How the University of Tokyo Measures Arctic Sea-Ice Interactions with Spotters

Overview

Over the past several decades, the sea-ice extent in the western Arctic Ocean has undergone a significant reduction. This reduction allows greater wave evolution and propagation in regions of the Ocean that have historically been dampened by sea ice. With shipping traffic in the Arctic Ocean increasing, there is a growing demand for accurate wave forecasting in that region. However, our understanding of the propagation of waves through and underneath sea ice is limited compared to the open ocean.  While the wave-ice interaction is complicated, understanding the physics of that interaction is critical in developing accurate wave forecasting models for the Arctic Ocean. 

Problem

Deploying real-time wave instruments in polar environments presents unique challenges. Not the least of which is that these instruments are likely to get frozen over. Instruments dedicated to monitoring polar environments are expensive due to the need for high cost, non-rechargeable batteries which typically last only one season before being discarded, while also being bulky to install, and not necessarily well suited to measuring wave spectrum data. Having devices that are rugged and durable enough to withstand a long winter at 80 plus degrees latitudes, as well as affordable and reusable enough to be deployed on non-Arctic specific missions, can help researchers by providing a reusable, cost-effective solution for even the most extreme environments.



Spotter in the Arctic Ocean with grease ice and pancake ice, deployed in October 2019. The picture was taken by Ryo Kusakawa.

Solution

At the University of Tokyo, Japan, a research team led by Professor Takuji Waseda is actively working on understanding wave-ice interactions in the Arctic Ocean. As part of its mission, the team deployed two drifting Sofar Ocean Spotter wave buoys in the western Arctic Ocean during the R/V Mirai Arctic Expedition in October 2019. The targeted observation area was the sea-ice edge, due to previously unreliable forecasts along the sea-ice edge (Nose et al., 2020). The first Spotter buoy was deployed in an ice-free, open ocean location; and, the second Spotter buoy deployed in a location covered by grease and pancake ice. With this precise observational data generated by the Spotter buoys, the team found that the observed wave attenuation rate showed good agreement with theoretical predictions (Kodaira et al., 2020). 

After a few weeks, one of the buoys got covered in ice and went offline. In late spring, as the ice receded, the buoy came back online in the Arctic Ocean, exciting the research team. The new position was more than 500 km away from the deployment point. The Spotter buoys’ rugged construction meant that they were not only able to survive the Arctic winter, but also were able to be utilized in future research missions once they were recovered from their new coordinates.


Spotter in the Okhotsk Sea, deployed in February 2020.

Benefits and Learnings

The team at the University of Tokyo had initially chosen the Spotter buoy because it’s ease-of-use, and real-time data access via API to the team onboard the Mirai research vessel. 

The deployments at extreme latitude also provided great learnings for the Spotter team. The sharing of data and insights from the University of Tokyo team has already led to important updates to the hardware and firmware so that Spotter can easily sustain extended periods in extreme polar conditions without running out of power. Ongoing advances to the Spotter platform will further push the boundaries on what is possible in autonomous ocean sensing—even in the most extreme environments.

Acknowledgements from the University of Tokyo team

Our research has been sponsored by the Japanese Ministry of Education, Culture, Sports, Science, and Technology through the ArCS project (Arctic Challenge for Sustainability Project, grant number JPMXD1300000000) and was partially carried out in the Arctic Challenge for Sustainability II (ArCS II) Project (Program Grant Number JPMXD1420318865). A part of this study was also conducted under JSPS KAKENHI Grant Number JP 16H02429 and 19H05512. The research team wishes to thank the R/V Mirai crew who made the Arctic expedition possible. The team also wishes to acknowledge the support from P/V Soya crew and Hokkaido University for the observation in the Okhotsk Sea.


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