Polar Science Center, Applied Physics Laboratory
University of Washingon, Seattle, Washington

 
 
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The Ice Retreat of the Summer 2007

 

    ABSTRACT:
    The minimum of arctic sea ice extent in the summer of 2007 was unprecedented in the historical record. A coupled ice–ocean model is used to determine the state of the ice and ocean over the past 29 years to investigate the causes of this ice extent minimum within an historical perspective. We find that even though the 2007 ice extent was strongly anomalous, the loss in total ice mass was not. Rather, the 2007 ice mass loss is largely consistent with a steady decrease in ice thickness that began in 1987. Since then, the simulated mean September ice thickness within the Arctic Ocean has declined from 3.7 to 2.6 m at a rate of –0.57 m decade–1. Both the area coverage of thin ice at the beginning of the melt season and the total volume of ice lost in the summer have been steadily increasing. The combined impact of these two trends caused a large reduction in the September mean ice concentration in the Arctic Ocean. This created conditions during the summer of 2007 that allowed persistent winds to push the remaining ice from the Pacific side to the Atlantic side of the basin and more than usual into the Greenland Sea, exposing large areas of open water, resulting in the record ice extent anomaly.
  • The ice thickness has declined more consistently than either the ice area or the ice extent since 1987
    thickness, area, extent
  • Here the mean ice thickness is for the entire Arctic basin and the area and extent are expressed as a fraction of the Arctic basin. The area is the same as the mean ice concentration and the extent is the region with ice concentration greater than 15%.

 

  • The ice-albedo feedback greatly adds to the melt in the summer.
  • Thin ice is more prone to being pushed around by the winds and currents.

  • The summer of 2007 winds blew the ice from the Pacific to the Atlantic side of the basin and pushed some of it out of the basin past Greenland.

  • The very thin ice is now more easily pushed around the basin by the winds. We expect continued large variability and gradual average declines in the summer ice extent.

     


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