December 21, 2009
Noise From Oceans Louder Due To Pollution
A study published by U.S. scientists on Sunday said pollution has caused the world's oceans to become noisier, causing more harmful effects to whales, dolphins, and other marine life.
These effects include death and serious injury caused by brain hemorrhages or other tissue trauma, strandings and beachings, temporary and permanent hearing loss or impairment, displacement from preferred habitat and disruption of feeding, breeding, nursing, communication, sensing and other behaviors vital to the survival of these species.
An increase in motorboats, primarily commercial shipping traffic, exploration and extraction of oil and other minerals, sonar and even coastal jet ski traffic are contributing to the increased level of underwater noise.
Man-made sounds are drowning out the calls of mates, calves and other pods that these mammals depend on.
The report, published in the science journal Nature, stated that the sound is absorbed mainly through the viscosity of the water and the presence of certain dissolved chemicals.
But the concentration of chemicals that absorb sound in the oceans has declined as a result of ocean acidification, in turn caused by rising concentrations of carbon dioxide.
Scientists say with the number of ships doubling over the past 40 years, levels of carbon dioxide have risen dramatically.
This causes pH levels to drop and acidity in the oceans to increase.
They found that the increase in acidity could reduce seawater sound absorption by as much as 60 percent by 2100 in high latitude oceans.
One of the negative effects of the increased acidity is the reduced rate of calcification, such as that seen in coral reefs.
The authors say, "However, a less anticipated consequence of ocean acidification is its effect on underwater sound absorption."
"A decrease in seawater pH lowers sound absorption in the low-frequency range and, as a result, leads to increasing sound transmission," they added.
The study said future global warming may further decrease the ocean's sound absorption capacity at certain frequencies.
"High levels of low-frequency sound have a number of behavioral and biological effects on marine life," it added.
The effects of noise pollution are not as easy to notice as are the other more obvious and visible pollutants like oil spills and marine debris. To what extent these manmade sounds are negatively impacting the oceans is not fully known.
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