Springice chokes the Bering Strait (7thMay, 2000).  Ice is flowing southwards from the Bering S

Springice chokes the Bering Strait (7thMay, 2000).  Ice is flowing southwards from the Bering Strait to theBering Sea.Thereis no land at the North Pole.  The sea ice occupies an ocean basinthat is mostly surrounded by land.Becausethe North Pole has no land, the ice is subject to the most extremeoscillations between winter darkness and summer sunlight.  Andbecause the ocean basin is surrounded by land, the ice has lessfreedom to drift to lower latitudes and melt.TheArctic Oscillation isthe main cause of atmospheric variability around the North Pole,causing fluctuations that can last from years to decades.  It is anatmospheric “see-saw” in which air masses shift between the polarregions and lower latitudes.  This shifting can intensify, weaken, ofshift the location of semi-permanent low- and high-pressure systems. These changes influence the strength of the existing westerly winds,and also influence the track that storms tend to follow.Ina “positive phase”, the winds intensify, making leads(narrow linear openings) in theice packs bigger.  The thin, young ice that forms in the leads ismore likely to melt in the summer.  The strong winds flush more iceout of the Arctic through the Fram Strait, which means that more ofit will melt at these lower latitudes.Ina “negative phase”, the winds are weaker.  Thicker, multiyear iceis less likely to be swept out of the Arctic Basin into lowerlatitudes, and thus more of it will last the summer.Themid-1990s had a strong positive AO phase, which flushed thicker,older ice out of the Arctic, replacing it with first-year ice that ismore prone to melting.  After that, the AO was often neutral ornegative, but sea ice failed to recover.  A steep pattern of Arcticsea ice decline began in 2002.Itis likely that the AO triggered a natural phase of accelerated meltthat continued into the next decade because of unusually warmtemperatures in the Arctic region.  So natural variability andclimate change have combined to cause this decline in Arctic sea ice. -- source link

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