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Future ocean increasingly transparent to low-frequency sound owing to carbon dioxide emissions


Low-frequency sound in the ocean is produced by natural phenomena such as rain, waves and marine life, as well as by human activities, such as the use of sonar systems, shipping and construction. Sea water absorbs sound mainly owing to the viscosity of the water and the presence of chemical constituents, such as magnesium sulphate, boric acid and carbonate ions. The concentration of dissolved chemicals absorbing sound near 1 kHz depends on the pH of the ocean1, which has declined as a result of increases in acidity due to anthropogenic emissions of carbon dioxide2,3,4. Here we use a global ocean model5,6 forced with projected carbon dioxide emissions7 to predict regional changes in pH, and thus sound absorption, in the years 1800–2300. According to our projections, ocean pH could fall by up to 0.6 units by 2100. Sound absorption—in the range between 100 Hz and 10 kHz—could fall by up to 60% in the high latitudes and in areas of deep-water formation over the same time period. We predict that over the twenty-first century, chemical absorption of sound in this frequency range will nearly halve in some of the regions that experience significant radiated noise from industrial activity, such as the North Atlantic Ocean. We suggest that our forecast of reduced sound absorption in acoustic hotspots will help in identifying target regions for future monitoring.

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Figure 1: Sound absorption attenuation as a function of frequency and seawater pH.
Figure 2: Projected changes in the seawater pH and the sound absorption coefficient in 2100.
Figure 3: Projected changes in vertical distribution of the sound absorption coefficient.
Figure 4: Temporal evolution of seawater pH and sound absorption coefficient in acoustic hotspots.

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We thank E. Maier-Reimer for discussing the model code and J. A. Colosi for his comments on the manuscript. This research was supported by National Science Foundation grant NSF: OCE07-51959.

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All authors contributed extensively to the work presented in this paper.

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Correspondence to Tatiana Ilyina or Richard E. Zeebe.

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The authors declare no competing financial interests.

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Ilyina, T., Zeebe, R. & Brewer, P. Future ocean increasingly transparent to low-frequency sound owing to carbon dioxide emissions. Nature Geosci 3, 18–22 (2010).

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