources of human-made ocean noise are the compressed-air guns used as sound sources in oil-industry seismic surveys. These devices use high-pressure gas to instantaneously blast out a bubble under water, a process that produces an extremely loud noise. These guns are arranged into tuned arrays which allow the sound of many different devices to merge into a single, much louder burst of noise. The volume of these blasts has been calculated to be 260 dB (re 1 μPa) at its point of origin.

The effects of seismic airguns on marine life is an ongoing subject of study, both in terms of their immediate and long-term effects. In fish, airgun blasts have been shown to cause temporary hearing loss in some species, and some evidence suggests that fish vacate areas where airguns are active. Another potential negative effect comes from what's called "masking", where the sounds of an airgun array (or other high-intensity anthropogenic noise) covers up the natural sounds that fish need to be able to hear.

In marine mammals, noise from seismic airguns has been shown to trigger a range of responses, including changes in vocalizations, diving patterns and migration movements. Some species of whale, for example, have been observed shifting the rate and volume of their calls in response to airgun usage (like a person shouting in a loud bar), while others appear to avoid areas where they have experienced loud noises in the past.

Another significant source of ocean noise is military sonar, which typically uses pulses of sound that have been measured at 235 dB (re 1 μPa at 1 m). Sonar creates noise over a much narrower bandwidth than airgun arrays, however, with only around 30 Hz between the lowest and highest frequencies.