海水酸化影響聲音傳導 衝擊海洋生物溝通

海水酸化影響聲音傳導 衝擊海洋生物溝通

國際環境資訊發報台
CIEREnv 2008-10-14 20:15:11
http://blog.yam.com/CIEREnv/article/17726455
水質保護_20081006_Tehran Times

石油與煤炭燃燒時產生的二氧化碳，不只加劇陸地上的空氣污染，也可能形成海裡的噪音污染。根據美國加州蒙特瑞灣水族研究學會的最新研究指出，過去10年來石化燃料產生大量的二氧化碳，其中約有40％為海洋所吸收，因此造成海水酸度增加，使人類在海中製造出的中、低頻聲音更不易為海水吸收，因而得以傳導得更遠。此波段的聲音主要由工業活動或船隻所產生，正好也是鯨魚、海豚等海洋生物用以搜尋食物或溝通的頻率，此外，近年來人類產生的噪音與日俱增，都將對海洋生物的溝通造成影響。


http://www.tehrantimes.com/index_View.asp?code=179327

Pollution makes oceans noisier

The ocean may soon begin to sound more like New York City to dolphins and whales.

As carbon dioxide levels rise and make the world's oceans warmer and more acidic, the increasing amounts of the gas could also make the seas noisier, especially in the soprano range, a new study suggests.

The increased burning of fossils fuels such as coal and oil in the last few decades has injected more and more carbon dioxide into the Earth's atmosphere. The oceans absorb a large chunk of this extra carbon dioxide (about 40 percent).

The more carbon dioxide that water absorbs, the more acidic it becomes; this is why sodas, with their carbon dioxide bubbles, are acidic. This change in seawater chemistry alters the way sound moves through the ocean, allowing it to propagate farther, particularly for sounds two and a half octaves above ""middle C,"" said researcher Keith Hester of the Monterey Bay Aquarium Research Institute in California.

The pH of a liquid is gauged on a scale of about -1 to 14, where 7 is neutral. Anything above that is basic (for example, household bleach has a pH of about 13), anything below is acidic (lemon juice has a pH of about 2). The standard pH of ocean water is about 8.3, or slightly basic/alkaline.

The Intergovernmental Panel on Climate Change (IPCC) estimates that the pH of ocean waters has decreased by about 0.02 units per decade over the last 20 years. The most conservative projections of the IPCC suggest that the pH of seawater could drop by a total of 0.3 units by 2050.

Not only does this increasing acidity threaten the ocean food chain by hampering the formation of shells and corals, it could also affect the communication of marine mammals by changing the way sound travels through the seawater. Essentially, the more acidic seawater gets, the farther sound travels in it. Sending sound farther

While the interactions causing this phenomenon aren't completely understood, chemists do know that seawater of different pHs absorbs specific frequencies differently. The more acidic that seawater is, the less low- and mid-frequency sound that it absorbs, letting those frequencies travel farther. With sounds traveling farther, the level of noise in the ocean will increase, Hester and his colleagues found in their study, detailed in the Oct. 1 issue of the journal Geophysical Research Letters.

Hester's calculations predict that the change in chemistry will have the greatest effect on sounds below about 3,000 cycles per second (or about two and a half octaves above ""middle C"" on the piano).

This range includes most of the frequencies that marine mammals, such as whales, use to communicate to find food and mates, as well as many of the underwater sounds generated by industrial activity and ships. (This human-generated noise has also increased in recent years, with evidence that it is affecting marine mammal communication.)