Can oceanic meridional overturning circulation cause abrupt climate change

Many evidences show that the abrupt climate changes occurred in the last glacial period are related to the changes of the oceanic overturning circulation (MOC) since this circulation has multi-equilibrium states and the changes from one equilibrium state to another are abrupt in some simple models. However, up to date, there is no state-of-art fully coupled climate model demonstrating that the MOC has multi-equilibrium states. Here we, using the National Center for Atmospheric Research Community Climate System Model version 3 (CCSM3), show that the MOC indeed has two stable equilibrium states only if the Bering Strait, a narrow and shallow sea way which allows the transport of the fresher Pacific water into the Arctic and subsequently into the North Atlantic, is closed. With an open Bering Strait, the MOC weakens as freshwater forcing is added, and strengthens as the freshwater forcing weakens. This result implies that the MOC changes played a key role in the abrupt climate change event in the glacial period, but the MOC changes in the future warm climate may not induce abrupt climate change.