91̽�� polar scientists are on Alaska’s North Slope this week for the 2016 Barrow Sea Ice Camp. Supported by the National Science Foundation, the event brings together U.S.-based sea ice observers, satellite experts and modelers at various career stages to collect data and discuss issues related to measuring and modeling sea ice. The goal is to integrate the research community in order to better observe and understand the changes in Arctic sea ice.

Check out the group’s , written by a who’s taking his first trip into the field, or follow updates on . The group is based just north of Barrow from May 26 to June 2, in the northernmost point in the U.S.

91̽��participants include , a 91̽��professor of atmospheric sciences, , an oceanographer at the 91̽��Applied Physics Laboratory, , a physicist at the Applied Physics Laboratory, , a 91̽��graduate who is now a research assistant at APL, 91̽��atmospheric sciences postdoctoral researchers and , and , an anthropology student who has a visiting appointment at APL.

While changes in weather may play a big role in short-term changes in sea ice seen in the past couple of months, changes in winds have apparently led to the more general upward sea ice trend during the past few decades, according to 91̽�� research. A new modeling study to be published in the shows that stronger polar winds lead to an increase in Antarctic sea ice, even in a warming climate.

“The overwhelming evidence is that the Southern Ocean is warming,” said author , an oceanographer at the 91̽��Applied Physics Laboratory. “Why would sea ice be increasing? Although the rate of increase is small, it is a puzzle to scientists.”

His shows that stronger westerly winds swirling around the South Pole can explain 80 percent of the increase in Antarctic sea ice volume in the past three decades.

The polar vortex that swirls around the South Pole is not just stronger than it was when satellite records began in the 1970s, it has more convergence, meaning it shoves the sea ice together to cause ridging. Stronger winds also drive ice faster, which leads to still more deformation and ridging. This creates thicker, longer-lasting ice, while exposing surrounding water and thin ice to the blistering cold winds that cause more ice growth.

In a computer simulation that includes detailed interactions between wind and sea, thick ice — more than 6 feet deep — increased by about 1 percent per year from 1979 to 2010, while the amount of thin ice stayed fairly constant. The end result is a thicker, slightly larger ice pack that lasts longer into the summer.

“You’ve got more thick ice, more ridged ice, and at the same time you will get more ice extent because the ice just survives longer,” Zhang said.

When the model held the polar winds at a constant level, the sea ice increased only 20 percent as much. A by Zhang showed that changes in water density could explain the remaining increase.

“People have been talking about the possible link between winds and Antarctic sea ice expansion before, but I think this is the first study that confirms this link through a model experiment,” commented , a polar scientist at the 91̽��Applied Physics Lab. “This is another process by which dynamic changes in the atmosphere can make changes in sea ice that are not necessarily expected.”

The research was funded by the National Science Foundation.

Still unknown is why the southern winds have been getting stronger. Some scientists have theorized that it could be related to global warming, or to the ozone depletion in the Southern Hemisphere, or just to natural cycles of variability.

Differences between the two poles could explain why they are not behaving in the same way. Surface air warming in the Arctic appears to be greater and more uniform, Zhang said. Another difference is that northern water is in a fairly , while the Antarctic sea ice floats in open oceans where it expands freely in winter and melts almost completely in summer.

The sea ice uptick in Antarctica is small compared with the amount being lost in the Arctic, meaning there is an overall decrease in sea ice worldwide.

Many of the global climate models have been unable to explain the observed increase in Antarctic sea ice. Researchers have been working to improve models to better reproduce the observed increase in sea ice there and predict what the future may bring.

Eventually, Zhang anticipates that if warmer temperatures come to dominate they will resolve the apparent contradiction.

“If the warming continues, at some point the trend will reverse,” Zhang said.

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For more information, contact Zhang at 206-543-5569 or zhang@apl.washington.edu.

New satellite observations confirm a 91̽�� analysis that for the past three years has produced widely quoted estimates of Arctic sea-ice volume. Findings based on observations from a European Space Agency satellite, published online in , show that the Arctic has lost more than a third of summer sea-ice volume since a decade ago, when a U.S. satellite collected similar data.

Combining the 91̽��model and the new satellite observations suggests the summer minimum in Arctic sea ice is one-fifth of what it was in 1980, when the model begins.

“Other people had argued that 75 to 80 percent ice volume loss was too aggressive,” said co-author , a polar scientist in the 91̽��Applied Physics Laboratory. “What this new paper shows is that our ice loss estimates may have been too conservative, and that the recent decline is possibly more rapid.”

The system developed at the 91̽��provides a 34-year monthly picture of what’s happening to the total volume of Arctic sea ice. The Pan-Arctic Ice Ocean Modeling and Assimilation System, or , combines weather records, sea-surface temperature and satellite pictures of ice coverage to compute ice volume. It then verifies the results with actual thickness measurements from individual moorings or submarines that cruise below the ice.

“Because the ice is so variable, you don’t get a full picture of it from any of those observations,” Schweiger said. “So this model is the only way to reconstruct a time series that spans multiple decades.”

