Geophys. Res. Lett. 35, L19601 (2008)

Credit: 123RF / VINCENT LAFON

The oceans could get noisier as an unexpected consequence of climate change, suggests new research. The continued use of fossil fuels is expected to make the ocean both more acidic and warmer, with the knock-on effect that it will transmit low- to mid-frequency sounds over longer distances.

It has long been known that acidity affects how sound travels in seawater, but until now the impact of climate change on ocean acoustics has been overlooked. Scientists led by Peter Brewer at Monterey Bay Aquarium Research Institute in Moss Landing, California, calculated that if ocean acidity drops 0.3 pH units by 2050, as projected by some studies, the absorption of sound waves at 1 kilohertz and below will decline by 40 per cent. Using previous experimental and field data, Brewer and colleagues also found that between the late nineteenth century and early 1990s, absorption decreased by up to 15 per cent in response to changes in ocean chemistry. This effect occurs largely as a result of pH-sensitive changes in the balance of borate compounds, which are tuned to absorb energy from sound waves of 1 kilohertz and below in seawater.

Ambient ocean noises in the auditory range for marine mammal communication and military activity are set to increase as a result of decreased sound absorption and could travel up to 70 per cent farther underwater by 2050, say the scientists.