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Thursday, September 17, 2015

Andrew Freedman: Arctic research ship probes frigid depths and 4th-lowest sea ice extent on record

Fractured sea ice, dotted with melt ponds and marked by ridges formed by the dynamic ice, seen from a NASA aircraft on July 17, 2014. IMAGE: (REX FEATURES VIA AP IMAGES/ASSOCIATED PRESS
Through Sept. 11 of this year, the Arctic — which serves a crucial role as the Northern Hemisphere's refrigerator — lost an area of sea ice nearly equal to the states of Texas, California, Montana and New Mexico combined. This led to the fourth-lowest sea ice extent on record since satellite data began in 1979, continuing the long-term decline in summertime ice cover throughout the Arctic.
Both the southerly route of the famed Northwest Passage through Canada and the Northern Sea Route north of Russia were open for navigation at various points this summer, the National Snow and Ice Data Center (NSIDC) announced on Monday.
In Alaska, so much ice melted in the Chukchi Sea that at least 35,000 walruses hauled out onto a narrow island in Point Lay in order to rest, despite the lack of available food on land and risk of trampling newborn calves.
The Northeast Passage, from Murmansk in Russia to the Bering Strait, was sufficiently ice-free to allow a racing sailboat to successfully make that voyage, nonstop, in just 13 days, finishing the journey on Wednesday. This marked the farthest north a racing sailboat has ever sailed, according to a press release from the sailing team.
One of the mysteries of the sea ice loss of the past few decades, particularly this year, is how the heat distribution is changing in various regions of the Arctic.
Right now, the National Science Foundation's R/V Sikuliaq is sailing in the Beaufort Sea, north of Alaska, to investigate the distribution of heat throughout the water column, as well as how layers of water are interacting with one another.


Scientists Ethan Roth and Matthew Alford guide the SWIMS instrument back onto the research vessel. IMAGE: THOMAS MOORE/ARCTIC MIX
The research mission, known as "Arctic Mix," is being led by the Scripps Institution of Oceanography and University of Washington's Applied Physics Lab. So far, scientists have been surprised by the strength of ocean mixing they have observed in ice-free areas of the Beaufort Sea.
The ship is sailing through waters that scientists at the NSIDC called "a striking feature" of this melt season, with large regions of water with less than 70% ice cover. This is unusual for the Beaufort Sea, where multi-year ice used to remain in relative abundance through each melt season.

"Our instruments are seeing billows of turbulence that look just like a wave breaking on the beach, but much larger," said Jennifer MacKinnon, chief scientist aboard the Sikuliaq, in a press release sent from the ship.
"As a result, heat is being mixed up towards the surface, and the remaining ice, at a remarkable rate," she said.
Mixing Scan

Scan of the waters in the Beaufort Sea during September 2015, showing unexpectedly strong upward transport of warmer water to the surface. IMAGE: NSF/SCRIPPS/UNIVERSITY OF WASHINGTON
This heat transport can eat away at the remaining ice from below, cutting down on the amount of ice that survives till the next winter.
“While we hypothesized this might be happening, we have been genuinely thunderstruck by how incredibly strong the turbulence is below the surface," MacKinnon said in the release.

"This heat is likely playing a substantial role in the melting of the ice that we can see all around us, growing thinner every day, and our job now is to distinguish summer melting from longer term change."
Of particular use to the scientists is an instrument known as the Shallow Water Integrated Mapping System, or SWIMS, which is a device towed behind the ship that provides a close-up snapshot of temperature, salinity, velocity and other aspects of the ice-free Arctic Ocean.
Matthew Alford, also from Scripps, says the Arctic Ocean in general contains waters that exhibit an upside-down temperature profile from other areas, with cold, fresh water at the surface, and warmer, saltier water down below.
Surface Mixing

A vertical ocean temperature profile from the research vessel, showing more significant upper ocean mixing than expected. IMAGE: NSF/SCRIPPS/UNIVERSITY OF WASHINGTON
"One hypothesis for a rapidly-changing Arctic is increasing open water allows storms to mix this deeper ocean heat upward through the generation of undersea beams of energy called 'internal waves', in turn melting more ice," Alford said in a statement.
"The marked energetic mixing we are seeing here at the heart of the Arctic ice-melt zone may prove key in understanding a potential new climate feedback," Alford said.
According to the researchers, the ongoing voyage is vitally important for understanding the rapidly changing Arctic environment, where past studies may no longer describe what's going on now, given the extraordinary pace of global warming.
On average, the Arctic as a region is warming at twice the rate of the rest of the world, for example, creating a challenge for researchers. "... We are out here trying to sample and describe a moving target," MacKinnon said.

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