The 91̽��system also checks its results against five years of precise ice thickness measurements collected by a specialized satellite launched by NASA in 2003. The Ice, Cloud, and Land Elevation Satellite, or , measured ice thickness across the Arctic to within 37 centimeters (15 inches) until spring of 2008.

The U.K.’s satellite resumed complete ice thickness measurements in 2010; this is the first scientific paper to share its findings about the recent years of record-low sea ice.

Between 2008 and now, the widely cited 91̽��figures have because of the substantial ice loss they showed.

“The reanalysis relies on a model, so some people have, justifiably, questioned it,” Schweiger said. “These data essentially confirm that in the last few years, for which we haven’t really had data, the observations are very close to what we see in the model. So that increases our confidence for the overall time series from 1979 to the present.”

Arctic sea ice is shrinking and thinning at the same time, Schweiger explained, so it’s normal for the summer ice volume to drop faster than the area covered, which today is about half of what it was in 1980.

Schweiger cautioned that past trends may not necessarily continue at the same rate, and predicting when the Arctic might be largely ice-free in summer is a different question. But creating a reliable record of the past helps to understand changes in the Arctic and ultimately helps to better predict the future.

“One question we now need to ask, and can ask, is what are the processes that are driving these changes in the ice? To what degree is it ocean processes, to what degree is this in the atmosphere?” Schweiger said. “I don’t think we have a good handle on that yet.”

The 91̽��system was created by co-author , an oceanographer at the Applied Physics Laboratory. The 91̽��portion of the research was funded by NASA and the Office of Naval Research.

Other co-authors are first author Seymour Laxon, Katharine Giles, Andy Ridout, Duncan Wingham and Rosemary Willatt at University College London; Robert Cullen and Malcolm Davidson at the European Space Agency; Ron Kwok at NASA’s Jet Propulsion Laboratory; Christian Haas at York University in Canada; Stefan Hendricks at the Alfred Wegener Institute for Polar and Marine Research in Germany; Richard Krishfield at Woods Hole Oceanographic Institution; Sinead Farrell at the University of Maryland; and Nathan Kurtz at Morgan State University in Baltimore.

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For more information, contact Schweiger at 206-543-1312 or axel@apl.washington.edu.

American Geophysical Union / Natural Environment Research Council press release:

Article on NASA role:

But new results from the 91̽�� show that the August cyclone was not responsible for last year’s record low for Arctic sea ice. The study was published online this week in .

“The effect is huge in the immediate aftermath of the cyclone, but after about two weeks the effect gets smaller,” said lead author , an oceanographer in the UW’s Applied Physics Laboratory. “By September, most of the ice that melted would have melted with or without the cyclone.”

Recent research showed that the was the most powerful ever seen during the month of August, and the 13^th most powerful of all Arctic storms in more than three decades of satellite records.

“The storm was enormous,” said co-author , a polar scientist in the Applied Physics Laboratory. “The impact on the ice was immediately obvious, but the question was whether the ice that went away during the storm would have melted anyway because it was thin to begin with.”

The 91̽��team performed the climate scientist’s equivalent of a forensic exam: They ran a computer simulation of last summer’s weather and compared it against a second scenario that was identical except that there was no cyclone.

Results showed the storm caused the sea ice to pass the previous record 10 days earlier in August than it would have otherwise, but only reduced the final September ice extent by 150,000 square kilometers (almost 60,000 square miles), less than a 5 percent difference. By comparison, the actual minimum ice extent was 18 percent less than the previous record set in 2007.

The study also revealed a surprising mechanism for the cyclone-related melting. Earlier discussions about the cyclone’s effect had focused on winds breaking up the ice or driving ice floes into areas of warmer water. The results suggest that neither process led to much increase in melting.

Relatively recent research shows that in the summertime, thin ice and areas of open water allow sunlight to filter down to the water below. As a result, while a layer of ice-cold fresh water sits just beneath the sea ice, about 20 meters (65 feet) down there is a layer of denser, saltier water that has been gradually warmed by the sun’s rays.

Blowing on polar water is like blowing on a layered cocktail. When the cyclone swept over the drifting ice floes, underside ridges churned up the water to bring sun-warmed seawater to the ice’s bottom edge. The model suggests that during the cyclone there was a quadrupling of melting from below, and that this was the biggest cause for doubling ice loss during the three-day storm.

“We only looked at one big storm. If we want to understand how storms will affect the ice cover in the future we need understand the effect of storms in different conditions,” said co-author .

More sunlight reaches the water in a year with unusually thin summer ice, such as 2012, so this process is a potential multiplier effect for sea-ice melting.

The results are of interest beyond understanding climate change. As sea ice thins and melts, economic and political concerns require better sea-ice forecasts to protect ships and instruments that might travel in those waters.

“One thing we are working on, and that needs to be included in future computer simulations, is how bigger waves created by wind blowing over more extensive open water help break up the sea ice into floes, and how these smaller floes respond to warm water,” said co-author .

The research was funded by the , the U.S. and .

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For more information, contact Schweiger at 206-543-1312 or axel@apl.washington.edu.