Ocean acidification and its impact on ocean noise level: An analysis using empirical and physical models of acoustic transmission loss.

Abstract

Over the next several hundred years, ocean acidification is expected to reduce average ocean pH. It has been reported that, given a 0.3 reduction in pH from 8.1 to 7.8, a 40% reduction in the acoustic absorption coefficient at low frequencies (less than 1 kHz) could result, suggesting a significant increase in ocean noise. Such extrapolations are based on the corresponding percentage change in the absorption loss only and ignore other dominant acoustic energy loss mechanisms, such as seabed attenuation, as well as the effect of ocean waveguide physics and the depth dependence of ocean pH. Presented here is an analysis of the impact of the reduction in ocean pH on ocean noise level using empirical and physical models of acoustic transmission loss. Three ocean acoustic environments are analyzed to elucidate the expected change in ocean noise level as a function of frequency: shallow water, a surface duct, and the deep ocean. Results show a negligible change in ocean noise in the shallow water and surface duct environments for all frequencies. In the deep ocean, the maximum change in ocean noise level occurs at approximately 2 kHz, with no significant change below 800 Hz.