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Melting icebergs add to ocean cacophony

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A new study has found surprisingly high noise levels in a large iceberg tracked from the time it calved from the Antarctic ice sheet until it disintegrated and melted at sea.  Three kinds of sounds dominated: early on, the iceberg scraped against the seafloor; later, it collided with another iceberg; and finally, it cracked into pieces and disintegrated within a couple of months.  At times, the sounds were loud enough to be recorded thousands of miles away, near the equator, and during one especially loud day, the sound was equivalent to that of over 200 supertankers. 

“You wouldn’t think that a drifting iceberg would create such a large amount of sound energy without colliding into something or scraping the seafloor,” said Robert Dziak, a marine geologist at OSU’s Hatfield Marine Science Center in Newport, Ore., and lead author on the study, who has monitored ocean sounds using hydrophones for nearly two decades. “But think of what happens why you pour a warm drink into a glass filled with ice. The ice shatters and the cracking sounds can be really dramatic. Now extrapolate that to a giant iceberg and you can begin to understand the magnitude of the sound energy.” 

“The breakup of ice and the melting of icebergs are natural events, so obviously animals have adapted to this noise over time,” Dziak said. “If the atmosphere continues to warm and the breakup of ice is magnified, this might increase the noise budget in the polar areas. “We don’t know what impact this may have,” Dziak added, “but we are trying to establish what natural sound levels are in various parts of the world’s oceans to better understand the amount of anthropogenic noise that is being generated.”

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