NSIDC Arctic sea ice news September 2011

Yesterday the National Snow and Ice Data Center (NSIDC) released its September analysis.

Some interesting tidbits:

The summer sea ice melt season has ended in the Arctic. Arctic sea ice extent reached its low for the year, the second lowest in the satellite record, on September 9. The minimum extent was only slightly above 2007, the record low year, even though weather conditions this year were not as conducive to ice loss as in 2007. Both the Northwest Passage and the Northern Sea Route were open for a period during September.

(...)

Average ice extent for September 2011 was 4.61 million square kilometers (1.78 million square miles), 2.43 million square kilometers (938,000 square miles) below the 1979 to 2000 average. This was was 310,000 square kilometers (120,000 square miles) above the average for September 2007, the lowest monthly extent in the satellite record. Ice extent was below the 1979 to 2000 average everywhere except in the East Greenland Sea, where conditions were near average.

(...)

Atmospheric conditions
In 2007, a persistent dipole anomaly weather pattern, with unusually high pressure over the Beaufort Sea and unusually low pressure over the Kara Sea, helped contribute to the record ice loss. This pattern resulted in strong southerly winds from the Bering Strait region across the North Pole, which brought warmer winds and ocean waters northward to melt the ice edge and push the ice northward. In addition, especially strong high pressure over the Beaufort and Chukchi Seas in June 2007 resulted in less than average cloudiness, allowing more sunlight to reach the ice.

The Arctic saw a similar weather pattern this summer, but not as strong and persistent as in 2007. The location of the high and low pressure centers was also shifted, so that the winds blew east to west instead of toward the north as in 2007. This shift is reflected in the movement of the sea ice, particularly during August.

Ice remains younger, thinner
Why did ice extent fall to a near record low without the sort of extreme weather conditions seen in 2007? One explanation is that the ice cover is thinner than it used to be; the melt season starts with more first-year ice (ice that formed the previous autumn and winter) and less of the generally thicker multi-year ice (ice that has survived at least one summer season). First- and second-year ice made up 80% of the ice cover in the Arctic Basin in March 2011, compared to 55% on average from 1980 to 2000. Over the past few summers, more first-year ice has survived than in 2007, replenishing the younger multi-year ice categories (2- to 3-year-old ice). This multi-year ice appears to have played a key role in preserving the tongue of ice extending from near the North Pole toward the East Siberian Sea. However, the oldest, thickest ice (five or more years old) has continued to decline, particularly in the Beaufort and Chukchi Seas. Continued loss of the oldest, thickest ice has prevented any significant recovery of the summer minimum extent. In essence, what was once a refuge for older ice has become a graveyard.

Read the whole report HERE.

Comments

[Chris Reynolds]

"Continued loss of the oldest, thickest ice has prevented any significant recovery of the summer minimum extent. In essence, what was once a refuge for older ice (Beaufort & Chucki) has become a graveyard."

Kevin O'Neill raised the following point in a discussion with me. It seems that the Beusfort Gyre has been seen as a stabilising flywheel, cycling old ice and ageing it. i.e. here.

However things have changed. As that page implies in it's use of the word 'healthy'.

The instability of sea-ice cover is more than just positive feedbacks and thinner ice being more responsive to weather. The entire system has changed in ways that are sometimes hard to conceive and are not apparent to shallow considerations. The entire pattern of change is vast and substantial.

[John Baez]

Your link to September analysis doesn't go to the NSIDC's September analysis. I think you want this link instead:

http://nsidc.org/arcticseaicenews/2011/09/

[Neven]

You're right, John. Because the summaries are there for a whole month I usually just link to http://nsidc.org/arcticseaicenews/. But readers who read the blog post later on and click on the link, see the latest summary.

I'll make more of an effort and link properly from now on.

Thanks.