Less ice, more waves in the Arctic Ocean

Researchers from the University of Washington, Seattle, have reported a perhaps overlooked outcome of a shrinking sea-ice cover in the Arctic Ocean: As a larger expanse of open water becomes exposed to summer winds, sea swells may become common, potentially impacting vessels plying Arctic waters and offshore oil operations, while also increasing the risk of coastal erosion and hastening the further breakup of sea ice.

According to a paper published in April in Geophysical Research Letters the researchers, Jim Thomson and Erick Rogers, placed a wave sensor at a location in the central Beaufort Sea between mid-August and November 2012. Thomson and Rogers also ran a wave model, using observed wind and ice conditions to predict the wave sizes.

Theory predicts that the size of the ocean swells should increase with what is termed the “fetch,” the distance across open water that the wind blows. Although the interaction between sea ice and waves is complex, with the possibility of ice dampening wave action, the increase in the fetch as the sea-ice cover retreats should lead to greater ocean swells, the paper says.

The researchers reported an excellent correspondence between the measured sizes of the waves in the Beaufort Sea and the sizes predicted from the wave model. Of particular note were two Arctic storms: one in August, and one in September.

The first of these storms pre-dated the start of the wave observations and took place while the area of open water was relatively small. In this situation, the wave model predicted waves of modest size. But, with a relatively large area of open water established by the time of the second storm, the observed and modeled swell size was very significant, with strong winds generating waves as much as 5 meters (15 feet) in height, the paper says.

- Alan Bailey