The soundscape beneath the ocean’s waves seems like it would be quite peaceful, punctuated mainly by the noise of whales and fish and the hum of passing ships. But quiet is far from what you’ll hear near the melting ice in glacial fjords, according to a study out of University of Alaska Fairbanks.
Through underwater recordings of three bays in Alaska and Antarctica, researchers have discovered that the areas where glacial ice flows into the sea and melts are the noisiest places in the ocean. No other sources, including weather, fish and machines, make as much sound as melting does, the researchers found.
And the bulk of the sound isn’t just coming the colossal crashes of ice calving from a glacier into the ocean, as one might expect. Such events are infrequent enough to not be the primary source of noise, say scientists. Instead, the team found that the main perpetrator of the commotion is air—in particular, its behavior as it bubbles to the surface upon being released by melting ice. Reports Sid Perkins at Science:
The team’s experiments suggest that the noise isn’t caused by bubbles rising through water or popping when they reach the surface. Instead, the main source of the clamor occurs when bubbles disengage from the melting glacier and suddenly spring back into their original spherical shapes after thousands of years of being squeezed by the ice.
How might this cacophany affect marine animals? The study’s authors say the finding raises questions about how marine animals might use the sounds in their daily struggle for survival. (Although glacial melt's often associated with current-day climate change, it's not exactly new.) The researchers hypothesize that harbor seals in search of breeding grounds may seek out noisy areas to help camouflage their movements from predators like killer whales. To some animals, lots of sound can equal safety.
What is newer to the era, however, is the rapidity with which glaciers melt. As climate change progresses and more glaciers retreat onto land, the lack of ocean noise may spell all kinds of big trouble for marine life and sea birds.
Lead author Erin Pettit points out that glacial retreat and its resulting silence may be partly to blame for declining harbor seal populations in many fjords. At Alaska’s Glacier Bay National Park, for instance, scientists recorded a staggering 75 percent decline in seal numbers between 1992 and 2002. (And that downward trend has continued.)
The research team plans to continue studying underwater noise levels in hopes of developing a way to use them to predict glacier melt, work that could one day go towards helping seals and other animals cope with the environmental changes.