Two weeks after a new record was set in
the Arctic Ocean for the least amount of sea ice coverage in the satellite
record, the ice surrounding Antarctica reached its annual winter maximum—and
set a record for a new high. Sea ice extended over 19.44 million square
kilometers (7.51 million square miles) in 2012, according to the National Snow
and Ice Data Center (NSIDC). The previous record of 19.39 million kilometers
(7.49 million square miles) was set in 2006.
The map above shows sea ice extent
around Antarctica on September 26, 2012, when ice covered more of the Southern
Ocean than at any other time in the satellite record. The map is based on an
NSIDC analysis of data from the Special Sensor Microwave/Imagers flown in the
Defense Meteorological Satellite Program. Land is dark gray, and ice
shelves—which are attached to land-based glaciers but floating on the ocean—are
light gray. The yellow outline shows the median sea ice extent in September
from 1979 to 2000. Sea ice extent is defined as the total area in which the ice
concentration is at least 15 percent.
The graph of NSIDC data shows the
maximum extent for each September since 1979 in millions of square kilometers.
There is a lot of variability from year to year, though the overall trend shows
growth of about 0.9 percent per decade.
According to a recent study by
sea ice scientists Claire Parkinson and Donald Cavalieri of NASA’s Goddard
Space Flight Center, Antarctic sea ice increased by roughly 17,100 square
kilometers per year from 1979 to 2010. Much of the increase, they note,
occurred in the Ross Sea, with smaller increases in Weddell Sea and Indian
Ocean. At the same time, the Bellinghausen and Amundsen Seas have lost ice.
“The strong pattern of decreasing ice coverage in the Bellingshausen/Amundsen
Seas region and increasing ice coverage in the Ross Sea region is suggestive of changes in atmospheric
circulation,” they noted.
“The year 2012 continues a long-term
contrast between the two hemispheres, with decreasing sea ice coverage in the
Arctic and increasing sea ice coverage in the Antarctic,” Parkinson added.
“Both hemispheres have considerable inter-annual variability, so that in either
hemisphere, next year could have either more or less sea ice than this year.
Still, the long-term trends are clear, but not equal: the magnitude of the ice
losses in the Arctic considerably exceed the magnitude of the ice gains in the
Antarctic.”
On their Arctic Sea Ice News and Analysis blog,
scientists from the University of Colorado wrote: “Comparing winter and summer
sea ice trends for the two poles is problematic since different processes are
in effect. During summer, surface melt and ice-albedo feedbacks are in effect;
winter processes include snowfall on the sea ice, and wind. Small changes in
winter extent may be a more mixed signal than the loss of summer sea ice
extent. An expansion of winter Antarctic ice could be due to cooling, winds, or
snowfall, whereas Arctic summer sea ice decline is more closely linked to
decadal climate warming.”
1.
References
2.
Parkinson,
C.L., and D.J. Cavalieri (2012, August 15) Antarctic sea ice
variability and trends, 1979-2010. The Cryosphere, Volume 6, pages 871-880.
5.
NASA
(2009, September 1) What's Holding Back
Antarctic Sea Ice from Melting. Accessed October 10, 2012.
6.
National
Snow and Ice Data Center (2012, October 2) Poles Apart: A record-breaking
summer and winter. Accessed October 10, 2012.
NASA Earth Observatory
images by Jesse Allen, using DMPS SSMIS ice concentration data provided
courtesy of theNational Snow and Ice
Data Center (NSIDC). Caption by
Michael Carlowicz
Instrument:
DMSP - SSMIS
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