First off, the areal extent of the ice has dropped below four million
square kilometers and has set a new record. This appears to have
been augmented by a fortuitous cyclone which broke up a lot of the
ice and caused enhanced melting much as unusual winds did the same in
2007. Whatever the case, it certainly confirms that we are dealing
with much less ice.
This report shares a lot of new information including a mapping of
the five year plus ice which appears to be structurally more stable
and positioned than I had any reason to ever understand. The
assumption of a circumpolar conveyor belt is surely wrong. We have
instead separate Gyres of which one is the mentioned Beaufort Gyre.
The result is that the old ice accumulates along the northern margins
of the Arctic Islands and additionally in a narrow arc that runs
north just west of the pole. Thus these areas of accumulation need
not flush out any time soon of ever for that matter. What has been
flushed out is the weaker younger ice on the way to been pushed into
these two strips of accumulation. This process can continue with
diminishing results as most of the input energy must be absorbed
eliminating the annual winter ice.
I suspect that we are already looking at optimal conditions in the
Arctic and even if the sea ice continues to deteriorate, we are down
to the stubborn core that must surely resist breakup even as
weakening continues. In the meantime both passages are now available
for sporadic shipping and can be used carefully.
Arctic sea ice
falls below 4 million square kilometers
September 5, 2012
Following the new
record low recorded on August 26, Arctic sea ice extent
continued to drop and is now below 4.00 million square kilometers
(1.54 million square miles). Compared to September conditions in the
1980s and 1990s, this represents a 45% reduction in the
area of the Arctic covered by sea ice. At least one more
week likely remains in the melt season.
Overview of conditions
Figure
1. Arctic sea ice extent for August 2012 was 4.72 million square
kilometers (1.82 million square miles). The magenta line shows the
1979 to 2000 median extent for that month. The black cross indicates
the geographic North Pole
Throughout the month
of August, Arctic sea ice extent tracked below levels observed in
2007, leading to a new record low for the month of 4.72 million
square kilometers (1.82 million square miles), as assessed over the
period of satellite observations,1979 to present. Extent was
unusually low for all sectors of the Arctic, except the East
Greenland Sea where the ice edge remained near its normal position.
On August 26, the 5-day running average for ice extent dropped below
the previous record low daily extent, observed on September 18, 2007,
of 4.17 million square kilometers (1.61 million square miles). By the
end of the month, daily extent had dropped below 4.00 million square
kilometers (1.54 million square miles). Typically, the melt season
ends around the second week in September.
Conditions in context
Figure
2. The graph above shows Arctic sea ice extent as of September 3,
2012, along with daily ice extent data for the previous five years.
2012 is shown in blue, 2011 in orange, 2010 in pink, 2009 in navy,
2008 in purple, and 2007 in green. The 1979 to 2000 average is in
dark gray. The gray area around this average line shows the two
standard deviation range of the data.
In 2012, the rate of
ice loss for August was 91,700 square kilometers (35,400 square
miles) per day, the fastest observed for the month of August over the
period of satellite observations. In August 2007, ice was lost at a
rate of 66,000 square kilometers (25,400 square miles) per day, and
in 2008, the year with the previous highest August ice loss, the rate
was 80,600 square kilometers (31,100 square miles) per day. The
average ice loss for August is 55,100 square kilometers (21,300
square miles) per day. This rapid pace of ice loss in 2012
was dominated by large losses in the East Siberian and the Chukchi
seas, likely caused in part by the strong cyclone that entered the
region earlier in the month and helped to break up the ice.
However, even after the cyclone had dissipated, ice loss continued at
a rate of 77,800 square kilometers (30,000 square miles) per day.
August air
temperatures at the 925 hPa level (approximately 3,000 feet above the
surface) remained slightly above average (1 to 3 degrees Celsius, or
2 to 5 degrees Fahrenheit) over the much of the Pacific sector of the
Arctic Ocean as well as at its central sector, with slightly higher
temperatures in the Beaufort Sea (approximately 4 degrees Celsius, or
7 degrees Fahrenheit above average). On the Atlantic side, the Kara
and Barents seas continued to have air temperatures around 1 to 4
degrees Celsius (2 to 7 degrees Fahrenheit) below average.
