With the Arctic Ocean undergoing significant change, the Sea State and Boundary Layer Physics of the Emerging Arctic Program, sponsored by the Office of Naval Research, set out to better understand the seasonal evolution of sea ice and the impact of more open water. The goals of the program and the 2015 field campaign were described in a Project Update on Eos.org. Now the enormous set of air, ice, and ocean measurements have been analyzed and the key results published in a Special Issue of JGR: Oceans.
In the last 30 years, the autumn ice advance has shifted a full month later in the season throughout most of the western Arctic.We wanted to understand more about the refreezing of the western Arctic Ocean—particularly the Beaufort and Chukchi seas—that occurs every autumn. The western Arctic has the most dramatic evidence of climate change in the seasonal ice cycle. In the last 30 years, the autumn ice advance has shifted a full month later in the season throughout most of the region. We set out to look at interactions between the air, ocean, and ice that have been changing in recent decades.
We conducted a large field campaign onboard the Research Vessel Sikuliaq, with a number of autonomous platforms deployed from the ship. Coincident with these in situ measurements, we had targeted satellite and airborne remote sensing. There has also been a strong modeling component of the program, including experimental forecasts that guided us during the fieldwork. Thomson et al. [2018] synthesize these results in an overview of the campaign.
Perhaps the most surprising finding was the extent of pancake ice.Perhaps the most surprising finding was the extent of pancake ice, a sea ice formation type cause by wave motions. This is ubiquitous in the Antarctic, which always has swells from the Southern Ocean, but to observe something similar in the Arctic is remarkable.
Sunset over extensive pancake ice. Credit Jim Thomson
We think it is related to the growing expanse of seasonally open water, and the fetch to make waves. It is certainly becoming more prevalent in the western Arctic. Wadhams et al. [2018] use remote sensing to quantify this ice type and the associated wave dispersion.
Another interesting finding was the large variations in space and time of the ice advance, many of which were modulated by the heat in the ocean and atmosphere. Persson et al. [2018] describe how these modulations occurred along the cruise track.
Overall, this research program revealed strong links in the air-ocean-ice system at all scales, including feedbacks that persist through a whole seasonal or annual cycle. Many of these feedbacks, such as accumulation of ocean heat that delays ice formation, are known, but their extent and importance have been underappreciated. Smith et al. [2018] show how important a single event can be in the seasonal evolution. Forecast and climate models must include these feedbacks to get accurate results.
Although this field campaign is over, we still have some unanswered questions. We still lack a complete picture of how the details of ice formation play out over the annual ice. Does pancake ice forming in autumn become a notably different winter ice cover, with a different melt process the following spring? Sustained autonomous observations are likely the only way to answer questions like this.
You can see footage from the research cruise, including some spectacular pancake ice, in this short video:
—Jim Thomson, Chief Scientist for Sea State and Boundary Layer Physics of the Emerging Arctic Program and Guest Editor of JGR: Oceans Special Issue; also Applied Physics Lab, University of Washington; email: jthomson@apl.washington.edu
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