Connection between Ocean Acidification and Sound Propagation

Abstract

Ocean Ambient Noise (OAN) results from both anthropogenic and natural sources. Varied noise sources are dominant in low (LFB: 10 to 500 Hz), medium (MFB: 500 Hz to 25 kHz) and high (HFB:>25 kHz) frequency bands. Mostly, LFB is dominated by anthropogenic sources. MFB that cannot spread over long ranges of sound sources contribute to the OAN. Ocean is an exceptionally noisy place. Ocean acidification (OAc) from rising Carbon dioxide (CO 2 ) levels will result in decreased sound absorption and therefore, amplified levels of OAN. Carbon dioxide spewed into the atmosphere by burned fossil-fuel which dissolves in the seawater causes more acidic condition in oceans which has strong connection between chemical oceanography and sound propagation. As the ocean becomes more acidic, sound absorption at LFB decreases and acidic oceans would result in significant decreases in ocean sound absorption. In the recent years, the acoustic environment of oceans has reacted to transformations in both natural and anthropogenic impacts. Greenhouse gases concentrations, especially CO 2 , rises in atmosphere due to industrial revolution. CO 2 dissolved in the seawaters deposited in two major forms (carbonate and bicarbonate), which both lead to decrease pH of surface waters. Over the last 400 million years, pH of oceans has been stable around 8.2 globally. Latest investigations suggest that global pH is around 8.1 globally and various general oceanic circulation models (GOCM) calculate that, emissions could reduce ocean pH by a degree between 0.4 units (according to moderate approach) and 0.7 units (according to an aggressive one) by the end of this century. This article discusses the CO 2 considerations both in the atmosphere and hydrosphere which are directly related with seawater pH and oceans noise levels.

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