The noisiest places found yet in the world's oceans are some of the most scenic -- saltwater fjords where glaciers drop chunks of blue-white ice, according to newly published research.
The noise was found mostly at Icy Bay, along the Gulf of Alaska coast, but also at two other sites where calving glaciers are depositing ice into marine waters.
The recordings were captured by devices placed underwater from July 2009 to July 2010 at Icy Bay, for two weeks in May 2009 at Alaska's Yakutat Bay, and for three days in May 2013 at Andvord Bay in Antarctica. The recording devices -- called hydrophones -- were attached to anchored lines and suspended about midway in the water column.
The results were surprising, said Erin Pettit, an assistant professor of glaciology at the University of Alaska Fairbanks and the study's lead author.
The noise starts with a "relatively loud background hissing sound," Pettit said. "Then you add on a not-very-good chorus of triangle players -- 1,000 triangles that aren't working at all."
Much of the noise is generated by air bubbles that are popped open as the ice melts, the researchers found. As pieces of ice calve off glaciers, more noise is added.
The noise from glacier ice at the studied fjord sites is louder than other natural underwater sounds that have been measured -- including noises from sea ice, weather and fish movement or communication. It is even noisier than what has been measured from manmade sources like ship traffic and sonar devices, the researchers said.
The constant ambient noise from the ice might be useful to animals like harbor seals trying to evade the predators that would eat them, Pettit said.
"They seem to use the noisy events as one way to hide from orcas," she said.
But that raises a question about what those prey animals will do when tidewater glaciers retreat so much that they are no longer shedding ice into marine waters, she said. Once that happens, "the sound should go down and then it will get really quiet," she said.
Already at Glacier Bay National Park, Muir Glacier has retreated far enough to stop calving, though other side glaciers continue to put ice into the marine waters, she said.
Concern about underwater noise and the impacts to marine mammals is growing as far north shipping and oil and gas exploration increases.
Noise from air guns used to conduct underwater seismic surveys -- important to oil and gas exploration -- and other manmade underwater noises tend to be at low frequencies that might affect whales and other marine mammals, Pettit said.
Seismic activities have been shown to alter the behavior of bowhead whales in the Beaufort Sea and hinder singing communications among humpback whales off Angola, for example.
In contrast, Pettit said, the noise from glacier ice, though loud, is at high frequencies, which appear to cause fewer problems for marine mammals.
"So they are not like a big boom-boom-boom that would generate a different response in the whales," she said.
In addition, the ice noise, though it waxes and wanes with seasons, ocean currents and other factors, is something of a fixture in certain areas, and animals can more easily avoid it than they can escape sudden and unexpected sounds from human activities like seismic testing, she said.
Of the studied sites, Icy Bay was the loudest, though results might be skewed by the longer period of time that recordings were made there and by the ability of the scientists to get sound recordings very close to the glacier terminus, Pettit said. The Antarctic site was the least noisy of the three sites studied.
Pettit and her study colleagues -- from the University of Texas, University of Washington and U.S. Geological Survey -- are hoping to learn more about glacier ice and the underwater noise it makes. Pettit said she has a hydrophone in place in Antarctica that has been collecting sound for three years, and there are plans to take recordings by tidewater glaciers in Greenland.