A computational assessment of the sensitivity of ambient noise level to ocean acidification.

Abstract

Low-frequency (<2 kHz) sound propagating through the ocean is attenuated by the pH-dependent boric acid chemical relaxation process. This well-studied process shows that lower seawater pH results in lower sound attenuation at low frequencies. Thus, the uptake of anthropogenic CO2 by seawater, leading to ocean acidification and lowering pH of seawater, has potential to change ambient noise levels. An important question is: By how much? Here, changes in ambient noise level due to theoretical changes in seawater pH have been calculated at three different locations, the Pacific, Atlantic, and Arctic oceans, using a hypothetical spatial distribution of pH based on the literature and forecasted to the year 2100 [Cao et al., (2007); McNeil and Matear, (2006)]. A range-dependent acoustic model has been applied using sound speed and winds based on climatology, and a historical shipping database to make ambient noise level predictions. Results of our model calculations are presented and discussed.