From: Roger Greenway, ENN
Published July 11, 2013 06:36 AM

How can glaciers calving make so much noise?

Icebergs in situ make little noise, right? What about when the calve?

There is growing concern about how much noise humans generate in marine environments through shipping, oil exploration and other developments, but a new study has found that naturally occurring phenomena could potentially affect some ocean dwellers.

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Nowhere is this concern greater than in the polar regions, where the effects of global warming often first manifest themselves. The breakup of ice sheets and the calving and grounding of icebergs can create enormous sound energy, scientists say. Now a new study has found that the mere drifting of an iceberg from near Antarctica to warmer ocean waters produces startling levels of noise.

Results of the study are being published this month in Oceanography.

A team led by Oregon State University researchers used an array of hydrophones to track the sound produced by an iceberg through its life cycle, from its origin in the Weddell Sea to its eventual demise in the open ocean. The goal of the project was to measure baseline levels of this kind of naturally occurring sound in the ocean, so it can be compared to anthropogenic noises.

"During one hour-long period, we documented that the sound energy released by the iceberg disintegrating was equivalent to the sound that would be created by a few hundred supertankers over the same period," said Robert Dziak, a marine geologist at OSU’s Hatfield Marine Science Center in Newport, Ore., and lead author on the study.

“This wasn’t from the iceberg scraping the bottom," he added. "It was from its rapid disintegration as the berg melted and broke apart. We call the sounds 'icequakes' because the process and ensuing sounds are much like those produced by earthquakes."

Dziak is a scientist with the Cooperative Institute for Marine Resources Studies (CIMRS), a collaborative program between Oregon State University and NOAA based at OSU’s Hatfield center. He also is on the faculty of OSU’s College of Earth, Ocean, and Atmospheric Sciences.

When scientists first followed the iceberg, it encountered a 124-meter deep shoal, causing it to rotate and grind across the seafloor. It then began generating semi-continuous harmonic tremors for the next six days. The iceberg then entered Bransfield Strait and became fixed over a 265-meter deep shoal, where it began to pinwheel. The harmonic tremors became shorter and less pronounced.

Glacier calving photo via Shutterstock.

Read more at Oregon State University.

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