Autumn in the Arctic – Eos

While the Arctic Ocean was undergoing profound changes, the Sea State Physics Program and the Arctic Boundary Layer emerged, sponsored by the Office of Naval Research , was intended to better understand the seasonal evolution of sea ice and the impact of an increase in open water. The objectives of the 2015 program and field campaign were described in an update of the project on Eos.org. Now, the huge set of measurements of air, ice and oceans has been analyzed and the main results published in a special issue of JGR: Oceans.

We wanted to know more about the refreezing of the Western Arctic Ocean – especially the Beaufort and Chukotka Seas – that occurs every fall. The western Arctic presents the most dramatic evidence of climate change in the seasonal ice cycle. Over the last 30 years, the ice advance in the fall has been modified a month later in most of the region. We undertook to examine the interactions between air, ocean and ice that have changed in recent decades.

We conducted a large field campaign aboard the research vessel Sikuliaq, with a number of autonomous platforms deployed from the ship. In parallel with these in situ measurements, we targeted airborne and satellite remote sensing. The program also includes an important modeling component, including experimental predictions that guided us through fieldwork. Thomson et al. [2018] Summarize these results in an overview of the campaign.

The most surprising discovery is perhaps the extent of the pancake, a formation of the pack ice caused by wave movements. It is ubiquitous in the Antarctic, which always has waves of the Southern Ocean, but observing something similar in the Arctic is remarkable.

We think this is related to the increasing extent of seasonal open waters and making waves. It is certain that this is becoming more and more prevalent in the western Arctic. Wadhams et al. [2018] use remote sensing to quantify this type of ice and the associated wave dispersion.

Another interesting discovery concerns the large spatial and temporal variations of ice advance, many of which are modulated by the heat of the ocean and the atmosphere. Persson et al. [2018] describe how these modulations occurred along the cruising path.

Overall, this research program revealed close links in the air-ocean-ice system at all scales, including persistent feedbacks throughout a seasonal or annual cycle. Many of these reactions, such as the accumulation of heat in the oceans that delays ice formation, are known, but their magnitude and importance have been underestimated. Smith et al. [2018] show how a single event can play in the seasonal evolution. Forecast and climate models must include this information to obtain accurate results.

Although this field campaign is over, there are still unanswered questions. We still lack a complete picture of how the details of ice formation are played on the annual ice. Does the pancake ice that forms in the fall become a distinct winter ice cover, with a different melt process the following spring? Continuous autonomous observations are probably the only way to answer such questions.

You can see images of the search campaign, including spectacular pancake ice cream, in this short video:

-Jim Thomson, Chief Scientist for the Program on the State of the Sea and the Physics of the Arctic Boundary Layer and Guest Editor of the JGR: Oceans Special problem; also Applied Physics Lab, University of Washington; E-mail: [email protected]

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