At the end of August,
ice remained in the Western Parry Channel, and neither the
northern or southern routes of the Northwest Passage were open. While
much of the ice has cleared out, ice still remains, as confirmed by
our colleague Steve Howell at the Canadian Ice Service. In the latter
half of August, more ice actually moved into the passage routes when
ice was pushed down into the channels from the north. Whether that
ice will clear out remains to be seen.
August 2012 compared
to previous years
Figure
3. Monthly August ice extent for 1979 to 2012 shows a decline of
10.2% per decade.
The monthly averaged
ice extent for August was 4.72 million square kilometers (1.82 square
miles). This is 2.94 million square kilometers (1.14 million square
miles) below the 1979 to 2000 average extent, and 640,000 square
kilometers (247,000 square miles) below the previous record low for
August set in 2007. Including 2012, the August trend is -78,100
square kilometers (-30,200 square miles) per year, or -10.2 % per
decade relative to the 1979 to 2000 average.
Evolution of sea
surface temperatures in August
Figure
4. A buoy deployed on August 8, 2012 in open water during the storm
initially shows a very warm 10-meter (33-foot) thick surface mixed
layer (upper left image). On August 12 (upper right image), the buoy
enters a relatively cooler patch, gradually warms, enters another
cool patch 12 days later (bottom left image), and then starts to warm
again through August 26 (bottom right image). Red, orange, and yellow
indicate higher temperatures, while blues and purples indicate lower
temperatures.
In recent summers,
Arctic Ocean sea surface temperatures (SSTs) have been anomalously
high (see our 2010 and 2011 end-of-summer posts),
in part linked to loss of the reflective ice cover that allows darker
open water areas to readily absorb solar radiation and warm the mixed
layer of the ocean. According to Mike Steele, Wendy Ermold and
Ignatius Rigor of the University of Washington, SSTs in the Beaufort,
Chukchi, and Laptev seas were once again anomalously high before the
strong cyclone (mentioned earlier and discussed in our previous
post) entered the East Siberian and Chukchi seas on August 5, 2012.
SSTs were as much as 5 degrees Celsius (9 degrees Fahrenheit) above
normal along the coastal areas in those seas. After the storm, the
warm water that developed through summer was interspersed with large
areas of cold water created by ice melt. By the third week of August,
sea surface temperatures were mostly back to levels observed before
the storm, but with a few more patches of colder water interspersed
from additional ice melt.
A closer view of the
variation in SSTs before and after the storm is recorded in the
University of Washington Polar Science Center UpTempO buoy data.
A buoy deployed on August 8, 2012 in open water during the storm
initially shows a very warm 10-meter (33-foot) thick surface mixed
layer, likely the result of solar heating. On August 12, the buoy
enters a relatively cooler patch, gradually warms, enters another
cool patch 12 days later and then starts to warm again through August
26. These patches of cooler water may be a result of ice melt and/or
the impact of advection from the storm.
Old ice continues to
decline
Figure
5. These images from March 2012 (left) and August 2012 (right) show
the age of the ice cover in spring and at the end of summer. Much of
the Arctic ice cover now consists of first-year ice (shown in
purple), which tends to melt rapidly in summer’s warmth. However,
the oldest ice, that had survived five or more summers (shown in
white), declined by 51%.
Ice age is an
important indicator of the health of the ice cover. Old ice, also
called multiyear ice, tends to be thicker ice and less prone to
melting out in summer. The last few summers have seen increased
losses of multiyear ice in the Pacific sector of the Arctic;
multiyear ice that is transported into the Beaufort and Chukchi seas
tends to melt out in summer before being transported back to the
central Arctic Ocean through the clockwise Beaufort Gyre circulation.
This summer, the tongue of multiyear ice along the Alaska coast
mostly melted out by the end of August, with a small remnant left in
the Chukchi Sea. The ice on the Pacific side of the Arctic has melted
back to the edge of the multiyear ice cover, which should help to
slow further ice loss in the region. In the Laptev Sea, by contrast,
a large amount of first-year ice remains. In the last two weeks, open
water areas have developed within the first-year ice in the Laptev
Sea, helping to further foster melt in that region.
Between mid-March and
the third week of August, the total amount of multiyear ice within
the Arctic Ocean declined by 33%, and the oldest ice, ice older than
five years, declined by 51%.
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