Tag: Arctic sea ice

The cracks are showing #2 (polar notes)

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Summer’s arriving on the Wilkins ice shelf, and its disintegration continues. New cracks are threatening to destroy the ice “bridge” that’s been holding the ice shelf pinned between Charcot Island (top left) and the Antarctic peninsula. This picture, captured by the European Space Agency’s ENVISAT satellite on November 26, shows the new cracks (coloured lines) and the dates they first appeared (NASA version here). If the chunk of ice under “21 July” breaks away, the long thin bridge will lose support and follow suit, the ESA analysts say.

Meanwhile, a team lead by Richard Alley at Penn State has worked out that ice shelf calving – where icebergs break away at the edge of an ice shelf – is critically influenced by the rate at which the ice shelf is spreading out. The PSU release notes:

For iceberg calving, the important variable — the one that accounts for the largest portion of when the iceberg breaks — is the rate at which ice shelves spread, the team reports in the Nov. 28 issue of Science. When ice shelves spread, they crack because of the stresses of spreading. If they spread slowly, those cracks do not propagate through the entire shelf and the shelf remains intact. If the shelf spreads rapidly, the cracks propagate through the shelf and pieces break off.

When ice shelves break up, the glaciers that feed them can speed up noticeably, dumping more ice into the ocean. Over recent years, the role of water as a lubricant for glacier flow has been receiving a lot of attention (rubber ducks were recruited as under ice research tools in Greenland this year), and the BBC reports that a sub-glacial “flood” under the Byrd Glacier which feeds ice at the rate of about 20 billion tonnes a year into the Ross ice shelf caused that to increase to 22 billion tonnes over 2006. It has since returned to normal.

Up north, the NSIDC reports (Dec 3) that it continues to be warmer than average, even though the sea ice is now covering the whole Arctic ocean.

The tracks of my tears

EarthApollo8.jpg NASA was 50 years old last July, and the Earth Observatory has been celebrating by reviewing some of the classic images they’ve captured over the years. The image of the Earth at left was captured by Apollo 8 astronauts on December 22nd 1968 – one of the first “blue marble” pictures. Forty years on, it’s sobering to realise that only 24 people have seen the planet from this perspective – from the moon. But the picture that really caught my attention this week was part of a feature where NASA asked earth scientists what “unique insights” spaceflight had given us about the planet.

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On page three, you’ll find this stunning image of “ship tracks” – the maritime equivalent of the contrails left by high flying aircraft – over the Bay of Biscay. If you ever doubted man’s influence on the atmosphere, here’s a dramatic confirmation of the large scale impacts brought about by our modern way of life. There are also satellite maps of ENSO sea level changes, Arctic sea ice decline, La Niña-related sea level changes, and many more pretty pictures. Educational eye candy.

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In the heat of the (Arctic) night

LWOct2008.gif Time for an Arctic update and a bit of “original” research. There’s been quite a bit of polar news around, and a rapid freeze-up is underway in the Arctic – so rapid that some are declaring that the sea ice is “back to normal” for the time of year, based on this graph from the Arctic Regional Ocean Observing System in Norway, which shows sea ice area climbing up towards to the average for 1979-2007, within one standard deviation (the grey area). On the other hand, if you look at the equivalent graph at Cryosphere Today, you’ll see that ice area is 1.25m km2 below the average – which in CT’s case is 1979-2000. So the ice is approaching normal, only if you define “normal” as including the significant ice reductions over the last seven years. How encouraging. But this autumn’s freeze-up has been pretty rapid. Does that mean that it’s been unusually cold up there? I thought I’d take a look…

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(The Village) Greenland Preservation Society

tintinmilou.jpeg The latest satellite data shows that this summer’s snowmelt in northern Greenland was “extreme”, according to Marco Tedesco, assistant professor of Earth & Atmospheric Sciences at The City College of New York. From the press release:

“Having such extreme melting so far north, where it is usually colder than the southern regions is extremely interesting,” Professor Tedesco said. “In 2007, the record occurred in southern Greenland, mostly at high elevation areas where in 2008 extreme snowmelt occurred along the northern coast.”

Melting was most pronounced near Ellesmere Island, where ice sheet collapses were observed, and around the Petermann glacier, which is also shedding ice. Melting lasted 18 days longer than average in these areas, and the melt index (area times days) was three times higher than the 1979-2007 average for the region.

Underlining the dramatic changes being seen in the far north, the National Oceanic & Atmospheric Administration (NOAA) released its second Arctic Report Card earlier this week…

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Freezing

NSIDCmultiyear081004.gif With this summer’s Arctic sea ice minimum done and dusted, the first analyses of the season are beginning to appear. The NSIDC’s latest press release suggests that ice volume decline continued:

NSIDC Research Scientist Walt Meier said, “Warm ocean waters helped contribute to ice losses this year, pushing the already thin ice pack over the edge. In fact, preliminary data indicates that 2008 probably represents the lowest volume of Arctic sea ice on record, partly because less multiyear ice is surviving now, and the remaining ice is so thin.”

Click on the thumbnail above to see the big picture on multi-year ice reduction. The large area of red first year ice will obviously become second year ice next year, but the continuing reduction in thicker, older ice sets the stage for further big losses the next time the Arctic has a warm summer. The European Space Agency confirms this, quoting US National Ice Centre Chief Scientist Dr Pablo Clemente-Colón:

Although last year’s summer sea ice minimum extent record was not broken, a record amount of the thickest multiyear sea ice was actually lost this season impacting the thickness of the sea ice presently found around the North Pole region and setting the stage for more minimum or near-minimum records in upcoming years.

The ESA also provide some nice images…

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