Since early 1980's (in red), the september Arctic sea ice minimum extension reduced regularly, passing from 7 millions km2 to less than 5 millions km2 in the last 2000's (4,2 millions km2 in 2007) - © www.iup.uni-bremen.de:8084/amsr/
Watching the Arctic Color Change
La tendance au retrait de la banquise boréale s'accompagne d'une modification de la “couleur” (albédo moyen) de l'océan Arctique qui conditionne les échanges d'énergie entre l'océan et l'atmosphère. Jean-Claude Gascard, spécialiste des glaces de mer arctiques analyse pour nous l'évolution de ce patchwork de glace.
par Jean-Claude Gascard, océanographe, France.
“The Arctic sea-ice cover appeared to be the most anomalous ever during Fall 2009 and Spring 2010”
Every morning, I like to start my activities in my office based at the UPMC (LOCEAN lab) in Paris (France) by consulting the web page of the Polar view center based at the University of Bremen (Germany) and also the NSIDC (National Snow and Ice Data Center) in Boulder Colorado (USA). Both centers are providing real time and accurate information concerning sea-ice conditions over the entire Arctic Ocean.
This past spring, the melt season started vividly all over the Arctic Ocean and particularly in the Atlantic sector as revealed by the AMSR-E data released on a daily basis.
It is striking to realize that the same regions (Barents Sea and Kara Sea, Hudson Bay and Baffin Bay) that revealed a peculiar situation during the past Fall (October 2009) regarding a very slow sea-ice growth rate, are now exhibiting (May 2010) a very fast sea-ice retreat. Both effects evidenced that the Arctic sea-ice cover appeared to be the most anomalous ever during Fall 2009 and Spring 2010. It is going to be quite fascinating to watch the evolution of the Arctic sea-ice during the upcoming summer season.
Since the IPY started in 2007, main sea-ice characteristics changed drastically. Not only sea-ice extent was reduced by almost 50% (from 8 millions km2 during late 70s down to 4 millions km2 in 2007), but sea-ice thickness was reduced by almost 50% too (from more than 3m thick on average during the 70s down to less than 2m during mid 90s). Combining these two variables, it would tend to indicate that sea-ice lost 75% of its mass. This is considerable. Two other aspects of Arctic sea-ice need great attention too. One is the sea-ice drifting speed that increased by a factor of 2 or even 3 if we compare modern situation with earlier observations. For instance it is worthwhile to remind that the Norwegian ship Fram led by Fridtjof Nansen crosses the Arctic in about 3 years (1000 days) compare with 500 days for the French schooner Tara during IPY in the context of the European integrated project Damocles. More likely and partly, this increase in sea-ice drift speed could be attributed to the thinning of the ice, a thinner ice being more mobile than a thicker ice. The other variable deserving a great deal of attention, concerns the sea-ice age. Arctic sea-ice is becoming younger and younger. The multiyear ice floes so typical of the Arctic sea-ice pack, are disappearing at a surprising pace. Arctic sea-ice is resembling more and more like the Antarctic sea-ice where all the sea-ice pack formed in winter, melts in summer.
These dramatic changes affecting Arctic sea-ice, seem to have a profound influence on the atmospheric circulation, the stratospheric polar vortex, cold air outbreaks from the Arctic towards mid latitude regions and the storm tracks in the northern hemisphere. During the past two years the polar vortex shifted during the first IPY and then fragmented during the second year. This was more likely due to the extra heat accumulated during summer in the upper ice free ocean and released in the lower atmosphere during the Fall, delaying the formation of sea-ice in winter. It looks like the Arctic shelf seas (Barents Sea and Kara Sea in particular) have a strong teleconnection with lower latitude weather pattern over northern Europe and Asia. Similarly the entire west coast of Greenland is now an ice free open ocean area for extended part of the year. This has also a profound effect on the weather pattern over North America and also is a main cause of the acceleration of melting ice over Greenland and causing sea level rise.
In contrast the Arctic Ocean looks like a very stable and robust element. Still one can observe fluctuations in water masses originating either from the North Pacific Ocean or from the North Atlantic Ocean and entering into the Arctic Ocean through Bering Strait and Fram Strait respectively. But these water masses appear to have limited and regional impacts on sea-ice that cannot account for the large scale changes being observed during recent years. However the strong positive albedo feedback due to a decreasing sea-ice cover and an increasing ice-free ocean area, is the major process contributing to a polar amplification of the global warming effect due to an increasing greenhouse effect.
The Arctic Sea-ice is a major constituent of the Earth climate system and all the changes actually observed in the Arctic are strong precursors of a future evolution of the Earth climate system.
Pour en savoir plus :
Visiter le site du Polar view center de l'Université de Bremen (Germany)
Visiter le site du NSIDC (National Snow and Ice Data Center)o (USA)
Visiter le site web de LOCEAN
Visiter le site web du programme européen DAMOCLES
© juillet 2010 - Le Cercle Polaire - Tous droits réservés