Right to Quiet Society Noiseletter
Spring 2015, page 3
< Prev 1 2 3 4 5 6 7 8 Next > Quiet Home Page
Drifting Iceberg Spins Out Ocean Tunes
By Gayathri Vaidyanathan
The sound is like ice cubes cracking in a glass of warm soda, except louder. Disintegrating icebergs generate significant noise pollution at the world's poles, affecting narwhals, whales and other aquatic life, according to a study published in Oceanography. And with temperatures rising at the poles due to climate change, the oceans will only get louder. The splitting of an iceberg over 20 minutes in the Antarctic's Southern Ocean produces enough sound energy to equal that of 214 supertankers, according to the study.
"Sound from ice breakup in the Southern Ocean can be significantly greater than anthropogenic noise sources and thus are a major contributor to the overall ocean noise budget," the authors state. It had been assumed so far by oceanographers that the loudest noises in the oceans of the Arctic and Antarctic are generated by direct human activity, such as the sonic booms emitted by vessels exploring for oil, by shipping traffic, and sonar.
Scientists have previously listened in on icebergs running aground and scraping against the sea floor. But this is the first time that an iceberg's final moments before disinte-gration have been documented in sound. Between April and June 2007, the A53a iceberg was drifting in the Weddell Sea of Antarctica when it hit a shoal. Robert Dziak of Oregon State University and his colleagues had installed an array of hydrophones in the area, and they were able to listen in to the sharp bursts of sound called harmonic tremors the iceberg made as it spun.
By July, the iceberg got free of the shoal, and floated north into the warmer Scotia Sea where it started melting. Melt ponds appeared on the surface, a sure sign it was disintegrating. By September, it was no more. Researchers were most interested in these final moments of A53a. They recovered the data from the hydrophone array and listened to the sounds, called icequakes. It was entirely different from harmonic tremors of an iceberg running aground.
Since sound is a form of energy, Dziak was able to calculate the energy flows through the ocean over a 20-minute period, which equalled the sound energy generated by 214 ships. A number of aquatic mammals are affected by noise pollution. At the poles especially, the oceans are usually so quiet that the animals are not habituated to anthropogenic noise.
For example, when there is a blast of sound in the Arctic, narwhals go out of their way to avoid the source during their annual migrations. Sometimes, the route change takes them into waters that are not quite out of winter leading to flash freezing of the animals in ice. A number of such ice entrapment events have been recorded in recent years.
website link to article
Monitoring and modelling sound levels at landscape scales
in US National Parks
Kurt Fristrup1 *, Damon Joyce1, Emma Lynch1, Megan Mckenna1, Daniel Mennitt2
(1) U. S. National Park Service (NPS), 1201 Oakridge Drive, Suite 100, Fort Collins, CO 80525, United
(2)Colorado State University (CSU), Electrical & Computer Engineering Colorado State University
Engineering, Room B104, 1373 Campus Delivery Fort Collins, CO 80523, United States
* Corresponding author
NPS has pursued a program of acoustical monitoring to inventory existing conditions in parks throughout the NPS system to estimate natural sound levels and evaluate the costs of noise to both wildlife and visitor experience. Acoustic data have been collected at over 300 sites within 73 parks. The NPS recently created a predictive map of sound levels throughout the contiguous U. S. by fitting geospatial data related to sound sources and propagation to the acoustic monitoring data.
These maps include predictions of existing and natural sound levels for A-weighted summaries and one-third octave spectra. The acoustic data were also analysed for broad patterns in bioacoustic activity that relate to ecological and seasonal variables, and visitor use.
To evaluate the human costs of noise, the NPS pursued measurement and modelling of the duration of audible noise using one-third octave spectrum levels. The median hourly percentage of noise audibility across all sites within park units is about 25%. Audibility analysis is complemented by evaluating the masking effects of noise, seeking to preserve opportunities for visitors to appreciate the rich auditory experience that is vital to many wildlife species, and to establish a framework for evaluating costs of noise that generalize across species.
Through partnerships, NPS has produced a standard for sound level measurement in parks and quiet rural areas, and sponsored studies of noise impacts to wildlife and visitor experience. Collectively, these efforts inform park managers and the public about the value of natural acoustic environments and the costs of noise.
Entire contents 2015 Right to Quiet Society. Cartoon, 1996, Right to Quiet Society
< Prev 1 2 3 4 5 6 7 8 Next
Right to Quiet Home Page