Comparison of 8.2ka flood simulations: A model sensitivity experiment

Since the Atlantic meridional overturning circulation (AMOC) 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 AMOC and any resulting climate impacts. The 8.2 ka event has been previously targeted for such a test. The hypothesized cause of the 8.2 ka event is drainage of freshwater from Lake Agassiz into the Hudson Bay and Labrador Sea, 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 realistic 8.5 ka boundary conditions in the NCAR CCSM 3.0 model, we have performed several freshwater forcing experiments to simulate the Lake Agassiz flood into the Hudson Bay at 8.2 ka. Freshwater was added to different areas across the Hudson Strait and Labrador Sea and distributed among several model grid cells at a rate of 2.5 Sv for one year to test the model sensitivity to the freshwater forcing. At the end of the forcing, the system was allowed to recover uninterrupted. We will discuss the differences and similarities in the response to the freshwater forcing among the experiments and compare the results to proxy records of the ocean’s response to the flood event.