Jurassic Acoustics: Global Warming May Take the Low Frequency Sound Transmission Properties of the Ocean Back to the Age of the Dinosaurs
David G. Browning email@example.com
139 Old North Road
Kingston, RI 02881-1418
Peter M. Scheifele firstname.lastname@example.org
University of Cincinnati, Dept. Communication Sciences
3202 Eden Road, P.O. Box 670379
Cincinnati, OH 45267-0379
Popular version of paper 2aUW14 presented at the 164th ASA Meeting, 2012 in Kansas City, Missouri.
During global warming, the major culprit, carbon dioxide, gets absorbed in seawater, causing oceans to become more acidic, hence the term ocean acidification. Surprisingly there is a link between this process and sound transmission in the ocean. The rate at which low frequency sound is absorbed in seawater, thus determining how far it will be able to travel, is determined by a chemical reaction, involving the element boron, whose effect decreases if the seawater becomes more acidic. In other words, if the ocean becomes more acidic low frequency sound, like a whale calling, will be able to travel further. Based on estimates of acidification (ref.1), we anticipate that by the year 2100 low frequency sound near the ocean surface might travel significantly further than at present.
How does this compare with the past? By analyzing the boron in ocean sediments scientists (ref.2) have been able to determine how acidic the ocean has been all the way back to 300 million years ago. We can then use this data to determine the low frequency sound transmission. It turns out that 300 million years ago the sound transmission in the ocean was quite similar to what we have today. It then improved as the ocean became more acidic, there must have been an abundance of carbon dioxide, reaching its best value around 110 million years ago – in the Age of the Dinosaurs – allowing low frequency sound to travel twice as far.
From then to near the present time there is a gradual decrease in sound transmission – but now indications, attributed to global warming, are that the trend has turned again and seawater acidity is indeed increasing again. Predictions of the change in ocean acidity suggest that in the future we may well be back to the same conditions for sound transmission in the ocean that occurred when dinosaurs roamed the land.
1. “Ocean acidification due to increasing atmospheric carbon dioxide”, The Royal Society, Policy document 12/05, June 2005. ISBN 0 85403 617 2 www.royalsoc.ac.uk
2. “The Geological Record of Ocean Acidification”, Barbel Honisch et al., SCIENCE, vol.225, 1058-1063, 2 March 2012.