A strange use for undersea fiberoptic cables: measuring sea ice
The same fiberoptic cables that are buried under the seafloor to allow for fast internet could also be used to measure sea ice coverage.
A study that was recently published in The Seismic Record, a scientific journal, demonstrated how this could be done using the existing Quintillion cable off Oliktok Point on the North Slope.
That same stretch of cable off Oliktok Point became very familiar to Nomeites this summer. It was sliced by a massive chunk of sea ice in June, cutting off high-speed internet to users in Nome, Kotzebue and other towns along the western and northern coasts of Alaska.
It wasn’t fixed until three months after the break.
This new research might not be able to help prevent another break, but the scientists hope their work might point to another tool for measuring ice formation with higher precision.
Quintillion President Mac McHale said the collaboration with Sandia National Laboratories in New Mexico started at least three years ago. The scientists at the lab and others at the University of New Mexico were curious about the kinds of environmental information they might be able to pick up using sensors that were already collecting data along the cable.
“We did not set out to do a sea ice tracking project,” said lead author of the study Andres Felipe Peña Castro, a researcher at the University of New
Mexico. “We only knew that there was a really rich data set for a lot of activity in this coastal environment.”
Fiberoptic cables send data as optical signals. They are attached to instruments called “interrogators” that can track slight vibrations along the undersea line by sending pulses of light into the cable and measuring the energy that bounces back. This method is called “distributed acoustic sensing.” Using the interrogator at Oliktok Point, the researchers could probe 25 miles of the cable. Beyond that, the reflected light became too weak to measure.
Just a day’s worth of data using this method could be up to three terabytes, Peña Castro said. That’s much more data than even an average personal laptop can hold. The researchers decided to focus on the two most dominant signals they saw over a week in July 2021 and then another week in November 2021.
“Those two dominant signals were where and when along the cable we can see open water, and when and where we see the sea ice,” Peña Castro said.
The cable vibrated differently when there was open water and when there was ice on top of the surface.
Peña Castro said he didn’t realize how quickly ice can appear. He saw in data from November that an area open water froze in a span of 12 hours. Satellites regularly monitor sea ice formation, but they might miss such quick events if they only pass the same spot once a day.
Researchers have previously suggested that an array of seismic stations, in conjunction with satellite data, could be used to monitor sea ice formation with more precision. But installing such an array would likely be too expensive. Using the internet cables that are being deployed on the Arctic seafloor could be a viable alternative, Peña Castro and colleagues wrote in their paper.
The method has limitations, though. The team could only detect the presence of sea ice along the cable, not how far the sea ice is present perpendicular to the cable. In theory, this method might also be useful for measuring ice thickness, the researchers said, but first it would have to be validated with another data set. And precise ice-thickness measurements can be hard to find.
McHale said that Quintillion was interested in these findings.
“We will definitely open the conversations with them to see what kind of data we can get that can help us monitor and be aware of activity in the area,” McHale said.
He added that more data could help the company make informed decisions. At the same time, he cautioned that events like an ice scouring might be hard to predict.
“This was a very strange occurrence that happened,” McHale said. “Who could predict the next earthquake? Or who could predict the next landslide? That’s just difficult to do.”