Lake Superior is quieter than 8 decibels in winter, the same volume as steady breathing. Image: National Parks Service.
By Daniel Schoenherr
Shipping vessels make Lake Superior one of the loudest freshwater lakes in the world, but ice makes it one of the quietest during winter, a recent study reports.
University of Minnesota researchers captured Lake Superior sounds with underwater microphones placed offshore of Duluth. The sound data was then run through an algorithm to separate noises into three categories: Sounds of weather and ice (geophony), marine life (biophony) and boats and other human activity (anthrophony).
Listen to this recording of two soundscapes, contrasting quiet natural sounds from loud anthropogenic sounds. Credit: Rosalyn Putland
“It was really insightful to take a look at the soundscape of the largest freshwater port in the world,” said Rosalyn Putland, an acoustics expert at the University of Minnesota and the study’s author. Large parts of Lake Superior freeze over in the winter months, allowing Putland’s team to collect samples of data absent of anthrophony.
The winter silence isn’t only valuable to researchers. It also plays a key role in conserving the lake’s marine animals.
The behavior of Lake Superior’s fish can be affected by noise pollution, according to Allen Mensinger, a University of Minnesota marine biologist. Loud underwater noises mask other important sounds from fish, impairing their communication and the ability to avoid danger.
“It’s like walking into a loud room with machines,” Mensinger said. “You can’t hear what someone is saying on the other end.”
Putland’s team found evidence that quiet months provide marine life with time to communicate uninterrupted.
“As sounds of anthrophony increased, sounds of biophony vanished,” said Putland. “You can’t see the impact, but you can definitely hear it.”
The algorithms developed through their research could be revolutionary in future studies of marine life, said Jay Austin, a University of Minnesota physics and astronomy professor.
“The ability to pick out sounds of fish from a recording makes tracking populations so much easier. The potential is incredible.” said Austin.