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Hear Ye, Hear Ye: Ocean Acidification and Ocean Noise
Volume 14, Number 23: 8 June 2011

Writing in the Journal of the Acoustical Society of America, Reeder and Chiu (2010) say "it has been reported that, given a 0.3 reduction in pH, from 8.1 to 7.8, a reduction in the acoustic absorption at low frequencies could result, suggesting a significant increase in ocean noise," while more recently, "it has been suggested that low-frequency sound will travel farther due to the ocean pH reduction expected by 2050," and most recently, it has been suggested that "in an ocean more transparent to sound, the resultant changes in propagation range will be noticeable in the operation of scientific, commercial and naval applications that are based on ocean acoustics."

But in a world where new bad consequences of earth's rising atmospheric CO2 concentration are invented almost daily, one has to ask oneself: Is this really so? And, fortunately, Reeder and Chiu did just that ... and much, much more. They reviewed "the fundamental principles of acoustic transmission loss in the ocean and how the multiple transmission loss mechanisms impact ocean noise levels within the context of changing ocean pH," after which they conducted "an analytical analysis involving physical and empirical models of all relevant transmission loss mechanisms," focusing on "three ocean acoustic environments ... to elucidate the expected change in ocean noise level from sources at the surface as a function of frequency: shallow water, the acoustic surface duct and the deep ocean."

So what did they find? The two researchers in the Department of Oceanography of the Naval Postgraduate School in Monterey California (USA) found that for even a large reduction in ocean pH from 8.1 to 7.4, there was "no observable change in ocean noise in the shallow water and surface duct environments for all frequencies -- two environments which host a large portion of the marine mammal population." They also found "a negligible change in ocean noise level in the deep water environment for all frequencies ... which also provides an upper bound to the maximum expected increase in ocean noise level due to the fact that it does not fully account for the range-dependent water column sound speed, bottom topography and distributed sources."

Putting their results into the context of average background ocean noise levels as represented by Wenz (1962) curves, they found "a statistically insignificant change compared to the inherent variability of ocean noise associated with shipping and surface-generated mechanisms." Thus, "after 250 years," as they describe it, "there would still be no significant modifications to the Wenz curves," which suggests to us that all's well that ends well. Hear ye, hear ye!

Sherwood, Keith and Craig Idso

Reeder, D.B. and Chiu, C.-S. 2010. Ocean acidification and its impact on ocean noise: Phenomenology and analysis. Journal of the Acoustical Society of America 128: 10.1121/1.3431091.

Wenz, G.M. 1962. Acoustic ambient noise in the ocean: Spectra and sources. Journal of the Acoustical Society of America 34: 1936-1956.