Squirting Air bubbles from Glacial Fjords Could be Used to Monitor Ice Loss in Greenland
Underwater glacial fjords create the loudest marine environment on earth as glacial ice sizzles while melting into the sea. The sounds of escaping air bubbles could be used to monitor changes caused by global warming, accordin to a study.
A fjord is a long, deep body of water that reaches inland. Fjords are often set in U-shaped valleys with steep walls on either sides. These structures can be seen in Norway, Chile, New Zealand, Canada and Greenland.
The Glacier Bay in Alaska and the Georgia Basin region of Puget Sound in Washington are also popular fjord sites. Recent research on fjords has shown that warm waters from the open oceans enter these fjords and melt glaciers at the edge of the ice-sheets.
One of the biggest ice calving events in Greenland was recently captured on camera by researchers at Swansea University in the United Kingdom. To get the Helheim Glacier melt on video, researchers had to get close to the unstable ice sheet and place cameras.
Since sound can travel long distances underwater, microphones were also used with the video recordings to monitor ice loss.
Researchers say that air gets trapped in glaciers when snow crystals pack pockets of air. These bubbles get compressed under pressure and are distributed quite evenly in the glacier ice. When ice melts, these pockets of air pop to create sounds, audible enough for the human ear.
Erin Pettit, a researcher at the University of Alaska, had often heard these sounds while kayaking near frigid northern waters.
Underwater microphones placed by researchers studying these structures also picked up a much higher level of din.
"If you were underneath the water in a complete downpour, with the rain pounding the water, that's one of the loudest natural ocean sounds out there," she said in a news release. "In glacial fjords we record that level of sound almost continually."
Pettit suspected that the sounds were made by trapped air bubbles escaping the melting ice. However, she needed a controlled experiment to prove her theory. So, she teamed up with Kevin Lee and Preston Wilson, acoustics experts from the University of Texas. Pettit sent them samples of the glacier. Lee and Wilson mounted the chunks of ice in chilled water and monitored them. They found that the audio-video recording obtained at their Texas lab matched with those obtained from the glacier site.
"Most of the sound comes from the bubbles oscillating when they're ejected," Lee said. "A bubble when it is released from a nozzle or any orifice will naturally oscillate at a frequency that's inversely proportional to the radius of the bubble," he said. Researchers recorded sounds in 1 - 3 kilohertz range, a frequency that humans can hear.
According to Pettit and Lee, sounds can be used to monitor both short-term and long-term changes in glacier activity.
The research will be presented at The 166th Meeting of the Acoustical Society of America (ASA).