Submarine cables measuring ice from the deep | Polarjournal
Estimating the amount of sea ice is limited by its complex composition. Image : Heiner Kubny

Researchers have just developed a new method for studying the extent of pack ice, using fiber optic lines – an ingenious idea that uses accessible technology in an inaccessible region.

Published in The Seismic Record on August 8, researchers from the University of New Mexico in the USA report the results of a sea ice detection method they have developed using an subsea cable that uses black fiber. “Unused pairs of fibre optic from cables deployed by telecommunications companies to connect Arctic communities”, explains Michael Delaunay, submarine cable specialist at the Arctic Policy and Security Observatory.

During the melting period, in July 2021, and the pack ice recovery period, in November of the same year, the researchers transmitted signals into the Quintillion subsea cable running from the north coast of Alaska, in a 37-kilometer section perpendicular to the shoreline. Their goal was to identify the different types of waves received by the cable, and to define a signal specific to the pack ice.

When the wind stirs up the surface of the water and forms waves, the ocean surface emits low-frequency waves that are picked up by the cables. Beneath the ice, these are absent, leaving only a high-frequency signal to which the researchers plan to pay close attention in future studies.

Their results are so accurate that they detect the formation of pack ice within a few hours along the cable during autumn. “It was definitely surprising that the sea ice can change so much […],” said Peña Castro, lead author of the study. “A few colleagues have mentioned that these rapid changes may be common but the temporal resolution of satellites makes it rare to observe such rapid changes in sea ice.”

The researchers compared their results with methods for assessing ice concentration using satellite data. In the end, the two methods are very similar. The few differences lie primarily in their sensitivity to sea ice concentration. For the future, the two observation systems could complement each other: satellites cover a larger area, but cables are more accurate on a time scale. These data are also crucial for gauging the evolution of climate change and could be very useful for navigational aids. “It could be useful for local fisheries”, notes Michael Delaunay.

Many communities depend on sea ice for travel, fishing and hunting. Image: Guy Omnik from Point Hope / Alaska Arctic Observatory and Knowledge Hub

Other cable networks could be used to cover more ground. “In Hudson Bay there are two sections and a third should see the light of day soon, the laying ship should be there soon,” he explains. “The EAUFON project consists of connecting 14 communities in Nunavut by 2025. There’s also Greenland, where the Government wants to make its network redundant with a possible third cable to come.”

Such new sections would be useful in the event of accidental or intentional rupture of the former. “Two service cuts, in 2019 and 2022, as well as the threat of cable cuts from Russia following the outbreak of the Ukrainian conflict, prompted them to seek funding to make their network redundant”, Delaunay recalls. Nine million Euros were recently released by the EU for the preliminary study of the work. The research vessel Explora will leave in November to study the seabed. There are also projects underway in Russia, which are more difficult to monitor at present. These infrastructures could therefore become new study supports for monitoring the evolution of Arctic sea ice.

In the Arctic, cables can be buried in the sediment to protect them from icebergs. Image: GCI

This new use of technologies is already having an impact on the construction of new subsea cables. The boxes that link the sections together can house specific sensors. “Last week, it was announced that a prototype SMART repeater would be manufactured, including devices sensitive to temperature, pressure and an accelerometer. Alcatel Submarine Networks has already committed to using them, and they may be used in the Far North Fiber cable, which plans to connect Asia to Europe via the Arctic. This will be a first on such a long cable and in the Arctic,” concludes Michael Delaunay.

The Far North Fiber includes the subsea cable in northern Alaska that researchers at the University of New Mexico worked on in 2021. Last June, it was severed by a grounded iceberg, cutting off Internet connections to towns and villages in the north and west of the peninsula. A maintenance vessel left at the end of July to attempt to repair the structure, in the hope of benefiting from an ice-free stretch of water.

Camille Lin, PolarJournal

Source: Peña Castro, A.F., Schmandt, B., Baker, M.G., Abbott, R.E., 2023. Tracking Local Sea Ice Extent in the Beaufort Sea Using Distributed Acoustic Sensing and Machine Learning. The Seismic Record 3, 200–209.

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