Report 2009:
The long drift of 2006C

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The Long Drift of Buoy 2006C


     Buoy 2006C is the longest lived IMB ever deployed. It is also one of the most interesting. It was deployed in September 2006 in the Beaufort Sea and is now in its third year of operation.

     The 2.10 m of bottom melt in 2007 in the Beaufort Sea was more than six times the annual average value of 0.34 m for the 1990s and two and a half times the 2006 result. This observation indicates that bottom melting was a major contributor to the 2007 ice loss in the Beaufort Sea. For the most part, conditions were typical of thick (3.2 m) multiyear ice in this region: minimum winter air temperatures of -45°C, snow depth of 0.4 m, winter ice growth of 0.33 m, and onset of melt in early June. What was extraordinary was the rapid bottom melting. In the month of August, bottom melting averaged 4 cm per day and reached maximum values of 11 cm per day in the last week of August, compared to characteristic averages of about 1 cm per day.

     The extreme amount of bottom melting observed in 2007 required considerable heat from the upper ocean. We believe that solar radiation was a primary source of this ocean heat. Open water reflects only 7% of the incident solar radiation, compared to 85% for snow-covered sea ice and 65% for bare sea ice. As the ice cover decays, highly reflecting ice is replaced by highly absorbing ocean, resulting in more solar heat absorption and more melting. Furthermore, an ice cover thinned by excessive bottom melt transmits more solar radiation directly to the ocean than the original thicker ice cover. This is known as the ice–albedo feedback mechanism.
 

Map showing drift of buoy 2006C from September 2006 to November 2008. Each color represents a three month period.


The total amount of surface (red) and bottom (yellow) melt during the summer of 2008 measured at sever ice mass balance buoys. The white dots denote an approximate position during of the buoy during summer. The two numbers associated with each plot are the ice thickness at the beginning and the end of the melt season  the ice measured at seven ice mass balance buoys. Also displayed is the ice concentration from the National Snow and Ice Data Center.