Acoustics Meets Global Warming: The impact of ocean acidification on underwater sound

The principal cause of the absorption of low frequency sound in seawater is a chemical relaxation that is pH dependent. The predicted increases in ocean acidification could reduce low frequency absorption by a factor of 2 or more. Increased acidification would start at the surface and, over a significant duration, evolve down the water column, the sound channel axis depth being 1,000 meters or more in many ocean locations. However, when a surface duct propagation mode exists, and all the ``players'' (ship and wind generated noise, transiting marine mammals, etc.) are located in it, the impact would become noticable much sooner. Acoustically it should be a mixed bag; reducing propagation loss and thus raising vocalization levels while at the same time increasing the background noise.