Abstract
Since the Atlantic meridional overturning circulation (MOC) plays an important role in determining the climate of the North Atlantic and beyond, it is essential to test the ability of coupled models to predict changes in the MOC and any resulting climate impacts. The 8.2 ka event has been previously targeted for such a test (i.e., Alley, 2003; Schmidt and LeGrande, 2005). The hypothesized cause of the 8.2 ka event is drainage of freshwater from Lake Agassiz into Hudson Bay, which appears to have slowed the MOC and affected climate in various parts of the Northern Hemisphere. The climate system before the 8.2 ka event was generally similar to that of today with a few notable exceptions, including, lower greenhouse gas concentrations, increased seasonality of insolation due to orbital forcing, a remnant of the Laurentide ice sheet near Hudson Bay, and enhanced ice melt runoff down the St. Lawrence River. Using the NCAR CCSM 3.0 model, we have run experiments to determine how adding these different boundary conditions influences the background climate state prior to the drainage of Lake Agassiz into the Hudson Bay. We find these boundary conditions have significant effects on the ocean properties in the North Atlantic. We will discuss the reasons for these changes and their implications for the effects of freshwater forcing at 8.2 ka.