Man-made din is filling the world’s oceans, and some say harming marine life.
High profile whale beachings have been linked to sonar blasts and sparked fierce public debate over the military use of sound for defence. But a broader concern for scientists are the rising levels of ocean background noise, much of it generated by commercial shipping and whether it interferes with the way the entire sea has operated for eons.
Hearing is the primary sense for marine life, which uses sound for navigation and communication. Some scientists believe the spreading “acoustic smog” is essentially blinding marine life, affecting feeding, breeding and other crucial activities.
“Their world is just being collapsed,” said Christopher Clark, a Cornell bioacoustics scientist. “They rely so heavily on sound. They can’t see anything.”
Despite concerns, evidence is scant of the real effects of sound.
Even with new technology, ocean animals are hard to track, and drawing conclusions about how sound influences their behaviour is difficult. No system exists to monitor ocean sounds worldwide, and the data that’s collected is often taken from a small number of sites that measure only certain frequencies. Underwater sound also seems to affect different animals in completely different ways.
Businesses and the military are unlikely to make major changes before more is known.
Brandon Southall, an acoustics researcher at the National Oceanic & Atmospheric Administration, said better research is urgently needed.
“People are inherently tied to the ocean for food, for cures to diseases, for weather,” he said. “We’re figuring out things are more interconnected than we ever could have originally envisioned.”
Sound, which is created when molecules collide, carries farther and five times faster in water than air because of water’s density. Since molecules in water are spaced closer together, they lose less energy before colliding with other molecules and sound is transferred more quickly and efficiently.
Through the ages, marine animals have learned to take advantage of the ocean’s natural sound stages. Whales, for instance, talk about basic things like where the best food or breeding is. They even seem to compete to produce the most intricate songs.
Some animals use the ocean’s natural “sound channels” to communicate over thousands of miles. The channel is created where dropping temperatures, which force sound waves downward, meets increasing water pressure, which forces sound waves upward. Animals have learned that at a certain depth, the sound gets caught between the two opposing forces and bounds ahead with little resistance.
Researchers suspect that dumping a cacophony of new noise into this system isn’t good. Southall said there’s convincing evidence of a phenomenon called “masking,” in which the increased ambient noise drowns out natural ocean communications.
Huge increases in commercial shipping have coincided with increased ocean noise. Between 1948 and 1998, the world shipping fleet has increased from 85 million tons worth of ship weight to 550 million tons, according to figures in a 2003 report, Ocean Noise and Marine Mammals, published by the National Academies. Scientists say the background noise in the ocean has increased roughly 15 decibels in that time.
Joel Reynolds, director of the Marine Mammal Program at the Natural Resources Defense Council, said there’s evidence marine mammals are changing their sound patterns or rates which could show their normal communication has been disrupted.
Sound is perceived by ocean animals so differently that it’s almost like a different sense, making it hard to apply what we know about the effects of certain decibel levels to ocean life.
Kathy Metcalf, director of Maritime Affairs at the Chamber of Shipping in America, advocates pre-emptive steps, such as installing quieter propellers in new ships, which would reduce noise and likely benefit the industry by increasing the efficiency by which ships move through water.
“We have to treat it like any other form of pollution,” Reynolds said. “We have to regulate it to protect other things we care about.”
Clark said uncertainties can’t be an excuse to do nothing, because the damage might be done by the time the effects of noisy oceans are known. “It’s like global warming. We’re going to get one chance.” — Samina Iqbal
Avoiding latex
Thousands of items in the house, workplace and doctor’s office contain latex, states a recent issue of the Medicine Digest. Natural latex is a milky fluid produced by the rubber tree and is used for manufacturing scores of every day items. Two types of products are produced by latex; hardened rubber is used in athletic shoes, tires and rubber balls. Dipped latex is found in stretchy goods as balloons, rubber bands and gloves. Latex can cause a deadly allergic reaction in some people. It is usually the dipped latex which comes in contact with the skin and is responsible for it.
In the medical setting latex is found in gloves, as they are a very effective barrier to prevent the spread of hepatitis B. Other products include, blood pressure cuffs, stethoscopes, intravenous tubing, respirators and electrode pads.
The common signs and symptoms of latex allergy are a stuffy nose, cough, hives or rashes, itching, watery eyes and difficulty in breathing.
The most serious allergic reaction to latex is an anaphylactic reaction. This occurs immediately after latex exposure in highly sensitive persons and causes constriction of the airway tubes. Blood pressure may drop to dangerously low levels, causing unconsciousness. The other symptoms include, wheezing, confusion, slurred speech, rapid and weak pulse, blueness of the skin more at the lips and nails, diarrhoea, nausea and vomiting.
Allergy to latex can also occur after inhaling latex particles that are shed in the air. The best way to protect oneself is to avoid latex contact. — Dr Fatema Jawad
