Earlier this year, several researchers traded the relative warmth of Albuquerque, N.M., for the bone-chilling winter conditions of far northern Alaska. They made the journey to monitor pulses of laser light zipping through a strand of fiber-optic cable buried under the Beaufort Sea. These observations, part of a 3-year project, will shed light on the prevalence of anthropogenic activity in the region and how it’s responding to a warming climate.
The Burden up North
Far northern latitudes bear an unusually heavy burden when it comes to climate change—temperatures are warming there faster than they are elsewhere. Permafrost in the Arctic that’s been frozen for thousands of years is thawing, rendering topsoil unstable and priming the environment for erosion and the accompanying release of greenhouse gases. “It’s a very critical region,” said Michael Baker, a seismologist at Sandia National Laboratories in Albuquerque.
In February, Baker and several colleagues traveled to the northern coast of Alaska to study the Arctic. But rather than bring with them sensors that would need to be deployed, regularly monitored, and finally retrieved, they relied on something far more suited to the fragile, changing environment: a fiber-optic cable already buried meters beneath the seafloor. Installed in 2017, the cable is part of a telecommunications network that will eventually span from London to Tokyo. It contains 16 glass fiber-optic strands, and one of those, not currently used, is being repurposed for science.
Flaws Reveal Vibrations
Fiber-optic strands are typically used to transmit light, which encodes data. But these strands, each about as wide as a human hair, can also function as sensitive detectors of environmental change, said Rob Abbott, a geophysicist at Sandia National Laboratories who is leading the investigation. By sending pulses of laser light into a fiber-optic strand and then measuring how a tiny bit of that light is reflected back by intrinsic flaws in the strand, it’s possible to trace how different parts of it are vibrating, he said. “Those vibrations can be caused by any number of environmental, anthropogenic, or biogenic sources.”
This technique, known as distributed acoustic sensing, is gaining traction in the field of seismology. It’s also useful for monitoring active volcanoes, detecting changes in traffic patterns during the pandemic, and even picking up ground shaking caused by a parade’s floats and marching bands.
Distributed acoustic sensing is perfect for monitoring landscapes that are difficult to access or benefit from minimal human interference, said Eileen Martin, a data scientist at Virginia Polytechnic Institute and State University in Blacksburg not involved in the research. The infrastructure needs to be installed only once, and data can be collected effectively continuously, she said. That’s “a huge win for distributed acoustic sensing technology.”
Don’t Forget Anything
In early February, Abbott, Baker, and another geophysicist traveled from Albuquerque to Oliktok Point, Alaska. The journey involved four airports and a 3-hour drive on an ice road. Oliktok Point is pretty remote, said Abbott. “If you forget something back in Albuquerque, there’s really not much you can do about it.” The winter conditions were tough, too, said Baker. “We saw −44°F with −70°F wind chill one day.”
The team monitored a 39-kilometer stretch of fiber-optic cable buried under the floor of the Beaufort Sea. Over the course of 7 days, they collected observations from roughly 20,000 distinct sections of the cable. “We take data every 2 meters,” said Abbott.
The researchers have already spotted a variety of events, some environmental and some anthropogenic, in the rich data set. They’ve detected the signatures of ice quakes, a hovercraft, and ocean waves, among other processes. The team plans to return to Oliktok Point seven more times over the next 2 years to collect more data. This longitudinal view, over multiple seasons, will allow us to trace how the Arctic is changing, said Abbott. It’ll be possible to monitor the thickness and breakup of sea ice and the intensity of Arctic storms, the researchers suggest. Whale song might also show up in the data sets, said Abbott, which would allow the team to trace the animals’ migration patterns. “It’ll be in the right frequency range.”
There’s an enormous amount to learn about how the Arctic is changing, said Abbott, but doing that will require sifting through troves of data. The February trip alone yielded about 20 terabytes, he said, so data storage is something to think about. “We’re probably going to buy a half-petabyte worth of disk drives.”
—Katherine Kornei (@KatherineKornei), Science Writer