The climate of the far-flung and frequently harsh Arctic is changing at a rate that is four times faster than that of the rest of the planet. Because of this, researching the Arctic climate is difficult but essential to comprehending climate change worldwide.
Researchers at Sandia National Laboratories are examining the Arctic seafloor's conditions up to 20 miles offshore by utilizing an existing fiber optic cable off Oliktok Point on Alaska's North Slope. The project lead, Christian Stanciu, will present their most recent findings at the AGU Fall Meeting in San Francisco on Friday, December 15.
Finding the seismic structure of miles of Arctic seafloor is their aim. Through the use of a recently developed method, they are able to identify regions of the seafloor where sound propagates more quickly than elsewhere, usually due to the presence of more ice. Numerous regions with a lot of ice have been identified, according to Sandia geophysicist Stanciu.
Additionally, the scientists monitored temperature variations over the course of the seasons and measured temperatures across the seafloor using the cable. Computational geoscientist Jennifer Frederick explained that these data, unlike any previously gathered, were entered into a computer model to infer the distribution of submarine permafrost.
"One of the innovations of this project is that we can now use a single fiber to get acoustic and temperature data," Stanciu stated. "We created a new system that uses a single fiber strand to remotely gather both kinds of data. Some intriguing results are being obtained."
Permafrost and beaming sunshine
Arctic permafrost is a feast that is just waiting to be thawed, much like leftover roast turkey that has been in the freezer since Thanksgiving. In particular, microbes start to break down the once-living material that was frozen during the last ice age and release waste gases like carbon dioxide and methane, according to Frederick. Researchers are examining the size of the microbial feast that is frozen in the Arctic and the potential impact of those gases on the Earth's climate.
Researchers used laser light pulses to study permafrost on the Arctic seafloor. The submarine telecommunications fiber optic cable was buried off the coast of Alaska and ran north from Oliktok Point. Light was reflecting back to a sensor system due to microscopic flaws in the cable.
Frederick stated that the researchers could ascertain the temperature of the cable every yard by recording this light at two different wavelengths, or colors, and comparing them. Distributed temperature sensing is the term for this.
The researchers were able to determine when a sound wave had stressed the cable by observing light with a different wavelength. According to Stanciu, information about the seafloor's structure was obtained using a technique known as distributed acoustic sensing, which reached depths of one to three miles.
By using this technique, the scientists think they have located the seafloor permafrost at a depth of about 0.5 miles. He added that they also discovered another area with abnormally high amounts of ice, which could be related to a pingo or "ice pimple," a domed hill created by ice pushing upward. The measurements' data analysis was primarily handled by Sandia intern Brandon Herr.
"The fact that we can monitor the temperature continuously, we can now pick up changes from year-to-year and season-to-season," Frederick continued. Specifically, we're searching for mysterious hotspots. We believe that patches of seafloor seeps—which resemble springs emerging from the earth but are located on the seafloor—will be visible to us. They are indicators of warming and change and carriers of deeper, carbon-rich fluids, which is why we are interested in them."
The past and the innovations
For over 25 years, Sandia has been gathering climate data from northern Alaska. The current study, which began about a year ago, expands on earlier research conducted by Sandia geophysicists Rob Abbott and Michael Baker on the same fiber optic cable.
A recently developed system by Stanciu's group enables remote data collection in almost real time. This lessens the chance of data loss when the system is left unattended, as well as the time and expense of traveling to Oliktok, according to Stanciu. While temperature and acoustic data cannot be collected simultaneously, they can now be continuously collected separately.
Finding a way to calibrate temperature data from the fiber optic cable was one of the challenges the team overcame in the first year of the project, according to Frederick. Distributed temperature sensing systems are typically constructed with integrated thermometers or self-check mechanisms like redundant fiber. But in order to verify the seasonal temperature variations they saw, the team needed to use computational models because they were utilizing a telecom dark fiber. Ethan Conley, a Sandia intern, was mostly responsible for the data analysis on this project.
Frederick constrains a geophysical modeling code created by Sandia using the information from the distributed temperature sensing and the outcomes of the distributed acoustic sensing modeling. The code simulates gases and liquids moving through subsurface soils. Using this code, Frederick models the geologic history of the studied area of the Arctic seafloor spanning 100,000 years, including the average temperature of the most recent ice age and the amount of sea level rise. Maps showing the present distribution of submarine permafrost are the model's output.
Frederick stated that the team's interrogator system's limitations, such as the laser's power and the sensors' sensitivity, prevent the scientists from gathering data beyond 18 to 25 miles offshore. She wants to increase the distance by making systemic changes.
Frederick stated, "There are many different pieces to this project." "To obtain a subsurface model, Christian is looking at acoustics while I'm looking at temperature. To truly understand the bigger picture of the distribution of permafrost today, whether seeps are occurring, and how that affects the overall picture of greenhouse gas emissions, you really need to consider all of these pieces together. It's great to be able to experiment with new instruments and push them to their limits to see what we can discover."
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