UW News

March 27, 2015

UW-built mic records noisy glacier melt

UW News

One would imagine a glacier’s melt to be fairly quiet. That would be wrong. Recordings by current and former University of Washington researchers in fjords shows that melting at glacier edges in the narrow rock-edged canyons are some of the noisiest places in the sea.

The study, published in Geophysical Research Letters, recorded the sound near glacier tongues in narrow fjords in the Arctic and Antarctica. The sounds were louder than any natural or human-generated ocean noise, at least within the audible frequencies of about 300 to 20,000 vibrations per second.

people in boat with ice in background

Researchers deploy the UW-built underwater microphone (inside the structure at the edge of the boat) in Icy Bay, Alaska.J. Nystuen / UW

First author Erin Pettit, now on the faculty of the University of Alaska Fairbanks, did her doctorate and postdoctoral work studying glaciers in the UW’s Department of Earth and Space Sciences. She’s a Seattle native and a third-generation Husky.

This project brought Pettit back in contact with her alma mater. A colleague suggested she contact UW’s Jeffrey Nystuen, an oceanographer at the Applied Physics Laboratory who developed a hardy instrument to record sounds from marine mammals, tropical cyclones and rainfall in the open ocean.

“Tidewater glaciers, ones that reach the fjord water, are tricky to study,” Nystuen said. “Erin is pushing the envelope, and I’m encouraging her.”

For this experiment, they installed Nystuen’s underwater microphones to record the noise around a melting glacier tongue. Pettit, Nystuen and Applied Physics Laboratory engineer Eric Boget made several trips to Alaska’s Icy Bay in 2009 and 2010 to install the instruments. They were placed more than 200 feet below the surface in an Alaskan fjord, where they recorded an average noise level of about 120 decibels throughout the year, or about as loud as a power saw.

Most of the cacophony comes from air bubbles released by the melting ice that pop once they enter the water. Pettit said she wasn’t entirely surprised to learn of the din.

“Anyone who has taken a boat ride or kayaked near glaciers and icebergs knows that they constantly pop and sizzle,” Pettit said.

The study detected a wide range of tones, spanning 300 to 20,000 hertz (cycles per second). Pettit has several other devices now recording in a Greenland fjord and hopes to place more in Alaska and Antarctica. She said she hopes the findings will inspire biologists to study how ambient sound affects marine mammal behavior.

Nystuen joked that his lack of biological expertise leaves him free to speculate on how the sound might affect animals.

“Icy Bay has a huge harbor seal colony, and orcas, who eat seals, have never been observed there,” he said. “Orcas echolocate for food using a frequency of 12,000 to 20,000 hertz – the frequency range that melting ice is particularly loud.”

Nystuen believes seals may be take advantage of how the sound of melting ice blocks the predatory orcas’ ability to navigate, adding that there is a research opportunity to prove it.

During her time as a UW grad student, Pettit founded a program called Girls on Ice that now runs expeditions in Washington state and Alaska. Each tuition-free trip matches nine teenage girls with three scientists and mountain guides for a 12-day trip to experience the wilderness and learn about glaciers. Maybe some of those trips will now include earplugs.