Fiber optic cables used to track effects of Arctic climate change

By James Gamble via SWNS

Fiber optic cables are being used for the first time to track the effects of climate change in the Arctic.

The American researchers are using the cables to determine permafrost temperatures under the seafloor and monitor temperature changes over the seasons.

The study team utilizes acoustic and temperature data from the cables to measure the seismic structure of miles of Arctic seafloor.

In tracking these elements, the scientists hope they may be able to identify 'seeps' of carbon-rich fluids which are an indication of warming and change.

The climate of the remote and harsh Arctic is changing extremely quickly - warming around four times faster than the rest of the planet.

This makes studying the region both challenging and vital for understanding global climate change.

Scientists at Sandia National Laboratories (SNL) have now turned towards using an existing fiber optic cable off Oliktok Point on the North Slops of the American territory of Alaska to track the conditions of the Arctic seafloor up to 20 miles from shore.

The study team's goal is to determine the seismic structure of miles and miles of Arctic seafloor.

Using a new acoustic technique, the researchers are able to spot areas of the seafloor where sound travels faster - typically a sign of more ice.

Applying this method using the existing fiber optic cable, they have identified several such areas with lots of ice.

Scientists have also begun using the cable to determine temperatures over the same stretch of the seafloor and monitor temperature changes over the seasons.

These data, unlike any collected before, were inserted into a computer model to predict the distribution of submarine permafrost.

“One of the innovations of this project is that we can now use a single fibre to get acoustic and temperature data,” project lead Christian Stanciu said.

The SNL geophysicist explained: “We developed a new system to remotely collect both types of data using one fiber strand.

"We’re getting some interesting results."

Much like leftovers shoved into the back of a freezer, Arctic permafrost is a dormant banquet waiting to be thawed.

As the once-living matter thaws - having been frozen during the last ice age up to 115,000 years ago - microbes begin to digest it and produce pollutive waste gases such as methane and carbon dioxide.

The SNL team, who have been collecting climate data from northern Alaska for more than 25 years, are now able to study just how large a microbial banquet lies frozen in the Arctic, as well as how much of an impact the potential gases released could have on the global climate.

To study the permafrost, the researchers used pulses of laser light shot down a submarine telecommunications fiber optic cable, buried off the coast of Alaska and running north from Olitok Point.

Tiny imperfections in the cable caused light to bounce back to a sensor system and, in capturing this light at two wavelengths and comparing them, the researchers can determine the temperature at every yard of the cable.

By looking at light of a different wavelength, the researchers could detect when the cable had been strained by a passing sound wave.

This so-called distributed acoustic sensing provided information about the structure of the seafloor to depths of between one and three miles.

Using this method, the climate scientists believe they have identified the bottom of the seafloor permafrost at around a quarter of a mile deep.

They also found another area with unusually large amounts of ice, possibly consistent with a pingo or 'ice pimple'; a domed hill formed by ice pushing upwards.

Dr. Jennifer Frederick, a computational geoscientist, said the team was specifically looking for unexplainable warm spots.

"The fact that we can monitor the temperature continuously, we can now pick up changes from year to year and season to season," Dr. Frederick said.

"We’re specifically looking for unexplainable warm spots. We think we’ll be able to see areas of seafloor seeps — somewhat like springs coming out of the ground, except on the seafloor.

"We’re interested in them because they’re carriers of deeper, carbon-rich fluids and are an indication of warming and change."

One recent innovation is a fully operational system that allows near-real-time remote data collection, which minimizes the time and cost of travel and the risk of losing data when the system is unattended.

Acoustic and temperature data cannot be collected at the same time, but one or the other now can be collected continuously.

The researchers have also solved the challenge of determining how to calibrate temperature data from the fiber optic cable.

Dr. Frederick uses the data from the distributed temperature sensing and the results from the distributed acoustic sensing modeling to provide constraints to a geophysical modeling code developed by Sandia.

The code models liquids and gases flowing through underground soils and Dr. Frederick uses this code to model 100,000 years of geologic history for the studied stretch of Arctic seafloor, including the average temperature of the most recent ice age and how much the sea level has risen.

The results of the model are maps of the current distribution of submarine permafrost.

The power of the laser and sensitivity of the sensors means the team's system is limited to collecting data from no more than 25 miles offshore, though Dr. Frederick hopes future improvements could push this distance out further.

“This project has many different pieces,” she said.

“I’m looking at temperature and Christian is looking at acoustics to get a subsurface model.

"Really, you need all of these pieces to say something about the larger picture of the current distribution of permafrost and whether we are seeing changes like seeps and how that plays into the larger greenhouse gas emissions picture.

"Being able to use new tools and push them to their extreme to see what we can learn is really cool."

Stanciu presented the team's latest findings at the American Geophysical Union's recent Fall Meeting in San Francisco.