Arctic sea ice extent 2nd lowest measured for December; Arctic Oscillation goes negative
08.01.2013 - Atmosphere & Space, Water & Oceans, Ice & Snow, Arctic
Despite the fact that sea ice extent expanded by 2.33 million km2 during the month of December, according to the NSIDC, average sea ice extent for December 2012 was the second-lowest on record, reaching an extent of 12.20 km2 – 1.16 km2 below the 1979-2000 average extent for the month.
Parts of the Kara and Barents Seas remained ice free, where temperatures were observed to be 3-5°C above average. Ice extent was well below normal in the Atlantic sector of the Arctic (Successive winters of extremely low sea ice extent in the Atlantic sector of the Arctic in the past have led to high mortality rates among seals). Ice cover has been forming slowly over the Labrador Sea, while Hudson Bay is now completely covered by ice. Temperatures over the Canadian Archipelago and Greenland have been slightly above average.
The only region of the Arctic with the higher than average sea ice extent and showing a positive trend in ice formation is the Bering Sea, where sea ice extended further south than normal. Temperatures over Alaska have been 2-7°C below average.
The Arctic Oscillation (AO) – a variation in the Arctic's winter atmospheric circulation that affects weather patterns elsewhere on the planet – has entered its negative phase. When the AO is in its negative phase, sea level pressure is above normal over the central Arctic while sea level pressure is below normal over the mid-latitudes. When the AO is negative, this allows thick ice to remain in the Arctic basin, reducing outflow of sea ice via the Fram Strait and strengthening the Beaufort Gyre (clockwise ice drift circulation in the Arctic Basin).
As the negative phase of the AO allows air masses to pass more easily from the Arctic into the mid-latitudes, this results in warmer than average temperatures to the Arctic and lower than average temperatures over Eurasia and North America.
Recent observations indicate that significant warming of the atmosphere over the Arctic during the autumn following a heavy summer sea ice melt season tends to lead the AO to enter its negative phase. However a negative AO in winter also tends to favour the retention of more Arctic sea ice in the summer, which was not the case during the 2009-2010 winter when the AO was in an extreme negative phase.