The University of Tokyo and NIPR succeeded in the observation of wave propagation over 1,000 km into Antarctica winter pack ice

A research group led by Project Assistant Professor Takehiko Nose, Professor Takuji Waseda, and Lecturer Tsubasa Kodaira of the Graduate School of Frontier Sciences at the University of Tokyo and Professor Shuki Ushio of the National Institute of Polar Research announced that they successfully measured waves propagating 1,000 km across the vast Antarctica winter ice-covered sea during their nearly yearlong observation from February 4, 2022, when the wave buoy was deployed during the 63rd Japanese Antarctica Research Expedition. They were able to make continuous buoy measurements for over 330 days and detect swell of a few centimeters that originated in the Southern Ocean and arrived at the buoy. Long-term observation provided opportunities to show that weak swell can be measured, which is expected to help elucidate the mechanism of fast-ice breakup. The results were published in the Coastal Engineering Journal on December 1.

The March 1980 breakup of the Kitanoura fast-ice adjacent to the Syowa Station caused an accident that sunk two airplanes. The cause of this is thought to be swell that propagated more than 100 km into the area of fast-ice within Lützow-Holm Bay; the bay-wide breakup of the fast-ice has been intermittently observed since then.

Fast-ice is sea ice that is "fastened" to the coast, and in Lützow-Holm Bay, the entire bay is covered with fast-ice. Far from the fast-ice areas along the continental coast, there are areas of drift ice that drift under the influence of wind and ocean currents. To measure waves propagating through the ice-covered sea, the research group collaborated with the University of Tokyo, the Norwegian Meteorological Institute, and the University of Melbourne in Australia to build their own wave buoys, which were deployed on an ice floe by the 63rd Japanese Antarctica Research Expedition members.

The wave buoy's microcontroller has low power consumption, but sufficient computing power for onboard analysis, this was combined with the industrial-grade inertial measurement unit IMU (measuring acceleration and angular velocity along three axes of an object), with operating temperatures as low as −40℃, which enabled long-term observation in the extreme environment of polar winter regions. The wave buoy, which was deployed on the ice on February 4, 2022, continued to transmit data for 330 days until January 3, 2023. During this time, it measured 4,000 wave spectra and more than 10,000 GNSS position data, and it drifted 5,000 km in the Antarctica ice-covered sea.

The incoming swell measured this time was not particularly large, with wave height estimated to be around 4 m. The swell attenuated as it propagated 1,250 km to the wave buoy position, and the maximum wave height at the measurement point was approximately 8 cm. This measurement demonstrated the high sensitivity of the buoy to capture weak swell signals during the yearlong continuous measurements.

The study estimated how far the waves retain the ability to breakup sea ice, which showed that the wave-induced ice breakup potential extended to approximately 400 km despite considerable attenuation of wave heights. The study confirmed that swell was a factor in the bay-wide sea ice breakup that occurred near Syowa Station in 1980. More observations with the developed wave buoy, together with ice thickness and sea ice strength information, are expected to shed light on the mechanisms of the ice-covered sea area variability along the continental coast, such as the swell-induced breakup of fast-ice.

T. Nose said "A sensor, built from a collection of relatively cheap and commercially available products, being able to take continuous measurements for nearly a year in an extreme environment with temperatures as low as −40℃ is a breakthrough in polar wave observation. The fact that swell propagated through the vast expanse of the winter Antarctica ice-covered sea was both surprising and interesting. We hope that the wave buoys we are developing will play an active role in future Antarctica observations."

Journal Information
Publication: Coastal Engineering Journal
Title: Observation of wave propagation over 1,000 km into Antarctica winter pack ice
DOI: 10.1080/21664250.2023.2283243