Global warming may give oceans the ‘sound’ of dinosaur-era

Global warming may give oceans on Earth the same hi-fi sound qualities they had more than 100 million years ago, during the ‘Age of the Dinosaurs’, a new study has found.

New research suggests that global temperatures directly affect the acidity of the oceans, which in turn changes the acoustical properties of sea water.

The reason for this surprising communication upgrade is that whales vocalise in the low-frequency sound range, typically less than 200 hertz.

The study predicts that by the year 2100, global warming will acidify saltwater sufficiently to make low-frequency sound near the ocean surface travel significantly farther than it currently does — perhaps twice as far.

Researchers led by Rhode Island acoustician David G Browning will present the findings at the 164th meeting of the Acoustical Society of America (ASA), between October 22 and 26 in Kansas City, Missouri.

“We call it the Cretaceous acoustic effect, because ocean acidification forced by global warming appears to be leading us back to the similar ocean acoustic conditions as those that existed 110 million years ago, during the Age of Dinosaurs,” Browning said in a statement.

Their work builds on the recent investigation by other researchers who analysed historic levels of boron in seafloor sediments to reconstruct ocean acidity for the past 300 million years.

Using boron’s sound absorption traits and impact on low-frequency transmission, Browning and his colleagues were able to predict the soundscape of ancient oceans to conclude that 300 million years ago, during the Paleozoic, the low frequency sound transmission in the ocean was similar to conditions today.

They also found that transmission improved as the ocean became more acidic, reaching its best transmission value around 110 million years ago, allowing low frequency sound to travel twice as far.

“This knowledge is important in many ways,” said Browning.

“It impacts the design and performance prediction of sonar systems. It affects estimation of low frequency ambient noise levels in the ocean,” Browning said.

The Hindu Business Line, 19 October 2012. Article.

1 Response to “Global warming may give oceans the ‘sound’ of dinosaur-era”

  1. 1 Scott Doney 23 October 2012 at 03:46

    Lowering pH due to ocean acidification does indeed lead to a reduction in the in-situ absorption of sound in seawater through changes in the acid-base chemistry of boric acid (Brewer and Hester, 2009). This led to earlier speculations that over the 21st century that there could be an increase in the acoustic noise environment in the ocean and effects on marine mammals (Brewer and Hester, 2009; Ilyina et al., 2010). In-situ sound absorption, however, is only a minor component of the loss or damping mechanisms for acoustic signals in the ocean that are dominated by surface and bottom boundary interactions. A series of papers demonstrated that pH changes will have only minimal impact on ocean noise levels compared to other environmental and human factors (Joseph and Chiu, 2010; Reeder and Chiu, 2010; Udovydchenkov et al., 2010).

    Brewer, P. G., and K. Hester, 2009: Ocean acidification and the increasing transparency of the ocean to low frequency sound, Oceanogr., 22, 86–93.
    Ilyina, T., R.E. Zeebe, and P.G. Brewer, 2010: Future ocean increasingly transparent to low-frequency sound owing to carbon dioxide emissions, Nat. Geosci., 3, 18–22.
    Joseph, J.E., and C.-S. Chiu, 2010: A computational assessment of the sensitivity of ambient noise level to ocean acidification, J. Acoust. Soc. Am., 128(3), EL144-EL149.
    Reeder, D.B., and C.-S. Chiu, 2010: Ocean acidification and its impact on ocean noise: Phenomenology and analysis, J. Acoust. Soc. Am., 128(3), EL137-EL143.
    Udovydchenkov, I.A., T.F. Duda, S.C. Doney, and I.D. Lima, 2010: Modeling deep ocean shipping noise in varying acidity conditions, J. Acoust. Soc. Am., 128(3), EL130-EL136.

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