Sound Absorption

The absorption of sound in seawater changes with the seawaters chemistry. Recent studies show that changes in ocean acidity will have an unexpected impact– it will affect how sound travels underwater. With a .3 pH unit drop (which is expected to happen by the end of the century if emissions continue unabated) sound could travel up to 70% farther underwater. The decreased absorption is especially true for sounds below 3,000 cycles per second. 1,2

Some marine mammals, including endangered blue, right and humpback whales, use low frequency sounds to communicate.  Low frequency noise is also generated by military sonar, shipping, and seismic exploration, and these human-generated sounds may interfere with whales’ ability to communicate.  When the oceans absorb less sound, these background noises can travel farther. In parts of the north Atlantic, low frequency sound absorption has decreased 15% as a result of ocean acidification.

One study conducted off of Point Sur, California found a 9 dB increase since the 1960s in a frequency range dominated by surface winds. Because there was no subsequent change in average surface winds over this time period, scientists believe ocean acidification is a factor.3

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