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 ocean, which has declined as a result of increases in acidity due to anthropogenic emissions of carbon dioxide. Here we use a global ocean model forced with projected carbon dioxide emissions 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.
Ilyina, T., Zeebe, R. E. & Brewer, P. G., 2009. Future ocean increasingly transparent to low-frequency sound owing to carbon dioxide emissions. Nature Geoscience: doi:10.1038/ngeo719.
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